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Dilemma : Basement Spray Foam but No capilary break

user-674428's picture


 Got a poured concrete foundation near Ottawa Ontario.    Am doing the basement and was going to go all in with spray foam R-20 full height with joist cavities sprayed...

However, the house has untreated sills resting on the concrete wall, with no gasket.   As well, the foundation is only dampproofed.    I am concerned about covering the sill plates in this situation ... 

Is there rotting potential?   Some internet resources seem to think so.   Others say the wall may dry to the outside above grade..

For the most part, the foundation is 2  feet above grade, but there is a 10 or 12 feet place where the grade was raised to about 8 inches from the sill.    Sill gaskets or treated plates are only required here when <8 inches from grade or below grade..

I removed the builder insulation (R-13).  Around here most basements are done to nominal R-13 with batts.  Tar paper is applied to the inside of the concrete wall to about grade, and poly VB on warm side.    They stuff batts in the joist spaces and cover with poly.   They are typically poorly detailed which migh actually be a good thing since the VB is not perfect and things can dry to the interior!  

My current thinking is to do full height R-13 closed cell, and do the joist spaces myself with Roxul batts or ComfortBoard, and VB..   The idea that it would be open for inspection (areas that are not drywalled), and I can control the details if needed.   

Any thoughts or experience with this?   



You might find the following (post #207296, reply #1 of 2)

You might find the following article helpful: "Internal Insulation of Masonry Walls:  Final Measure Guideline," Research Report 1105, December 2011,

What is the flooring (post #207296, reply #2 of 2)

What is the flooring situation? I've seen some good details where the poly or platon is wrapped up the wall by several inches to allow for any water that infiltrates in through the wall to drain down behind the spray foam (it will always find a way) then drain down under the platon or vapour barrier and out the floor drain without ever causing you any issues. Any time you encapsulate the sill, you take away its drying potential and therefor increase its chance of rot. Look closely for any signs of water infiltration and deal with any areas at their source first. Well worth it to take care if that now. Also keep in mind that the city of Ottawa is now inforcing much stricter insulation values and may call for these exterior walls to be brought to r24 instead of the old r20. They do also not consider spray foam as a vapour barrier unless it is completely continuous as wood could be a vapour transmission path.. Hope that helps, and the shovelling doesn't take away too much time from your project this year!