Expert: Bruce E. Johnson - 7/15/2011

Question
I own a 3rd old raised ranch home in a mixed climate.  We are in southern Ontario.  I have recently noticed mold spotting behind the insulation on the exterior side.  There is a vapor barrier but due to the stupid building codes we have that lets the builder get away with leaving the barrier 2 ft from the floor. there was no seal so it was allowing the air to move and condensate and create the mold as I am sure that you are aware.  My question is what is the best way to seal or not seal.  I have had some conflicting conversations about how to deal with this problem.  I have been told everything from cut the plastic to allow the walls to breath and also that even if I seal all the air gaps the problem will reoccur.  I feel that if i keep the air leaks to a min. I will reduce the ability for the rapid change in temperature inhibiting condensation and reducing the risk of mold.  I would love to hear your opinion I just don't know what to think.

Answer
Hi Dena, I'm not sure what to think..I am not aware of any code that requires vapor barriers to be left unfinished.  Also, how were you able to look behind the insulation? Is the interior wall unfinished? And just when I think I understand that you have some wall framing issues I see the title of your post "sealing a basement" and I think, what are you talking about? A concrete wall? and if so why would the concrete wall have its vapor barrier incomplete at the bottom?  Anyway, as far as I'm concerned vapor barriers belong on the exterior portion of a wall and should encompass the entire wall and it should be the layer just beneath the finish siding or sheathing and should be evaporative type of material such as Tyvec or Typar or impregnated felt paper. The walls should be sealed at the outside to prevent moisture intrusion into the living space.  Also you didn't mention if you air condition your home or in any way adjust the moisture content of the living space.  A healthy moisture content should be 40-50% humidity.  Less than that and your starts to become too dry and more than that and you could begin to see some mold issues.  As far as sealing goes, a good silicone caulking or urethane caulk is recommeded for crack sealing.  A good elastomeric paint can help prevent moisture penetration as well..I hope this information helps please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com