Q: My dad tells me I should cover my crawlspace vents when the temperature drops below 25 degrees. My concern in so doing is that we might be inviting problems. Specifically we have had...

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My dad tells me I should cover my crawlspace vents when the temperature drops below 25 degrees. My concern in so doing is that we might be inviting problems. Specifically we have had rat problems, although exterminators have been very good about quick eradication when signs appear. I worry that a warm space may invite more, and that if there were any carcasses we would get a nasty smell in the house.

We’ve also had moisture issues under the house, although nothing more than you would expect in this climate (Whidbey Island). I’m also concerned about more exotic issues such as radon gas. Internet searches turn up differing opinions. To vent or not to vent, that is the question.


The differing opinions you encounter are the result of differing weather patterns in other areas of the world (or even the two sides of this state). We battle moisture more than cold. In Wisconsin and Okanogan, it is the other way around. So yes, you theoretically could close your vents for a day or two, just remember to open them back up again quickly.

But why go to the hassle? Your plumbing pipes should be insulated against freezing, so this exercise really serves no purpose and can lead to other problems if you forget to remove the vent plugs.

If you close up those vents and leave them closed for a winter, add natural water leakage from below like so many of us have, add an uninsulated rim joist, and you’ll have a problem of unimaginable proportions. A completely “sealed and heated crawlspace” is another deal altogether, designed to be dry, but you can’t close off an area designed to be vented and expect to be trouble-free.

With regard to rodents and radon, neither will become an issue if they weren’t before. If the crawlspace gaps were previously screened and sealed, vermin won’t be any more likely to get in if the internal temperature comes up two or three degrees. It’s all about keeping an intact perimeter barrier. Fortunately, radon levels are at the lowest levels in the country here on the soggy side of the hills.

I have condensation (at least I believe it is condensation) dripping out of the exhaust fan in the bathroom. This has been happening on the cold clear mornings we have been having recently. How can I prevent this?


The top of the fan housing is not insulated. Cold attic air is touching the exterior of the fan housing. Condensation occurs as the warm humid air in the bathroom comes into contact with the fan housing.

The first line of defense is to run the fan a bit more to eliminate the bathroom moisture, but this won’t completely solve the problem. You need to crawl up in the attic and do some insulating.

If it is a stand-alone fan, then cover the fan housing with insulation. The exhaust pipe also may be warm, causing condensation and needs to be wrapped with duct insulation or thin fiberglass batt insulation.

If your fan has an integral light, it will have little vent holes (assuming it is an older unit) to let heat escape. In this case you cannot put insulation directly on the housing.

Newer fan units with lights will be marked “IC,” meaning they are approved for direct insulation contact. The “IC” marking may be inside or outside the housing. If it is marked “IC,” cover it with insulation.

If it has vent holes or lacks an “IC” marking, then you need to build a box of drywall, plywood or sheet metal. Make the box large enough to completely cover the unit and give it several inches of airspace above. Install the box over the housing and insulate the outer portion of the box. Then insulate the exhaust pipe as described.

Sewer stewardship

Several weeks ago I wrote briefly about maintenance of homeowners’ sewer systems, focusing on penetrating roots. After that column ran, members of a municipal sewer-maintenance crew contacted me to share tips on preventing sewer-system problems. They suggest that the following not be flushed or poured down a drain:

Dental floss. This product does not decompose. It catches on valves and pumps and must be manually cut away. Toss it in the trash.

Hypodermic needles. Unbelievably, these are routinely flushed! Don’t throw them in the trash, either — they are medical waste and need to be disposed of properly. Cap them and dispose of them in a “sharps container.”

Feminine-hygiene products and paper products (other than toilet paper). These can cause backups.

Cooking grease. Scrape it and toss it in the trash. I have been guilty of this myself at times, thinking that washing small amounts of grease down with hot water will render it fluid enough to prevent solidifying. But sewer lines are not scalding all the way to the treatment plant. Somewhere it is going to cool enough to solidify, and that may or may not be on your property. Eventually, someone is going to have to deal with it.

Darrell Hay is a local home inspector and manages several properties. He answers reader questions — call 206-464-8514 or e-mail dhay@seattletimes.com. Sorry, no personal replies. More columns at www.seattletimes.com/columnists.