Basement Next to Slab

bigmike440October 12, 2007

My house is 10 yrs old and built on a slab with block walls. I want to build an addition but with a basement instead of a slab or crawl space.

The problem is that everyone has a different opinion on how to place a basement beside a slab. The structural engineer has come up with some complicated plan that is very expensive and the architect agrees that it is overkill.

I thought the general rule was for every foot you dig under the original foundation you need to come away from the foundation one foot. For instance, I have to dig about 4 feet deeper than the original foundation so my basement would effectively be about 4 feet more narrow than the first floor. The soil is very hard and sturdy according to the soil engineer.

Does this seen right?

Thanks, Mike

Thank you for reporting this comment. Undo

Where are you located? Are the walls set on a separate footer, or is the slab structural (i.e., the slab is the footing for the wall)? If on a separate footer, how far below the top of the slab is the footer?

    Bookmark   October 12, 2007 at 4:29PM
Thank you for reporting this comment. Undo

I am located in Southwest Ohio.

The existing block wall is on a 10"x 16" footer 56" (7 Blocks) below the slab.

The engineer is worried the block might not be reinforced. He wants to install controlfort walls every 8'. Another engineer is going to look at it tomorrow.

Thanks, Mike

    Bookmark   October 16, 2007 at 5:22PM
Thank you for reporting this comment. Undo

Mike - what did you come up with? I think people here, and future people, would be interested.
I moved here to the Dayton area 5 months ago and am finding that many if not most of the ranch style housing outside of subdevelopments are on slabs. Quite disappointing.

    Bookmark   October 27, 2007 at 7:38AM
Thank you for reporting this comment. Undo

Re: "I thought the general rule was for every foot you dig under the original foundation you need to come away from the foundation one foot." - You got this right. What you've said is the civil engineering rule of thumb for worst-case foundation conditions, that is, loads are transmitted down and outward at a 45 degree angle. So, one foot down and one foot out. It typically is better than this, but this is the worst case possible. Most construction is based on this to be safe. Just be sure to not disturb the soil that is supporting the existing foundation and pour a concrete retaining wall against the existing soil wall after excavating to hold everything in place. I'd probably place a slab on top of the remaining soil ledge and try to work some sort of storage or mechanical equipment into the space. Good luck!

    Bookmark   October 29, 2007 at 9:24AM
Sign Up to comment
More Discussions
water in unfinished basement
Well its in the 50s here in NJ and the snow is melting....
Walk-out basement design
Building a house in western Massachusetts -- it will...
Basement wall insulation
Hello, I live in a 1952 English bungalow in Chicago...
Which drywall to use in the basement?
Hi, I am finishing a basement that is under the attached...
Replacing Steel Column With Stud Wall?
I am interested in replacing a steel column with a...
Sponsored Products
Amerelle Under Cabinet Lighting 20 in. Halogen Bar Nickel Metallic UB3KBAM
$18.61 | Home Depot
Fairmont Designs Amelia Ottoman - D3525-09
$409.99 | Hayneedle
Westek 39.17 in. Flourescent Nickel Slim Line 21-Watt Direct Wire Cabinet Light
$15.99 | Home Depot
Dramm Aluminum Quick Disconnect - 1403-1116
$30.99 | Hayneedle
Westek 20 in. White Halogen Cabinet Light UB3HB
$22.49 | Home Depot
Basic Ventilated Cedar Closet Wall Kit
Signature Hardware
Dramm Jet Nozzle - 1403-8061
$24.99 | Hayneedle
Globe Electric Recessed Lighting 5 in. White Recessed Sleek Directional
$16.99 | Home Depot
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™