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Virtually all roofs on new homes today are built with pre-fabricated trusses which
go up much faster than hand-framed roofs, and even on smaller additions it's often
easier to order a few trusses and raise those than to frame the roofs by hand.So we'll assume that most people will lean toward trusses in their own projects and explain the following basic steps on how to build a simple gable roof with trusses. For definitions used throughout this section see Framing Glossary But
there's always a bit of hand-framing to be done on a new roof, even if the main
structure is built with trusses--especially on additions where the new roof usually
has to be tied in to the old roof or to an existing house wall. And you might
be interested in a couple other roof projects. So
in our next roof framing page, Special Roof Techniques, we'll give you a quick
idea on how to tie a new roof into an existing one, how to hand-frame a small
hip roof and how to build a gable dormer.
On most projects, your lumberyard or home center can place the order for you,
but you must supply the dimensions, pitches and styles (gable, hip, flat). Those
are usually available on the plan (which you need to get your permits anyway). Because
of that 2 to 3 week lead time, you have to build your walls to pretty much the
exact specifications and keep them plumb, level and square or the trusses won't
fit.
They're usually secured 24 inches on center, so you just start on one end marking
the first truss flush with the outside edge of the cap plate and making marks
for the subsequent trusses at 24-inch intervals (including a mark at the other
end for the last truss).
Mark the truss positions on the opposing cap plate starting from the same end
where you started measuring off the first cap plate to line the trusses up properly.
Raise one of these into position first at one end of your truss run, usually at
the point where you started your measurements, make sure it's flush with the outside
edge of the cap plate it's resting on and toenail it in place.
Nail 2 or 3 2x4 braces from the truss down to the ground outside the structure,
use those to position the truss plumb to the ground and screw the braces into
stakes driven into the ground to hold the truss in place.
On large projects, contractors will often hire a crane to lift the trusses up, but that's expensive. Doing it by hand is possible (and cheaper) but it requires adapting steps similar to those below to fit your situation.
But
ideally, there would be a couple people up on the wall plates pulling the trusses
up and a couple people below pushing--especially on 2-story buildings. (And possibly
a fifth person with a pole or a 2x4 to help tilt up the peaks)
Positioning and Bracing Trusses
It's
a good idea to brace the second gable end, plumb it and secure the same as described
on the first gable end. But don't try to brace each of the following trusses like
that. Instead, have a few 8-12 foot lengths of 1x4 pine on hand to serve as braces.
Then once you have a few of the trusses in place, nail the end of the brace over the second gable end truss up along the peak and then nail it to the other trusses, lining each one up with the marks you made. That'll not only set the proper spacing but it will also plumb up the other trusses (assuming the gable end truss is still plumb).
Once the other trusses are in place but before you start sheathing, mark the tops
of the gable end trusses and the trusses next to them 24" on center. Cut a series of 2x4 lookouts to a length equalling the distance between the 2 ends trusses plus the length of the overhang (usually 6 to 12 inches).
Nail 2x4's cut to the proper length along the ends of the lookouts to strengthen
the overhang.
Set a level against the wall and use that to measure along a level line to the
bottom of the first rafter tail, moving the level up or down till the tail hits
the length of your overhang minus 1-1/2" for a sub-fascia. Put a mark there, make
the same measurement on the last rafter tail and snap a chalkline between the
two marks, marking the bottom of all the rafter tails. Use the level to mark a plumb line up the side of each rafter tail at the chalk mark and cut along those lines with a circular saw. Then cut and nail the sub-fascia's in to the ends of the rafter tails, extending as needed at each end to account for the gable end overhangs.
Nail in as many pieces as needed to reach the other side, letting the end of the
last piece run wild. Start the next course of sheathing on a different truss to
stagger the seams and strengthen the roof and continue sheathing the roof till
finished.
You
can also let the last course of your sheathing run up past the top of the trusses
and then cut those to the proper height when all the pieces are in.
Once the sheathing is finished, you can roll out and staple down 15-pound builder's
felt to protect the sheathing from moisture and heat.
Measure the distance between the inside of the sub-fascia and the nailer you just
installed, cut one 2x4 lookout at that length for each rafter and nail those in
between the nailers with their bottoms flush with the nailers, nailing one end
into the sides of the rafter tails and toenailing the other end into the nailer
on the wall.
Nail your soffit material up into the bottoms of the sub-fascia, nailers and lookouts,
measuring and cutting the pieces to make sure any joints fall on the lookouts
for proper strength. Later you can nail fascia board material (usually 1x6's if you've used a 2x4 sub-fascia) over the sub-fascia to finish off the edge and crown molding along the wall to cover any gaps between the soffit material and the siding. | |||
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Roof trusses are generally made to order for a given construction or remodeling
job, and they usually require about 2 to 3 weeks of lead time. 
Once the walls are plumbed, squared and straightened, they're ready for trusses.
But before raising them into position, it's best to measure and mark on each cap
plate where the heel of each truss will land.
To frame a gable roof, the truss manufacturer will include 2 gable end trusses
which are assembled with more vertical members than the other trusses to support
the gable end sheathing.
Once the gable end truss is fully secured, plumbed and braced, you can raise the
other trusses up onto the walls. But that can be awkward since trusses are usually
long and unwieldy.
Two people can handle this routine if they have ladders and scaffolding standing
by to safely climb up into position to swing the trusses up and stack them up
one by one.
After the trusses are all stacked up on the wall plates, you then walk them back
into position one at a time starting with the second gable end truss which goes
on the other end and working your way back to the first gable end.
Mark
those off with the same 24" on center sequence that you marked on the wall plates.
Sometimes gable end trusses are made 1-1/2" or 3-1/2" shorter than the other trusses
you order. That's to help you extend the roof out a few inches over the gable
end.
Nail
the lookouts in place with their ends nailed to the sides of the first full trusses
and the other ends running out over the gable end trusses with the tops of the
lookouts flush with the tops of the full trusses (lookouts on edge if the gable
end trusses are 3-1/2" shorter than the other, lookouts on sides if the gable
end trusses are 1-1/2" shorter than the others).
Before putting on the sheathing, you should plumb cut the rafter tails to their
proper lengths and install a sub-fascia board (if that's to be part of your soffit
framing) so you know where to start the sheathing.
The
first course of sheathing then goes in along the bottom of the trusses. You can
set the first piece on either end lining it up with the outside framing, but if
you've built an overhang that's not exactly 24" you'll have to cut the piece land
the other end in the middle of a truss as required. 
Snap
chalklines over the wild ends to reflect the overhang and cut the ends off with
a circular saw. 
Once you've plumb cut the rafter tails to a uniform length and installed a sub-fascia
board (as described above), use a level to mark a point on the wall at each end
of your rafter run level with the bottom of the sub-fascia board. Snap a chalkline
between your marks and nail up a 2x4 or 1x4 nailer with its bottom flush with
the chalkline.