I am surprised to see the rigid foam under the dry space material, the one contractor here I got a Quote from said if they did rigid it would be over the dry space liner. I have seen other web sites with it over. Who is correct?

JP Jenny,

Thanks for the comment and its a good question. There are two reasons the rigid needs to be installed against the foundation wall and not on the DrySpace barrier. The first reason is because for the insulation to work properly it needs to be directly against the foundation. Any amount of air or gap between the insulation and the wall will allow the cold to enter the space. Second, our DrySpace vapor barrier is made of very dense polyethylene and most adhesives will not stick to it well. If the rigid foam was glued to the DrySpace you are taking a chance it would not stay stuck for any length of time. If you mechanically fasten the board to the foundation (while on top of the DrySpace) you will poke holes in the DrySpace all along the foundation walls.

By installing the insulation on the foundation first and then the DrySpace over it you allow the insulation and the DrySpace to do there jobs independently.

The sites you saw showing the foam board over the vapor barrier was not that at all. In the south east there is a process where they install the barrier up the wall only 12" or so and then the rest of the way with rigid insulation having no vapor barrier under it. So it appears that the insulation is over the barrier, but it really is not.

Hope this helps,

Matt

Matt,

I couldn't agree with you more. The only thing that I might add would be to add some type of insulation (spray foam or rigid board) in between the floor joist against the bandboard.

Larry,

Thanks for the comment. Actually we recommend not using spray foam or rigid insulation in the rim (band) joist area. Spray foam will make it impossible to inspect for insect or water damage and to repair any of that damage. When it comes to rigid board, well that is a very tedious job to get a good seal. Once the crawl space is encapsulated a fiberglass insulation will get the job done. It can be removed for inspection and repairs as well as properly insulate.

Isn't rigid foam insulation a vapor barrier in itself and by placing the DrySpace over it aren't you creating two vapor barriers next to each other? I've been told this should be avoided?

Scott,

Thanks for the comment!

You are correct that rigid foam insulation can act as vapor barrier it it is installed with edges tight to each other. In effect you are creating two barriers, which in my opinion is not a bad thing. The only place I can think of where two vapor barriers would be thought of as a bad thing is if you have two layers of polyethylene on the floor and there is a water problem that has not been taken care of. Even if this situation existed and there was water trapped between layers it will not hurt either barrier. In other words they won't break down faster or come apart sooner. To keep the water from collecting between the barriers I would make sure the water problem is properly addressed.
On a side note there is a process where a vapor barrier like DrySpace is installed across the floor and 10-12" up the wall. Then the rigid insulation is installed over the 10-12" portion that is attached to the wall. This process works well when there is no water entering the crawl space from the foundation walls. If there were water, then it would run behind the rigid and then on top of the DrySpace because it is attached to the bottom of the wall.

I hope this answers your question, but if not please feel free to contact us.

Matt

What about the top 5 inches without any insulation?

Doug,

The top 5" is basically the place where the building code, energy code and termite inspection gap can not agree on what is more important. The space goes from 3" to 5" because the installation requirements of the DrySpace to be attached directly to the foundation. If the crawl space is properly insulated everywhere else this 5" area will have some but not much impact on the crawl space as a whole, certainly less than opening and closing doors in the main level. Until homes are built with this process required along with a termite shield, I'm sure the debate in this area will continue.

Matt

Has anyone considered using rigid foam board under the Dryspace on the floor surface?

Also a comment on rim joist insulation. Spray foam and rigid board will reduce air infiltration Fiberglass batts do a poor job at this. Rigid board can be placed in the joist pockets by under sizing the board and filling the gaps with foam using a Dow Pro series gun. This address insulation and air infiltration with out spraying.