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Old 05-26-2009, 10:24 PM   #1
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Basement addition foundation questions


I am putting a 16'x16' addition on my house. I have decided to go with a full basement addition under it, which will be connected to my existing unfinished basement. I have 8" thick poured walls with brick facing. The new addition will also be done with brick faced forms. I have a few questions about this process and the contractor seems to be pretty non-chalant about it, so I thought I'd get some other opinions.

1. How should the new addition be attached? Bolts, rebar? Should the existing walls be notched out and the new ones poured within them, or just butted up?

2. My existing foundation has Form-A-Drain on the inside and socked 3" tile/rock around the outside. My soil is very sandy, and I've never had a problem with leaking in the 5 years we've been here. I have never noticed the sump pump running, even during heavy rainfall periods. So, what should I do for drainage around the addition?

3. What should I do for waterproofing on the new walls? The existing foundation has damproofing to grade.

I appreciate any info anyone can provide!

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Old 05-26-2009, 11:02 PM   #2
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Basement addition foundation questions


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Originally Posted by hoggin03 View Post
I am putting a 16'x16' addition on my house. I have decided to go with a full basement addition under it, which will be connected to my existing unfinished basement. I have 8" thick poured walls with brick facing. The new addition will also be done with brick faced forms. I have a few questions about this process and the contractor seems to be pretty non-chalant about it, so I thought I'd get some other opinions.

1. How should the new addition be attached? Bolts, rebar? Should the existing walls be notched out and the new ones poured within them, or just butted up?
Definately rebar , probably #4 or #5's on 16-24" centers.

2. My existing foundation has Form-A-Drain on the inside and socked 3" tile/rock around the outside. My soil is very sandy, and I've never had a problem with leaking in the 5 years we've been here. I have never noticed the sump pump running, even during heavy rainfall periods. So, what should I do for drainage around the addition?
This is kind of an odd set-up, at least for my region. I've never seen a combo system with Form-a-Drain & 3" corragated. I would probably suggest just sticking with the 3" in this situation, or whatever your mason suggests.

3. What should I do for waterproofing on the new walls? The existing foundation has damproofing to grade.
A spray-on damproofing shoud be adequate in you situation.

I appreciate any info anyone can provide!
Most importantly, find a contractor you feel comfortable with, & all these concerns can be put behind you.

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Old 05-27-2009, 06:23 AM   #3
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Basement addition foundation questions


Good reply above, especially the last suggestion. But check local code, they have the final say. And find a contractor that builds to 'code +' specs. Building to code is just getting by, 'code +' goes a step further, and usually results in fewer porblems over time.
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Old 05-28-2009, 09:51 AM   #4
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Basement addition foundation questions


Thanks for the replies. Does anyone else have any input?
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Old 05-28-2009, 05:48 PM   #5
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Basement addition foundation questions


rebar as post'd,,, those of us in the waterproofing trade'd probably choose a trowel'd-on coating of sonneborn sonolastic ( or equilavant ) protected by pvc dimpleboard ( miradrain ) leading down to 4" perf pipe in a filtercloth lined trench cover'd by 3/4" stone,,, the spec, far's i know, is still 3mil dampproofing ( roll'd on asphalt emulsion ) not acceptable for my home ESPECIALLY that cold joint ! ! !
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Old 05-28-2009, 06:02 PM   #6
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rebar as post'd,,, those of us in the waterproofing trade'd probably choose a trowel'd-on coating of sonneborn sonolastic ( or equilavant ) protected by pvc dimpleboard ( miradrain ) leading down to 4" perf pipe in a filtercloth lined trench cover'd by 3/4" stone,,, the spec, far's i know, is still 3mil dampproofing ( roll'd on asphalt emulsion ) not acceptable for my home ESPECIALLY that cold joint ! ! !
I gotta admit, you are a little above my pay grade here! I understand what you're saying about the rebar, perf pipe/stone for drainage, and rolled on asphalt; but the stuff about sonneborn sonolastic and dimpleboard is a little out of my league. If you could give me some more info on that it would be much appreciated!
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Old 05-28-2009, 08:44 PM   #7
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Basement addition foundation questions


I would have your concrete contractor drill rebar dowels into the existing footings and walls in order to make sure your new foundation moves with the existing foundation. Also, even though you mention you don't have a water problem, I would install a vertical waterstop at the cold joint between new/old walls. You can get a peel and stick bentoninte (sp?) waterstop specifically for this application.
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Old 05-29-2009, 07:28 AM   #8
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that's why we have google bentonite - w r grace - sonneborn - miradrain - sonolastic - euclid chemical ( euco ),,, none of the above're avail at the apron stores - that's why its above your pay grade pro const supply houses carry these products,,, good luck ! ! !

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