Expert: Bruce E. Johnson - 1/24/2009

Question
QUESTION: Hello,

I live in the Chicago area and I am finishing my basement.  I did much research on the vapor barrier issue.  I feel the proper way to insulate basements is to use the 1" - 2" pink board against foundation, then stud, batt insulate if desired, then rock...no vapor barrier.  There are many opinions on this but I feel that you should not trap any water between the foundation and wall board if it does get wet.  I have decided against using the pink board because of space and cost.  I do not have any water issues or condensation issues at this time.  However, I want to try to avoid any future problems as best as I can with what I have decided to go with.  This is what I am doing / have done.  Foundation wall sealed with waterproofing paint, 1/2 inch space between foundation walls and 16 O.C. studs, Kraft faced mold resistant insulation with a vapor retarder not barrier, then mold resistant sheet rock.  My main question is whether or not I should seal the 1/2 inch gap between the top plate and the sill plate.  If I do, it is basically going against my thinking that I would like an air gap between the foundation wall and studs just in case it ever did get wet or condensate without me knowing.  However, if I do leave the gap open, will this allow warm air in to condensate against the cold wall?  I will be insulating the areas above the sill and between the joists'.  Any opinions or advice is much appreciates.

Thanks


ANSWER: Hi Dan, it sounds like you are on the right track for sure.  I wouldn't seal the top gap.  For one thing the drywall will seal this area once it is taped and finished so no need to even worry about it.  I can't think of anything else you need to do.  One last point though, water intrusion into a foundation begins at the outside and works its way into the interior.  If the exterior of the foundation is not properly sealed and a foundation drain installed to keep water from building up against the wall then whatever you do on the inside for waterproofing can be pushed off the wall from the hydrostatic pressure.  So for anyone reading this that are in the process of building a new foundation, start your waterproofing from the outside.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com


---------- FOLLOW-UP ----------

QUESTION: Thank you for your quick response Mr. Johnson.  Just to clarify....I have never had a problem with any moisture/water coming from the foundation.  There is a foundation drain.  As for the gap I am mainly concerned about condensation.  I have noticed a very little bit of condensation on the walls only a few times on very cold days.  Of course this is now, with bare walls that are completely open.  The drywall will seal the front but the 1/2" gap between the top plate and sill plate/foundation wall will still be open to the warmer air in the floor joists'.  Do you think this will/can cause condensation and should be sealed to stop warmer air from the joist space getting in there?  Or do you think it is better to have a small opening in there to let air in and out.  Some of the top plate lengths run right along duct work.  Warm air will come off of this in the winter.  I had also thought about just sealing the gap in every other stud cavity.  I could seal it with expanding foam or when I put the insulation on the sills between the joists.  Thanks again Mr. Johnson.  I just want to do the best I can before I close it up.

Answer
Hi again Dan, do this, take some strips of the wall insulation you are using and plug the gap with that.  It will seal the gap and yet be porous enough to allow for any minute traces of moisture to escape should it become trapped behind the wall.I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com