Keeping in mind budget and greenness, what is the best type of insulation for a basement crawl space and attic walls?

Asked by elizabeth
Portland, OR

The crawlspace is under my kitchen and I have an ant problem , the crawlspace is also pretty narrow and the adjoining space is a finished basement. The attic really heats up and it surronds a finished room


Edward Wright

Answered by Edward Wright

Cincinnati, OH

Wright Design, LLC

June 4, 2012

For your location in Oregon, I'd recommend what the 2011 Oregon Residential Specialty Code (ORSC) requires -- R-15 for walls.

This can be accomplished by installing approximately 2.5" minimum of closed-cell spray foam insulation.

  • Closed cell foam provides the dual benefit being both an air and moisture barrier - important for controlling moisture migration into the crawlspace.
  • Sealing between the joists can also assist in energy reductions and pest control by sealing gaps and holes.
  • Also a vapor barrier is recommended across any exposed soils.
  • These measures combined with treating for ants, will be good pest management.

Attic walls insulation recommendations: wall insulation levels are R-15 as noted above and in the sloped roof areas the ORSC requires R-25 for > 10" and R-21 for >8" of nominal rafter depth.

  • In this case open cell foam - installed full depth in the walls and rafters is recommended to seal air gaps and provide an air barrier.
  • A lower cost alternative would be to seal the gaps with 1" of the open cell foam and fill the cavities will fiberglass batt insulation to the required depths.


For more information:

Read Florian Speier's Q&A "We have an unheated crawlspace under our house that we would like to insulate."

Also, read Danny Kelly's Q&A "What kind of waterproofing can you use in crawlspaces to help with going green?"

Tagged In: insulation

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