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Question DetailsAsked on 5/5/2016

Why would a crawl space require a sump pump?

We are currently looking into a house and we noticed there is a sump pump in the crawl space. Does this mean that there is a lot of water? Also will this be an ongoing issue and will it be become greater? Is there anyway to fix it if we do buy this house?

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1 Answer


Would not be there unless they hit water during construction, or the area is generally prone to water issues. How much water - you would have to look around for any signs of flooding outside the sump - like along foundation walls - and of course also outside along walls for staining or other signs of high surface water at times.

Generally, a normal sized sump pump with underdrains (piped or graded gravel) under the slab keeps the water level under control in normal comditions - though in areas subject to rising water table in flood events it can get to the point where it exceeds pump capacity. However, over the years, excepting external flooding/extreme rainfall events, the amount of pumped flow would not be expected to change noticeably.

Generally, if the crawlspace is level with or above an adjacent basement you can see in the basement if flooding has been a problem - rusty marks on appliances, staining on walls, watermarks on foundation, waterline on the sump pump pipe above the pit level, etc.

If the crawlspace is a partial crawlspace at a higher level than the basement, like half-house area and divided from the basement by a concrete half-wall, AND the sump pump is in the crawlspace area rather than in the basement area (an unusual occurrence but I have seen it) your risk of basement flooding in wet seasons or due to sump pump failure is higher than otherwise because that higher elevation sump pump is probably only marginally keeping the basement dry.

You could ask your realtor - and even maybe your potential new neighbors - about any historic surface flooding or basement flooding problems in the area. Realtor can also direct you to or provide local flood limit maps.

A sump pump is not a deal-killer for most people, though I would be concerned if it is running with any consistency - as opposed to the normal maybe few times a day to couple of times an hour for normal wet-footed but not out of control basement.

Of course, consider the consequences of flooding under there - generally occasional flooding will not hurt the foundation - tends to be more of an issue regarding insects and rodents liking the dampish conditions, and of course the risk of mildew/mold/fungus growing in the subflooring if the conditions stay damp for extended period of time, so ventilation under there is of critical importance. Basically, with a sump pump under there, you have to assume a fair amount of moisture is coming up out of the dirt due to the relatively high water table, so putting in a vapor barrier might be a good idea. Could be on the ground if the ground is basically always dry - if gets wet at times, then under the floor joists and partway down the foundation wall would be a better place.

As for doing something about the water - if topography allows, you can put in buried french drains outside the foundation (from several thousand to as much as ten thousand $ range typically) down at or below the basement slab level, free-draining to the surface downslope somewhere or if necessary to a wet well with sump pump, to permanently draw down the water table around the house.

And of course, having gutters and downspouts to collect and drain roof runoff (the most common cause of wet basement issues) and sloping ground and/or berms or swales as necessary to drain water away from the house and prevent surface runoff from coming near to the foundation are common ways to reduce the amount of water making it to the foundation. Of course, if in a low-lying area where the permanent water table is near the surface, like near a stream or river, you are basically in a bathtub and cannot do much about it short of putting in a very expensive wellpoint system and pay for a lot of electricity to keep it running most of the time.

I would be certain that the current owner, inthe property disclosure statement or a supplement thereto, makes a detailed statement about any basement drainage or waterpoofing or crawlspace/basement mold/mildew remediation he has done or had done or knows was done by previous owners, and a definitive statement about any flooding of the basement/crawlspace of which he is aware - so you can judge how big an issue this could be.

Of course, if only a crawlspace without basement, then not as serious a thing if the power goes out or sump pump fails or water level rises - you need to be concerned if there is wetness under there for extended periods of time, but a day or two dampness (not reaching to the point it wets the subfloor/wall wood of course) on occassion will probably not be a matter for big concern - though it might eliminate plans you had for using it for a storage area.

Answered 4 years ago by LCD

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