Advanced Topics of Straw Bale Construction Report

7/27/2019 Advanced Topics of Straw Bale Construction Report

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Seven Advanced Topics of Straw Bale Construction

Below are seven advanced topics to help you plan and build your straw bale home. You

may not need to know about all of these topics for any one project, but they are allimportant details to have an understanding about. There's always more to learn, and this

is a simple introduction into these advanced details. I hope that there is enough here toinspire you and to give you the confidence you need to tackle your own project.

1.Electrical Installations

If you plan to have electrical service in your home, you will need to know how to install

it as, chances are, the electricians will not haveexperience with straw bale structures. The

electricians may therefore turn to you for advice onhow best to outfit your home with power. If you run

photovoltaic power to your home, you will also haveto find someone versed in those systems as

individuals accustomed to wiring standard residentialapplications, no matter how skilled they are, may not

have the required expertise to satisfactorily tie in the solar system to your power system.All of the wiring will be buried in the walls behind your beautiful finish plaster, so make

sure you get it right the first time. Ripping out finish plaster to fix a faulty wiring job issomething we hope nobody should have to endure.

Timing is everything in construction. If you call for a subcontractor and are not ready for

them when they arrive, you will very quickly find yourself on the bottom of their returncall list. Your electrician will have to make a number of visits to the house, especially if

you pour a slab floor. In that case, they will need to rough in their work after the formsare up, but before the concrete is poured. Accurate form layout is essential for this. If

your forms are off, your wiring conduit locations will be too. If the conduit is off, itcould land in a room rather than in a wall. That is ugly and hard to fix.

After the rough-in below the slab, the electricians will need to return and finish the rough

in above the slab. For this, the house needs to be dried in, otherwise, the electricianscannot rough wire per the National Electric Code (NEC). Unlike conventional

construction when the electrical is installed before theinsulation, do not call the electricians without having the

bales in place. The wiring is best installed directly in thebales after they have been stacked but before they have

been meshed and shaped. Have a clean surface for themto work with. In other words, if you plan to weed whack

an inch of material off the face of the bales in certainplaces, do that first and then call the electricians. If you

plan on creating nooks in the face of the bales, it is good practice to cut those in beforethe electricians run their wires. If you are on a tight schedule and cannot complete the


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nooks, be sure to spray-paint their locations on the bales so the electricians know to avoidthose areas with the wires.

Anchoring the electrical boxes is important and quite simple. If the boxes are not

adequately anchored in place, they may twist out of plumb during the application of

plaster. Once the boxes are knocked out of place and plasterhas hardened around them, they are difficult to fix and ahome made look will pervade the house. Code usually calls

for the boxes to be anchored with wood spikes into the bales.This is a good start, but the box can still move quite freely

and should be anchored with a piece of plaster lath as well.The spike stops the box from sinking into the wall, while the

lath stops the box from tilting side to side and pulling outfrom the wall.

This has been a common way of attaching electrical boxes for years. That doesn't mean

it's still the best way. in fact, I have moved to using plywood squares with holes cut outof them instead. The whole is the exact size for an "old work"

box, the kind that has "ears" on it to grab the back of drywallwhen adding a box to an existing wall (see picture). The

plywood is about 3" larger than the box all the way around andso gives adequate space to nail the wire mesh which ultimately

locks the electrical box in place.

Here's another tip. Make sure that all of your boxes in any oneroom match in height off of the floor. All plugs and switches

should be at the same height (for plugs and another forswitches) per code, but small variations are common in straw

bale construction, so be sure to at very least make each roomconsistent. Also, remember that plugs and switches above cabinets have different height

requirements. It's easy to forget cabinets will be placed against the wall when it's justexposed straw!

2. Plumbing Details

Keep as much of the plumbing out of the bale walls as possible.

Thats it, end of lesson. Okay, so theres more to it than that, but thatis perhaps the most powerful tip I can offer. If you can manage to

keep all of your plumbing within interior, stick framed walls, youwill eliminate most of the hassles associated with plumbing straw

bale structures. In fact, if designed properly, a straw bale house willdiffer very little from a conventional house as far as the plumbers are

concerned.


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A typical problem area is the kitchen sink. Most home owners want a kitchen sink with aview. In most cases that means the sink is against an exterior wall centered on a window.

That makes it difficult to keep the plumbing out of the wall. In some scenarios theplumber can wet vent the lines to allow them to exit the building through a framed

wall. If not, you have two options to best protect the bales. The first is to sleeve the

pipes in wider conduits so that if there is a leak, it will be contained within a secondarysection of pipe. Another option, and the one I strongly prefer, is to block out the wallwith framing and place the pipes within the block out. The interior of the block out can

be water proofed to contain any leaks and direct them out of the house without contactingthe bales.

Another plumbing detail commonly used in conventional homes is the placement of the

tub/shower against an exterior wall. Unlike conventional homes, the tub/shower wallswill be well insulated against a straw bale wall; however, the risk of water damage to the

bales is high and special care must be taken. The extent of the risk is proportional to thepermeability of the finish materials for the shower. In other words, if a drop in fiberglass

unit is used to create the walls of the shower, the bales can be adequately protected withminimal extra effort. On the other hand, if some porous tile or natural stone is used, the

substrate will have to be protected with extra care as waterwill find its way through thefinish. The less permeable the finish material, the better. For example, the fewer grout

joints the material has, the less likely there will be a problem as grout is very permeable.There are many options out there including tile (well backed), solid surface material like

that used on counter tops, metal roofing, natural stone, glass, drop in fiberglass units, andothers.


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Whenever it is not possible to protect the bales from contact with water, consider framingthe area out as shown in the sketch above. In this scenario, the framing and wall

insulation can be wrapped in waterproof materials that drain to the exterior. This notonly gives you more space in your bathroom floor plan, but also eliminates the risk of

damaging your bales with water. Another place this comes in handy is when placing a

hose bib through an exterior bale wall. This total isolation of plumbing from bales is, inmy opinion, the best way to manage water in bale homes.

Finally, follow standard practices for wet locations in the design. Keep kitchens,bathrooms, laundry rooms and other wet areas close to each other to minimize costs and

material use. When building with a concrete slab, locations on the first floor need to beaccurate and well planned as they will literally be set in stone once the concrete has been

poured.

3. Hanging Cabinets

If possible, eliminate the use of upper cabinets in the kitchen. A well designed pantry can

easily replace many upper cabinets. This will simplify the baling process by eliminatingthe need to provide horizontal nailers for the cabinetry. If you cannot design the kitchen

to avoid the use of upper cabinets, you will have to install nailing backers in the bales onwhich to hang the cabinets. Notice the black felted, horizontal nailers on the right hand

side of this photo. There are nailers for the top of the base cabinet as well as the top andbottom of the upper cabinets.


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A bit off topic, but notice also in the picture the partition wall anchors against the strawbale walls. The vertical studs with felt covered plywood backers extending on either side

provide nailing surface for the interior wall drywall and the bale wall mesh.

Bale walls are not known for their flatness. In fact, they are somewhat treasured for their

natural undulations. That said, the cabinet and counter sub-contractors will want toinstall against as flat, straight and square of a surface as possible for a solid and secure fit.Without a flat and straight wall, the counter tops will not fit tightly to the wall. This not

only looks bad, but also creates a problem for the bales which run the risk of getting wetfrom splash dripping down behind the counter. In addition to improving the quality of

the job, creating a flat, straight and square wall makes the installation faster and thus lessexpensive.

A great advantage to straw bale construction is the thickness of the walls. When it comes

to cabinetry, it is possible to recess the cabinets or shelves into the bales walls. Thiscreates extra storage space without sticking the cabinets further out into the room. Or,

you can set the cabinets back even further and place theface frames flush with the plane of the wall. This

works well in Japanese style architecture and creates aclean line for any set of cabinets or shelves. It is also a

good idea to recess refrigerators as they are oftendeeper than the cabinets around them. By recessing it

into the wall, you can line the face of the refrigerator upwith the face of the cabinets.

Even if you do not hang cabinets within the depth of the walls, you can still create

beautiful accent pieces by cutting niche into the walls. The niche can be any shape yourimagination conjures up and can be cut to any depth. In general, do not cut them too

deep as the insulation value of the wall will be reduced by cutting out the straw in thenook. Often, it makes sense to mimic a window or door opening in order to balance the

language of the building.

4. Creating Round Walls

Round buildings have long been a part of the construction world. Creating round detailsin conventional homes has been a hassle for just about as long. Straw bale walls, on the

other hand, lend themselves nicely to the creation of roundshapes. The pliability of the bales enables them to be bent

to the right shape while still retaining their structuralstrength. The hardest part about building round walls in

straw bale construction is still the conventional part: theframing.

The key is to get as close to the shape as possible with the

rigid materials of wood and steel and then use the pliablebales and plaster to smooth out the differences. You will


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find that certain radiuses become too much for even a bale wall to handle. The larger theradius, the easier the round wall is to create.

When windows and doors are added to the

equation, it gets harder. Once again you are

dealing with a rigid building material and tryingto conform it to a bend. In general, the samerules apply as those outlined above; however, you

will have to create extra sill protection to stop thewalls from taking on water. This happens

because the center of the windows will berecessed into the bales by the simple fact that

they are straight and the walls are curved. Withproper attention to flashing details, and the creation of a sill, this does not present a

problem and can actually enhance the look of the building.

Round walls are a great application for using load bearing construction. Although loadbearing straw bale construction is outside of the scope of this course, it is important to

note that curved walls are significantly easier with load bearing detailing. As mentionedabove, the hardest part of building round walls with in-fill construction is the rigid

framing members. If the framing is removed, the only other difficulty is in the door andwindow buck design. The same solutions available for in-fill construction can be utilized

for load bearing bucks as well.

5. Baling Without Running Bond

Time and time again, the importance of laying the bales in running bond is reiterated. If

the bales are not run in this fashion, i.e. so that the joint created by two bales next to eachother is spanned by a solid bale above and below (like bricks), the wall will be weak and

unstable. There are, however, situations where runningbond is not a viable option and the wall must be stacked

one bale directly on top of another. A perfect exampleof this situation is when two windows are placed close

enough to each other in a home that there is onlyenough room for one width of bale in between them.Stacking seven or eight bales on top of each other is not

very strong, especially if they are not full length bales.In a situation like this, you must anchor the bales to the frame to increase their stability.

Additional blocking may be required within the frame to make this possible. Install theblocking after several courses of bales so you dont create additional notching

requirements. The blocking, installed after a bale, can also help secure the wall bysqueezing the bale into place.

Another place where a continued running bond can be interrupted is when you need to

switch from baling on the flat (strings on top and bottom), to baling on edge (strings onthe sides). This is sometimes required if a section of wall needs to be thinner than the


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section next to it. Rather than running the bales through a band saw or ripping them witha chainsaw, they can be laid on edge. The problem with this, of course, is that they are

no longer the same size as the bales on the flat so the running bond cannot continue.Again, the bales at the transition of these two techniques need to be anchored to the frame

with additional detailing.

Running bond construction is not possible if the bales are interrupted by something overthe entire height of the wall, no matter what it is. To that end, windows that extend to the

floor and ceiling, doors, bookcases, and all other interruptions may require extra attentionfor the bales. In these areas, it may be possible to rely on the strength of the mesh to

anchor the bales to the frame; however, if the wall feelsweak, it probably is and additional anchoring will be

necessary. The bales can be anchored to the frame in anumber of ways including twine, strapping, mesh, or

additional framing. I have found the simplest method isto install "squash blocks" as described above. Small

additional sections of wood blocking installed after a fewcourses of bales work extremely well. Remember that tight bales are essential for a

quality plastering job as loose bales make a weak wall and force the plaster to act as astructural bridge in loosely baled areas.

6. High Rain Environments

If you live in an area where rain, and lots of it, is the norm, you will need to make someadjustments to the detailing of your building. It is

very important the walls be protected fromcontinuous rain. The best way to accomplish this is

by designing adequate roof overhangs to stop therain from hitting the sides of the building. In the

case of multiple story homes, you may need to addan additional roofline at the floor level of the top

stories. Without this, the structures main roof willnot be able to protect the lower storys walls well

enough.

Roof overhangs will only help as much as they themselves are protected. In other words,

a roof overhang will help prevent water landing directly on the walls as it rains downfrom the sky; however, if there are no gutters on the overhang, the rain will have an

opportunity to splash up onto the walls as it falls off of the roof and hits the ground.Even with gutters in place, you may choose to add housewrap to the bottom two or three

courses of bales to protect the bales from rain splash. Another option is to build a smallpony wall and place the bales on top of that. This idea has two major benefits. First of

all, it keeps the bales away from rain splash. Secondly, it provides an area for theplumbers and electricians to run their materials without having to get into the bales. One

downside to building a pony wall is the extra lumber used for the construction whichcould otherwise have been avoided.


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A detail often overlooked when building a straw bale house is the placement of

waterproofing material on top of the bales before the walls are plastered. The idea behindthis is that if the roof ever leaks, the water will run down the rafters and into the bales.

With the waterproof membrane in place, the water cannot enter the bales. Instead, it will

be directed towards the plaster. When it hits the plaster, a wet mark will eventually showup and alert you of the leak. Then the investigation begins and the search for the leaksource is on!

The most common leak in any home is around the wall openings: windows and doors.

Proper flashing details are a must in any home and perhaps even more so in a straw balehome. If the proper counter flashing and flashing are

not installed, leaks may find their way into the buildingand saturate the bales. The presence of the leak may

not be detected until it is too late. With proper flashingof the openings, water that manages to make it past

your first line of defense will have to navigate its waythrough a series of waterproof membranes before it can

reach the bales. With extra defense against waterinfiltration, you should never have trouble with water damaged bales.

7. Patching Holes in the Bales

No matter how precise you are when baling, there will be spots that need to be filled in.In most situations, this takes place during the stuffing phase. There are spots, however,

that you may have missed while stuffing. With thewire mesh in place, it can be difficult, if not

impossible, to stuff straw into these gaps. Whenthat is the case, a few options are available. You

could simply fill the holes with plaster, but thisbecomes expensive and the strength of the patch is

directly related to the strength of the plaster. Mostplasters are not rated for structural fill and so

depending on it for such a fix is unwise.

Packing cob, a mixture of clay, sand and straw, into the holes is a great option. It is

cheap, especially if you have the materials on the site (i.e. clay rich dirt, sand for plaster,and straw), and it is very strong. Another option is to use expansion foam. Although less

environmentally sound, it works well to fill voids. The best example of a good use ofexpansion foam is in areas where cob cannot fill the entire void due to the shape of it. In

other words, areas where the opening is small but the void is large. The foam can fit intothose spaces and fill them up well.

Before the mesh is attached to the bales, you can use

loose straw, cob, or a straw/clay mixture to fill gaps.There are some cases where the material, no matter


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what it is, will not stay in place. This can be very frustrating. In these cases, use burlappatches. The burlap is fastened to the bales in small pieces and then straw is stuffed

behind the patch. This way you do not have to work behind the sharp metal mesh whichcan sometimes be a struggle to add your stuffing and have it stay put.

No matter what type of fill material or patch you choose, be sure to keep the structuralmesh free from it. If the foam, clay or cob engulfs the wire grid, then the mesh will nolonger act as a part of the plasters structure in that area. Although the impact of such a

structural gap would likely be minimal, it is best to pay attention to all the details, nomatter how small they may seem, in order to end up with the best project possible.

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Advanced Topics of Straw Bale Construction Report