Why does drywall crack on interior stairways?

Q: This might be a really stupid question, but why is the drywall in so many homes blemished at stairways, when it might be otherwise perfect throughout? I see the insides of a lot of very nice homes in the course of my work as a housecleaner, and see this repeatedly. The drywall seams might be visible, a dimple or blemish, and occasionally a crack. Always seems to be related somehow to a stairway. What's up with that?

A: Wood expands and contracts with changes in moisture and temperature. Most of the change occurs perpendicular to the grain of the wood. The wood grain in a conventionally framed wall (the stud) is on the vertical plane, so expansion and contraction are minimal. Now consider a log home; these are exactly the opposite, wherein multiple logs are stacked, forming a wall. The grain is horizontal. Log homes are notorious for vertical movement between seasons, more than an inch in some cases. But that's part of the charm, and this movement is accounted for in the design of the stairs, and other areas.

So why are stairway walls different than regular walls in a conventional home? The horizontal floor framing (joists) sandwiched above and below by vertical studs is subject to expansion and contraction. Drywall and plaster are brittle and do not allow much movement without dimpling, bowing or cracking.

The stairway is the only area inside most homes that transitions from one level to the next. Sure, this expansion occurs everywhere, but you might only see it at the stairway. Of course, this movement (called "rim joist movement") occurs outside the building as well.

Brittle siding materials such as stucco quickly crack right along the joists unless expansion joints are positioned correctly. More flexible siding does not telegraph this damage.

Q: The salesman at the wood-stove store told me that I absolutely should not install a new woodstove or fireplace insert without lining the chimney. Problem here is that he estimated the chimney liner would cost about $1,000 per channel, which is way more than I can afford. (I recently was laid off, and I was hoping to find a decent used stove.)

I can understand a chimney liner is a good thing, but I have trouble understanding why a super-efficient woodstove or fireplace insert would create any more creosote or be any more of a fire risk than the bare fireplace or cast-iron stove I'm using now. What do you think — would I be taking a risk or otherwise foolish to upgrade the stove without installing a liner?

Also, any advice you have regarding shopping for an efficient used woodstove would be much appreciated.

A: Without a liner all the way to the chimney top, you cannot sweep the creosote out, increasing the risk of a chimney fire. With a liner, a chimney sweep puts a brush down the flue and the creosote comes out into the firebox, like it should. Lacking a liner, she can sweep the original flue fine, but the creosote will collect down on top of the insert itself, around the insert, and everywhere behind it. There's no way to get the stuff out of these areas without removing the insert.

A chimney fire could quickly become a full house fire as the area between the insert, the interior of the home, and original chimney is not sealed or protected against a fire. While yours may vent properly, not all do. The insert is designed to vent and be most efficient with a given flue size, and you can be sure it is smaller than the typical 14-inch clay flue liner or a 2-foot-wide open brick chimney in older buildings. In searching for a used woodstove, be aware that it is illegal to sell or purchase a non-certified unit.

Q: I recently ripped down a false ceiling in a bathroom, only to find the plaster in mediocre condition. The ceiling looks fine after a good coat of paint, but the walls need help. I know people often rip out the old lathe and hang drywall. Wanting to avoid this, my plan is to hang ¼-inch drywall over the plaster. I know the walls aren't perfectly flat, but they aren't too warped. Can you tell me the pros and cons of hanging Sheetrock over the plaster in a bathroom? The other alternative is to put a very rough texture on the walls before I paint. My concern is that the nooks and crannies would be good spots for moisture. (Yes, I have an exhaust fan.)

A: Pros of a ¼-inch drywall overlay: It's easy, fast and cheap. Con: You will have issues with terminations at the door and window casings, and at electrical and plumbing penetrations. But these can usually be overcome. If not shimmed correctly, waviness in the wall can be seen through the new drywall.

As far as adding a heavy texture over the original plaster, use a moisture-blocking primer and enamel paint containing a mildewcide, and the moisture issue will be moot. I would be more concerned with future cracking at the repaired joints than moisture in a bathroom with a working exhaust fan.

Check the exhaust fan by putting a piece of 8 ½-by-11-inch paper up to the grille. The paper should stay on the ceiling with the fan running. Half of all fans (or the venting systems connected) have problems and won't hold the paper up.

Darrell Hay answers readers' questions. Call 206-464-8514 to record your question, or e-mail dhay@seattletimes.com. Sorry, no personal replies. More columns at www.seattletimes.com/columnists.