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Rolling

oof trusses offer many advantages.They are lightweight (generallymade from kiln-dried 2x4s), so theyare fairly easy to handle. Because

trusses are engineered, they can span longerdistances without having to rest on interiorbearing walls, allowing for more flexibilityin room size and layout. Finally, installingtrusses on most houses is pretty simple. If youwant to get a house weatherized quickly, rooftrusses are the way to go. Ceiling joists andrafters are installed in one shot, and no trickycuts or calculations are required.

Lay out braces as well as platesLaying out the top plates for trusses is thesame as for roof rafters. Whenever possible, Imark truss locations on the top plates beforethe framed walls are raised, which keeps mefrom having to do the layout from a ladder orscaffolding. For most roofs, the trusses arespaced 2 ft. on center (o.c.). I simply hook a

Factory-made trusses save time and give you a roof engineered for strength and stability

R

DECEMBER 2004/JANUARY 2005 95

Roof TrussesBY LARRY HAUN

IT’S EASY TO KEEP A STRAIGHT FASCIA

Even if the walls aren’tperfectly straight, thetrusses can be. To keepthe eaves aligned and thefascias straight, you cantake advantage of trussuniformity. Snap a chalk-line along an outside topplate (top photo). Align amark on the truss with thechalkline when you set thetruss (photos right).

96 FINE HOMEBUILDING Drawings: Vince Babak

measuring tape on one end of the plate andmark the truss positions every 2 ft., putting an“X” on the far side of each mark. I also markthe layout on several 16-ft.1x4s, which serveas top-chord braces during installation.

A straight fascia is just a snap awayRemember to order trusses well in advanceof when you’ll need them. In Oregon, whereI work, a three-week lead time is common.Before I ask for truss delivery, I make sure allthe exterior and interior walls are upright,nailed off, and braced properly. Interior wallshelp to keep the exterior walls straight andplumb. In addition, with all walls in position,I have more support for the bundles oftrusses when they’re delivered.

Even when the walls are straight, it’s worthtaking some trouble to ensure that when thetrusses are installed, the rafter ends line upperfectly. There’s an easy way to do this.

I measure in 1 in. from the outside edge ateach end of the top plate. Then I snap a

chalkline the full length of the wall as astraight reference line (photos p. 95). As I seteach truss, I measure from the tail of therafter chord the distance of the eave overhangplus 1 in. I mark this point on the bottomchord of each truss and align the mark to thesnapped reference line, keeping the ends ofthe trusses straight.

I also snap a chalkline along the gable end-wall plates to locate and align the gable truss.Unless it’s required by code, I usually don’tsheathe gable trusses. The gable truss is setflush with the outside face of the wall sheath-ing below. I snap the chalkline along the gableend-wall plates 1 in. from the outside. Whenthe gable truss is set on this line, it overhangsthe right amount.

Cutting blocks to nail between trusses is another important step to complete beforeyou start setting trusses. In seismic and high-wind areas, code requires blocking betweentrusses at the plates and often at the ridge aswell. I cut 221⁄2-in. blocks to maintain the

Trusses gain their strength from light-weight components assembled in triangu-lar shapes. In most cases, they can spanthe width of a house with no supportfrom interior walls. Here are three common trusses.

Truss terms

W truss or fink truss

Scissor truss

Gable truss

Erected to ease installation, a temporarycatwalk is completed before the trusses arrive in bundles (photo below). Lay downthe bundle with the peak pointing in thedirection the trusses will be dragged.Spread out the trusses near their layoutmarks, overlapping each truss like fallendominoes (photo right).

UNLOADING AND SPREADING TRUSSES SET THE STAGE

Nonstructural gablestuds take the place ofstructural webs.

Bottom chord or joistchord creates a flat ceiling.

Bottom chords are pitched for vaulted ceiling.

Web

Web

Top or rafter chord

Bottom chord

Top or rafter chord

Top or rafter chord

24-in.-o.c. truss spacing and to help keep thetrusses stable as they go up.

Lifting trusses onto the plates To help with setting the trusses, I build a cat-walk scaffold down the center of the house.Framed with 2x lumber, the catwalk gives thecrew a safe, temporary platform to workfrom as we raise trusses into position and nailthem to the wall plates.

The next step is getting the trusses onto theplates. Around here, trusses are delivered inbundles held together with steel strapping.The number of trusses per bundle dependson the size of the roof and usually the types oftrusses. For this project, there were three bun-dles: the porch trusses, the scissor trusses, andthe trusses for the rest of the roof. With thehelp of a job-site forklift or the boom attachedto the delivery truck, the bundles are posi-tioned on top of the framed walls. If the house

is too tall for the forklift or boom, or if thetrusses are heavy or wide, a crane is the bestway to lift the trusses into place.

To be safe, I lay the bundles of trusses flatacross the walls at the opposite end of thehouse from where I’ll begin installation.Avoid the temptation to set the bundle oftrusses upright on the plates. If the trusses arestanding up when you cut the bands hold-ing the bundle, they can fall and hurt some-one. Lay the bundles down with the peakspointing in the direction you’ll be spreadingthe trusses.

Start at one end with a gable trussWhen the bundles are resting safely on thewall plates, I use tin snips to cut the metalbands holding the bundles together, takingcare to avoid getting sliced. The first truss isfor the gable end of the building and usuallyhas vertical studs instead of angled webbing.

Most trusses are lightweight, so one personwalking on the catwalk should be able to graba truss by the peak and pull it into position.

The gable truss is dragged to the end of thehouse first. Then, before any trusses areraised, the rest of the trusses are dragged overto their approximate locations, with each trussoverlapping the one below, like fallen domi-noes (photo facing page). With the trussesspread out in this fashion, the raising processgoes quickly and efficiently. On this house, thefront gable was the first to go up. While thetruss is held upright, I line it up with the ex-terior wall sheathing and toenail it every 16 in.with 16d nails. I also brace the truss temporar-ily until it can be tied to the rest of the roof.

Roll the trusses into placeWhen the gable truss is set, I roll the nexttruss into place, which in this case was a scissor truss (drawing p. 96). The truss com-

If the first gable truss isplumb, the rest will follow.On this house, the gabledoesn’t require sheathing,so the author aligns theoutside face of the trussflush with the wall sheath-ing below (photo top left).Holding a long level againsta tall truss web is a goodway to plumb the truss(photo bottom left). A temporary diagonal brace isinstalled to hold the gabletruss plumb.

BRACE THE GABLE TRUSS PLUMB AND IN PLANE WITH THE OUTSIDE WALL

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pany sent an extrascissor truss, so Inailed it to thegable truss to pro-vide nailing for the

end of the vaulted-ceiling drywall. A 2x4nailed to the gable truss could have done thetrick as well.

With the first gable resolved, I turn to raising the rest of the trusses. A team of threeframers is ideal for “rolling” trusses (photosabove). You need to have one framer who islocated in the middle and one who is placedat each exterior wall. Each truss is nailed tothe top plate with one 16d toenail on one sideand two on the other side. After the truss is

set, I install the blocking. As shown in thecenter photo at left, these 2x members main-tain a uniform distance (221⁄2 in.) between thetrusses and help the roof assembly to resistlateral loads.

When the first couple of trusses havebeen put in place, I nail one of the 16-ft.1x4s that I had laid out earlier to the rafterchords near the ridge. An 8d nail in eachchord holds the truss at the proper spacing tokeep the trusses stable until the roof hasbeen sheathed.

Once four or five of the trusses have beenput in place, I put in a permanent sway brace,which adds lateral stability in the event of anearthquake or high wind. A sway brace has

The 1x4 top-chordbrace helps to keeptrusses properlyspaced until roofsheathing is installed.Cut to a uniformlength of 221⁄2 in., 2x8blocking is nailed toadjacent trusses andto the top plate,bracing the lowerpart of the roof. It’salso important to install a permanentgable brace, extend-ing it diagonally fromthe tallest gable stud.

The middle man“rolls” each truss upright while his twopartners toenail trussends to top plates.Accurate spacing isensured because theauthor marked the 2-ft.-o.c. layout withthe plates and top-chord braces gangedtogether on the sub-floor before thetrusses were deliv-ered (below).

A TEAM OF THREE CAN MAKE QUICK WORK OF ROLLING TRUSSES

Top-chord brace

Blocking

Gable brace

heavy, they should be handled carefully untilthey’re secured.

Tying up loose endsWhen all the trusses are in place, I nail 16-ft.2x4s to the tops of the joist chords in the attic space, near the center of the span. Over-lapping each other and running the fulllength of the house, these permanent bracesstabilize the joist chords and hold them at thecorrect spacing.

If diagonal web braces are called for in theengineered specs, I nail them on at this point,along with any other braces. Metal hurricaneclips keep the roof attached to the houseframe in a heavy wind. The metal clips nail

45° angle cuts at both ends and extends fromthe top plate of an exterior wall up to the topchord of an inboard truss. Building code requires the use of sway braces at each end ofthe building and every 25 ft. between. But Ilike to install sway braces more often foradded insurance.

Now the rest of the trusses can be broughtinto position and nailed into place on the lay-out. For this project, we used scissor trussesover the kitchen, dining room, and livingroom to create a large open area with a vaulted ceiling. The scissor trusses have a 5-in-12 roof pitch with a 3-in-12 ceiling pitchfor the interior. Scissor trusses are set just likeregular ones, but because they tend to be top

to each joistchord andthen to the topplates of the ex-terior walls (Simp-son Strong-Tie Co.;800-925-5099; www.strongtie.com). They canbe nailed on the inside or outside of a wall. Besure to use the “hanger” nails made specifi-cally for nailing these clips. �

Larry Haun, author of The Very EfficientCarpenter and Habitat for Humanity: Howto Build a House (The Taunton Press),lives and works in Coos Bay, Ore. Photosby Donald Blum. continued

The trusses are up,but the framing jobisn’t done until the final bracing is installed. A combina-tion of steel framingconnectors and woodbraces strengthensthe roof assemblyand ties it to thewalls of the building.

HARDWARE AND BRACING GET THE ROOF READY FOR SHEATHING

BOTTOM CHORD BRACESRunning the full length of thehouse, 16-ft.-long 2x4 bracesare nailed across trussbottom chords to strengthenthe roof structure. ROOF TRUSS CLIPS

Installed where the bottomchord crosses an interior wall,these clips can help to preventdrywall cracks by allowing thetruss to move slightly inresponse to temperature andhumidity changes.

HURRICANE CLIPSInstall these metal connectorswherever a truss crosses anexterior wall. By securing thetruss to the top plate, hurri-cane clips keep the roof inplace during high winds.

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Reader Response

Don’t cut trussesExcellent article about roof-truss installa-tions (FHB #168, “Rolling Roof Trusses,”pp. 94-99). But I wish to add a cautionarycomment that trusses cannot be cut, drilled,notched, or modified in any way unless astructural engineer approves that alteration.Here’s a photo of an improper alterationfrom a three-year-old house that I inspect-ed (below). The rough framing was inspect-ed and approved by the city, and this webwas altered by the furnace installer after-ward. The tile roof was beginning to sag,and repair estimates started at $3,000.

—JOE NERNBERG

Agoura Hills, Calif.

$3,000 mistake