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Question DetailsAsked on 4/25/2017

Increase headroom in the basement, how much would it cost?

I have a 880 sq home build in 1926. There is a half daylight basement with 7' headroom. Want to gain 2' headroom. Is it better to dig or lift the house? How much would it cost without counting finishing the space? thanks.

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Answering two similar qeustions in one here - and the answer is it depends a LOT on the foundation type, soil type and groundwater level, size of house, type of foundation construction, etc.

Generally speaking - usually a house can be lifted up and the foundation raised to the new level - means disconnecting utilities for a few days and not being able to live in the house for that time, and of course raising ground level around it or building new raised entry porches or decks.

A foundation can also be deepened - very old brick and stone foundations do not take so well to this, concrete and concrete block more amenable to it. Taking the perimeter wall down a foot or two can be done one of two common ways - 1) excavating and removing the inner stickout of the footear so the wall contionues basically straight down (at least the finished wall) to the new footer, or 2) excavating to the footer and then putting a new foundation and footer below it - either with the new wall basically flush with the inside edge of the old footer, or sometimes "taked" onto the inside face of it. In that case, you end up with the old footer acting as a ledge or shelf in the finished room, with a typically 6-12 inch setback at that level - like is common at the top of the foundation in daylight basements, where the wood framing sits on top of the foundation wall but leaves a shelf on the inside. The latter is generally cheaper, but you also lose about 1-3 feet of floor space in each direction in the basement because the deeper addition is "inside" the original wall line.

Hard to give a ballpark cost or say which is "better" - lifting the house and raising the foundation, assuming the existing foundsation is structurally suitable, is generally a lot quicker, but is pretty much guaranteed to cause at least minor drywall cracking, and if not professionally done correctly can cause more serious structural cracking and warping of door and window openings and such. Lifting the house is generally much harder on brick and stone wall houses, which tend to crack a lot more - and if old (unreinforced) can be seriously damaged by this.

Of course, deepening the foundation also has substantial risk, especially if the contractor hits poor bearing capacity material or water at the old foundation level or below or gets too aggressive about how much of the foundation he excavates and undermines at one time - to put the new foundation section under it - commonly done in 3-6 foot stretches where the existing foundation is unsupported while the new deeper section is put in.

Generally speaking - if you have poor soil conditions or wetness in the basement slab level soil and below, or old deteriorated foundation raising the house (with foundation repair/replacement for deteriorated sections) is probably usually the better choice. Ditto with solid brick (as opposed to brick facing) and mortared stone foundations. Ditto with houses that sit on a lot of posts or piers - deepending each of them can be a real high cost so just lifting the house up in one unit to raise the foundation walls, then put in new longer posts can be cheaper in some cases - but it can be a real tossup in houses with short joists and a lot of support posts or columns without main supproting lead transfer beams to allow you to pick the house up in one unit.

Cost varies by location and your specific situation, but generally tends to run similar for either option - but if I had to say one is more likely to be cheaper or be less likely to overrun on cost, I would have to say jacking the house up and raising the foundation would be the better of the two for that. Cost commonly $10,000 minimum, and $10,000-20,000 is a pretty common range for smallish (say under 800 of so SF footprint) rectangular footprint houses, getting into the $20,000-40,000 range for larger houses and ones with a non-rectangular footprint, and of course can go up from there in special cases or large houses.

One other thing to look at if you have the land available - sometimes just building an adjacent addition with or without new basement (especially in areas where foundations do not have to be deep to get below frost line) can be as economic as deepening an existing basement or raising the house. - using the old basement mostly for storage or uses where the low headroom is not a problem, the new addition for living space.

I would talk to an Architect (with Structural Engineer evalluation) about your situation and for some conceptual costs for alternatives

Answered 3 years ago by LCD

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