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Question DetailsAsked on 2/24/2018

How much would it cost to put a basement under an existing 1900 sq/ft home with a crawlspace?

Looking to buy a house and we want to work this into the budget.

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1 Answer


Since this is a cost you are looking at as part of your capital investment in the house, and probably would not buy the house without this plan, you need a FIRM bid from a contractor, good for start of work for say 60-90 days AFTER the planned escrow closing date, so you have a real number - especially for something like this where the cost is substantial and will vary probably dramatically - 2 or 3 fold differences problably - between contractors. You do NOT want to start with an off-the-cuff estimate and then, after closing, find the real cost is double or triple that.

I would say with great confidence that you are talking at leat several and probably many tens of thousands of $ - if that makes up your mind for you right off the bat. And in many cases, building a new basement with a single story addition on it next to the house may be close to or even as cheap as putting a basement under an existing house, especially if this is not a straight-forward rectangular frame house sitting ONLY on the foundation walls without intermediate supports - and VERY likely adding an above-ground addition of same size alongside will be significantly cheaper than adding a basement underneath - not to mention putting new construction alongside (or even as second story on a one-story house) largely eliminates the risk of significant cracking or even structural damage to the house during the process.

Therefore, you should have a serious scoping talk with an Architect on this about conceptual construction costs - assuming you have property space to do an addition off the existing house. Also - what are you going to use the space for - in many cases, a specialty addition for storage or a Florida room or screened/enclosed deck/porch or such can fill the bill far cheaper.

The other considerations - is there a reason houses in this area do not have full basements - like high groundwater or very shallow bedrock or subject to periodic flooding, and will putting that much money into the house have any chance of substantial recovery at time of resale ? Your Realtor and Architect can help with those questions.

The Realtor should also be able to help you with estimates of what this will do to house saleability - in some areas basements are undesireable to buyers in general, and certainly their recovery percentage is much less than for an above-ground equivalent space.

The other thing to talk to the Realtor about - two in fact - can this sort of plan and estimate be reasonably gotten in-hand (typically a several week to month process) and still get a contract on the house - in general, getting those sort of numbers would leave you far behind the eight ball in terms of getting a meaningful offer in before someone else snaps it up, unless in a depressed market or a real fixer-upper.

Also - and probably the bottom line - sinking those $ into building a basement under an existing house, with its inherent risks, probably does not make a lot of sense unless this is your got-to-have dream house - you can commonly (unless in a real pricey area like inside desireable areas of a major city) find dozens of houses for sale in the area which already have besements or equivalent above-ground square footage for about the same or less than buying this house and putting in a basement - plus they would be move-in ready without the construction disturbance and move-in delay of putting a basement under the existing house.

Also consider that probably about 80-90% of this sort of "we will fix it up after we move in" plans go by the wayside and sit on the honey-do list for decades till they fade away - potentially leaving you with a house you would not have originally bought without the upgrade.

Below are links to a LOT of previous questions with answers about putting basements under houses - the third and fourth ones in particular have a bunch of links (some will be duplicates) to other similar questions with answers:

Answered 2 years ago by LCD

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