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I need a new basement floor
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posted
Hi. I live in upstate NY. My basement has cider block walls and poured concrete floor, however the basement floor is aweful. Yestday while walking on top of it I noticed it sounded more hollow then usual. So I took a steel rod and easily punched a hole in the floor. The flooritself was only about 2 inches thick. So I removed an area of about 2 and a half ft in diameter. I then dug down to the bottom of the footing that supports the cider block walls.The footing travels out from the wall 2 1/2 inches and into the ground 7 more inches.(I measured it) Here's the question. I want to go deeper then the footing if possible. I need room for the stone (which they never put in) and a fresh layer of concrete. I would like to put the floor at the base of the footing. I am aware that I have to take out tons of dirt, rocks, and concrete, but I really want to lower the floor and have a higher ceiling down stairs. Is there any way of doing this? Oh, and we have one sump pump and water comes in in the spring. Is this too risky to try? Will I ruin the foundation? Any help would be gladly accepted. Thanks
 
Posts: 8 | Registered: 15 December 2006Reply With QuoteReport This Post
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What you want to do is certainly possible, but it will be quite labor-intensive, and there are a couple of IMPORTANT precautions you must take.

1. You MUST not dig below an imaginary line extending out and down from the bottom corner of the footing at a 45 degree angle.

2. In order to drop the floor level to the bottom mof the footing, you will have to underpin your footings. To do this, you dig all the way under the footing to the outside edge, at least eight inches deep, but ONLY for a width of three feet. Then you can do the same thing six feet away, and so forth until you have these three-foot wide gaps with six feet between each one, all around your foundation.

Then you place a wooden form board perhaps 4 inches inside the inside face of your footing, at each of these three-foor gaps, and fill the space beneath the footing with concrete, preferably 3000-psi ready-mix concrete .

Wait a couple of days for the concrete to achiebve strength, and then dig another 3 foot gap under the footing, leaving 3 feet of earth still between the new gap and one side of the ones filled with concrete, place the from boards as before, and pour concrete again.

If you have posts in the center of your basement, those footings must be underpinned also, in the same manner.

Now your footings are safely underpinned, and you have 8 inches of soil to remove over the entire area of your floor, so you can place 4 inches of gravel, a 6-mil polyethylene film vapor retarder (with all joints lapped six inches and taped, and securely taped at all walls and penetrations such as pipes, etc.) and a four-inch floor slab with 66-1010 welded wire mesh embedded in the concrete.

That's what's involved...it is a huge undertaking for one person, but it can be, and has been, done successfully.

Good luck.

Wait two more days, and repeat the process for the remaining three-foot gaps, and now your foundation is underpinned.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Hello! I hope Richard or someone equally knowledgable of this stuff sees this post.

I am looking at doing almost the same thing, though I think I might have a few things working for me.

I recently purchased a 104 year old house with a basement that exists because the lot is sloped, not because they dug down.

Their is no poured slab of concrete, but instead there are hefty wood pillars throughout the basement that sit on top of poured concrete squares (probably about 3x3) that look fairly new.

I'd like to lower the floor in the front section of the basement so that it is equal level with the back part of th basement. Probably a change of 2 ft. of elevation. The front part of the basement is probably already 5-6' tall, with the back part being 6-8' or so. However we are going to lose height with the poured floor and the dropped ceiling, so I'd like the front part to be 6-8' as well.

My question is: I've seen several people (Richard's post included) saying how you should not dig within the 45 deg. slope from the footing... but Richard's post then seems to indicate that you should dig UNDER the existing footings and pour a new footing (underpinning). Wouldn't you need to dig inside this 45 deg "no dig zone" to go under the footing? Perhaps I'm just picturing this all wrong Smiler

Thanks all!
 
Posts: 2 | Registered: 21 December 2006Reply With QuoteReport This Post
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Yes, when you underpin footings, you do indeed dig into the "forbidden zone" and then directly under the existing footings, but only for a limited width at any one time.

However, in a 104-year-old house, it is possible that there are no footings under the walls at all. You don't say what the basement walls are made of, or in what condition they are. If they are of brick, with failing mortar (quite common), then the width that you may dig under the foundation will be very narrow. If there are substantial concrete footings (8-inch thick or more), then the excavation can be up to three feet wide.

But for things like continuous drain pipes, etc., digging into the "forbidden zone" is...well...forbidden.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Richard, thanks for your reply. Smiler

I have a few more questions. When underpining the footing, how do you fill the concrete up to the top of the bottom of the footing? I know about using boards to contain but wouldn't there be some settling? Also, can solid blocks of concrete, along with mixed concrete, be used in place of poured concrete for the underpinning?
 
Posts: 8 | Registered: 15 December 2006Reply With QuoteReport This Post
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Oh, we also have an oil furnace in the corner of the basement on a poured rectangular pad of concrete. When underpinning that area is it necessary to go under this pad or can I work around it, creating a new footing around this pad?
 
Posts: 8 | Registered: 15 December 2006Reply With QuoteReport This Post
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To fill the concrete up to the bottom of the existing footing, the form boards must extend out about 4 inches from the face of the existing footing, and perhaps an inch or so higher than the bottom. The concrete is a thick liquid when it is placed, so it will fill the area completely.

I don't advise using solid concrete blocks, because there will be joints between the blocks and the concrete, and the blocks may be more porous than the concrete. I think that would be asking for water problems, and all the other evils of cracked basement walls.

The furnace pad would have to be underpinned in the same way as the walls, unless you want to disconnect your furnace and extend pipes, ducts, wiring, etc. to its new location on the lower floor.

Josh, you would do all the same things, with the same cautions. Your walls may or may not have concrete footings, so if they are just brick footings, when you dig under them, maybe limit the width of each individual dig to about two feet. Some bricks may fall when you dig, but a brick wall will arch over a small gap...it isn't that a whole two-foot section of wall will fall into your dig. If they fall, save the bricks, and after the concrete is set, mortar the bricks back into place. But from the looks of your basement, I don't think I would attempt underpinning. It would probably be cheaper and easier to build the equivalent amount of space above ground, if you have room.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Thanks Richard. After considering all the work involved (mostly to underpin everything) I might just rip up the old 2 inch floor, dig down to the base of the footing, place some stone, add a vapor barrier, and repour a new slab. This is less than half the work and it might solve my problems, as there wasn't a vapor barrier, stones, nor 4 inches of concrete. I did place a sump pump in there 2 yrs ago and it helped. Before that there was a passive system to a dry well that would fill up and flood the basement any way. It's very difficult to dig on the outside of the house. Do you think it is necessary to put in drainage tile under the slab before I pour? If it helps a little I'll do it bc I already have the dry well in place. Also, with respect to the vapor barrier how do you install it around concrete pads and posts? I want to make sure I am doing this right.
 
Posts: 8 | Registered: 15 December 2006Reply With QuoteReport This Post
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The vapor retarder should be 6-mil polyethylene film. Install it with all joints lapped six inches and taped, and tape it sceurely to any penetration, such as posts, pads, pipes, and all walls. Tape it in such a way that your concrete slab will cover the tape.

If you are not able to dig outside the foundation and waterproof properly, then a perforated pipe drainage system cannot hurt. It is inexpensive enough to do once your old floor is gone. Use rigid plastic pipe, not the flexible stuff. Cover the perforations with filter fabric to keep fine soil particles out of the pipe, and pitch the pipe toward your sump. Fill all around the pipe with gravel.

Your sump will probably have to be made deeper when you lower the floor.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Hello Richard,

I am about 60 percent of the way done on the digging. I have replaced the old support beams but was wondering how far apart do they have to be to meet code? Also I am placing drainage tile under the floor. I plan on having both active and passive systems because the water table is so high. On the drainage tile under the floor what do you suggest in the lay out of the design? How far away from the footing etc.? This digging out of the basement is a once in a life time thing. I want to thank you once again for the information you've previously supplied.
 
Posts: 8 | Registered: 15 December 2006Reply With QuoteReport This Post
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The drainage tile should be right up against the edge of the footing.

I can't help you with your support beams (I presume you mean columns) because I don't know the girder size or the amount of weight it is carrying. If you put the columns back where they were before, you can't go wrong.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Thanks Richard. They had cedar posts for the support columns and they had some dry rot too. The house was build in the 60's, darn hippies (wink). I replaced the columns with metal adjustable posts. I feel safer now. How was it missed the home inspection? They were hidden behind pine boards and the property was a foreclosed VA listing.
 
Posts: 8 | Registered: 15 December 2006Reply With QuoteReport This Post
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quote:
Originally posted by needananswer:
Also I am placing drainage tile under the floor. I plan on having both active and passive systems because the water table is so high. On the drainage tile under the floor what do you suggest in the lay out of the design?


If you are taking out your whole basement floor and have a high water table, I would definitely lay more tile than just the permiter. If it were mine I would also lay it on the interior, probably about 6 ft on center for the whole interior of the house. Drain tile is cheap and like you mentioned, this is a once in a lifetime job - better to overkill that under.


General Contractor/Home Builder
 
Posts: 498 | Location: Minnesota | Registered: 15 January 2007Reply With QuoteReport This Post
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Can someone provide some insight on this project.

I'd like to lower a section of our basement floor to allow more ceiling height for a gym space. The basement is poured concrete, poured footings and walls. The home is 30 years old. A footprint of 1300sq ft. I would just want to lower a section - 800sq ft - of the basement. This section does not need to butt against an outside wall. Would this project be possible and what estimates (range)could you provide.

Thanks
 
Posts: 1 | Location: Niagara Falls, ON | Registered: 23 March 2007Reply With QuoteReport This Post
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I often tell my clients that anything they can say in words can be done. The issue is whether it will be worth the cost.

So, yes, the project is POSSIBLE. The cost is impossible to estimate because I can't see your basement, do not know thw depth of excavation necessary to produce the ceiling height you need, know nothing about soil and subsurface water conditions in your area, and do not know labor rates or availability in your area. I don't know how many columns will have to be replaced, or how many new column footings will have to be built. I don't know what utilities will have to be relocated or rerouted, nor do I know if it is even possible to do so.

I do know that the cubic feet of additional volume that would be produced would be very very expensive in terms of dollars per cubic foot. Exactly how expensive is something that will be determined by a contractor in your area who is willing to tackle such a project.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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I can guarantee you will have a difficult time locating someone who will do this project. I would never even consider it if someone asked me to do it. Even after the project is done, there are too many unknowns, water being the biggest one, soil movement, and vapor movements are others. Even if you can find someone, they are going to charge a small fortune to do it. I've seen it too many times that a contractor will purposely bid a job outrageously high so because he doesn't want to do it, but he promised you he'd give you a bid.
If by some small chance the homeowner accepts the bid, then the contractor is smiling because he knows he about to make a bunch of money. Your project would be a magnet for these contractors. It's sad that this happens, but it does. Contractors in general have a hard time maintaining integrity as it is, these people don't help matters any. Your money is better spent on an addition or possibly a second floor over a garage or something.


General Contractor/Home Builder
 
Posts: 498 | Location: Minnesota | Registered: 15 January 2007Reply With QuoteReport This Post
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I have 110 year old home where the basement is concrete but not nicely done at all(who knows how many years ago). The walls are mortor and stone and I have no leaks but the foundation needs to be remortored. I would like to stand up in the basement in order to put my laundry room down there. right now I really could use 6 inches or more to do that. The celing is realcut timber trees and the foundation walls are at least a foot thick. How realistic is it to lower the floor to accomplish my goals???
 
Posts: 1 | Registered: 05 June 2010Reply With QuoteReport This Post
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The stone walls could be sitting on soil. If a foundation does exist its not going to be much deeper then the four or five inches below the top of the current floor and you cannot go below this point unless you move the new floor in several inches and pour another lower foundation to prevent the current one from shifting.
Dropping a floor by even just six inches is tricky and can be quite expensive to do.

If everything is dry and fine. I would do nothing to disturbe this fact and find another place to put the laundry. With the cost of lowering the floor have you thought of putting on a small addition off the rear of the home such as a mud room with the laundry located there? It may end up costing you the same amount as lowering the floor and you gain not having to walk down another level of stairs to do the laundry.
 
Posts: 1933 | Location: New Jersey | Registered: 31 January 2006Reply With QuoteReport This Post
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