Denver Crawl Space Advice


Old 06-01-13, 10:53 PM
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Denver Crawl Space Advice

I have a 1956 tri-level, brick veneer home. The main floor is a little under 400 square feet and features a vented crawl space that is approximately 4' tall. Currently, there is no vapor barrier installed on the dirt floor. There is also no insulation to speak of on the walls or on the floors. I would like to remedy both of these situations before winter comes about, again.

I understand I have two paths: 1) Seal up the basement from the outside, 2) Seal the floor joists with insulation.

I have been reading a number of posts on this subject, but most appear to relate to homes in the east/southeast. In each of the scientific reports that were presented, the studies indicated that in dry areas of the west (Denver for me), insulating the floor in a vented basement is equally as effective as creating a fully conditioned crawl space.

Based on the reports, I'm thinking of simply 1) Adding a durable poly vapor barrier ( or and 2) putting non-backed fiberglass R-21 insulation on the floors and interior walls.

A few additional notes that might be relevant:
We do not have AC.
I have not observed any moisture collection in the crawl space.
There are 2 vents, one on each of opposite sides of the crawl space.

I'd like some advice on the best course of action for a dry climate area. I'd also like to know the best method of installing the vapor barrier... i.e. how to attach/seal the barrier to the wall, should simply go up 6", or the entire below-grade portion?

Is a sealed crawl space really worth the investment for me? A home inspector mentioned to me that I should not close the vents for fear that combustion air would be insufficient for my furnace (seems unlikely if the space is so large and it breathes through my wood floors).
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Old 06-01-13, 11:38 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
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If your furnace draws combustion air from the crawlspace I would be reticent about sealing the crawlspace.

I have thought long and hard about encapsulating my crawlspace and finally came to the conclusion that while a totally enclosed and conditioned crawlspace is the ideal the economics are such that it makes little sense for me. The numbers may be different for you.

I would, however, think long and hard over the use of fiberglass insulation. Fiberglass will do nothing in regard to air sealing. It would be best to have a vapor barrier/retarder between any insulation and the sub-floor. Although the cost is high I would suggest closed cell, two pound density sprayed polyisocyanurate a minimum of two inches thick as ideal. Also good (also expensive) would be Roxul batts. Yet another option might be two inch foil-faced polyiso boards. You can cut them for a somewhat sloppy fit and then use one-part foam insulation to seal the edges. Having the four foot clearance would make this easier for you than my two foot maximum clearance.

Look into utility programs that might underwrite a portion of the cost of insulation. While I personally dislike fiberglass it IS the standard and is most likely what I will go with because of the utility co-payment.
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