Formulas For A Warmer Floor

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

In each case, the insulation above grade should be fitted beneath the wall siding, and protected below the sill plate with flashing, sheathing or a fiberglass-reinforced cement coating.

Insulation after the fact is a limited option when dealing with slabs.

Slabs
The very nature of a slab-on-grade doesn't allow a whole lot of flexibility where retrofitting is concerned. On one hand, the pad is right at the surface, so moisture problems are seldom extreme. On the other, any work within the perimeter of the slab footing is out of the question.

If recurring dampness is a problem, especially after rain, the appropriate surface drainage steps can be taken with an eye toward shedding water from the vicinity of the house. Should run-off collect between a walk and the foundation, a drain trench or ground sloping might be in order.

Insulation after the fact is a limited option, as well. For new construction, it's now understood that full-width, uniform protection under the slab can't be justified economically or in heat savings. Instead, it's best to insulate most heavily beneath the perimeter, gradually decreasing the thickness of the material toward the center of the slab, which may not need to be insulated at all.

The second-best choice, then, is to place up to 4" of extruded polystyrene against the outside of the perimeter footing, to the same depth as the concrete. Ideally, the insulation should extend as far downward vertically as it would have horizontally, but this probably wouldn't be possible even in northern climates, where the frost walls can be fairly deep. Settle for what you can get, and be sure to cover any exposed insulation board with flashing or structural coating.

Done carefully, protecting your foundation from moisture and heat loss is like putting money in the bank. It takes it out of your pocket in a hurry, but you'll always get more back in the long run.

Editor's Note: What may be the most thorough book on the subject of residential foundation planning, Building Foundation Design Handbook, has just been released and is currently available at a cost of $30 plus $3 shipping and handling, payable to the Underground Space Center, University of Minnesota, 500 Pillsbury Dr. S.E., Minneapolis, MN 55455.

RSS | Comments | E-mail | Print