How much does a sloped lot add to slab foundation cost?

9 years ago

I'm looking for some advice from general contractors, foundation experts, etc. Please see the attached photo. If I were to build a simple 2000 sq. ft. house on Lot 58 with the front of the house facing down the slope, would the foundation costs be significantly more due to the slope? From the image, you can see the lot rises from 990 ft. to 1020 ft. towards the back. So that's a 30 ft. rise across approximately a 450 ft. distance, which is about a 6% or 7% grade.

There is a house on Lot 59, on the very western part of the lot where the 1040 mark is on the image. It looks like they had to do significant foundation work and excavation to make it work. I don't think my lot would be as bad because the slope isn't nearly as steep as the neighbor's.

There are no houses on the lot to the East (Lot 57).

Typically, at what % grade would I start encountering additional costs for building this slab. Any advice would be greatly appreciated. Thank you.

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Comments (4)

mushcreek
9 years ago
There's no way to put a number on it without someone going out and looking at it. Location is one thing. It will cost a lot more to do this Washington DC than in TN. What is the soil type? Sand? Clay? Bedrock? I prefer to dig down rather than build up. If you build it up, it takes a lot of material to grade it out to look natural. The added fill has to be very well compacted so it will be stable. I would guess that a crawl space would be the best option.
PRO
GN Builders L.L.C
9 years ago
There is allot of things must be taken into consideration before designing your foundation.i.e.

What is your front,side and back setbacks? What is the width and the depth of your house? What type of a house is it? Is there a basement, if yes what is the desired ceiling height? What is the soil conditions.... is the region known to have a high water table? etc.

With that being said, the foundation shouldn't add any additional costs... You would have a higher front elevation which is typical which will require steps, the amount of steps will depend how high you want the foundation to be out of the ground in the back and that would depend if you want to have windows along the back or not. Some houses designed with stepped foundations, split floor levels which control the amount of steps in the front and also designed to better fit on the sloped terrain.

Most of the time when the house slopes from back to front, you can have full size windows in the front of the house (again depending on the home style and design) and have larger windows on the sides, and no windows along the back where usually you will have a deck or a patio.

Most of the work will be grading and diverting water away from the house along the back wall which might require a retaining wall and some excavation depending on the size of the backyard area you prefer to have it flat.

Your best bet is to talk to your architect he can give you a visual of the slope and your house being on it, some Architects have software to show you that in 3D. If not, you can message me your lot location and I can take that region location and convert to a 3D model and put your house on it so you can see exactly how it will look, but I would need a floor plan as a picture that shows dimensions, a plan or a PDF.

Good luck
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Ron Natalie
9 years ago
I agree with GN. Actually, a sloped lot often gives you more flexibility than a dead flat one. My architect went all googly when he saw the terrain of our lot. The incremental grading is a small amount of the overall home price and as GN alludes,

See here:

http://www.ronnatalie.com/house.html

The grade gives me some options like the garage and the hangar share the same roof line, but the slope allows the greater ceiling height in the hangar. The back side of the house (the architect had a photographer take a lot of shots and I forgot what site they are on) is all terraced allowing a walkout on three levels: The same level as the garage/front door, one at the hangar level, and one at the floor below the front door.
PRO
Virgil Carter Fine Art
9 years ago
Without a house design, no one can tell you if the "...costs be significantly more due to the slope...! Obviously the least cost will be building parallel to the slope and the greatest cost will be building perpendicular to the slope. This is a site where a site analysis should be a strong factor in the design of the house.