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What’s Wrong With This Crawl Space?

Readers are invited to spot all of the problems shown in a photo of an old crawl space

Image 1 of 2
A typical crawl space in an older house.
A typical crawl space in an older house.

The photo shows an unvented crawl space in a cold climate. The home was built in 1885. This crawl space is attached to an adjacent concrete-floored basement. The foundation walls are made of mortared limestone.

Even in the small area captured in the photo, there are a number of problems that compromise energy efficiency, building durability, and life safety.

Next week, we will post the answers that a Building America team, NorthernStar, came up with.

2 Comments

  1. Jeffrey Melvin | | #1

    Missing thermal
    Missing thermal boundary
    Missing air barrier
    Asbestos plumbing
    Knob and tube wiring
    Clay floor serving as a resevoir to foundation
    No capillary break

  2. Ted Clifton | | #2

    How not to close a crawl space!
    Unfortunately, this picture could easily have been taken of the crawl-space of a house I happen to own. It was built in 1871, and is on the National Historical Register. The home worked well for over 100 years, because the crawl-space was left completely open. There were two wood-stoves and a masonry fireplace in the house, and a very leaky envelope, especially the wood plank floor. Wind would blow in under the floor, be warmed by the heat radiating through the floor, and pass through the crawl space much dryer than when it arrived, due to the fact that warm air with the same moisture content will have a lower relative humidity.

    At some point about thirty or forty years ago, the owners decided to close in the crawl space with mortar and rock, to make it appear that the house had a rock foundation, rather than wood piers. The mortar and rock not only sealed the crawl space, it also provided a cold surface on which to condense moisture. The leaky floors allowed moisture to enter the crawl space from above, and the moist soils and high water table allowed moisture to enter from below. That moisture condensing on the rock "foundation" was in direct contact with the wood rim-joist and siding. As areas of the rim and siding rotted away, the owners then decided to add more rock, following the rot up into the walls. More rock caused more rot, and now what was once considered a National Treasure will need to be destroyed, as the entire floor and the bottom several feet of the walls are rotten.

    Yes, there are many other problems with this picture, including the lack of a vapor-barrier on the ground, but the big culprit is closing off the foundation to the outside, without providing for the elimination of moisture within. I am a big fan of closed crawl space designs when they are done right, but it is usually very difficult to get it right on an existing home. If a vented crawl space is working well, I would usually advise leaving it alone!

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