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Question DetailsAsked on 5/12/2017

cost to underpin a 7 x 15 covered porch

house built 1930, prior owner made old covered porch part of the living room. Corner is sinking about a inch or two, we dug down; no footings under the porch. Ball park what would it cost to support the 'porch' and build a proper blocked footing/ crawlspace?

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If this was an old porch, likely supported (or supportable) on just a few foundation blocks like you would use for a normal deck or porch - probably around $100/footing assuming accessible from outside or from crawlspace, to put in prefab concrete support blocks like this -

I am assuming here this is a one-story room, and that you do not have significant frost penetration in your area. Note also this would NOT generally meet code so could cause an issue at resale - but for a 1930's house that might well be the least of the issues a pre-sale inspection would bring up so not likely to be a deal-killer.

The "right" way to do it - put in cast-in-place concrete piers under the support points (typically every 3-6 feet for typical deck construction turned into a sunroom or enclosed porch), or as yuou mentioned put in a strip footer and concrete block wall all along the perimeter to fully support it.

Cost of course depends a lot on access - concrete piers you might get for around $300-400 each (assuming doing 6-10 or so probably) if there is some way to access - typically by pulling up flooring/porch decking if ground clearance is low, or working from crawlspace or outside if at least 3 feet or so ground clearance.

Retro-installing a strip footer and block wall likely in the $10-20/SF (of wall) range so typically around $30-80/LF depending on ease of access, and whether doing a crawlspace or full-height basement wall. Unlikely to be as low as $10/SF because they will have to be working around the existing building overhead, not in open space.

In most areas you would need Architect or Structural Engineer plans of the design to be able to get building permit - contractor for the work could be a General Contractor or a Mason (with block wall), or a Foundation Repair company (your three Search the List categories).

Answered 3 years ago by LCD

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