Expert: Bruce E. Johnson - 2/4/2011

Question
QUESTION: Bruce,
I just a question from Lyn and your response. My situation is a little different. I have a concrete block building that I want to insulate. I don't plan on putting stucco on the outside. Right after it was built about 4 years ago I put a coat Dry Lock on the outside. Last year I put on a second coat. My idea for the inside is to put a vapor barrier on the wall and then stud it out with 3 x 3's and install rigid foam insulation between the studs and then cover it with some type of paneling, pegboard or something. After reading the responses to Lyn, I'm confused as to whether the vapor barrier goes against the wall or before the paneling. My plan for the ceiling is to put rigid Styrofoam between the ceiling trusses and then cover that with paneling. I'll put a door on the attic space and not worry about insulating that area. I also have an addition on the back of the building. It is about 3.5 to 4' off the ground at the highest point. I have extruded polystyrene on the exterior and then vinyl and sheet metal. I haven't insulated underneath nor on the inside. What do I do? I did however put down clear plastic on the ground but I don't think is enough to stop moisture.

ANSWER: Hi Michael, I am not a big proponent of putting vapor barriers on the inside walls of buildings.  This practice has a tendency to trap moisture inside the wall and create mold/mildew issues especially if the outside is not properly sealed.  I am also not thrilled with your idea of insulating between the wall furring.  The best form of wall insulation using rigid foam is to put the rigid foam on the wall first using adhesive.  Then you attach your furring strips (in most cases 1x4 PT) to the wall through the insulation using long screws, cut nails or pneumatic nails made to penetrate masonry.  This way you don't have gaps of missing insulation at every stud location.  The same goes for the ceiling.  Attach the insulation to the bottom or top of the trusses and then apply your drywall.  As far as your addition goes, you can get underneath and install batt insulation in your floor system between the joists or over the joists using fiberglass webbing made for this purpose.  Keep your moisture barrier on the ground.  I hope this information helps please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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

QUESTION: Bruce....Thanks so much for your response. I do have a follow-up question and a clarification. As far as the addition, I failed to mention it is sitting on posts and open underneath. What do I put under the batting across the floor joist. I hope that make sense.

Answer
Hi again Michael, you can get some house wrap that would work good as a cover to the underside of the floor insulation.  To cover it with house wrap you should run the insulation between the joists so you can tack the house wrap material to the underside of the joist.  Felt paper works as well if you cant find the housewrap..either tyvec or typar are usually available at most homeimprovement stores.. I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com