I have a 5' crawl space and I would like to lower its floor by 3'.
Along three walls I don't really need to get 'all the space' - I'm proposing to dig 2'away from the existing wall - then pour a concrete wall and at its top pour a 2' horizontal part to the existing wall.
The question: do I pin this new wall and horizontal section to the existing wall, if not how do I let it float and still maintain integrity?
Any advice or suggestions would greatly be appreciated.
What you really need to do is underpin all the walls, or else you must not enter beyond a plane that extends from the inside bottom edge of your footings down at a 45-degree angle. If you do what you propose, your footings will exert horizontal pressure against your new walls, and they may bow or tilt or crack or perhaps do all three things.
Underpinning the footings isn't really complicated, but it takes a lot of hand labor, which is why it can be expensive if done by a contractor.
What you do is dig out a section of earth beneath your footings about three feet wide, extending all the way back to the back edge of the footing. Then you move six feet away and repeat the process, and continue all around your crawl space. Then you place a wooden form four inches or so inside the inside edge of your footing, and you fill all those excavations with concrete, up to about an inch from the footing bottom.
When the concrete sets, you pack the space under the footing bottom with non-shrink grout.
Then you proceed to dig out another set of three-foot wide spaces under the footing, repeating the process outlined above. When that concrete and grout are set, you dig out the remaining spaces, and again repeat the process.
The bottom of your excavation should be about eight inches below your new finished floor elevation.
If you were to use a method similar to what you propose, you would locate the back of your new footings 3'-8" out from the inside bottom edge of your existing footing, and build your wall up from there, so you would lose over four feet all around. That's why underpinning is better.
Architect (NY) and Home Designer (PA)
Posts: 2572 | Location: Tobyhanna, PA | Registered: 24 October 2005
Richard, Great advice. Based on your titles it sounds as though you might have a great deal of experience in this area. Do you have anyone in Denver, CO you can recommend for this type work? Thanks, ~Aaron
quote:
Originally posted by Richard Hetzel: What you really need to do is underpin all the walls, or else you must not enter beyond a plane that extends from the inside bottom edge of your footings down at a 45-degree angle. If you do what you propose, your footings will exert horizontal pressure against your new walls, and they may bow or tilt or crack or perhaps do all three things.
Underpinning the footings isn't really complicated, but it takes a lot of hand labor, which is why it can be expensive if done by a contractor.
What you do is dig out a section of earth beneath your footings about three feet wide, extending all the way back to the back edge of the footing. Then you move six feet away and repeat the process, and continue all around your crawl space. Then you place a wooden form four inches or so inside the inside edge of your footing, and you fill all those excavations with concrete, up to about an inch from the footing bottom.
When the concrete sets, you pack the space under the footing bottom with non-shrink grout.
Then you proceed to dig out another set of three-foot wide spaces under the footing, repeating the process outlined above. When that concrete and grout are set, you dig out the remaining spaces, and again repeat the process.
The bottom of your excavation should be about eight inches below your new finished floor elevation.
If you were to use a method similar to what you propose, you would locate the back of your new footings 3'-8" out from the inside bottom edge of your existing footing, and build your wall up from there, so you would lose over four feet all around. That's why underpinning is better.
Posts: 1 | Location: Denver, CO | Registered: 13 April 2008
Aaron, soil conditions in Denver are a whole lot different than here in the northeast. You have expansive clay soils in your region, and that requires careful foundation design by a qualified design professional in your area who is familiar with the local soil conditions. That includes the design of a floor slab.
Get a professional on board first, and he or she will lead you to qualified contractors in your area.
Architect (NY) and Home Designer (PA)
Posts: 2572 | Location: Tobyhanna, PA | Registered: 24 October 2005
I am considering having the job of lowering my basement floor contracted out. What is the price range for lowering the floor of a 1930's home in NY by 2 feet? Total square footage is around 450.
With all due respect, the price is what a qualified contractor says it is, after thorougly examining all conditions which may affect the project. There are far too many variables for anyone to quote even a range sight unseen...much manual labor involved, and all the utilities must be examined to see what must be done with them, and the center posts probably need to be replaced and new footings poured for them. Availability of staging area is also a factor.
Architect (NY) and Home Designer (PA)
Posts: 2572 | Location: Tobyhanna, PA | Registered: 24 October 2005
It is impossible to figure out that cost without knowing several factors. Type of foundation. Soil Conditions, Amount of posts holding up center of home. Mechanicals Plumbing and drainage. Access for the machine to get under the home.
Its going to be expensive. So much so it does not warrant the costs. As the payback for doing a basement only gets you around 80% of your return on your investment. Of course if your hurting for space. It would wiser to do an outside addition.
Posts: 1124 | Location: New Jersey | Registered: 31 January 2006
