What do I need to know about vapor barriers and wall insulation. I will be re-doing some of my outside walls and want to add insulation. Some walls will be accessable from the inside. Some, from the outside (maybe). Some may be accessable from the inside now and the outside later. What do I need to know about insulation and vapor barrier?

I heard once along time ago that you never want to put vapor barriers on both the inside walls AND the outside walls because it could cause condensation and mold. Is that true? If so, which is preferred? can you do some walls one way and others the other way? What’s best in what case? What are the pros, cons, and best types and applications for each?

As a general rule, the vapor barrier goes on the conditioned side of the wall.Where you are, what climate zone, will determine the best type.

The vapor barrier goes on the hottest side of the wall. In Florida, it’s common to face it to the outside of the wall.

I’m in Southern Illinois. It gets down to -10 in the winter and up to 110 in the summer.

Tour local building dept is likely to have a standard hand out for new construction. Even though this is not new, the methods apply.

Installing the insulation to the exterior walls while inside the house, you need to place it so the paper is facing you. Then the wallboard (sheetrock) goes up on top. Cut to get it around pipes and electrical. Do not compress it.