In temperate climates where frost heaves aren’t an issue, older houses are often supported by unreinforced foundations only a foot or two deep. Consequently, when they fail, replacing them one wall at a time is pretty straightforward once you transfer loads to shoring (temporary support beams and posts). Getting a structural engineer involved is good insurance–and frequently required by local building codes.
When replacing a mudsill or sections of a foundation whose joists run parallel to the foundation wall, you’ll need to run needle beams through exterior walls, and support each beam with one post underneath the house and a second post outside, roughly 2 ft. beyond the foundation wall. (Illustration A.)
For this, you’ll need to remove sections of siding so you can insert a beam every 6 ft. to 8 ft. If the siding is stucco, you’ll need to punch large holes through it. To keep the rim (outer) joist from deflecting under the load, nail a second rim joist to it, doubling it before jacking. Also, add solid blocking from those doubled rim joists to the first adjacent joist. Use metal connectors to affix the blocking and 10d nails to face-nail the rim joists.
When replacing a mudsill or sections of a foundation whose joists run perpendicular to the adjacent foundation wall, place a 4×8 or 4×10 carrying beam on edge under the joists, within 2 ft. of the foundation. A jack every 6 ft. under the beam should suffice. (See Illustration B.)
This blog was adapted from Renovation 4th Edition, recently published by Taunton Press. Renovation 4 contains thousand of field-tested tips and techniques, 250+ illustrations and roughly 1,000 of the 40,000 photos I have taken on job sites. I hope you find R4 useful. –Mike
© 2013 Mike Litchfield
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A. Where joists run parallel to the foundation wall, remove a section of siding and run a needle beam through the wall as shown. To prevent its deflection under pressure, double the rim (outer) joist and run solid blocking to the next joist inward.
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To determine the height of the shoring posts, jack the beam to the desired height, level the footing block, and measure between the two. Nail the post cap on before inserting the post. Because this needle beam is simply holding a wall in place-not raising it-it was jacked just snug to a wall plate.
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B. Supporting the structure: When joists run perpendicular to the foundation wall, support their load with a beam parallel to the wall. Allowing yourself room to work, put this beam as close to the wall as possible--in most cases, 2 ft. is optimal.
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This big needle beam needed to fit under the top plate of the pony wall (short wall) on the right. As a result, the top of the beam needed to be built up with a 4x4, which now supports the floor joists. The metal connector atop the post keeps it from drifting out of plumb.
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Renovation 4th Edition contains thousands of field-tested tips and techniques that master builders shared with Mike Litchfield, a founding editor of Fine Homebuilding.
View Comments
Mike,
Replacing support framing is always a challenging task. However, as your blog post shows, it is possible. It's good that you include photos along with drawings to show theory in practice.
I got into related work as shown and described here:
https://www.finehomebuilding.com/item/12351/light-in-the-tunnel-a-moldy-crawlspace-nightmare-part-4
Both cases show that with a plan and some hard work new life can be built back into old and failed structures.