starting basement

14 years ago

I am ready to start basement and just want to double check myself. I was hoping Worthy would give some tips.

House in central NJ, block walls fully below grade.

I want to glue 1" xps to walls than 2x4 walls with batt insulation.

Is 1" sufficient or do I need 1.5"? (I did the plastic test and had no signs of moisture).

What adhesive is best?

I plan on purchasing spray foam kit for rim joist area.

Will batt insulation be just as effictive for my area?

I was planning on laying 3/4" plywood on top of 3/4" p/t strips that are hiti into the concrete floor. ( This method was suggested by a contractor to avoid any problems in case of future flood.)

Would the building science method of 1" xps be better?

In case of any future flood that may happen will the xps hold-up?

Thanks for all the help.

Sort by:Oldest

Comments (3)

worthy
14 years ago
I want to glue 1" xps to walls than 2x4 walls with batt insulation.

I've used that method a couple of times, except that on poured walls--which are more uneven due to the joints and tie holes-- a mechanical attachment is needed. Only use an adhesive specifically designed for the purpose, such as PL300 Foamboard Adhesive.

In some jurisdictions, a mechanical attachment is required.

Is it enough insulation? It more than meets Code. However, Dr. Lstiburek of Building Science Corp. recommends R20 as a minimum for basement walls anyplace north of the Mason Dixon line.

Will batt insulation be just as effictive for my area?

Unless you use Membrain vapour barrier--and it's virtually impossible to find, I understand--batts will result in moisture and mould problems in a short time.

I'd keep wood off the floor, as recommended by Building Science Corp. Use XPS, Dricore or equivalent, orDeltaFl or equivalent. XPS is used under concrete floors for insulation and for floating docks. So any moisture will not affect it.

Here is a link that might be useful: Building Science Corp. on Basement Insulation
amy2202
Original Author
14 years ago
Worthy, thanks for the help and all you do on this site.
Just to clarify. The 1"xps and additional r-13 is all I need.
Will the 1" be enough to avoid any problems with mold issues?( I will tape and foam seal any seams and gaps).

I will go with the xps on the floors followed by the plywood all which will be hilti into concrete floor.

Another question.
Should I purchase the diy spray foam for the rim joist area and if so what thickness should I apply?
worthy
14 years ago
High-density R15 fiberglass batts and one inch R5 XPS meets Dr. Joe's criteria.

enough to avoid any problems with mold issues?

You still have to provide mechanical dehumidification in the summer-fall months and keep the windows closed. In modern tightly-insulated homes, a.c. alone is not sufficient to reduce humidity levels below 45% relative humidity.

The rim area is the most important part of the basement to insulate and seal. Three inches of polyurethane foam should provide the required R18-21. I have no experience with the diy foams, so I can't say how easy (or hard) they are to use.