Hi all – I’m about to start renovating an old house that I own. It was built in many phases – this question pertains to what I believe is the last phase, probably added about 40 years ago. It appears that it was a porch that was subsequently closed in. I am going to rebuild the porch to fully winterize it, and close in a room under it. The current foundation looks inadequate – a perimeter footing poured at grade (or about a foot deep) – not acceptable in eastern MA. It has been suggested that I don’t have to excavate and replace the entire foundation – all of the weight from above comes down in 3 locations, so I’m thing of digging by hand just under those spots and pouring decent footings. My idea:
dig a hole 4 ft deep, pour about a foot of concrete at the bottom, then slip in an 8″ tube that comes within 4″ of the bottom of the old footing, fill the tube, back fill, then slide in some sort of a 2×4 form near the top so I can pour the last of the concrete in a way the fills the hole right up to the old concrete. Not sure if this description makes sense, but does it sound like a reasonable approach?
Thanks! Bill.
Replies
Without knowing what the original "porch " design load, you may or may not have a workable solution.
Many porches and decks were only designed for 20 or 30 psf live load. You are now wanting to convert it to a living space that requires a live load design of 40 psf. Than changes your beam sizes and point loads to the foundation/footing and the size they must be base on the soil loading capacity for you area.
My mechanical approach to your situation would be :
(1)Support the the porch between the new footing points with temporary walls or post.
(2) Remove the existing post, cut out the old grade beam at those points and pour new piers fully to the elevation needed for resetting new post.
job done with out a lot of additional digging, forming etc. I like KISS
Other will be along shortly to take up your question.
I've put new footers under several structures.
My favorite method is to excavate several small areas under the foundation large enough to fit a 4x8x16 solid CMU laying flat in. The hole needs to be deep enough to fit a hydralic jack between the CMU and the bottom of the foundation/footer.
Start jacking until you've pushed the CMU down into the earth 4". Remove the jack and slide another CMU on top of the 1st one and repeat until the structure starts to lift. Replace the jack with a jackpost and repeat as often as necessary along the length of the foundation, keeping the holes several feet apart. When you've got as many bearing points as you think are necessary, pour your holes full of concrete up to the bottom of the footer.
If you want the footer solid around the perimeter, repeat between your pours after the 1st round has set up.
http://www.quittintime.com/ View Image
thanks for the idea... i hate to ask but what's a CMU? Thanks
concrete masonry unit.http://www.quittintime.com/ View Image