Expert: Michael Curry - 11/8/2007

Question
i have an addition on my home that is my dining room.  it is a 17' X 15' room that is new construction from the floor up.  my issue is that this room was built on a concrete slab with a crawl space of almost 3'.  i'm now ready to insulate under my floor for added insulation.  currently, i have only i vent for the crawl space and i'm going to be adding another when i do the insulating.  i do get a bit, not much at all, of dampness under there during the hot summer months.  my issue is that i want to use r-19 insulation for under the floor but i don't know what application i should be using.  i was planning on using faced, but was concerned that if i continue to have just minimal dampness under there in the summer months that the paper facing would pull of the wood joices causing the insulation to sag or even fall down completely.  i was even planning on using a great deal of staples when i put it up, hoping, that more the better, would be best.  i also heard that i could use unfaced and use plastic sheeting, visqueen or whatever, to hold up the insulation and that it would act as my moisture barrier.  i'm concerned that this application would cause sweating and would be worse off than the other way.  i would appreciate any and all advice you could give me regarding insulating under a floor above a crawl space.  and by the way, this crawl space is not a heated area.

Answer
Hi Adam,

First of all do not insulate the floor - period. Insulate the walls of the crawl space and heat that area. Use Styrofoam if dampness is an issue and add closeable vents in the walls. Insulating the floor will make it cold and may encourage frost in the crawl space.

Thanks,
Michael.