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Discussion Starter · #1 ·
I am doing a small addition on the back of my house, approx 13' x 13'. With this addition, I would like to get to a full 8' deep finished as the rest of my house sits on a block foundation over approx 3' - 4' of crawl space.

One wall (the wall with two windows) sits on a block foundation with about 4' of crawl space behind it. I will be squaring off the back of my garage with the back of my house (notice the survey I sketched quickly to get an idea of what I'm doing).

With about 1' of the foundation exposed and approx 3' of it currently buried, I will have to dig about 5' beneath the existing block to get to a finished 8'.

I understand the underpinning process of digging and pouring in sections. If I can avoid that and simply shore (build temp wall) up the house from the crawl space (floor joists run left to right not front to back) as it is only a 13' run, could I avoid the typical underpin process and simply dig, form and pour that wall all at once?

Any advice is greatly appreciated. I've spoken to a few architects all of whom have different opinions. I'm looking for a site guy who does work like this on a regular basis.









 

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I............
as it is only a 13' run, could I avoid the typical underpin process and simply dig, form and pour that wall all at once?
No.

And as someone who has done more underpinning than the average contractor......I would not do that at my house.

I sure as heck would not recommend you cut corners at yours.
 

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Discussion Starter · #3 ·
Thanks Tom.

Only reason I considered it was because an architect recommended it. I have only witnessed an underpinning once and it was a different situation. Had to get a 6' ceiling to 8'.

Now I have a sense of which architect not to hire! :no:

Being that you've underpinned many jobs, if you were contracted to do this job, how would you go about it? Trying to gain some insight prior to hiring my excavator.

Thanks in advance.
 

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Main thing is to stay away from the underpin wall at a 45 degree angle from the bottom of the footing, so as not to undermine.

I would do the center section first, then the adjoining sections.

Not sure what else you need to know.
 

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Discussion Starter · #5 ·
Tom,

Thanks for the response.

Do the middle 4.5' in one day then the other two approx 4.5' sections a few days later? Basically a two day process? Just trying to wrap my head around the big picture & overall scope.
 

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Yep, that is pretty much it, but I looked back at your drawing and photos...Will you not also have to underpin the back wall of the garage? That does make it more interesting.

You would have six sections, and you cannot do adjoining sections at the same time.
 

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Discussion Starter · #7 ·
Yes, forgot to bring up back portion of garage.

I am knocking out that back exterior wall. I am building up the floor in the back portion of the garage (shown in red) to match the existing floor of the house to create a hallway and will put an an ''L'' shaped staircase that leads to the basement. I will have to chop out parts of the existing slab and yes, underpin the back wall of the garage.

As an experienced underpinner, how do you see the excavating process of this project being handled? Keep in mind the roof (flat) joists of the garage run left/right not front/back.

If you're saying 6 sections basically start at the middle portion of the garage and the middle portion of the house wall on day one then complete the rest day 2? See what I sketched out. My concern with my sketch is that corner is a total span of about 9'.
 

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If you have not yet, you should consult with an engineer. As you know, you have adjoining sections, which is a no go.

Soil conditions and wall loads can also play into this, and I am not qualified to give engineering advice.
You have a basic understanding of what needs to be done, but I would not underpin my own house, (or someone else's), with out consulting an engineer.
 

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Or you could just forget doing it in sections and do it all at once. I am sure that slab will hold everything. :eek::eek:
 
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