Roof Structure: Install Trusses, Frame And Sheet The Roof

8.01 – Check the walls

Check your walls for square, curve and bow. You can’t fix the square at this point, but you can fix the other 2.

Square

Pull a tape measure diagonally from corner to corner to determine if the top of the walls are square.

There is nothing you can do to fix the square. But you want to know if it’s not square so you can anticipate problems with the sheeting. This way you’ll know there is going to be an issue and can make adjustments as you do the sheeting.

Curve and bow

Pull a chalk line along the top plates to make sure the walls aren’t curved. Add bracing as necessary to straighten them out.

Also measure across center of walls to make sure they aren’t bowed in or out relative to each other. Add bracing as necessary to straighten them out.

8.02 – Layout top plates

Mark the top plates for the trusses. The truss manufacturer will specify the spacing but it will typically be 24 inch on center.

Pull your tape from the same end for both walls so as to not compound any errors. And make sure to start the tape at the end of the top plate and not outside the siding.

Mark the edge or edges of the trusses and not the center because you will not be able to see a center mark when the truss is on top of it.

8.03 Prepare gable end trusses

There are 3 things you need to do to the gable end trusses before they are ready to install:

  • Sheet them
  • Router the vent opening
  • Make the flying rafter cutouts

Sheet the gable end trusses

How you sheet the trusses will depend on if you install them flush with the top plates of if you hang the siding over the edge of the wall.

If you will install them flush then install the sheeting to the bottom of the truss. If you will install them with the siding hanging over the wall then install the siding with a 2 or 3 inch overhang below the bottom of the truss.

For appearance purposes its nice when the siding on the gable end matches the siding on the wall below. To do this you need to start the siding on the same end of both.

You can work with the truss up on the stack of trusses or move it to the floor of the garage. I prefer to move it to the floor of the garage.

Cut pieces of siding to length and nail them to the truss beginning on the same end as the wall, and watch your bottom overhang if any.

Trim the excess off the top with a skill saw or router.

Route vent openings

When you order the trusses you will specify if you want a vent in the end trusses, and what size. You can usually buy the vent and have it delivered with the truss package. That way you know it will fit.

Route this vent opening with a router or cut it out with a skill saw.

Flying rafter support cut outs: See Figure 8.03

Start 12 inches below the peak of the truss and mark your first cut out here. Then space the rest of the cut outs at 48 inches on center max. Adjust them so the spacing is about even from the first cutout to the end of the truss.

Use a 2 inch 2×4 scrap and mark the width and depth of the cut out on the front or back side of the truss.

Adjust your skill saw blade to the depth and make lots of small cuts to remove the material. Clean up the bottom of the cut with a wood chisel or wood file and test for fit with a piece of 2×4.

Make the cut outs on both ends of each truss. Use your first side as a master for the other 3 truss sides.

8.04 – Raise gable end trusses

Raising the trusses is basically a 3 person job. You will also need 2 tall ladders.

Secure two 2x4x8ft braces to the face of each end wall. These braces will hold the truss vertical until you get it nailed in place.

If you are going to offset the truss so the siding extends below the top plate then you will need to use spacers the thickness of the siding between the braces and the wall. These spacer will allow the siding to slide between the wall and the brace.

Hang the truss on the top of the walls with the siding facing inside and push it all the way to the end wall. Center it from side to side.

Get 1 person up on a ladder on each end of the truss. The 3rd person in the center will raise the truss with a 2×4. As the truss is raised the 2 end people will maneuver the bottom of the truss so it rests on the top plates. This will take the weight off the center of the truss. Otherwise it might break.

Continue raising the truss until it’s vertical. The 2 people on the ladders will make sure it is centered and that the siding overhang slips down in between the braces and wall.

When it’s in place then secure it to the braces with a few screws. Then secure the truss to the top plate with nails through the siding overhang into the top plates, or toe nailed into the top plate along the base of the truss.

Raise and secure the other end truss the same way.

8.05 Install the rest of the trusses

See Figure 8.05a

Make a truss raising stick like in figure 8.05a. You will use this to raise the trusses and hold them while they are nailed in place.

If you want to vent the soffits you will need drill several 2 inch holes in the truss blocking and cover it with screen to keep the critters out. Otherwise use solid 2×4’s.

See Figure 8.05b

Measure from the inside edge of the gable truss to your first truss layout mark and cut a 2×4 block this length. Toe nail it to the top plate even with the outside of the siding on both walls. This will space the first truss properly.

Be careful when you handle the trusses because they are easily broken and that will put your project behind schedule until a replacement arrives.

Carry the first truss in upside down and put one end up on the wall, then raise the next end so the truss is hanging upside down on the walls. Slide it close to it’s final location and centered on the wall.

Raise the trusses

One person will be up on the ladder at the end of the truss. Another person will be at the base of the truss and the third at the peak of the truss.

Hold the base of the truss level as you start to raise the peak end of the truss. The truss has no strength while laying horizontal. This is why you need someone supporting the base.

As it nears horizontal, take your truss stick and hook it into the truss and continue raising it until it is nearly vertical. The person from the base goes up on the ladder and the 2 people on the ends bring the truss up to it’s layout mark and center it from side to side.

Toe nail the truss to the top plate and nail through it into the truss blocking on the other side. Do this for both ends of the truss.

The truss should stand up on it’s own now. But if you want to be safe, nail a 2×4 from the gable end truss to this truss near the peak of the truss.

Continue installing all trusses in this manner until you get to the last 4 or 5 trusses. Because the space is becoming limited you will need to raise the last few trusses up and stack them against the gable end truss.

Then move them into place and nail them down one at a time.

8.06 Truss framing, see Figure 8.06a, b

Ridge blocks

Make sure your gable end trusses are vertical. Use a level and brace them in place if necessary. Cut a 2×4 block the same length as the 2×4 truss blocking at either end of the truss. Loosen or remove your temporary braces on top of the truss and nail this block in between the peaks of the 2 trusses.

Measure from the outside of the gable truss (not including the siding) to the center of this first truss. It should match the spacing at bottom of the truss, and either be 24 inch or 24 inch plus the truss offset (the width of the siding). This is assuming the truss manufacturer has specified 24 inch spacing.

Cut and install the rest of the ridge blocks. They all should be the same length (22 1/2 inch) for 24 inch center spacing, except the last block. Which will be the same length as the first block.

Rat runs

The truss manufacturer will specify the spacing for some braces for the bottom of the truss. They are typically called rat runs.

Snake some long 2×4’s into the bottom of the trusses. It’s often possible to get them in through the gable end vent cut outs.

Measure the center spacing and nail the brace to the truss through the top of the brace. Do this for both sides and the same for all trusses. Make sure to secure the ends of the braces into the gable end trusses also.

Now the tops and bottoms of the truss are spaced and secured on their proper centers.

Trim truss ends

Snap chalk line and mark the ends of the trusses for their proper eave overhang and trim the truss ends. Make sure to use a square to transfer the cut mark to the side of the truss.

Install truss end boards, see Figure 8.06b

Measure and cut the truss end board. Make sure it extends the proper amount beyond the gable end trusses. You will probably have to splice this board so cut the inside end at a 45 degree angle. Hold it in place and begin nailing it to the truss ends. You might have to move it up and down a little to match the trusses.

Place the matching but opposite 45 degree end in place and nail through both boards and into the truss. Then nail to the rest of the trusses.

Flying rafter supports

Cut the flying rafter supports so they extend beyond the gable end trusses 1 1/2 inches less than the eave board ends. This is because they will sit inside the flying rafters and the end boards will extend to the outside of the flying rafters.

Nail them in place to the first inside rafter and the gable end rafter.

Flying rafters

Measure from the peak of the gable end rafter to the bottom end and cut a flying rafter this length, with the proper angle on the end.

Hold it in place and nail the bottom end to the truss end board. Then nail to the next flying rafter supports.

Hold the other side up and nail in place. You might want to drill a 1/8 inch pilot hole and use a 3 inch screw to hold the top joint together.

Do the same on the other gable end.

8.07 Sheet the roof

Check the edges

Check the truss end boards and flying rafters for straightness by pulling a chalk line along the outside corner. It’s not uncommon to have them rise and fall or bow in and out along their length.

You might have to remove and relace the nails in a truss or two to make it straight. This will put the truss a little high or low but that will show up less than a crooked facia.
When it comes to straightening out the edge you can often just tap the board away from the truss and leave a little gap. Then caulk these gaps before you paint and they will disappear.

Optional plywood around edges

OSB is cheaper than plywood but it doesn’t hold paint as well. It will flake over time, even if it’s under the eaves and out of the weather. A solution to this is to use plywood around the edges where they will be painted. Then use OSB for the interior of the roof.

If you are going to enclose the soffits OSB flaking will not be an issue.

Install sheeting

Begin the sheeting at a bottom corner and work your way up the roof. Space the sheeting apart about 1/8 inch on all 4 sides to allow for expansion. You can do this with the bottom edge of a speed square or use plywood clips. Plywood clips will provide a little extra strength to the joint, as well as spacing the sheets.

If your trusses aren’t perfectly square then you might need to cut the edges of the sheeting to fit.

Nail in an organized fashion so you don’t miss anything because verifying that it is properly nailed is part of the nailing inspection. If the inspector finds some missing sections that will delay your project.

Hurricane ties

Hurricane ties (or H25’s) are metal straps that tie the trusses to the top plates.

They require special nails that are sold just for the job. Put a tie on both ends of each truss, and a nail in each of the holes. You don’t need to install them on the gable end trusses because they are tied together through the framing.

Inspection

This is the time to call for a nailing inspection, if one is required. The building inspector will come out and make sure you have put enough of the approved nails into the framing, siding and roof sheeting.

They have to see the nails before you install any roof covering or paint.

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