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I’m looking to lower the floor in a 12 x 24 room in my basement. Three outside walls and one inside are all 80+ year old CMUs. I’d like to take down the floor 12″ – 18″. Can it be done and if so, how?
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Replies
A little more information is necessary.
Concrete floor or dirt?
Footings under the CMU walls? If so, how deep? Are you going to undermine them?
What's your goal? Increased headroom?
What's the space going to be used for? Finished, conditioned living space?
Solar & Super-Insulated Healthy Homes
Concrete floor or dirt? - Existing concrete floor which I'll replace with insulated, radiant heat in concrete.Footings under the CMU walls? - I assume so, but would first break up a small corner of floor to confirm.Are you going to undermine them? - Yes, I would assume so.What's your goal? Increased headroom? - Yes.What's the space going to be used for? - Finished, conditioned living space? - Yes, a finished laundry and sewing room for my wife. Current ceiling height is 6' 6".
Edited 3/15/2008 9:49 pm by pino
I would not recommend undermining existing footings.
Unless you wife is taller than 6'-6", I'd make do with what you've got and figure another, less expensive, way to heat the space.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Wild suggestion...but what about raising the house?
In the 'better' neighborhoods (ie, making it worth the effort) around here I've seen a couple of cape cod/bungalows build entire new basements that way.
I'd pour new concrete under the footings, in short sections which ultimately join up with rebar connecting them. The goal is to only have a small part of the foundation supported by air at any one time. You may be able to pick up some of the loads with temporary posts or beams to help prevent any movement during the underpinning process.
Another option might be to create a shelf around the perimeter and only lower the inner part of the floor. Less flexibility in design and layout but no underpinning necessary and less risk.
All that being said. The weight of the structure, the condition of the masonry (and footing?), soil type, water levels, and outside finishes etc. need to be factored into a project that presents considerable risk.
Edited 3/15/2008 10:26 pm ET by sisyphus
basement floors are already lower...thats why it's called the basement...geeez!
Yes basements can be lowered but I dont think it qualifies as a DIY project if that is what you are thinking. Small sections around the perimeter of the building are dug out to below the depth you want to go. New footing section poured along with wall up to the bottom of your existing wall. Allow to cure. Repeat the above again until a new footing and wall are complete around the whole basement. Then dig out the rest of the basement floor and pour a new one at the new lower level.
There are companies that specialize in this type of work..so get in touch with them in order to get accurate info. for this type of work in your area.
Just finished a very similiar basement. About the same sq footage. Hand dug 18"+ one 5 gallon bucket at a time out a window. It was alot of work.
Per the engineers design we dug down flush with the old foundation, then poured a wall 8" thick overlapping the old foundation by about 4". So this new wall was about 22"-24" high. Two runs of #4 rebar.
With this option we lost some floor space, but we were able to finish the wall in one pour vs his other option which was digging out under the footing (actually there was no footing, stone foundation) 5'-6' at a time, and pouring concrete. I assume allowing time for each section to cure before digging beside it. But, since we opted for the other suggestion, we didn't ask to much about this one.
Now this is what the engineer looking at our project designed. Yours maybe very different. All standard disclaimers apply.
Edited 3/16/2008 1:00 am ET by 9ENGEL
Edited 3/16/2008 1:01 am ET by 9ENGEL
Your solution is what I was hoping to do here.I should have added that I underpinned 2 existing basement walls on an 1922 addition to our house and it was a b!tch. I'm not so worried about loosing floor space, as you mentioned, as I plan on studding out and insulating the walls so the net loss would be minimal. Thanks all for your advice and warnings.
You don't undermine the footings, you underpin them in 3' long sections usually in consultation with an engineer. You're in for a ton of work. The slab is almost always right on top of the footing, which given the 80 YO age is probably 6"-8" thick. The footings will probably have a 'toe' to the inside which makes it even more difficult.
Jeff
Pino, I did almost exactly the same as you are proposing to a house in Ottawa years ago. It was hard work, but not rocket science by any stretch. We used a rented conveyor belt that went out to a dumpster which was filled everyday. The excavation actually went rather quick, (a little over a week IIRC. We just through lot's of labor at it and got it done. The underpinning is straight forward (typical 1/3 rule). Finished basement came out great, we even put in an exterior access stair as well the interior stair. bathroom, laundry, nice new deep window wells, etc.
A buddy of mine also just did the same on his 1850's federal style house in Cold Spring, NY complete with under slab radiant heating. Put his kitchen down there, worked out great.
Thanks for the insight.
Whats the 1/3 rule?
Do you have any sketches on how to do it. Im starting to get a good idea on how to do it. I would just like to locate rebar and get a few more details. Did you extend the new wall inward a few inches beyond the old foundation? I imagine you guys extend the rebard beyond the footing that your pouring so you could catch it and tie in with pour next to it.
Essentially what I term the 'one third rule' is that the length of the interior footing / foundation wall is divided into increments approx. 2' wide and marked off into multiples of 3 such as: A, B, C, or 1, 2, 3. Use bright orange spray paint to make clear markings. All the section A's are removed, excavated to the new depth, rebar installed and new concrete poured against formwork that is inboard the basement (I have usually seen 4" - 6" for typical residential structures. Once the concrete underpinning has set up (I would wait a few days) you do the all section B's and so on. And yes the rebar should be as continuous as possible. Of course you should get a structural engineer to design this properly.Here are 2 websites with some info that may be interesting. One is a publication and one is a blog on a house in Williamsburg, Brooklyn with some good pictures. If you google underpinning you will come up with others.http://books.google.com/books?id=2M2sCZD_-RAC&pg=PA85&lpg=PA85&dq=concrete+underpinning&source=web&ots=pzORctARxH&sig=UkYoY3VrS9Oe5RljDU-uBIksuo0&hl=en#PPP1,M1http://images.google.com/imgres?imgurl=http://www.danabushman.com/here_is_the_house/images/front_landing2.jpg&imgrefurl=http://www.danabushman.com/here_is_the_house/2006/09/index.html&h=667&w=500&sz=107&hl=en&start=10&um=1&tbnid=LZ1Iw7kk1bEIyM:&tbnh=138&tbnw=103&prev=/images%3Fq%3Dunderpinning%2Ba%2Bhouse%26um%3D1%26hl%3Den%26sa%3DN
FYI
Excellent link, thanks. Now I don't feel so bad, or insane for wanting to take this on.