Monday, December 27, 2010

The problems with basements

In an urban setting where maximizing space is a major concern, including a basement in the building of a house is almost mandatory. Basements, though, can present a lot of problems if not built properly and looking at some of the on-line literature on basement construction techniques, it seems that until recently, the majority of basements were less than stellar.

Basements are most importantly the structural foundation of a house so they have to be built sturdy enough to solidly hold up everything above it and they have to be able to do it for the life of the house which is certainly expected to be at least several decades long. It's for this reason that most basement foundation walls are made out of cement as cement remains pretty stable even when buried in earth after long periods of time.

The basement should also ideally keep water out and keep heat in and maybe these are a new expectations because it seems that in so many older homes (like mine for example), the basement does neither very well. The inability for basements to do these two jobs properly is not too surprising given that these tasks, especially when required to be done together at the same time, can actually be quite difficult to achieve.

The main problem is that cement is both a water porous material and also a terrible insulator and yet it sits in ground which can be both wet and cold.

Once upon a time, when energy was free, I guess the thinking was that since basements were underground, the earth would act like a good enough insulator and so no additional insulation was necessary. Unfortunately, as it turns out, uninsulated basements can lose a substantial amount of heat, accounting for on average, one third of a home's heating cost.

And also, once upon a time, when we were all made of hardier stuff and a puddle or lake of water leaking into the basement meant free baths, people weren't that bothered with infiltration but nowadays we prefer drier, if possible, and so that means putting up some sort of water barrier.

We've got three components then, a concrete structure, insulation and a water barrier, which we need to put together somehow to hold up the house, keep the heat in and keep the water out. You wouldn't think it would be so difficult to slap these things together and be done with it but it turns out it's not so simple.

Let's take for example what was and for some, still is, a common building method and yet is also what many builders now believe to be a common mistake: We're inside the basement and there's the bare concrete wall and it needs some insulation. Easy enough. Put up a 2 x 4 frame and stuff in some bats of fiberglass. If we just left it at that, the problem is that the insulation is going to get damp and damp insulation is a poor insulator.

The insulation gets damp because of water condensation. It's like in the winter when you see water condense on a cold window except in this case it's not a cold window but a cold concrete wall of the basement. The moisture in the air condenses against the concrete wall which the insulation is pushed right up against so the insulation gets wet and stays wet because water keeps condensing.

In order to prevent this, a vapour barrier can be put up. This can be big sturdy sheets of plastic attached to the 2 x 4 frame which is holding up the insulation. It's quite difficult to put up these big sheets of plastic so that they create a continuously sealed vapour barrier but let's say the installer is successful. The problem now is that the insulation is still going to get wet because the bare concrete wall, as mentioned earlier, is not waterproof, and water from the outside will get in.

There are several ways water can get in past the wall. It may just leak in through cracks and pre-existing seams. It may get sucked up from the ground, called capillary action, similar to the way a sponge absorbs water. It may come from the concrete itself if the concrete hasn't yet cured and dried completely.

So all this moisture gets dumped into the insulation from the concrete side and now that there is a vapour barrier on the other side of the insulation, this moisture is trapped. The insulation is not only degraded but the trapped moisture can also lead to odors, mold and decay.

A water barrier, then, can be applied to the exterior surface of the wall to try to keep any water from penetrating through the wall. This sounds good, but in practice it's really hard to do and if there is any break in this exterior membrane and water gets into the wall, that water will really be trapped for a long time because it is now between two vapour proof membranes.

For a more detailed discussion about these problems and more, you can refer to the excellent Building Science website and this report in particular: Basement Insulation Systems.

You can see how this circuitous process can lead to some major headaches. An alternative strategy, foregoing the interior insulation and putting foam board insulation on the exterior side of the wall, while it may make more sense in theory, can also be tricky to do and has its own set of problems as well.

In recent years, though, builders have come up with some really innovative solutions to address these issues and in the next post we'll take a look at how a lot of these basement problems can be solved using something called insulated concrete forms.

1 comment:

  1. Good Posting. Seeping water is a harmful sign for this basement waterproofing is important to maintaining a great structure.