Keeping Sill Plate Dry
We purchased a 10-year old brick veneer home with a basement. The lot is fairly level in the back yard and has good slope away from the house in the front yard. There was some minor ground settling around the foundation causing slight water entry into the basement during heavy rains. The grade has been repaired to create positive slope away from the house, which has stopped the water entry. While doing this grading work, I realized that the builder did not raise the concrete foundation wall high enough out of the ground in the back of the house resulting in the top of the foundation wall/sill plate being at or just below grade level. (sketch attached) The brick veneer made this difficult to observe from the outside. The grade can’t be lowered as this would create negative slope towards the house. After realizing this, I dug about 2′ down along the back wall the entire length of the house and applied 2 coats of Tam-O-Seal cementitious water proofing to the masonry wall, then 2 coats of a rubberized waterproofing material over the Tam-O-Seal. The concrete wall below grade had a tar type waterproofing material applied. I was considering installing some 24″ aluminum flashing on top of the ground at a slope next to the foundation to help divert rain water away from the house. The flashing would have a 4″ ninety-degree lip upturned next to the brick veneer to help prevent rain splash onto the brick wall. Would condensation buildup under this flashing be a concern as I am also trying to keep this soil as dry as possible so as not to attract termites? I also considered an underground roof, but I don’t believe this would offer any extra protection for the sill plate as the membrane would be below the sill plate. I am monitoring the interior of the sill plate for moisture content and it is staying at about 9%.
Thank you in advance for any advice you may provide.
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Replies
The only real solution is to regrade the back yard. You need to remove enough dirt to get that sill at least six inches off the ground and the ground sloping at least 2% for at least ten feet away. Then you'll probably want to grade on the other side so you don't have an 8" drop in the middle of the yard.
It will be more dirt than you think, maybe 20 yards to do it right. But anything else is just a patch.
Thank you very much for your response. I failed to mention that there is a serpentine brick sidewalk running parallel to the house in the back about 6-8' from the house. To lower the grade 6" below the sill with 2% slope, the grade would be about 10" below the sidewalk where they meet. I have revised my sketch to show the sidewalk.
MudJack,
If the grade slopes away from the house, another solution would be to make the equivalent of a continuous window well by digging out next to the foundation to expose the lower courses of brick, and retaining the soil with a ground contract rated 2"x10" about 6" away from the foundation.
Mr. Taylor,
Thank you for very much for this suggestion! The grade does slope away and I believe this would work. Would it be necessary to cover the 6" gap with some type of flashing to prevent water intrusion? I have about 16" roof overhang above this wall.
MudJack,
I have an above ground version on one wall of my house, which is there to act as a break between the raised garden beds and the foundation. During most rains the overhang means the crushed rock at the bottom remains dry. Any small amount of water that does end up there drains straight down through the rock.
I second Malcolm's suggestion. If you get a lot of water, you could put some perforated drain pipe under the gravel to carry away water. This gives you a sort of aesthetically pleasing slot drain around the perimeter of the house, which will prevent you from ever having standing water near the exterior of your home. Ideally you could just drain to daylight somewhere downhill, but you could also put in a dry wall in a convenient spot and drain to that.
Bill
Thank you very much for these suggestions! I greatly appreciate the advice and will start planning the project.
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