Unvented Roof Using Sips

Four options for building an unvented roof assembly.

Unvented roof using sips.

Closed cell spray polyurethane foam can be used to create an unvented roof assembly that works in all climate zones. Do use sip tape or equivalent vapor retarder on roof panel joints. 1 1 2 t g decking. Need to make a final decision on which underlayment to use under a metal roof on an unvented roof system.

This will create an air space over your panels which will allow them dry out if moisture escapes. Extreme s pre insulated sips offer an option for a high performance roof framing solution that is 15 times tighter than conventional construction practices making it easier to control indoor air environment. Next i ll be screwing down 5 1 2 raycore sips panels over heated space and framing boxes over the eaves covering everything with 5 8 cdx. Build for the future with extreme s structural insulated panels sips the high thermal values and strength properties of extreme s sips are highly beneficial for roof construction.

The only way i know of venting a sip roof is to build a cold roof over the existing sip roof which brings up another question as to the benifits if any of a cold roof with a sip roof. Why use closed cell spray polyurethane foam ccspf. Beams on 5 centers. Unvented roof here again the choice of what insulation to use and whether to install it over or under the roof deck depends on the condition of the present roof the depth of rafters the r value you must attain and cost.

Cost aside the most straightforward route is spraying closed cell polyurethane foam on to the underside of the roof deck. Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. Sip s are almost air tight and won t leak air so you don t need ventilation. 3 8 plywood diaphragm seams taped.

This is a pretty common procedure when using roof sips. We feel a cold roof is not necessary if your roof sips are sealed properly. With tribuilt granulated self adhering underlayment on top of the plywood. A use a material that is not vapor permeable over the t g ceiling boards and under the roof sips to prevent moisture migration from inside the building to the underside of the roof sips.

Cold roof a cold roof is achieved by adding strapping and another layer of sheathing over the sips. The design approach is the same for all climate zones. Do install proper flashing and sealants around all rough openings and penetrations as required. The ventilation space can be eliminated and the construction greatly simplified by using an unvented roof assembly.

Do use sealant on wood to wood wood to eps and eps to eps connections. A sure bet would be to use 6 of eps above the roof deck or a 6 sip for r25 then finish it out with 6 of better quality high density spray fiberglass sprayed onto the underside of the roof deck to acheive an even better clear assembly r value than 14 of blown fiberglass since the eps is now thermally breaking the i joists. If you don t want to use sips or nailbase there are four basic approaches.