Rigid foam aside, other home products just as combustible

Q. I would like to share with you my knowledge of the performance of rigid foam insulation in a fire, in connection with -- what I consider -- your ill-advised recommendation to install 2 inches of rigid foam insulation under a mattress. You did not state what kind of rigid foam insulation, but I think most people would go out and get a big block of rigid polystyrene foam.

Polystyrene foam should never be present within a building envelope. In the course of my research, some years ago, which resulted in a book on flame-retardant materials, I discovered that 1 cubic inch of polystyrene foam will produce enough smoke to fill the house, killing everyone in the home.

The fine particulates in the smoke are respirable; to wash them out the body flushes fluid into the lungs. "Death by smoke inhalation" is actually death by drowning. The amount and the density of smoke produced by burning polystyrene foam are unbelievable, until one tries it (outside). Of course, there are other foams that your readers might acquire. At the time of my research, there were no common ones, even fire-retardant, that did not produce toxic fumes and smoke, and I believe that to still be the case today. Of inorganic rigid foams (e.g., glass) I am not aware that any are practical or available for the use that you suggest to your ordinary reader. I would be interested to know if there are such.

Certainly there are foams within a home, such as in upholstery and even perhaps in the mattress in question, but death from "smoke inhalation" from these foams cannot be laid at your doorstep. I offer these comments constructively only and hope they will be useful.

Via e-mail

A. You make a very good point, but what you may not take into account are the other materials that are in every home, some used daily, that are far more deadly than polystyrene foam. Whereas extruded polystyrene rigid foam (XPS) will incapacitate in 17 minutes and kill in 23 minutes (polyisocyanurate rigid foam in 19 and 22 respectively), wool will do so in 5 and 8. Silk will incapacitate in 7 and kill in 9, cotton in 8 and 13, and polyester fabrics in 8 and 11. Yet we have these fabrics in clothing, carpeting and other household furnishings exposed at all times. Wood is also more lethal than foam insulation, incapacitating in 10 and killing in 14.

I know that burning foam exudes a lot of smoke, but so do wood and the other materials mentioned above. So to keep things in perspective, the creature comfort offered to the sleeper under the conditions that were presented to me by the reader seems more important than the smaller risk of potential combustion of the insulating foam compared to the wool or polyester blanket the sleeper may be using. Let's hope that the sleeper does not smoke in bed and that every sleeping area has working smoke and carbon monoxide detectors. And in the case of fire anywhere in a building, occupants must get out as quickly as possible and call the fire department from another location.

Q. We purchased a new home in 2004. It is on a two-acre lot that is all clay. A porch runs the full length of the house and its roof is contiguous to the house roof. Four posts support the porch roof, and the builder told us they extend 5 feet into the ground.

Each winter, the posts are pushed upward, and the porch movement is such that the main trim board and cedar clapboards are displaced, some by 2 to 3 inches. They settle back to their original position in the summer. During the frigid winter, loud cracking is often heard. One individual informed me that moistened, freezing clay is known to crack cement basement walls. In the case of the upward lift of the exterior porch floor, this is caused by clay "strangling" the posts, which thrusts them upward.

His solution is to envelope the posts in Styrofoam, expand the holes considerably and surround the posts with stones. A civil engineer who is a former home builder stated that the only solution is to extend support posts down to about 10 feet, etc. There is a drainage ditch filled with stones that runs below the exterior edge of the porch.

Should the fix entail the above? Could there be any concern relevant to possible damage from freezing clay to the basement cement walls?

Morrisville, Vt.

A. The fix proposed by the presumed contractor is not likely to work. By enlarging the holes around the posts and filling them with stones, water and melting snow will simply fill the holes, freeze and lift the posts -- either by "bear-hugging" them or by lifting them from the bottom as the clay freezes and expands. Wrapping them in Styrofoam will not prevent this from occurring.

His proposed fix could work only if the stones connect to a drainage system located below the bottom of the posts that will allow water to drain away, and if the tops of the stones are covered with geotextile fabric and capped with a sloping collar of soil to prevent water from getting into the stone beds. The fix suggested by the engineer/former home builder is impractical -- excavating down 10 feet once the porch has been built is going to be very difficult to do and somewhat risky. It's OK to do during the original construction project, but not as an afterthought. Moreover, unless the backfill around the posts is made of coarse material and capped with a sloping collar, the posts can still be "bear-hugged" by freezing clay.

Your problem can more likely be blamed on the drainage ditch; it is causing the post uplift unless the ditch is fully lined with heavy plastic in order to prevent percolation of roof water in the clay at the bottom and sides of the ditch. As the clay absorbs water, ice lenses form and "bear-hug" the posts regardless of how deep they are in the ground. Get rid of the ditch, and make sure that there isn't a low area under the porch to collect water. The expanding clay may cause the foundation to crack. Also make sure that the grade slopes away from the porch. If there isn't one, you may also want to consider installing a gutter and downspout system on the porch fascia, as long as you make sure the downspout discharges the water onto a splashblock and the ground slopes away.

© 2008, United Feature Syndicate, Inc.