Q: We have a small 1924 cottage in the flatlands east of San Francisco Bay. Our lot has a minor slope and we have a high water table. Our house continues to shift and settle, resulting in cracks in the walls, etc.
We have talked to both foundation and drainage contractors. The foundation guy says drainage won’t help but a new foundation will solve all. The drainage guy says a French drain and associated drainage will solve all and no foundation work is needed.
How can we determine which (approach) is correct? What’s the best way to get the best advice?
If we were to do only one to get, say, 80 percent of the benefit, which one would be more likely to provide us the 80 percent (benefit) for the cost?
A: The drainage guy is all wet. The movement of your cottage is likely caused by your proximity to the bay. Groundwater rises and falls with the tidal ebb and flood, causing the house to, as you say, shift and settle. There’s no way a French drain system is going to hold back the tide.
A French drain is useful for diverting groundwater around a house foundation either farther down the hill or into a dry sump. In this case, there is no water flowing downhill. Rather, the water pressure is pushing up from below, causing the house to shift and the walls to crack.
Solving the problem by replacing the foundation is also questionable. To get a definitive answer, we suggest you consult with a soil engineer to determine if foundation repair is a feasible fix.
Be prepared for a recommendation involving drilling concrete pilings far enough into the ground to reach stable soil, which will stabilize the new concrete foundation. You’re looking at the cost of a soils engineer, a civil engineer and draftsman to draw the plans. Then you’ll need a contractor to do the job. As you might imagine, this fix won’t come cheap.
If a new foundation is cost-prohibitive, you might consider another option. Because the endgame is to minimize the cracks, consider redoing the walls. Without a doubt, your 1924 home has lath-and-plaster walls.
The lath is horizontal 3/8-inch wood strips with a space between them to allow the plasterer to force plaster through the gaps and form keys. These keys hold the wall in place. Unfortunately, this system has little, if any, diagonal support, so does not resist cracking.
Replacing the plaster with drywall could well solve your problem. The 4-by-8-foot sheets will provide much-needed lateral support, more likely than not eliminating the cracking. Best of all, if you do it yourself, your only cost will be the materials.
This is a big project, so we suggest you attack it one room at a time. Seal that room off with plastic to keep the grit localized as much as possible.
Only remove the plaster from the walls — leave the lath in place and use 3/8-inch drywall. This will mimic the 3/4-inch thickness of the plaster wall and allow the new surface to fit flush to door and window casing, baseboards and existing electrical boxes.
To remove the plaster, punch a hole in the middle of the wall with a large screwdriver or the claw end of a rip hammer. Enlarge this hole until you can see the lath. Then use your hammer and a flat pry bar to gradually pull the plaster away from the lath.
Many of the plaster keys will remain. If they don’t pop out easily, use your pry bar to push them back into the wall cavity. It’s a dusty job, so don’t forget to wear a mask.
You’ll want to add insulation bats to all exterior walls, so remove the lath there and insulate. Before you rock, fur out these walls by tacking pieces of lath along the length of each stud. As a bonus, this is a great time to install additional electrical outlets and wall sconces.
Install the new drywall with drywall screws placed every 7 inches and screwed into the wall studs. Then it’s time to tape, texture and paint.
There is some good news. You can rock right over your plaster ceilings. Use 3/8-inch drywall and 2-inch drywall screws in the ceiling joists.
Make no mistake, this is lot of work. But, especially in this economy, it’s worth the time it will take to avoid the cost of a new foundation.
Finally, unless you have a couple of strong, experienced buddies working with you, rent a drywall lift. It will be money well spent.