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Nobody loves crawlspaces - they are often damp, dark, cold and claustrophobic. Contractors don't like working in them - you can't move around easily, or get equipment and materials in without a hassle. And most homeowners would never consider spending money on improving their crawlspace. In fact, apart from storing stuff there, you probably never think about it at all.

But, the truth is, how well a crawlspace is built has a lot to do with a home's comfort and heating costs.

Many crawl spaces in older houses are unheated, and some have dirt or gravel floors. It's really important that they are vented and the floor above is properly insulated. But if the floor is cold and there is dampness coming into the house, don't be surprised if they aren't. What's more, any ducts or pipes running through the space should also be insulated.

You can easily tell how well the heating ducts in a crawlspace are insulated - without actually crawling in. On a cold day, measure the temperature of the air coming out of the vents the ducts supply and compare it with the temperature of the air coming out of the other vents inside the house (ones that aren't supplied by ducts that run through your crawlspace). There should be no difference. If there is, your ducts probably need some insulation.

Put on a dust mask and go into your crawlspace. Take a look at the plumbing lines. They should be wrapped with foam or installed on the warm side of the floor insulation.

You'll probably find, however, that the builder will sometimes have forgotten to insulate the lines properly in short runs - where the line temporarily goes under the insulation or where there is a transition from the crawl space to the rest of the house. That's a recipe for disaster; you could have frozen pipes in a very cold winter.

If the floor is insulated, make sure the fibreglass batts are carefully placed so the insulation covers the entire surface, with a vapour barrier on the warm side and house wrap laid on the cold side to keep the insulation in place and free of animal infestation. (Believe me, rodents love crawlspaces, and insulation provides a comfortable nest.)

If there is no insulation, properly installing batt insulation after the fact is almost impossible. You can't have any voids or you'll have cold spots on your floor. And you have to somehow get a vapour barrier on the warm side of the insulation and ensure it is sealed. No one can do that perfectly.

If I have to retrofit a crawl space, I won't use batt insulation. The only thing to use is a closed-cell, two-pound spray foam insulation. It not only fills every possible void when it is properly installed, it acts as its own vapour barrier. I have to say, however, that I have never been in a room above a cold crawl space - no matter how well insulated - where the floor is not cold.

The best way to deal with a cold crawl space is to make it part of the warm side of the house. That means closing off the venting to the crawl space, insulating the foundation walls - preferably on the inside - and supplying some heat.

If there is ductwork in the space, you can have your heating, ventilating and air-conditioning (HVAC) contractor modify it to provide the heat needed. But remember, if you are adding vents to supply heat to the space, you may need to also add a cold air return for proper air flow. Think of a sealed bottle - you can't blow into it. Your crawlspace is the same - you can't blow hot air in if you haven't allowed for cold air to be removed. This can create other problems; if your crawlspace has a dirt floor, you may be drawing dirty air into your furnace. And, depending on the size of the crawlspace, your furnace may not be big enough. Be sure to ask your HVAC specialist.

A well-constructed, warm crawl space will reduce the likelihood of your house "stacking." Stacking happens when cold air gets sucked in through the gaps in the bottom of your house (and believe me, every house has gaps, especially older houses). This cold air pushes the warm air up, which reduces the effectiveness of your heating.

We say "hot air rises," but what really happens is that denser cold air - like that in your crawlspace - pushes up the lighter warm air - to your ceiling, your second floor, into your attic and out your roof, if it can. And that warm air is replaced with cold air - not good.

If the floor of the crawl space is gravel or dirt, you definitely should install a vapour barrier to keep ground moisture from getting in. You should also install vents that can be opened in the summer months to let moisture build up from condensation escape.

It's easier to insulate the outside walls of your crawlspace than the floor above it, and takes less material to do so. The outside wall insulation will not only keep the crawl space warm, it will provide an added layer of protection for the footings, which are not always as deep as they should be in a crawl space. It also will drastically reduce the amount of moisture getting into the house. You no longer will have to worry about insulating the ducts and mechanicals, and the floor will be nice and warm.

The cost to heat the extra space is minimal, and will definitely be offset by the increased efficiency of your heating system in general, and by the comfort you'll feel.

So, crawlspaces may not look like much, but building them well is part of making it right.

Mike Holmes is the host of Holmes on Homes on HGTV. E-mail Mike at or go to

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