exterior rigid foam- should i or shouldn't I Hello Martin, we are building a new house in north Ontario- zone 6 and have triple glazed windows. we want a tight house and very well insulated as we have extremely cold winters. our thoughts were to use a 2x6 wall filled with open cell spray foam insulation and plywood exterior sheathing. then we were going to use 3 or 4 inches of rigid EPS covered by Typar and then 1-1/2" drainage/ventilation space and wood siding. After reading your comments, I wonder if this could be a big mistake. should we move the wall sheathing to the outside of the rigid foam or possibly consider a type of structural rigid insulation like Tuff R. or maybe we should just eliminate the exterior rigid foam? we really appreciate your help. mike
Posted: 12:04 pm on September 18th 2015
exterior rigid foam Martin, This information is what I was hoping to hear, in terms of keeping the wall sheathing dry and avoiding future dew point concerns. From what Dana has indicated, 3" rigid will work well. And I can keep the sheathing against the wood framed wall assembly! I have decided on using the "outies" windows to help minimize any water infiltration potential and give us some decent size window sills for the cats to sit on. The windows will be needing fasteners that penetrate the 3/4" plywood window box, the 3" rigid insul, the 1/2" sheathing and anchor about 1-1/2" into the studs. Do you see any problems using long screws or will they compress the rigid insulation? thank you for your help.
Posted: 07:41 pm on September 18th 2015