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Heating crawl space

I have a 42 inch crawl space under my home. Its constructed out of cement blocks and not insulated. There is a vapor barrier and the sub floor is not insulated My question is would it be more economical to heat this area or keep it closed off. My heat source is forced air ,natural gas and I live in mid michigan. The area is 1040 sq. ft There are two registers in the main heat run that I have closed off. Thanks

Timothy Miller
Re: Heating crawl space

Howdy ,adding insulation would be the most cost effective over time. You can run it down the walls or in the joist cavities and if done before end of year take advantage of the federal tax credit up to $1,500 tax rebate. If you live where there are termites i would install it in the joist bays so the little buggers cannot infiltrate the home without being seen.

Re: Heating crawl space

Actually your best and most cost effective option would be to do both.
Encapsulate and air seal the crawl space, condition it and then properly insulate the walls with foam board.

If you simply insulate between the joists as suggested here, your crawl space will still be exposed to moisture. From the ground and from the outside. That moisture, overtime, will favor mold growth. Your floor joists will begin to rot and, if you happen to have used fiberglass batches to insulate between the joists, like so many do, your crawl space will turn into a mold farm.
Fiberglass is known in the industry as "mold candy".

Additionally, fiberglass only works in closed cavities and, it soaks moisture. When damp, it looses all its R-Value.

If you can't afford the encapsulation along with the insulation, go with the encapsulation and leave the insulation for later.

Studies show that, in most areas, just by completely encapsulating and conditioning the crawl space, you can improve your home's overall energy efficiency by and average of 18%.

That is because encapsulation will stop outside air infiltration through the crawl. It includes the crawl space into the internal building envelope, so that it benefits from the environmental controls that are set for the conditioned living area.


Timothy Miller
Re: Heating crawl space

Howdy you might want to consider some issues CyFree brought up.

Fiberglass insulation does not promote mold growth in fact mold does not grow due to the glass but must have a food source and moisture.

I assume the vapor barrier is on the dirt. This if installed properly seated to the foundation stops moisture transfer from the soil into the air-- evaportransportation.

Fiberglass woks only in closed cavities = non sense!

Moreover the assumption that this or for that matter most crawl spaces are supersaturated bogs that will result in rotten joists is funny....

The brightest area alluded to is to retard air infiltration into the heated structure. One can use spray foam along the foundation plate junction. Also at the rim joists even installing foam board into the rim joist bays to reduce the heat transfer threw the wood framing to the exterior. Reducing the heat sink...

Oh by the way if you have a supersaturated crawl space i would install an french drain and sump pit pump to remove the moisture & and then a properly installed vapor retarder, barrier.

Heck if you have ample funds have a couple of inches of closed foam insulation sprayed on the framing members it does several tings at once....

Re: Heating crawl space

If you properly insulate the joist bays, AND if your pipes are sufficiently protected from freezing (ideally they should be run up in the joist bays, encased in the insulation), AND you have adequate ventilation in the crawl space, moisture shouldn't be a concern.

However, since you live in Michigan where it gets (insert colorful word here) cold, you may not want to leave the vents open when it gets down into the teens or lower.

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