Modular Structures and Related Techniques Don O. CarIson

Modular Structures andRelated TechniquesDon O. CarIsonEric Dluhosch

Don O. Carlson

I want to very quickly cover the backgroundof light-frame residential construction. A brieflook at history, a look at where we are today,and some looks at where we might go and thepossible impacts.

The biggest change that we had in this na-tion in housing was when a guy by the name ofTaylor, a carpenter in Chicago, created whatwe call balloon framing — the first use of two-by-fours in 1833. This was the major departurefrom the old European system of heavy timbersand heavy masonry construction.

Strange as it looks, that system really turnedthe United States into a nation of homeowners.One hundred seven years later in 1940 in La-fayette, Indiana, Jim and George Price came upwith factory panelization. About twelve yearsafter that in 1952, this man, A. Carroll Sanford,invented what we call the toothed metal con-nector plate, This created the component indus-try, which in a sense allowed site builders tocompete with what was going on inside factoriesby panelizers.

About 1973, the next big breakthrough wasthe flat-chord floor truss, again, metal-plate con-nected. Simple as it looks, it enabled us togreatly conserve our natural resources by mak-ing it unnecessary to use heavy-dimension lum-ber in our floor systems.

If you think about America’s industrializedhousing machine and visualize down the centerof that picture a big piece of machinery, thereare five manufacturing segments. At the farleft, we have what we call the productionbuilder, the big-volume site builder; next, thepanelized-home manufacturer. Across from thatwe have the mobile-home manufacturer, themodular-home manufacturer, and the component manufacturer.

As to who builds what in the U.S. housingpie, these figures are based on our research for1983. The site builders do about 51 percent; thepanelized, 26 percent; the mobile, which weprobably should more accurately call the HUD-Code home today, builds 19 percent; modulars

about 4 percent. Other segments of this indus-try include the dealers for the factory-builthomes, the component manufacturers who buildfor the production builders, and of course thespecial-unit manufacturers, who are all factorybuilders, but they don’t build housing. Theybuild everything else except homes and apart-ments.

The production builder builds single-familyhomes, low-rise or garden apartments up tomid-rise apartments. We call him a productionbuilder because he usually builds in metro cen-ters, and one house after another. In the metrocenter, he is served by the component manufac-turer who usually sells these units erected. Inother words, when the component truck leavesthat house, it’s weathered in and the buildercan take one month to a year to finish the in-side, if he wishes.

Turning to the component manufacturer, thisindustry was created by Sanford; today thereare two thousand of these companies across thecountry, primarily serving production builders.They are among the most sophisticated ma-chine people because they will serve up to onehundred different builders at one time.

Component manufacturers make wall panels,roof trusses, floor trusses, gable ends, plus othercomponents for homes. They use highly sophis-ticated machinery. This $52,000 componentcutter could be compared to a carpenter with ahand saw over his knee at a job site or even acircular saw. There’s not much comparisonwhen it comes to the kind of quality you canget into a factory to the lack of quality in our,as someone said, primitive methods at job sites.

Component manufacturers all make rooftrusses. Today this roof truss is engineered forthe specific house in the specific area where it’sgoing to be used, for span, wind load, snowload, live load, dead load and so on. It’s createdwith metal connector plates. You see the in-verted truss there in the background.

Additionally, the industry is becoming moresophisticated. Here they’re using what we callmachine-stress rated lumber. This is lumberthat’s run through a nondestructive testing ma-

Figure 1

Hud-Code (Mobile)Home.When built to the Manu-factured Housing Con-struction and SafetyStandards Code, admin-istered by the Depart-ment of Housing &Urban Development, andplaced on a permanentfoundation on landwhich IS sold with thehome, this variety ofhousing becomes virtu-ally indistinguishablefrom any other type ofhousing, except that theunit will be more afford-able, ranging in pricefrom 5 percent to 30 per-cent less than otherstyles of housing in thesame area,

Figure 2

Finished PanelizedHome.Panelized home manu-facturers, approximately600 across the U. S., arethe most versatile pro-ducers of architecturalstyles. Their homes canrange from low-cost va-cation cabins to expen-sive mansions in excessof 10,000 square feet.

48 Modular Structures and Related Techniques

chine to actually find out how much it willbear. This puts this industry’s products on apart with steel and concrete.

Component manufacturers also machinedoors literally by the thousands. Turning next tothe panelized-home manufacturer, there areabout six hundred of these companies — ofwhich probably twenty-five are large size.They’re very versatile in what they build. Theycan take an architect’s blueprint and create thehouse that the customer wants. One of the larg-est plants happens to be in Fort Payne, Ala-bama, the old Kingsbury Home plant, probablyhalf a million square feet under roof.

Today, the important thing to remember re-garding all of these phases of housing that we’rediscussing is that it is a duplicative process.We’re all building the same way. Two-by-fourstuds, usually sixteen inches on center.

In the panelized plant, if a panel such as thiswould have sheathing on it, windows inserted,siding on the outside, and then it’s delivered tothe job site in that condition, even thoughthere’s insulation between the studs, we call it‘open-panel,’ or ‘open-panel panelization.’ If thatwall panel is finished on the inside and the wir-ing, plumbing, and so on is put inside that wall,then it becomes closed-panel.

Some of our panelizers use cores, mechanicalcores. This little self-contained building will con-tain one or two bathrooms, the furnace, the hot-water heater, and usually the electrical junctionbox. That structure goes down on the deck first,and then the interior and exterior partitions andthe roof system goes up around it.

Also included in this panelized industry, eventhough they don’t build panels, are the two-by-four pre-cutters; and we do include the log-home manufacturers, of which there’s abouttwo hundred and fifty. We also include thedome-home manufacturers in the panelized seg-ment, of which there are around sixty, Now,the dome manufacturers actually panelize usingfive triangles to create a pentagon.

Turning now to the modular home manufac-turers, like the panelizers, the log, and thedome, they build to our model building codes;that is, a conventional building code. There areabout two hundred modular manufacturersacross the nation. Their technique in construc-

tion is very similar to what goes on in a mobile-home plant, except they’re building to differentcodes.

This is a typical kind of jig they use for theirroof system.

Here’s one of the newer plants which hap-pens to be Summey Corp. down in Georgetown,Texas. Their technique is to fabricate theirwalls on wall-panel machines at the head end ofthe line and then tip them up onto the floor sys-tems as they go down the production line; andthen in the far background, you see the modu-lar boxes, as we call them, getting ready to beshipped out of the plant,

The technique in many plants flows along aproduction line with fourteen to sixteen stations.The flooring systems are stacked up there atthe right. They put down their resilient flooringand their carpeting. They put in their plumbingfixtures, interior partitions, exterior walls and aroof system as the units go down the factoryline.

Modulars are about 95 percent completewhen they leave the factory if they are going tobe a single-family house. We call the modularthe strongest of all construction systems used today simply because it’s glue-nailed, plywoodconstruction all the way around. Even the mar-riage wall has plywood glue-nailed onto the wallstuds. This makes each half of the house essen-tially a self-contained box beam, and themodulars are traditional over-builders. If ittakes two two-by-fours to do the job, they’ll usethree.

At the job site, if the terrain is rough, they’llplace them with cranes. Now, that wet wall of amodular will weigh up to twenty-six-thousandpounds, and yet, as you can see, it’s being totally supported by cables at just two points.

A major trend along the coast, the EastCoast of the US. and the Gulf Coast, is whatwe call the stacked modular, up to five or sixstories tall. These units are sold primarily nowas recreational condominiums. They’re very,very attractive.

As in all industrialized construction, whichcovers all of these units, the biggest saving is inyour construction loan interest costs. A projectof this magnitude, if it’s modular, can be fin-ished in about six months compared to about a

Don O. Carlson 49

cut construction timefrom more than one yearto less than six monthswith resultant interestcost savings.


year if it’s site-built; and a project of this sizewill probably save up to $100,000 per month onconstruction loan interest costs.

Finally, the HUD code manufactured home,which we used to call the mobile home. Ofcourse, they’ve not been mobile for many, manyyears. This industry has two of the greatest ad-vantages going for it ever visited on any seg-ment of housing: one, it has a nationalpreemptive building code; and two, as of aboutthe middle of last summer, you could financethese units just like conventional real estate,providing they were permanently mounted onfoundations on their own lot.

Trends in this industry are to make theseunits look more and more house-like, to makethem more appealing to the consumer/buyer.

Construction technique is the same as we usefor anything else, two-by-four studs, sixteeninches on center. In this case, you can seethey’re getting their shear strength from glue-nail on the interior materials. However, when itcomes to insulation, you can order what youwant — R-1 1 or R-19 walls.

One of the departures is lighter frame con-struction than we use in most other housing.Like in this particular mono-roof system,they’re using two-by-threes instead of two-by-fours. Well, the question is: What do you wantto buy, a Chevrolet or a Cadillac? These homesare in the Chevrolet class.

Going down the production line, they’re simi-lar to the modular production lines: the floorsystem first; then their plumbing, partitions,wall systems and roof systems put on at theend.

By law, the mobile must have a metal chassisbeneath it, and you can identify them if you canget down underneath to see that it has a metalchassis. If you see this, you know that it’s aHUD-Code unit.

Manufactured-home dealers — there arearound fifteen thousand of these dealers (proba-bly nine thousand handle mobiles), and the restare into panelized, combination mobile-modular,the log, the dome, and so on.

The special-unit manufacturer, as I men-tioned earlier, is a factory builder. He buildsthings like doctors’ offices, prisons, motels, ev-erything except private housing per se.

One of the difficulties in marketing today isto tell the difference between a modular unit,which is what we’re looking at here. Those unitsbeneath it are not chassis — they’re transport-ers. They’ll go back to the job site after thisunit is set at the site.

Here’s the mobile, or HUD-Code, home.Both mobiles and modulars have house-type sid-ing, roofing, windows, and doors. They’ve gotthree and four 12-roof pitches. They look likelittle houses, but depending on the marketyou’re in, the mobile (HUD-Code) homes aregoing to run anywhere from 10 to 35 percentless costly than the site-built, comparable unit.

They’re striving to make these HUD-Codehomes appealing to the consumer. And whenthese units are placed on permanent founda-tions, such as this particular project in RanchoVentura, California, which went on permanentfoundations and was sold with the lot, they lookgood; but the price in that area, even though itmight sound high to you, was $71,000 to$91,000. A comparable site-built house startedat $130,000. As you might guess, they sold likehotcakes.

The interiors of HUD-Code units are veryprofessionally decorated today. The kitchens usebrand-name appliances. If there’s a choice, ofcourse, between good, better and best, theyprobably go for the good because we’re talkinglow-cost housing.

Other Trends in Our Industry: Because ofthe rise of the component industry, the com-puter has been used for many, many years(over twenty) because every roof truss we buildhas to be engineered on a computer. Todaywe’re getting computers into wall panelization.In this case, a girl can look at a builder’s blue-print and do the input into this computer. Thecomputer will actually drive this wall-panel ma-chine out in Gardina, California; and that ma-chine will turn out walls for a three-bedroomhouse in about three-and-a-half hours. However,it’s limited. They can’t build gable-end wallssuch as this. So there are many other semi-automated systems of wall panelization. This is justone. It happens to be a wall-panel plant inChino, California.

The high-speed plotter has already replaceddraftsmen to a great degree inside our compo-

Don O. Carlson 51

Figures 5 and 6

Log Homes and DomeHomesare considered part ofthe panelized homegroup There are ap-proximately 250 loghome manufacturers inthe U.S. and Canada,mostly small firms, andabout 60 dome homemanufacturers Whilegreatly desired by someconsumers, the totalnumber of units of bothbuilt each year IS lessthan 150,000


nent plants. That high-speed plotter is computerdriven, and it can do the work of about fivedraftsmen in about an hour.

One of the minor trends through the South(Louisiana, Texas), is what we call metal-plate-connected rough openings. It’s one of the tough-est jobs at a job site to get a square opening foryour windows and doors, and this componentsolves that problem for most of the apartmentsbeing built down in the Texas area.

Another trend that we expect to see more ofbecause it makes so much sense is the perma-nent wood foundation, sometimes called the all-weather wood foundation. This is made frompressure-treated lumber and plywood; and asyou can see by this scene, you can build it any-time, including in a blizzard. You don’t have toworry about what the climate is outside.

The permanent wood foundation creates abasement level that is just as livable as the up-stairs. And, depending on where you are andwhat insulation is being done, this unit willrange anywhere from 20 to 50 percent lesscostly to heat in the basement area. Since thiswas invented by NAHB and a few other groupsback in 1969, we’ve built about one hundredseventy thousand of these. We expect them toproliferate.

Another trend is that the big builders are get-ting bigger. These figures show the top one hun-dred home builders. Now, these top onehundred cut across all lines that I’ve mentioned.In 1982, they built 304,000 units; in 1983,377,000 units. The percentage of what theybuilt went down, as it always does, during a pe-riod of prosperity in housing simply becausemore small builders come into the marketplace.

Japan — let me just touch on that briefly. Iled a study mission to Japan in April of thisyear. When I left this country, I was very smugabout our superiority in housing technique, mar-keting, manufacturing, and so on. It took abouta day and a half for those ideas to get knockedout of my head. My conclusion today is thatthey’re about eight to ten years ahead of us inmarketing techniques and manufacturing tech-nology.

This is how they sell their homes. You’relooking at an aerial view of a model citywherein sixty to seventy builders bring their

homes into one place. Mr. and Mrs. JapaneseHome Buyer can go in there. After they pickout the architectural design and their housestyle, they can sit down with a salesman at acomputer, do the final analysis right on thatcomputer, literally draw the house on the com-puter. Then they can go in a make selections ofall of their wall finishes, what color they wantthe kitchen cabinets and so on.

If the order is finally approved, the salesmancan punch a button on the computer, and theorder is electronically transmitted to the fac-tory, and the house starts down the productionline.

In terms of code, they have a national codeset by the Ministry of Construction. They wanttheir homes to not only be energy efficient, butcapable of standing up to earthquakes, their ty-phoons and so on. Of the ten largest Japanesecompanies, about four have capabilities of com-pletely testing the total house inside their laboratories.

This machine is capable of hitting that full-size house with winds and rains of 140 miles perhour, and those windows don’t blow out.

In terms of conveyorization and automationin the factory, they’re much further advancedthan we are. That happens to be a wood panel,a stressed-skin wood panel plant up in Matsu-moto, Japan. That production line went at asteady rate of fourteen feet per minute; it liter-ally never stopped. Every station was controlledby a sidebar computer, which in turn was con-trolled by a master computer.

They’re deeply into robotics for the steel pan-els they build. This is a robotic unit to createsteel trusses. They wouldn’t let us photographthe wall-panel system, but it was all roboticallywelded. The members came down very, veryquickly; went into a system where eight roboticwelders hit it all at one time and then movedthe panel out; and it only took a matter of a fewseconds to create a complete steel-wall panel.

The Manager in that plant told me very glee-fully, “We’re building houses the way we buildcars.”

This is a new material invented by MisawaHomes. That white panel you see at the endthey call precastable autoclave light weight ce-ramics, or more simply PALC. The PALC

Don O. Carlson 53

Figures 7 and 8

The Major Trendamong HUD-Code (mo-bile) homes is to makethem look more andmore like ‘conventionalsite-built dwellings. ’ Thetop photo shows howpanelized garages canbe placed in front of dou-ble-section HUD-Codehomes to make themlook like typical Californiatract homes; the lowerphoto shows that the‘conventional home look’is even being adaptedfor single-section homes.


panel in one unit there gives you your exteriorfinish, your interior finish, your structural sup-port, vapor barrier, and insulation.

In talking with all of these Japanese compa-nies, I naturally asked the question: What areyou going to do regarding the U. S.? They allsaid, “We’re not going to do what we did to youin automobiles, However, we would like to formpartnerships with major U.S. companies andbring our technology to the U. S.”

Misawa claims they will have a factory inthis country within three years.

Even by Western standards, what they’rebuilding is attractive.

Today we already know how to build afford-able houses which are also affordable to oper-ate, even with present levels of technology,without going into a sophisticated $20,000 solarsystem. This is a building we built inCarpinteria, California, to house our office facil-ities. It has an all-weather wood foundation, aheat pump, an air-to-air heat exchanger; and, tomake a long story short, we run thirty-sevenitems of electrical equipment, twenty-fourlights, and the heating, the air conditioning, thefurnace fan and the air-to-air heat exchangerfans, and the whole ball of wax, costs us about$2.50 a day to operate.

The foundation was built in a factory in twodays or — pardon me — one day by two menwho had never seen a wood-foundation blue-print before. The building was built in a factoryin eight days. The foundation went in on theground in one day, and the building was set inabout a half a day.

But then as we always say, building at thesite is ‘building by surprise.’ So after the build-ing was set, it took us eight weeks to move insimply because the environmental people in thearea wouldn’t let us move in until every singleblade of grass was planted, and they picked outthe blades they wanted planted.

Possible Changes and Impacts: As I men-tioned, Japan is eight to ten years ahead of usin CAD/CAM manufacturing, controls, con-veyorization, automation, and robotics. They dowant to form U.S. partnerships, and I think, ifnothing else, we need some sort of a study tocope with what’s going to happen in terms oftheir future intentions in housing in the U.S.

Other Possible Changes and Impacts: Wenow have one national preemptive buildingcode. That’s the HUD Manufactured HousingConstruction and Safety Standards. We havethree model codes, which are used by the restof the nation — the basic, the uniform and thestandard. Beyond that, there’s anywhere fromseven to actually fifteen thousand local or re-gional jurisdictions that decide on what goesinto a house. I think what we need is a nationalpreemptive building code, performance-orientedto certain locations, revised to include knownmethods of cost-cutting (the NAHB has a li-brary on what we already know about cost-cut-ting), and the new performance code can bemerged to include the three model codes andthe one HUD Code.

We probably need a similar national preemp-tive zoning and infrastructure code. Using theknown techniques of cutting down costs in subdivisions, this would cover things like streets,sidewalks, sewers and so on; this, I think, wouldbe one of the major methods we could use to re-duce costs of housing in the U.S.

Today we have a Department of Housingand Urban Development. It never seemed to methat was a logical marriage, simply becausethere’s not an awful lot in common between thetwo. When you’re talking about urban develop-ment, you’re talking probably about rehabilita-tion. You’re talking about heavy construction,old infrastructure. Housing deals with thingsthat will go further out in the country. It maymake sense, therefore, to divide the two.

Additionally, we have no less than three Gov-ernment agencies who get their fingers into thehousing pie with inspections, mortgage insur-ance and so on, Perhaps the time has come tomerge the FHA, the VA, and the FarmersHome Administration and their separate codesunder the Department of Housing and have aseparate Department of Urban Development toconcentrate on revitalization, primarily throughfree-enterprise zone systems.

It seems to me the only way we’re going tobe able to rebuild our cities is the way we builtthem in the first place. They were built in thefirst place literally like free-enterprise zones.

Other Possible Changes and Impacts: TheJapanese are well along in working toward util-

Don O. Carlson

*

55

Figures 9 and 10

A Major Problemfacing the housing in-dustry today IS the inabil-ity of people both withinand outside of the indus-try to discern the differ-ence visibly betweendouble-section HUD-Code (mobile) homes,shown in the abovephoto, and double-sec-tion modular homes,shown in the lowerphoto Mobile homes arebuilt to the HUD-Code,modular homes are builtto any one of the threenational ‘model’ buildercodes which in turn havebeen adopted by statesand cities. In general themodular homes are builtwith a much heavierframing system than ISused by the mobile-home industry The ma-jor difference is in thefact that, by law, theHUD-Code (mobile)home must have an inte-gral metal chassis be-neath each section; themodular section, on theother hand, IS simply de-livered on a flatbed trailerwhich is returned to theplant after setting Never-theless, since both unitsare beginning to useconventionally-pitchedroofs, house-type siding,windows, and doors, it isvisually most difficult todiscern differences Themajor difference IS incost where the mobile ISbuilt to meet the Chevro-let budget, and the mod-ular IS more like theBuick or Chrysler bud-get


ity self-sufficient homes and apartments. If wetap Mother Earth and Father Sun, I don’t thinkit’s too far a conclusion to come to that we caneventually, not too many years down the road,have a home or an apartment complex that’s to-tally self-sufficient of utilities.

I think one of the solutions to our energyproblem is right under our feet where, youknow, if you go down into the earth, regardlessof where you are, even three or four feet, youhit an even temperature, which is alwayswarmer in the winter and cooler in the summer.We’re tapping this in the building inCarpinteria, and I think that’s one of the rea-sons that our heating and energy costs havebeen so low.

Also, we’ve got to mentally reposition ourtrees to be renewable and harvestable large-cornstalks, and not just museum pieces. The Ameri-can forests have to be repositioned in our mindsto be enclaves of multiple use rather than just alow-use bank vault for two or three people thathike into the wilderness forests every year.

Perhaps we should consider home projects orcommunities for the homeless. How manyhomeless are there? You hear figures rangingfrom three hundred thousand to three million.Who can count the homeless? You can’t findthem. The point is there are a lot of them outthere. Perhaps some of these families should beallowed to involve themselves and build theirown experimental low-cost homes; and there’s

all kinds of experimental systems that we coulduse, whether adobe, pre-cut logs, dog-bone (pro-file) lumber, etc. It maybe possible to developsystems that we could export to underdevelopedcountries.

Other Changes and Impacts: I think we needa national 10 percent home mortgage plan. It’saxiomatic that when housing is going up, thecountry’s prosperity goes up and vice versa.Why should we continue to crucify the Ameri-can economy on a destructive down cycle ofnew home construction?

Our present mortgage interest tax deductionsystem has been historically insufficient to headoff recessions in this nation. If we had this 10percent plan aimed at the first-time buyer, Ithink we could achieve a steady rate of two mil-lion starts every year. This would bolster 330groups of separate businesses and industriesthat depend on housing for a large share oftheir cash income. Literally tens of thousandsof individual companies are involved in these330 groups.

It would obviously increase employment andcertainly increase the Government’s tax incomeat all levels, helping to reduce the deficit, and, Ithink, finally head off recessions and possiblesocial upheavals that could occur if too manypeople are homeless.

Don O. Carlson is Editor & Publisher of Automation inHousing and Manufactured Home Dealer Magazine

Don O. Carlson 57

Figures 11 and 12

Constructionof all homes in theUnited States today IS aduplicative processsince all types of resi-dential buildings aremade with 2x4 studwalls spaced 16” o.c., forall exteriors Thesephotos show typical pro-duction scenes in a mo-bile home plant. In thebottom photo, theworker IS shown spread-ing glue on studs towhich gypsum drywall orwood paneling will beglued and nailed This ishow a HUD-Code homewall achieves a majorportion of its shearstrength from externalglue nailed sheathing,which the mobile indus-try does not use Produc-tion steps for mobile andmodular homes withintheir respective factoriesare quite similar

58

Don O. Carlson

Figure 15

59

Aerial Viewof one of the nation’slargest panelized homefactories, KingsberryHomes, Fort Wayne, AL,which is in excess of100,000 square feet. Par-ticipants in the nation’spanelized home industrynumber over 600, butrange from huge plantsof this size down tosmall retail lumberyardswhich panelize homesfor preferred builders.

Figure 16

Non-Destructive Test-ing of lumber forstrength qualities now isbeing performed by anumber of lumber pro-ducers for the compo-nent industry. Theindependent componentmanufacturer, whichmakes major house partsfor site builders, needsMachine Stress Ratedlumber for critical rooftruss projects such asnursing homes, commer-cial buildings andschools, and homes withunusually large clearspantrusses.


Figure 17

Floor Trusses,made of 2x4’s andjoined with metal con-nector plates on bothsides of each 2x4 mem-ber, are now used inabout 80 percent of US.homes and apartments.Floor truss actually is amisnomer becausethese ‘flat-chord’ trussesoften are used for roof-ceiling systems.

Figure 18

ComponentManufacturersoften assemble wall pan-els in the factory for useby site builders. Approxi-mately 30 percent of thesite-built homes andapartments utilize wallpanels made by the na-tion’s 1,800 componentfabricators.

Don O. Carlson

Figure 19

ComponentFabricatorsalso machine doorblanks to order for pro-duction builders. Theyinstall the windows to or-der, put in the hinges,put in the lock sets, andpre-hang the door in itsframe before delivery tothe site builder.

Figure 20

Wall Panel Machinesused by component fab-ricators today are capa-ble of making straightwalls or gable end walls.


Figure 21

ComponentFabricators are amongthe most sophisticated interms of machining, andmany use high-speedcomponent cutters(saws) as seen in thisphoto which are capableof five angle cuts on theends of 2x4 members atthe rate of 60 pieces perminute. In-plant qualitytoday far exceeds qualityat the job site,

Figure 22

About 95 Percentof all component fabrica-tors make roof trusses,and this is a mirror of theroof systems for singlefamily homes and apart-ments in the U.S. today,These triangular trussesall are engineered for thespecific in a specificgeographic area by com-puter.

Don O. Carlson 63

Figure 23

Some Componentmanufacturers use com-puter-driven, high-speedKellner wall panel ma-chines which are capa-ble of turning out walls

Figure 24

All Stylesof in-plant home builderstoday use simple or elab-orate cutting depart-ments to preparemembers for wall panels,roof trusses and floortrusses


Figure 25

A Typicalwall panel productionline for either a compo-nent plant or a panelizedhome manufacturer mayconsist of a steel-toppedor wood-topped produc-tion table with roller con-veyors on both sides.Some wall panel ma-chines are totally fabri-cated of steel, andcontain lugs to hold 2x4members in positionwhile they are pneumati-cally nailed. When a wailIS finished on one side itis said to be built by an‘open-panel panelizer;when a wall is finishedon both sides (and hasplumbing and electricalinside) it is said to be a‘closed-panel’ panelizer

Figure 26

Mechanical CoreStructuresare made by bothpanelizers and compo-nent plants. The self-contained structureshave a completely fin-ished bathroom, the hot-water heater, thefurnace, electrical junc-tion box, and sometimesthe wet wall for the ad-joining kitchen. By doingall of this electrical andplumbing work inside aplant, the in-plant pro-ducer can save from$300 to $1,500 over thecost of plumbing andelectrical work done atthe site. In construction,the mechanical corestructure is placed onthe deck of the home orthe concrete slab first,then the panelized homeIS erected around it.

Don O. Carlson 65

Figure 27

More and More Plantstoday are multiple pur-pose plants. This factoryin Austin (Georgetown),TX, produces both mod-ular units and panelizedunits.

Figure 28

Jigs Are Usedin both mobile and mod-ular plants for fabricationof complete ‘half-house’ceiling systems, whichwhen complete, aretransported by crane tothe house productionline and set in place ontop of the half-housebox.


Figure 29

Some Modular Plantsbuild their homes withboth sections joined to-gether to insure perfectfits. At the end of theproduction line, the twohalves of the house aresplit apart for transportto the job site. All modu-lar homes are heavilysheathed with plywood,and they usually are builtwith unusually heavyfloor decking and roofsheathing.

Figure 30

A Small OfficeBuilding, built to resem-ble a home but parti-tioned like an office, wasbuilt in a mobile homeplant in San Bernardino,CA, in eight days. Itswood foundation wasplaced in the ground inone day, and the build-ing was set on the foun-dation in one day. Thisstructure could havebeen occupied in lessthan three days after de-livery to the site.

Don O. Carlson 67

Figure 31

Many of the Nation%component manufactur-ers located near metro-politan centers sell theirmajor house parts‘erected. ’ Thus, by thetime the last componenttruck leaves a job sitefor a site builder, thefloor trusses are inplace, the walls are inplace, the roof trusseshave been added, andthe home has been com-pletely sheathed, orweathered in. Thebuilder at the site thencan take as long as hewishes to finish thehouse at the site usingsite subcontractors,

Figure 32

Many ComponentFabricators, such asthis one in Ogden, UT,have separate buildingsfor the production of wallpanels, floor trusses androof trusses.

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Figure 33

The Settingof modular homes fre-quently is done by crane.It is also fairly routine toset mobile homes bycrane, providing space isavailable. By havingthese half-house sec-tions completely finishedinside a factory, the ‘cos-metic and stitching upwork’ to be done at thejob site usually can behandled in less than oneweek, and the family canmove in quickly. Thespeed saves consider-ably on construction in-terest loan costsbecause of the muchfaster occupancy time atthe site.

Figure 34

This Is Wherethe modern U.S. housingindustry got its start. Theinvention of the 2x4 or‘balloon’ framing systemin Chicago in 1833 madeAmerica a nation ofhomeowners.

Modular Structures and Related Techniques

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Eric Dluhosch

It is encouraging that the impact of techno-logical change on the building industry is re-ceiving national recognition and Congressionalattention. The question is: Why now, and whythe focus on building technology?

Clearly, there must be a feeling of uncer-tainty about the future performance of this im-portant sector of the American economy, calledthe building construction industry, which ac-cording to the Report of the President’s Com-mittee on Urban Housing was expected toproduce enough new homes between 1968 and1978 to ‘provide a decent home for every Amer-ican family’ during that decade. The dream ofan affordable decent home seems to be reced-ing, rather than becoming reality. For this rea-son alone, it is good to meet here and look atthe problems of change and innovation again.For, in the meantime, we had Operation Break-through, the energy crisis, and the effects oftechnological change on the steel and automo-bile industries. If one adds to all this the manychanges in American life styles, and continuingdemographic age and geographic redistributionof the U.S. population, and the incipient entryof Japanese and European home manufacturersin the U.S. market, uneasiness may easily turninto alarm,

The fact that we are meeting here, and thefact that the problem has been recognized asworthy of national attention, brings hope that astate of alarm can be avoided, and that lessonshave been learned from past mistakes, and thatanother ‘crisis’ situation can be avoided.

If there is indeed an uneasiness about the fu-ture of the building industry, the first questionto be addressed is whether we are, in fact andas a matter of perception, dealing with a bona-fide manufacturing industry, or whether it maynot be more useful to regard the home-buildingindustry as a service industry, since it is thehome-building industry which I wish to discuss.In many respects it is indeed similar to manyother service industries, such as health, educa-tion, recreation, and communications, for thehome building industry delivers much morethan just a short-term consumer product. Be-yond building houses, it is inextricably involved

in providing a host of other services, from fi-nancing to financial security, from status toostentation, and from despair to pride. For theremainder of this discussion, and in order toprovide a better conceptual frame for the fol-lowing suggestions to be made, I will proceedon the assumption that home building is indeedas much of a service than a product, and that itacts as such in an integrated and highly coordi-nated manner in providing a host of specializedservices, regardless of the fact that it may beregarded as highly fragmented as a productionindustry. This makes it also possible to neutral-ize the perennial controversy of fragmentationvs. integration, and also makes it much easier tolook at technological change as a subservient as-pect of service, rather than as the purely tech-nical calculus of production efficiency.Technological change per se may thus beviewed as secondary to the achievement of de-sirable and/or feasible human goals, ratherthan as a quasi-autonomous end product. Be-yond that, the assessment of change, if relatedto service, allows a more inclusive definition oftechnology, i.e., the inclusion of ‘soft’ technol-ogies as an equivalent partner to past over-emphasis on ‘hard’ technologies.

Thus, if the operations of the home buildingsector are viewed as a continuum of multi-fac-eted but integrated services, it is not only possi-ble, but necessary, to include such ‘soft’technologies as planning, programming, design,management, scheduling, procurement, andgeneral goal setting and decision-making in ourconsiderations. Institutional constraints can belegitimately factored in as part of the servicemission of the housing sector, and questionssuch as the environmental impact of housingand quality of various life-style options can belinked to qualitative as well as quantitativestrategies for the deployment of concrete ‘hard’technologies (products, materials, systems, andassemblies). Based on the imperatives of ser-vice, technology assessment of hardware avoidslimited definitions of what may or may not beassigned to a narrowly defined construction sec-tor, thus allowing for the transfer of both tech-niques and products from the ‘outside.’ Theintention is to break out of existing conceptualcages, and to broaden the scope of the discus-

Eric Dluhosch 71

sion to include experiences and opportunities of-fered by all emerging and new technologies,regardless of their origin, while keeping in mindthe ultimate goal of a quality environment forall citizens, with least damage to be inflicted onour already strained natural resources.

Keeping the above in mind, what then arethe major technological changes which havehad an impact on housing? Is there a new anddifferent way in which we plan, design, procure,and assemble our houses today that is differentfrom that of a few decades ago?

I submit that indeed changes in home build-ing techniques and materials have been exten-sive and significant, even though, on thesurface, the actual appearance of the averageAmerican home has changed very little. Thereare two reasons for this: the first is the nature ofthe product, the house, as a symbol of socialstability and financial equity; and the secondhas to do with its long-term life as an invest-ment asset tied to land and location. Realchange has occurred, however, in the way thehouse is being put together, or, to use theproper technical term, assembled. Here majorchanges have affected the selection of substitutematerials, the introduction of mechanizedequipment and hand-held power tools, the deliv-ery to the site of prefabricated components andassemblies, and the substitution of traditionalfasteners, such as nails, staples, nail-plates,glues and zippers.

In that sense, the industry has learned its les-son well as an aftermath of the failed expecta-tions of Operation Breakthrough to create aviable mass market for fully-prefabricated mod-ular units by large quantity producers on largesites. In general, the trend has been away fromso-called ‘proprietary’ or ‘closed’ systems, to-wards a more evolutionary (and more orderly)emphasis on highly-rationalized subsystems,components, and elements, produced under con-trolled factory conditions, and supplied at con-trolled cost and quality.

In addition, the disappearance of large tractdevelopments in the seventies has forced pro-ducers to serve a more diversified market ofscattered sites distributed over larger geo-graphic areas. This has led to more careful con-siderations of ease of transportation, handling,

and product customization in assembly.Let me list some of the more dramatic

changes which have occurred along these lines:

Planning and Design

● More compact site planning, with savingsachieved by providing better planned and lesswasteful infrastructure services (i.e., sewers,water, power, and communications).

• Introduction of new dwelling types for newlife-styles such as cluster housing, zero lot linezoning, ‘theme’ villages, garden apartments,condos, and other ‘specialty’ types.

■ Better space utilization by more compact planlayouts, and the combining of functionalspaces into lofts and galleries, including theprovision of unfinished spaces for future ex-pansion.

• Better understanding of energy saving sys-tems as part of integrated design packages,using design as a means to minimize energyconsumption. This includes both active andpassive systems, such as solar heating, trombwalls, insulation sandwiches, atriums, solargreenhouses, and many more.All of the above-listed developments have

generated new markets for new products, suchas ‘life-style’ supermarkets for do-it-yourselfers,TV home-improvement programs, and newmagazines for yuppies and other new life-stylegroups. New home owners have become moresophisticated in their understanding of the waytheir homes are constructed, and thus may beexpected to demand better quality and higherperformance from their houses in the future aswell.

In terms of new techniques, the gradual in-troduction of low- and medium-cost microcom-puter systems in the design of housing has ledto the establishment of national as well as localdata bases, readily accessible to professionaland layman alike, thus allowing both access to awide range of services, product catalogs, andother related life-style information.

The linking of computer-aided design pro-grams with compatible software, with the ca-pability of almost instant energy calculations,cost estimating, inventory checking and design-


originated production control of automated ma-chines, has made it possible for the first time tocontrol the entire process by means of fully in-tegrated design-decision programs. Thus, deci-sions made in the design office can beelectronically linked with inventory and costcontrol, procurement, as well as controlling pro-duction in the factory, scheduling assembly onthe site, and delivering a customized house, asper specifications, at a guaranteed cost to thehome buyer. In addition, the increased memorycapacity of the new generation of microcomput-ers allows for simulated or real-time testing ofalternative designs in terms of cost, productionease, and customer acceptance. Given this ca-pacity to manipulate and combine, standardiza-tion by repetition becomes redundant, since it isnow possible to program the computer to takecognizance of complex and/or sophisticatedcompatibility rules for dimensional and/or posi-tional coordination, without necessarily repeat-ing the end product. This promises more, notless, design freedom in less time at equal, if notlower, cost to the end user.

As an extension of the above, it is now tech-nically feasible, both in the US. and to an evenlarger extent in Japan, to combine computer-aided design directly with the sales office,where the customer can actively participate inthe design of his or her future home plan and atthe same time get instant feedback on cost anddelivery.

Many of these innovations have been intro-duced piecemeal and, more often than not, weredeveloped independently of each other and on alimited application basis. It is now becoming ev-ident, especially in view of the Japanese exam-ple, that a fully-integrated, computer-aidedsystem which covers all aspects of decisionmaking from design to erection is not only feasi-ble, but virtually inevitable. This, in turn, willsignificantly affect the entire practice of design.An opportunity will be provided for the de-signer to again become a true ‘master builder,’since he or she will be able to assess the conse-quences of each design decision on every aspectand phase of the total design-delivery process,rather than having to depend on time-consum-ing and indeterminate processes of delegatedcontrol. The impact on design-office organiza-

tion, professional decision-making roles, andeducation is yet to be assessed, but surely willbe dramatic.

Beyond that, the capability of computer-aided design-delivery systems to communicatewith each other may be expected to have anequally dramatic effect on all other aspects ofdecision-making in the construction industry,both in terms of horizontal and vertical commu-nication flow, to wit:Horizontal:● Quick access to powerful local as well as na-

tional data-bases on a fee-for-service basis(e.g., Specwriter, AEPIC, etc.)

● Nationally coordinated and periodically up-dated catalogs of products, assemblies and en-tire home packages, including performanceand cost data (e.g., a Sears catalog of build-ing)

● Linkage between electronic-specification databases, testing, and code administration. Forexample, a given design can be matched byentering its specification ‘profile’ into a code-checking program, to give the designer instantfeedback on code violations or alternativecode-compliance rules

• Electronic control of inventories, linked tocost and availability

● Customized, as well as automated, productioncontrol

• Robots for productivity and quality control● Positive cost control and accurate quantity es-

timates, linked to design● Testing and comparison of alternative design

solutions against all or some of the above.Vertical:• Elimination of ‘back-f-the-envelope’ bidding• Bidding based on combination of best or least

expensive modular packages, rather than low-est overall estimate

● Direct end-user input into design process, al-lowing simulated as well as real customizationof plan, linked to instant cost estimate of de-sired solution

● Time-lapse monitoring of energy consumptionas part of budgeting home-maintenance ex-penses

• Scheduled operation and maintenanceroutines as part of electronic home-controlsystems

Eric Dluhosch 73

■ Full-service professional services that are inte-grated both horizontally and vertically andare multidisciplinary. Elimination of divisionbetween design and production.

Product/Process

■ Substitution of cheaper and/or better perfor-mance products, with better characteristics interms of handling, connections, interface andmaintenance ease

• Substitution of hand tools by power tools, andeventual transfer of most conventional site op-erations into the factory

● Introduction of computer-controlled machinesin production process. Increased diversifica-tion of end product

● Introduction of robots, both in production andin the home

● Gradual shift from ‘constructing’ a house bymeans of semi-processed and extensively site-modified materials to fully-processed and pre-coordinated elements, assemblies or entiremodules. Elimination of waste in cutting andother manipulations on-site.

Some examples of products or processes now onthe market:Materials:■ Annular ring- and spiral-shank nails● Single-layer siding/sheathing■ Improved paints● High-pressure, melamine-laminated, counter-

surfacing materials● Prefinished siding● Stress-rated lumber■ Self-sealing shingles• Epoxy coatings for plywood• Polyethylene vapor barriers■ Rubberized/plastic, single-sheet roof mem-

branes● Hardboard roofing panels■ Fiberglass insulation blankets/sheets• Prefinished large ceiling panels■ Prefinished tapeless, vinyl-covered, gypsum

drywall• Resilient tension flooring, applied without ad-

hesives and stapled only at edges● Solar-film window glass● Vinyl-extruded window sash.

Assemblies:■ Split-ring trusses■ Component wall panels (stapled or glued)• Wall-hung closets• Prehung doors and windows■ Pre-fab stairs• Wood foundations● Fiberglass modular bathrooms/showers■ Raised bathtub assembly with above-floor

trap• Washerless faucets■ Single-vent bathroom plumbing■ Snap-on pipe connections• Water-saving faucets, toilets, and shower

heads● Compressed-air-assisted toilet flush■ New air-to-air heat exchangers■ Self-diagnosing appliances.

The above list is far from complete, but is of-fered here as a sample of the rich variety ofnew products and assemblies which have en-tered the market since Operation Breakthrough.The impact of these innovations on all aspectsof construction practice is both subtle and all-pervasive. There is a clear shift from traditional‘craft’ skills to industrial-type ‘assembly’ skills,even on-site. In general, no work that can behandled mechanically (with some rare excep-tions, such as brick laying), is done manually.There is a parallel tendency to reduce the num-ber of joints by larger basic elements, and tomanage jointing operations as much as possiblefrom the factory. Joints constructed on-site aremore accurate and tighter due to power handtools, better joint compounds, joint fillers, andcover strips, all of which promise easier mainte-nance (as well as better performance) and meanless or minimal maintenance. Diaphragm con-struction permits the use of thinner wood sec-tions and wider spacing of framing members.The list goes on. As a consequence, homes areput up much faster and require less labor inputper unit. Quality control has shifted, to a largeextent, from the site to the factory. This has se-rious implications on inspection and code en-forcement. In fact, the whole system of codeadministration and enforcement is due for ex-tensive revision and will rely more and more oncomputerized data banks and mixed material/performance specifications.


Training of construction labor will require anew approach to specialized skill development,as well as periodic retraining in mid-career.

Unions will have to cooperate in negotiatingnew trade responsibilities, options for trade inte-gration, and a certain degree of skill reorienta-tion on a continuing basis.

Current distinctions between designer, devel-oper, contractor, and producer will becomeblurred, with integrated ‘full-service’ organiza-tions — teams providing comprehensive design-to-delivery services, possibly including financingand periodic upgrading options.

As a service sector, construction will rely onmaterials from both traditional constructionsupply sources, but also from formerly non-con-struction-oriented industries, such as electronics,plastics, fabrics, etc.

New specialities, such as geodesic domes,space-frame structures, inflatables, and fabric/tension structures are already entering the mar-ket as mature industries and are expected to in-vade the leisure and recreation segment of thehome-building market. Different skills in bothengineering/design and production/assemblywill develop as demand for these ‘exotic’ struc-tures increases.

With the exception of the mobile home, thetrend will be in the direction of ‘open’ or cata-log component systems.

Emphasis will be on the development of ‘fool-proof’ and easily maintained joints and connec-tions, allowing easy installation andmaintenance-free operation.

Factory production will continue to rely evenmore on computer-controlled machines and ro-bets, and will compete with conventional con-struction for a diversified and customizedmarket.

Craft skills will become part of a lucrative,but limited, market for retrofit, conversion, re-habilitation and historical preservation.

Houses will be sold with component warran-ties by manufacturers and may be financed bycomponent mix rather than as a finished prod-uct.

The development of plug-in, zip-in, and hook-up connections for telephone equipment, andthe use of plastics in plumbing, heating, andelectrical equipment will ease maintenance

problems, both in terms of currently outrageousservice fees for even minor repairs, and as an in-tegral part of self-monitoring devices, combinedwith home security, climate control and com-puter-controlled communication centers.

Much of routine maintenance will be per-formed on a do-it-yourself basis, with the pos-sibility of linking computer-controlledmonitoring systems with pre-recorded or locallybroadcast TV do-it-yourself instructional mes-sages. This will help the home owner to diag-nose, as well as correct, minor failures orcommunicate for help with warranty servicecenters.

Impact on Policy

Historical experience has shown that innova-tion responds to change, and change to innova-tion, in most unexpected ways, and that itusually manifests itself first at the interface ofthe frontiers which appear on the horizon of ourexpectations. If we fail to search for signs ofchange on the horizon of our hopes and expec-tations, crisis usually forces change and imposesinnovation. Much of our past reaction has beena response to crises of various origins, ratherthan the expansion of our freedom to act. Oper-ation Breakthrough has been mentioned beforeand may be seen as a reaction to the housing‘crisis’ of the sixties. The energy embargo of1973 precipitated another ‘crisis.’ Few of uswho have devoted years of our professional livesto the ‘solution’ of these crises have continuedto receive support for continuing our efforts,even though the ‘crisis’ may have lapsed. In-deed, we are asked to respond to new emergen-cies, to study new problems, to re-tool for newresearch. The tragedy is not that these projectshave failed, for they have not — at least not en-tirely — but the cost at which their limited suc-cess was purchased.

Thus, after having responded every five yearsto a new ‘crisis,’ it is my humble opinion thatwe do not need or deserve another ‘break-through’ or another heroic ‘if we can put a manon the moon’ effort.

What we need most is genuine continuity andthe removal of unnecessary institutional barriers

Eric Dluhosch 75

and restrictions, which have stunted sustainedefforts to take the long view of things, andwhich impede the ability to carry experimentsto their full maturation, including the chance offailure.

Since innovation by its very nature is impos-sible to predict — for then it would cease to beperceived as true innovation — it may be moreuseful to remove existing constraints which pre-vent us from breaking out of present conceptualcages and to develop a climate of confidence forlong-term institutional as well as private centersof excellence, which may or may not invent newgadgets, but which will act as powerful intellec-tual and technical brain trusts, and whose mem-bers will act as a vital source of basicknowledge and understanding for both govern-ment and industry. The former to act as a facili-tator, the latter as producer. In concrete termsthis implies:■

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Agreement on long-term national goals, be-yond party or factional concerns;Assurance of long-term support for so-calledcenters of excellence in universities and not-for-profit think tanks;Removal of institutional barriers, restrictiverules, and bureaucratic interference withlong-term research and development;A clear mandate for short-term initiatives andresearch, without false promise of long-termand sustained support, if not expected orlikely to be forthcoming;Clear allocation of responsibilities and com-mitments to research and development be-tween government, industry and theuniversities;Monitoring of objective assessment of new

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technology as to its side effects, and in rela-tion to long-term goalsRemoval of conflicting jurisdictional rules be-tween local and national levels of governmentNon-adversary partnership between govern-ment, industry and universitiesReview of all restrictive zoning, based on newtechnical and life-style conditionsOperation and maintenance of urban infra-structure systems made independent of dis-continuous political mandates. Establishmentof minimum quality standards and technicalperformance criteria for capital investment inthe public sectorShort-term policy cycles to be coordinatedwith long-range national goalsAppointment of ‘technology watchers’ bothdomestically and abroad (based on Japaneseprecedent). Regular reporting to Office ofTechnology AssessmentEstablishment of national data base and in-formation exchange for construction technol-ogy advancement and dissemination ofresearch results and reports by technologywatchersEstablishment of regional construction tech-nology centers, say on the model of DutchBowcentrum, including affiliated continuedtraining and education programsSet up bonded warranties for new productsand processes to be introduced in market fortesting purposesUpgrading of equipment in trade schools anduniversities.

Eric Dluhosch is a Professor at the Massachusetts In-stitute of Technology, Cambridge, Massachusetts.

Documents

Modular Structures and Related Techniques Don O. CarIson