Closed cell spray polyurethane foam can be used to create an unvented roof assembly that works in all climate zones.
Unvented roof using sips.
Cost aside the most straightforward route is spraying closed cell polyurethane foam on to the underside of the roof deck.
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.
This will create an air space over your panels which will allow them dry out if moisture escapes.
Sip s are almost air tight and won t leak air so you don t need ventilation.
With tribuilt granulated self adhering underlayment on top of the plywood.
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.
3 8 plywood diaphragm seams taped.
Why use closed cell spray polyurethane foam ccspf.
Four options for building an unvented roof assembly.
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.
Do use sip tape or equivalent vapor retarder on roof panel joints.
Do use sealant on wood to wood wood to eps and eps to eps connections.
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.
Need to make a final decision on which underlayment to use under a metal roof on an unvented roof system.
B use a wrb that is vapor permeable on the top of the roof sips underneath the standing seam metal roof so that if somehow any moisture does get down to the roof sips it has the ability to permeate outward.
Cold roof a cold roof is achieved by adding strapping and another layer of sheathing over the sips.
Beams on 5 centers.
Do use only continuous 2 bys i beams and insulated i beams for spline connections.
The design approach is the same for all climate zones.
Do install proper flashing and sealants around all rough openings and penetrations as required.
1 1 2 t g decking.
We feel a cold roof is not necessary if your roof sips are sealed properly.
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.
The ventilation space can be eliminated and the construction greatly simplified by using an unvented roof assembly.
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.
The roof is currently built as follows.
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.
