Installing plywood sheathing and house wrap membrane
Installing plywood sheathing and house wrap is a straightforward task that even moderately skilled craftsmen can tackle provided they exercise patience and pay attention to detail.
Once framing is complete, the next step is usually installing plywood sheathing, which helps keep moisture out of the structure and also serves as a shear surface to add integrity to the framing.
Plywood installed horizontally was specified as the sheathing material on this project. The plywood comes in standard 4×8 sheets lined at 16-inch intervals to allow you to quickly locate studs during installation.
There are several choices for sheathing: plywood, as specified; OSB, as a cheaper alternative; or a combination of both. Substituting OSB can help keep the project within budget.
Installing plywood sheathing – vertical or horizontal?
If you are using both plywood and OSB, the plywood can be used for the first level of sheathing with the subsequent rows of sheathing in OSB. Always check code in your area to see if it specifies the sheets be installed vertically or horizontally. Some codes specify vertical at corners for maximum shear strength.
This begs the question: Should all the sheathing be installed vertically? One of the benefits of vertical sheathing is that the long edges come together at the studs and the required ⅛-inch gap between boards is sealed.
Code may also require blocking to add structural integrity to the walls. This can be done before sheathing or after. On this job, it was done before.
Using an adjustable, table-mounted radial-arm saw, we cut forty 14½-inch blocks in less than 15 minutes, as well as individually measured blocks positioned near the main frame support beams.
Measure each wall section separately and use a chalk line to establish the plumb line for the blocking. The blocks are then installed in a standard, alternating, under-over pattern to allow easy nail placement with a framing nailer.
Installing plywood sheathing
With blocking installed, we begin installing plywood sheathing horizontally. First, we lined up the plywood sheets flush with the corner of the building and checked to be sure everything was plumb.
We used a level to see if the corner was off or a stud was out of alignment. Once satisfied with the alignment, we attached the sheathing using 2½-inch 8p nails hammered into the studs. Ring nails are often recommended as they are less likely to pull out once installed.
Always complete your first row of sheathing before starting the next level. Each level of sheathing should be offset a half board to avoid continuous seams running up the wall.
Temperature and humidity can cause plywood to expand and contract. Therefore, it’s essential to give the sheathing material room to “breathe” during this process. One way to do this is to use spare nails tacked into studs between plywood sheets as a guide when placing adjoining plywood sheets.
The slight open spacing provided by the nails gives the wood plenty of room to adjust to changing weather conditions. Once the plywood sheet has been nailed into place, remove the positioning nails and use them to align the next one.
When installing the top level of sheathing, it may be necessary to accommodate rafter ends protruding from the exterior wall. This can easily be done by taking measurements and then using a portable circular saw to cut the desired pattern out of a plywood sheet before installation. This will also add to the tightness of the roof space when insulation is added later.
Cutting window and door openings
Once the plywood is installed, it’s time to go back and cut out any window or door openings. A reciprocating saw is the ideal tool for this task. Simply locate the corners of each window opening and drill a hole in the plywood sheeting large enough to fit your reciprocating saw blade through.
Once you have enough clearance to accommodate the saw blade, cut through the plywood taking care not to cut into the surrounding rough sill and bracing. If possible, have a helper stand by to hold the sheet and keep it from falling on you.
If a helper is not available, finish any cuts on window or door openings at the bottom of the plywood sheet (as opposed to the top) to better control it once the piece comes free. Or leave a small section of plywood holding the panel in place and then simply knocking it free with a hammer.
Tips for installing house wrap membrane
With your rough window and door openings cut, it’s now time to install house wrap, which adds an additional layer of protection from the elements. This step should be completed promptly after sheathing to protect the sheathing from rain.
Installing house wrap membrane is fairly straightforward. Starting at a corner of the building, unravel the roll of wrap about 2 inches around the starting corner and staple the wrap to the plywood. A slap stapler is the ideal tool for this job, as are sheeting nails.
Once the wrap is secure, continue to move slowly and steadily around the corner of the building and down the wall being covered. Take care to keep the wrap tight and level as you move, putting in staples generously as you move forward to keep the wrapping material as tight and wrinkle-free as possible.
Standard house wrap rolls are 9-feet wide and 150-feet long. Ideally, you should use single rolls of wrap fitted to the wall you’re covering. Since this isn’t always practical, a radial saw can be used to cut wrap rolls down to smaller sizes, if necessary.
If you do have to overlap wrap sections, take care to overlap sheets by at least 6 inches and staple them firmly into place before continuing to move forward covering unwrapped plywood.
Once the wrap is installed, you have to decide if you want to leave the window openings covered or not. Doing so will help protect the interior of the building from rain, but you run the risk of having high winds damage or even blow your freshly installed wrap off the building.
If you opt to cut rough openings in the wrap for the windows, simply take a box cutter or knife and cut an X in the wrap. This will give you four equally sized triangle-shaped wrap sections that you can then fold inside the window opening and staple to the framing.
Once the window openings are done, your final step is to walk around the building and cut away any low-hanging sheathing that’s contacting the slab.
−By Jack Roberts, builder and remodeler