Protecting against termites

Q. I’m wondering if the walls of our new den addition have a correct “termite shield” or even need one. The carpenter told me he always puts one in, but the rest of the house doesn’t have it, and he put metal on the concrete foundation wall, then put some thin foam on top of the metal. What does this do, and do you think we even needed it? I don’t see how it stops termites.

A. Good point! Termites only go to certain homes. They’re very selective, preferring soft music, a comfortable sofa large enough for all their little legs … or maybe not. The termite shield is a barrier that, properly installed, limits or prevents termites from getting to untreated wood. Treated wood, especially older treated wood, was poisoned to repel insects from entering and gnawing on your wall’s wood base plate and studs. I assume the older adjacent walls are treated wood.

Poisoned lumber, using arsenic and cyanide, was banned in the 1990s due to the possibility that it can cause cancer. That was also the reason that playground climbing equipment was replaced. Unfortunately, the average person with a treated wood deck didn’t get the memo (or ignored the warnings) about their bare hands and feet being subjected to poison that can be absorbed through the skin. I cringe when I think about all those people who innocently come in contact with treated lumber. Just like global warming, it’s hard to persuade some people about cause-and-effect issues that happen over long periods of time. In our age of instant gratification, if something can’t be proved because it doesn’t happen right away, some will ignore it.

Termite damage is like that, also. Those silent little teeth are still gnawing away, and we either choose to find mechanical and chemical means to repel them or we accept the consequences: the damage they’ll do. So, yes, you do need a termite shield. But the way you described the installation, it won’t do much to prevent termites on the march. The metal shield has to be placed on top of the thin, compressible insulation strip, not on the concrete foundation top. Why? The compressible strip fills the rough concrete gaps, which are very small, but not to a termite, which goes right through the small openings.