Do It Yourself: Roof leak causes odor that won’t go away

Q. We had a roof leak some time ago and got a very strong sour odor in one of the rooms and water stains on the ceiling. We had the shingles replaced less than a year ago and fixed the stain, but we still get the odor during heavy rains. There is no new stain. What do we do next?

A. If you think the roof is still leaking, you should ask the roofer to check it.

Many leaks result from poor flashing or poor sealing of flashing, so the shingles might not be to blame.

It is also possible that the odor results from the effects of the first leak. It could originate in wet insulation in the attic or drywall that was not properly sealed in the leak area.

If possible, check the underside of the roof and attic floor in the first leak area. Any wet insulation should be removed and replaced – wet insulation is useless anyway.

Also check the drywall under the first leak area. A couple of coats of shellac, or a shellac-based primer such as B-I-N, will seal the drywall.

Roof leaks can often be spotted from inside an attic by dark water stains on the framing and roof sheathing.

Even better, get into the attic during a heavy rain and you might see telltale dripping. If you spot any new leaks or stains, let the roofer know about them; if a roof less than a year old is leaking, the roofer should make repairs.

Q. I have a home that is built over a crawl space and has insulation between the joists over the space. There is an aluminum skirt around the space, but animals sometimes get in and tear up the insulation and the vapor barrier, which is on the bottom of the insulation. Can you explain if this is the right place for the vapor barrier.

A. In most of the United States, where winters get cold and heating is needed, the rule is that vapor barriers (the plastic, paper or foil covering one side of some blanket-type fiberglass insulation), should always face the heated or “warm” side. This is because water vapor in the air tends to migrate from warm to cooler spaces.

So, in most areas, vapor barriers in walls should face the inside, in attics or ceilings they should face down, and in crawl spaces they should face up (assuming that the insulation is between the joists in the floor over the crawl space).