How To Foam Board Roof

Foam board insulation is easy to cut with a circular saw with a masonry blade or scored with a utility knife and snapped like you would drywall.

How to foam board roof.

The 4 x8 sheets of rigid foam board insulation were then laid out in a staggered pattern across the entire surface of the flat roof. Measure the depth of the rigid foam. If you want to install rigid foam above your roof sheathing in climate zone 3 then 1 2 inch of rigid foam board is not ideal this rigid foam layer needs a minimum r value of r 5 and that s impossible with 1 2 inch of foam. On small porches as long as you use a 2x plate where the rafters meet the foam it should be fine.

Some parts of the country necessitate a vapor barrier under the rigid insulation however this wasn t necessary in our case. You may need to buy longer roofing nails to reach the plywood through the. Most foam sheathed walls include a rain screen gap between the foam and the siding. There are typically 10 to a pack.

As for the porch roof you could either remove it entirely or cut back the sheathing and framing enough to allow the new foam to slide into place. Remove existing roofing and non adhered underlayment to expose roof sheathing. This video shows how to make a roof. As my article states you need a minimum of about 1 5 inch of eps 1 inch of xps or 1 inch of polyiso.

Install rigid insulation board in multiple layers with joints offset vertically and horizontally between adjacent layers. Apply continuous air control membrane to existing roof sheathing or implement continuous air control at roof sheathing. For extra protection dab a small amount of caulk over each nail used to secure the rigid foam insulation to the plywood. Repeat along all of the edges across the entire roof.

After the foam is tacked in place temporarily with a few nails it is secured in place with vertical 1 3 or 1 4 strapping that is screwed through the foam to the underlying studs. Most foam board comes in 8 feet x 4 feet sheets although different sizes are available 8 feet x 2 feet is common. Measure the roof area and cut your rigid foam boards to fit by scoring it with a razor knife and snapping the board at the incisions. By this video you can learn how to cut foamboard 45 degrees.

Use a straight edge knife or utility knife to cut the panels to size. The foam panels need to be secured to the roof around every 12 inches for safety.