My wife and I continue to look for a home in Maine.
We have come across a couple homes built on ledge.
The first one was a summer home perched on a ledge with the ground dropping off on three sides. The ledge had a slope and the slab/foundation rested on top. We could not tell if the foundation was anchored to the ledge.
We did notice a problem, we suspected, held the answer to our question. On the view (salt marsh) side of this two story house there were large sliding windows on each level over top of each other. The right pane of each slider on both levels was shattered but did not collapse, just like a car windshield. The other side of the sliders, which were the sliding halves, would not close. Obviously, the frames had raked.
We were told the house was unused for 7 years. I thought the freeze/thaw of water flowing on the ledge under the unheated house had caused all or part of the foundation to move and/or slide.
The second house on ledge is a mostly a summer house also. This house has a stepped crawl space revealing how the grade moves down hill. The owner says the foundation wall is anchored to the ledge and the concrete slab rests on a bed of sand with a vapor barrier on top.
I’m wondering whether people familiar with this kind of foundation would agree with my reasoning on the first house.
And whether the second house, even with the foundation perimeter anchored to the ledge could have problems with frost heaves if left unheated in the winter.
What is the best way to build a foundation on a sloping ledge?
Shouldn’t there be a water diversion strategy to keep water away from the ledge foundation interface?
Thank you!
I’m wondering if there could be problems with this second foundation on ledge
Replies
I build in Maine, often on ledge - you can't get away from itr. You ask good questions.
First, water should be kept away from any foundation as much as possible, but there are times on ledge where this is not possible. Evenm if you seal the edges tight and provide drainage, water can follow crevices and spriong up within so there should always be a planned path where the water can win egress from the interior.
On most ledge, the surface is very rough providing a key for the concrete to seat and not move, if poured on clean ledge, but it is proper to drill rebar into the ledge to have a more certain lock. I can't say from here whether your first example was done right or not. Something about that one screams that it was a DIYjob to begin with and there could easily be other reasons for the cracked glass. One way to check that foundation is to see if it is still level and has no cracks. od course, if water is runnning in under it and freezing there, it could be lifting every winter and settling back into the same place without moving downhill and thqat could account for the glass problem too.
In the second example, I have built one like that, it actually has a spring under the house which had to be channelled and directed to run through and back out the lower wall. It has been there for seven years with no problem, but it does see year round heating too. I'm not sure what the resuilt would be if things were alowed to freeze up.
For that final question -
The ledge should be swept, washed, and blown clean and free of debris where the footing settles on it. a layer of dust or dirt prevents good bonding and later allows a path for water to flow.
A conrete bonding product should be painted on prior to pouring. Rebar should be drilled in to the ledge to anchor.
excessive attention to drainage should be given to the exterior perimeter drain. First rule of any waterproofing is to give the water a path to follow.
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