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Crawlspace Walls and Ducts

SteveGrind's Avatar

Join Date: Oct 2004
Posts: 7

10-18-04, 04:01 PM   #1  
Crawlspace Walls and Ducts

For the walls, do you have to use a poly insulation(2"-3"),or can I use just regular (r19?) on the walls. My main concern is since I have uneven ground to work on, loose insulation might be much easier than the poly stuff. Am i wrong?
And if I can use the loose stuff, what is the best r rating to use? and batts or No Batts?

As far as the ducts, to add heat down there, is it as simp0le as just cutting a few holes in the ducts? If so, how big?
Thanks very much

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twelvepole's Avatar

Join Date: Aug 2000
Posts: 15,834

10-18-04, 04:31 PM   #2  
Crawl space insulation

A polyproylene (plastic) vapor barrier is installed on the soil after you finish insulating crawl space.

In unheated crawl spaces, insulation in the joists above the crawlspace can be held in place with short pieces of wire. The vapor retarder faces toward the heated area above. To insulate the walls, a lath strip can be nailed to the sill plate to hold insulation. Cut to length with about 2' of overlap at soil level, but not touching soil. Building codes require that all ducts be insulated with recommended insulation and that duct tape not be used. This includes both heating supply and return ducts located in crawl spaces, attics and garages. Insulation can be iberglass building insulation, vinyl-backed fiberglass metal building insulation (similar to water heater insulation), or foil scrim kraft (FSK) duct insulation. It is secured with polyethylene twine or rust free wire.

If the crawl space is unvented and contains a heating system, water heater or significant heat source, you may want to insulate the crawl space walls (unfaced insulation) instead to contain the heat and warm the floor above. You can use fiberglass batts or blankets or one of the various foam board insulation materials. Cut pieces of insulation to fit between the joists and tightly press them against the rim joist. If using the foam boards, check local fire codes, as they may require covering the insulation with a fire retardant material.

To get heat in the crawl space area, you will need to determine if existing system can support both the upstairs and the crawl space areas. The crawl space area will be an additional drain on your energy. You might want to consult with an HVAC professional to determine if it is feasible for you to heat this area with existing system and how to go about doing so without reducing heating/cooling in home above. When you cut holes in the ducts, it means you will be robbing air from rooms above. This is probably not a good plan. If a good HVAC contractor evaluates the system and says you have the capacity to run air into this space, then you can either replace the existing ducts with larger ones or run additional ducts into the area.

Ed Imeduc's Avatar

Join Date: Aug 2002
Posts: 18,389

10-18-04, 04:47 PM   #3  
As far as the ducts, to add heat down there, is it as simp0le as just cutting a few holes in the ducts? If so, how big?
We put in two heat outlets and one return if its down there in the sealed crawl space. Any heaat you let out down there will go to the floor so its still in the home. This way the crawl space works as a big heat sink for you.The 6 mil poly on the ground and over lap it 2' tape all seams up the wall about 12". A good R 13 on the walls if you can do it, tack it to the sill plate . A R-19 cut to fit up in the joist space on the sill plate all around the home called the belt board.
You might like to go read.

This last www. will show you that you save over insulation in the floor.


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