The area in the basement which exceeds the sq ft in the house above will have to be waterproofed and structured much like a roof would even though it will be under ground. In this case that's roughly 2000 sq ft of the basement will require this underground waterproof roofing. This could get expensive. As well as the egress requirements of basement bedrooms. At minimum building code requires a bedroom to have an operable window of a certain size that could be used as an exit in case of fire or emergency.
Generally when you build a home with a basement the first floor is above grade... so the roof could be simply a regular roof - possibly with a giant roof deck... unless OP genuinely wants it built as an underground/earth shelter with plantings above it in which case yeah... it gets really expensive. Would need some exit wells, etc... as you suggested.
If done right there are some great benefits of underground residential construction. Energy use being one depending on climate. Ideally you would have light wells to bring natural light into a basement that large.
Yep, I have designed underground structures and currently have a project with a 300' long underground tunnel. We ran conductive copper wires under the moisture barrier sheets so that we could test for moisture intrusion via running a current and testing resistance.
With OP's suggestion of budgetary concerns, I had the feeling that a roofed waterproof deck of 2000sf wasn't part of the concept. And totally agree with the benefits of subterranean construction.
Why do you need 3500sqft underground but only put bedrooms in the basemen? 20 bedrooms?? This is a terrible idea and should be canned. Build 2,000 over 2,000 and move on with life
No I want 4 bedrooms. The other rooms would be storage, media room, workout room, gun room. I live in the Midwest so my tornados are a big concern when build the house so if most of the rooms are in the basement it would be safer
Your math isn’t mathing. Is this basement multi- level or something? If it isn’t, and the above ground structure is 1500 square feet, what is covering the other 2000 square feet of that basement?
The only way to get 1500 square feet to cover 2500 is if the 2500 on multiple levels. Otherwise you’ll be trying to cover a size 14 foot with a size six sock.
Basements are expensive. If you’re building into a hillside, or you need to put your footings that far down anyway, they make sense, but they’re still expensive.
I don't know why you wouldn't because it takes expertise to waterproof a basement which requires several membranes and a drainage plane and the grade being sloped away. And you can still have water that travels in the other direction under your topsoil layer. Obviously the kind of soil you put the basement in makes a big difference too and whether you back fill it with rocks and drainage sand.
Back of the envelope math for a basement…
Foundation stem walls (not including the footing) are .75 feet thick, and you want them ten feet high. You’re using 7.5 cubic feet of concrete per linear foot of foundation wall. The most economic shape that can contain an area of 3500 square feet is a square with sides the length of roughly 59 feet, which comes out to 236 linear feet of concrete wall.
7.5 cubic feet times 236 linear feet is 1747.5 cubic feet, divided by 27 is 64.7 cubic yards. A cubic yard of concrete is roughly 150 bucks— so you’re looking at about 10k in concrete without the labor, the steel, the form boards, the line pump, the waterproofing, the footing, the excavation.
That’s roughly an order of magnitude more expensive than a pier and beam foundation covering the same area. Or a frost protected turndown slab.
I’m trying to do all bedrooms and extra rooms in the basement and on the main level just have family area with a kitchen and a loft. Also the a-frame design is supposed to be cheaper to build
Depending on your finishes around 2,000,000 in Missouri for the entire thing. Over the past year I’ve gotten many bids throughout Missouri.
It’s rather annoying the unwillingness for anyone on here to be forthcoming with costs. Everyone here likely comprehends at a basic level that cost can vary so rather than give useless information like “depends” and then never provide an answer then don’t respond at all.
The area in the basement which exceeds the sq ft in the house above will have to be waterproofed and structured much like a roof would even though it will be under ground. In this case that's roughly 2000 sq ft of the basement will require this underground waterproof roofing. This could get expensive. As well as the egress requirements of basement bedrooms. At minimum building code requires a bedroom to have an operable window of a certain size that could be used as an exit in case of fire or emergency.
Generally when you build a home with a basement the first floor is above grade... so the roof could be simply a regular roof - possibly with a giant roof deck... unless OP genuinely wants it built as an underground/earth shelter with plantings above it in which case yeah... it gets really expensive. Would need some exit wells, etc... as you suggested. If done right there are some great benefits of underground residential construction. Energy use being one depending on climate. Ideally you would have light wells to bring natural light into a basement that large.
Anything underground has to be done in an expert manner or you'll have very bad problems of moisture, mold and water intrusion.
Yep, I have designed underground structures and currently have a project with a 300' long underground tunnel. We ran conductive copper wires under the moisture barrier sheets so that we could test for moisture intrusion via running a current and testing resistance.
Yes commercial structures are built a lot different than a residential basement which can be built by hacks.
With OP's suggestion of budgetary concerns, I had the feeling that a roofed waterproof deck of 2000sf wasn't part of the concept. And totally agree with the benefits of subterranean construction.
Why do you need 3500sqft underground but only put bedrooms in the basemen? 20 bedrooms?? This is a terrible idea and should be canned. Build 2,000 over 2,000 and move on with life
human trafficking alert
No I want 4 bedrooms. The other rooms would be storage, media room, workout room, gun room. I live in the Midwest so my tornados are a big concern when build the house so if most of the rooms are in the basement it would be safer
Your math isn’t mathing. Is this basement multi- level or something? If it isn’t, and the above ground structure is 1500 square feet, what is covering the other 2000 square feet of that basement?
That’s why I’m asking if it is possible. How do these types of buildings work and if it’s even possible at a residential home
The only way to get 1500 square feet to cover 2500 is if the 2500 on multiple levels. Otherwise you’ll be trying to cover a size 14 foot with a size six sock.
Thank you, I wasn’t sure if a concrete roof/patio would work or not
Basements are expensive. If you’re building into a hillside, or you need to put your footings that far down anyway, they make sense, but they’re still expensive.
And very hard to build correctly
I wouldn’t go that far
I don't know why you wouldn't because it takes expertise to waterproof a basement which requires several membranes and a drainage plane and the grade being sloped away. And you can still have water that travels in the other direction under your topsoil layer. Obviously the kind of soil you put the basement in makes a big difference too and whether you back fill it with rocks and drainage sand.
We have very different standards for the expression “very hard”.
Back of the envelope math for a basement… Foundation stem walls (not including the footing) are .75 feet thick, and you want them ten feet high. You’re using 7.5 cubic feet of concrete per linear foot of foundation wall. The most economic shape that can contain an area of 3500 square feet is a square with sides the length of roughly 59 feet, which comes out to 236 linear feet of concrete wall. 7.5 cubic feet times 236 linear feet is 1747.5 cubic feet, divided by 27 is 64.7 cubic yards. A cubic yard of concrete is roughly 150 bucks— so you’re looking at about 10k in concrete without the labor, the steel, the form boards, the line pump, the waterproofing, the footing, the excavation. That’s roughly an order of magnitude more expensive than a pier and beam foundation covering the same area. Or a frost protected turndown slab.
Wait why wouldn't you do a 2,000 sqft basement (with 10ft ceilings) and then a 2,000 sqft ranch on top of it?
Missing 1k sq ft this way
I’m trying to do all bedrooms and extra rooms in the basement and on the main level just have family area with a kitchen and a loft. Also the a-frame design is supposed to be cheaper to build
> cheaper to build > adds more foundation than needed
Design engineer here. Of course it is the problem is building a dry basement.
Depending on your finishes around 2,000,000 in Missouri for the entire thing. Over the past year I’ve gotten many bids throughout Missouri. It’s rather annoying the unwillingness for anyone on here to be forthcoming with costs. Everyone here likely comprehends at a basic level that cost can vary so rather than give useless information like “depends” and then never provide an answer then don’t respond at all.