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Question DetailsAsked on 6/4/2017

Cost to dig out a shallow crawl space - about 400 square feet. Current depth is 20 inches, would like to make 48 in

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3 Answers


Here are a couple of previous similar questions with answers - in your case because even the finished crawlspace will be low the unit excavation cost will go up - but assuming this is just for access for maintenance or maybe some insulation space, can also be easier than deepening a basement where one normally wants the full room space full depth - you may be able to excavate the bulk of the area but not the last foot or two from the foundations and more cheaply put in laterall support under the foundation - or maybe even (depending on soil conditions and chances of it getting wet down there) keep 3 feet or so away from the sides (which would still leave working room around the sides) and maybe not put in any remedial foundation support at all.

I said staying away from sides - assuming there perimeter foundation only, not post and pier support underneath - though it can be done the same way but of course requires one-by-one shoring up of the supports till they can be replaced at the new excavation level.

Answered 3 years ago by LCD


Answered 3 years ago by LCD


One other thing I did not mention - assuming this is being done to provide more maintenance accessibility - most maintenance repairs can be done at about 18-24" reach from the torso, so sometimes, especially in houses with rows of post and pier supports under them, shallow swales will be dug out between the lines of supports (along the long dimension of the house normally, and of course connecting to the access doorway or hatch), leaving the soil intact at the pier lines and digging down between the rows. The long very lightweight plastic snow sleds from box stores are also very useful in pulling oneself along these swales (especially if lined with heavy plastic liner) and towing another for tools and materials.

Depending on the soil type and year-around moisture conditions, the soil is usually kept intact for at least 6-12 inches around each pier/support pad (especially if bearing on ground surface and not embedded in the ground), and then sloping at typically 1.5:1 to 2:1 (horizontal to vertical) slope or whatever slope a geotechnical engineer says the ground will be stable at given your foundation loads and type, sloping away from the pier rows towards the centers of the gaps between the rows, leaving a deep enough swale between each pier/support row for workers to crawl or scoot along between the pier rows and still reach out far enough to each side to access the entire area. This can also be done in a crawlspace without intermediate supports, with swales spaced roughly every 4-6 feet on centers along the (usually) long dimension of the crawlspace - or sometimes onlyu in certain places as needed to access pipes or wiring or such. Ends up looking sort of like a set of windrows or plow lines.

This type of triangular or more commonly rounded bottom swale can give the required access clearance for a person (though may need to be flat bottom if providing access for HVAC equipment movement) with as little as about 20% of the excavation required for dropping the entire "floor" level - and can commonly be done with zero supporting post/pier/foundation modifications, making it a LOT cheaper in many instances than generally dropping the overall floor level.

Sometimes, especially if needed to access and install/remove HVAC equipment, a slot trench is put in to provide a headroom-height or equipment-height passage (preferably more or less down the middle, not along a load bearing foundation) - after consulting a geotechnical engineer about allowable depth and how close it can be to supporting piers or foundation wall.

One other consideration - if you are looking at dropping the overall crawlspace elevation (meaning maybe underpinning or extending foundations down too) is whether it will be worth the added cost to go to full normal headroom (assuming you do not have groundwater issues at that greater depth) and make it into basement space, which would then (if norminally finished) give you added square footage to use and added SF value when it comes to sale time.

Answered 3 years ago by LCD

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