Formulas For A Warmer Floor

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Basements

It stands to reason that if you're willing to bear the additional cost of a basement, it should be a dry and comfortable place. Sadly, far too many are just dank holes in the ground.

A basement, for the purpose of discussion, is merely a tall, unvented crawlspace, its floor surface perhaps 7', rather than 2', below grade. In this light, the drainage procedures are the same as those detailed earlier, though during new construction, a second subdrain may be added along the inside of the footing to carry water from under the basement's concrete floor.

Shrinkage or stress cracks that appear in the wall after it's built, and that ooze water on a regular basis, may require more than standard waterproofing techniques. Epoxy or urethane foam injections are often used professionally in poured concrete walls, but probably the most common fix for stressed block walls is an interior drain system.

Usually, water enters from the outside and flows through the block cores to run out the floor joint. The repair involves boring into the cores at the base of the wall-either at floor level or beneath the slab, once a trench is dug-and installing individual relief tubes that connect to a larger drainpipe. The pipe is covered if it's set in the floor, and is routed to drain into a nearby sump pump.

If outside excavation work is inevitable, additional waterproofing measures are highly recommended. Rather than rely on coal pitch or poly films, it may pay to invest in butyl or EPDM elastomer sheets, or rolls of modified bitumen, in combination with a foundation drainage mat specifically made for permanent belowground use. Several companies make plastic mats that keep water pressure from building up at the wall, and there are a couple that combine a drainage layer and insulation in the same product.

The most practical exterior insulation, by the way, is probably extruded polystyrene board, for the reasons mentioned earlier. There are two ways to make it work, both handled from outside the wall, which minimizes condensation problems. The most effective is to cover the foundation from the top of the band joist down to the top of the footing. Since heat loss to the soil is greatest at the upper part of the wall, it's best to stack the insulation at the top and taper it to a single thickness near the bottom, figuring on a reduction of about R-2 for every foot of depth. A 7'-deep wall averaging R-16, for example, would have 4" of board at ground level and 1 " at the footing. Performance can be further improved by filling the cores of foundation block with loose vermiculite or perlite, and flaring a 2' insulation skirt over the footing and subdrain.

As an alternative (for unvented crawlspaces, too), you can insulate to a point about 2' below grade, then extend 2' of rigid board outward from the face of the foundation. This tends to reduce heat loss from the lower section of wall and is well suited to an existing home because it's easier to accomplish.

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