To underpin or not to underpin -- is that the question?
If Shakespeare had been a rehabber, that might have been Hamlet's lament over his crumbling old castle. However, the Bard didn't settle the issue, so today's old-house owners often have to wrestle with the thorny -- and expensive -- quandary of how to alter basement-level construction without causing a wall to collapse.
In newer construction, the outside walls rest on concrete and steel pads, called footings. But old houses often weren't built on footings. Instead, builders dug a shallow trench on the perimeter of the structure and began building the walls right there, on the dirt. If there is a basement, it may be surrounded by a ledge of dirt that helps hold the walls in place.
If people still lived in the houses as their ancestors did, such construction wouldn't matter. But suppose the current owners want to add a basement laundry room or recreation room? Or put on an addition, or change the location of the basement stairs? It's going to mean changing the way the walls are supported.
In general, this is not a task a homeowner should tackle on his or her own. The issue is more likely to arise when there's a conflict between contractors or between a contractor and an architect over whether or not a particular project will require underpinning. Since it can add several hundred dollars to a contract, it's not a trivial matter. It may come as a surprise to the homeowner, who doesn't know why the basement can't just be dug out, and may even suspect the contractor or architect of "requiring" something that's not necessary.
Part of the problem is that there's nothing scientific about the bidding process. Contractors can honestly differ over how much work is needed in a particular area, and architects, who most likely are not builders, may be too optimistic or too pessimistic about the existing situation.
The other part of the problem is that homeowners aren't experts and often simply can't determine what's the best thing to do for the house.
The process of underpinning a wall requires digging out the dirt beside it (if there's a ledge) and beneath it, pouring a steel-reinforced concrete footing, and building a new section of wall from the new footing to the old wall.
Any time you start digging next to the old wall you're taking a risk. Mortar tends to crumble over time; the dirt could be the only thing holding the wall in place. Removing the old dirt could cause the lower part of the wall -- or the entire section -- to collapse.
Contractors are naturally reluctant to take such a risk without knowing they'll be able to afford to fix any problems.
There are several approaches to resolving a conflict over whether underpinning is necessary.
For the most part, if the house walls rest on dirt, and your project requires disturbing that dirt, you should underpin. You can't just take the dirt out and then put it back: The existing dirt has compacted over time, to a particular degree. If you fool with it, you'll loosen it, and it won't provide the same kind of support.
If underpinning seems too expensive, or makes a project financially unworkable, you might consider a design change that will avoid having to dig next to or under the wall.
If someone is suggesting you don't need to underpin, you might want to get a second opinion. You might even want to consult a structural engineer. Ask for an opinion and a proposed solution. It may cost a few bucks, but it could make your house feel a whole lot better.
Mr. Johnson is construction manager for Neighborhood Housing Services of Baltimore. Ms. Menzie is a feature writer for The Sun.
If you have questions, tips or experiences to share about working on houses, write to us c/o HOME WORK, The Sun, 501 N. Calvert St. Baltimore, 21278. Questions of general interest will be answered in the column; comments, tips and experiences will be reported in occasional columns.