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Dean Johnson

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Roof Basics

roof trusses


Virtually all roofs on new homes today are built with pre-fabricated trusses. These go up much faster than hand-framed roofs, and even on a small addition it's often easier to order a few trusses and set those than to frame the roof 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 throughout this project, 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.

CAUTION: Roof work is always dangerous, so please read over some Important Safety Information we've filed on site here before starting your next project.


Ordering Trusses

pile of trussesRoof 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.

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).



Marking Cap Plates

marking cap platesOnce 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.

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). (Depending on the design, it may also be necessary to space the first two trusses 23-1/4" on center to ensure that the first piece of 4' x 8' roof sheathing is flush on the outside of the first truss but lands in the middle of a subsequent trusses.)

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.


Securing Gable End Truss

gable end trussTo 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.

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 hold the truss plumb and screw the braces into stakes driven into the ground.


IMPORTANT: Be sure to add any lateral or vertical bracing required by codes in your area to resist high winds. Your local building officials will help familiarize you with the necessary steps during the permit process.


Lifting Trusses

Lifting a TrussOnce the gable end truss is fully secured, plumbed and braced, you can raise the other trusses up onto the walls. This can be awkward since trusses are usually long and unwieldy.

On large projects, contractors will often hire a crane to lift the trusses up. Doing it by hand is possible (and cheaper) but it requires adapting steps similar to those below to fit your situation.


  • Set one end of a truss on one wall plate with the truss upside down.

  • Set the other end on the other plate.
  • Swing the truss into its upright position.
  • Rest it against the gable end truss already secured.
  • Raise the other trusses the same way, one by one, and stack them against the gable end truss, making sure the other gable end truss is the last one to go up.

lifting trussTwo 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. 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

roof trussesAfter 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 far end from where the trusses are stacked) working your way back to the first gable end.

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 on hand to serve as braces.

truss spacerMark those off with the same 24" on center sequence that you marked on the wall plates.

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).

TIP: Sometimes that second gable end truss is NOT exactly 24" on center from the neighboring truss. In that case, just measure the exact distance between those two trusses along the cap plate and move the mark on the end of your brace as needed to match that distance.



Building Gable End Overhangs

gable end overhangSometimes 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.

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 equaling the distance between the 2 ends trusses plus the length of the overhang (usually 6 to 12 inches).

nailing lookoutsNail the lookouts in place with their ends nailed to the side 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.


Sheathing Roofs

dean johnson cutting with circular sawBefore 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.

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-fascias in to the ends of the rafter tails, extending as needed at each end to account for the gable end overhangs.

first sheet of wood on roofThe 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 at the other end in the middle of a truss as required.

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.

Mark wild ends of roof sheetingSnap chalklines over the wild ends to reflect the overhang and cut the ends off with a circular saw.

You can also let the last course of your sheathing run up past the top of the trusses and then cut that row 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.


Building Soffits

sub-fascia in soffitOnce 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.

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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