It is assumed here that you will be applying plywood, particleboard or wafer-board for your garage sheathing. If you have chosen to use rigid roofing like metal, wood shakes or shingles, tile, etc, you can use 1 x 4 slats instead. With wood roofs, slats are a must to avoid rotting the wood shakes.
Plywood particle board or wafer-board roof sheathing is most commonly used, being low in cost and easy to apply. Choose an exterior C/D grade. The thickness will range from 3/8 to 3/4 inch depending upon local code*.
When ordering the sheathing, divide the total number of square feet of roof surface by 32 square feet (a 4' x 8' panel) and add an extra 15% for waste. An air compressor with a nail gun comes in handy for nailing large flat areas like this.
Most Common Mistakes:
- Not staggering the seams of the sheathing.
- Aligning sheathing with the edge of the roof rather Than perpendicular to the rafters.
- Attaching the sheathing wrong side up.
- Inadequate nailing.
- Panels not meeting in the center of a truss or a rafter.
1. Check the rafter ends (tails) to be sure they are all on a straight line. If the walls are crooked, the rafter tails will also be crooked. Try to correct this problem; but if you are unable to, pop a chalk line across the rafter tails and trim them with your saw before attaching the sheathing. This is crucial because this building line will be a very noticeable one when viewed from below.
2. Begin applying the sheets from the bottom of the roof (the eaves) and work your way up to the ridge. The last course at the top may need to be rip cut if the roof is not in 4-foot increments. It is important here that the sheathing at the eave line be exactly perpendicular to the rafters so that the sheets will meet at the centers of the rafters it is even more important that it be perpendicular than that it is flush with the rafter tails. A tapered piece of sheathing can be cut to fill in at the eave if necessary.
3. Usually, code* requires nails every 6 inches on the edge and 2 inches in the field. Pop a chalk line across the sheets to 'mark the centers of the rafters for a nailing guide.
4. Do not nail the edge rafters where the sheathing meets until the adjoining sheet is in place. This will enable you to move the rafter a bit if needed so that the sheathing meets in the center of the rafter.
5. Stagger the joints of each course of sheathing. This can be done efficiently by cutting a panel in half and using these half sheets to start every other course. Special metal plywood clips will add stability to the splices where the sheets meet between rafters.
6. Carefully work your way up to the peak of the roof. Check for alignment and end support as you go. For safety, temporarily nail a 2 x 4 "toeboard" horizontally across the lower panel of sheathing to brace yourself against as you add the second and subsequent courses of sheathing.
7. Sheath one slope of the roof at a time, ripping the top course to the needed width at the ridge. When one slope is completely sheathed, pop a chalk line down any slope edge (as in a hip roof) that needs to be cut at an angle. You may prefer to cut these panels before you nail them in place.
8. Set your circular saw to the correct depth and angle for cutting along the edge and saw off the excess overhang.
9. Repeat this process for each slope of the roof.
Wall Sheathing is often not needed or required below the siding. Check with your local building code*. If plywood siding is used, this may act as the sheathing as well as the siding; therefore, only the siding is applied. Applying plywood siding is the same as described here. For other types of siding, it will be necessary to consult the manufacturer's instructions.
Most Common Mistake:
1. Reading window or door sizes incorrectly.
1. Begin applying the sheathing from the same corner you measured out from when laying out your studs. Position the first sheet so that the edge of the 4' x 8' sheathing will be flush with the end of the wall while the opposite edge falls at the middle of a stud for secure nailing.
2. Hold a level against one side of the sheathing to determine if it is plumb while still aligning it over the center of the stud. Tack it into place with 8d nails.
3. Nails should be spaced 6 inches along all four edges and 12 inches in the center of the sheet over each stud.
4. Apply each subsequent sheet of sheathing in the same manner, butting one edge tightly against the previous one over the middle of the stud.
5. Should you encounter a stud that is bowed out of line, simply tack the sheathing into position; then, place another starter nail nearest the bow. As one person pushes the stud into line, another can drive the nail home, thereby holding the crooked stud in its proper position.
6. To cut sheathing around openings, press the sheet into position over the opening while another person marks the opening onto the back of the sheet from the inside of the garage.
7. Place the marked sheet on sawhorses and cut along the penciled lines with a circular saw set to the proper depth.
Covering Sheathing With Tarpaper: The
Most Common Mistakes:
- Neglecting to use the waterproof tarpaper between sheathing and siding.
- Not overlapping each layer sufficiently.
1. Use 15 lb felt paper as a waterproofing membrane between the sheathing and the siding. If no sheathing is used, the felt is placed on top of the studs and under the siding.
2. Begin at the bottom and wrap the felt paper around the perimeter of the garage. Attach the paper with staples.
3. The second and subsequent levels of tarpaper should overlap the lower one by at least 4 inches.
4. You can wrap this membrane right over the doors and windows, then cut the openings out with a utility knife.
5. We also recommend lining the rough opening of windows and doors with strips of felt paper.