How to install rigid styrofoam insulation on a below grade cinder block wall behind a 2 x 4 framed wall?

Question

Our new home had water damage on two basement walls from several years of a clogged gutter. Gutters cleaned, landscape regraded - drywall and insulation have been down for 3 or 4 months, through many downpours and perfectly dry.

I want to use more moisture tolerant materials - rigid foam insulation and paperless drywall. I have read so many different opinions of how to install the insulation.

Here are my main questions (this is in Maryland - I assume climate affects the install process)

1 - Should there be a plastic barrier between the foam and the cinder block? Should the foam be placed right against the cinder block with no vapor barrier? Should there be a slight air gap between the cinder block and the foam insulation? Should there be a plastic barrier on the other side of the foam insulation facing the drywall?

2 - How do you attach the foam insulation to the wall? Liquid nails?

Thanks

Answer 1

I would apply a sealer to the cinder block wall, then place the foam directly against the wall. Liquid nails should work as well as any other construction adhesive that is compatable with the foam board.

Answer 2

The foam you are talking about axts as its own vapor barrier. Use a construction adhesive for adhering foam and glue directly to the concrete block wall.

Answer 3

Good job on handling the original problem.  Now to the repair.  You have 3 considerations:  heat loss, water vapor (and possible condensation) and ground water.   You are getting a lot of cross information because this type of insulation is sometimes applied on the exterior as well as the interior.  The applications are different.   Tar, Plastic and/or a layer of plaster (mortar) might all be install outside to keep ground water from coming through the wall.  Foam may also be applied on the exterior for insulation.  Once water is already inside you have a different problem, mold from water vapor (humidity build up) and; yes, water damage from ground water coming through the wall.  

Unfortunately you have two things working against each other.  You need ventilation behind the 2 x 4 wall to keep humidity from building up against the block wall and encouraging mold to grow.  You want static air for its insulation qualities.  (Most insulation includes some means to limit convection currents.)  And you need a vapor barrior to keep room humidity from going through the 2 x 4 wall and condensing on the cooler block wall.

Because of these considerations I now tend to insulate only down to the frost line.  In your neighborhood it is probably 2 to 3 feet below grade.  Below this point I feel that ventilation is more important than insulation.  This makes your insulation decisions easier and the job slightly more difficult.   You can insulate your 2 X 4 wall with fiberglass insulation normally.  Be sure to insulate the area between the floor joists above the foundation.  Any sheetrock on the studs will be installed at least 1/2 " off of the floor.  If the basement design allows ventilation of the area behind the walls into some utility area, your job might be done.  

Foam where it is applied directly to the concrete is attached with glue.  (and spray foam can be applied to gaps.)  Concrete that is not solid and clean will not give a good surface for bonding.  PL200 is one example.  

Any vapor barrior is ALWAYS on the side of the insulation that faces the heated/cooled room.  If you want to use plastic sheeting as a vapor barrier, put it on the studs and consider separate ventilation for behind the wall.  

When putting foam on the EXTERIOR of a house under stucco, a gap is encouraged to allow condensation behind it (coming from the water vapor (humidity) of the  heated room hitting the cool outside wall) to drain.  In the case of INTERIOR foam insulation the relative higher humidity of the room would be on the other side.  If you have water coming through the block wall your foam is going to tend to trap it there and allow the mold build up concerns I mentioned earlier.  Initially, the mold build up would also be "trapped" from the room but I would rather ventilate and attempt to avoid a buildup.

Hope this is more explaination than confusion.

EDIT:  the white sealant is to keep water from coming through the wall.  It is not as permanent a repair as exterior waterproofing but is far less costly.  (doesn't require digging)  Depending upon the surface preparation and continued presence of water, you might expect it to last 3 to 5 years.