I recently had an Energy Evaluation completed on my 985 square foot, 50 year-old home. Although not part of the evaluation, per se, the contractor did comment that I should bring up the grade around the house to improve drainage and help out with the moisture problem in the basement. This surprised me because when I look at the house, the ground does not appear low, and during the major thawing period this spring I was the only homeowner for blocks who did not have to pump standing water out of the backyard. However, if I do bring in soil, how would I calculate the amount required? I hope that this question makes sense, as I am not sure if you would require other information.
It would not surprise me a bit that your 50 year-old home needs to have the soil built up around the foundation. Most homes I inspect, that are older than a few years, require soil to replace that lost by erosion and settlement. Your Energy Auditor may have been correct that this would help somewhat with the moisture in your basement. Just because your yard was dry in the spring does not necessarily suggest that the grade and drainage is not toward the foundation, which will promote seepage if your older weeping tiles are blocked.
It is very important to have the soil sloping away from the foundation to provide adequate drainage of excess rain and snow runoff. This is particularly critical with older homes that may have blocked weeping tile and deteriorated damp-proofing on the foundation walls. The last few weeks have demonstrated to many homeowners just how important rainwater management can be. Ideally, the entire area around the foundation should have a slight slope away from the home, but this may not be possible on many homes. If this is not possible, special attention should be paid to the first 2 – 3 metres from the foundation. It is often suggested that this area should have a slope of not less than approximately 8 cm per metre, or 1 inch per foot. In my opinion, the first metre is the most important and should always have this as a minimum slope.
Building up the soil next to the foundation may be a simple job if there is little vegetation or paving next to the house. If there is extensive landscaping, trees, bushes or sidewalks, the project may be much more involved. If there is nothing to obstruct the new soil installation a level and straight edge, the length of the new soil to be added, may be used to determine the amount of topsoil required. With the end of the straight edge against the foundation wall and level, measurements can be taken to see the required height of soil needed to meet the above slope at the foundation wall. The height can be taken at the far end of the straight edge, as well, if it is not already sitting on the ground. This measurement should be taken in several areas along the foundation walls and averaged. Once an average depth is determined, the amount of soil can be calculated.
The best way to figure this out is to draw a rough sketch of the area to be filled. This sketch, in cross section, will allow you to calculate the square footage of new soil required at any given point along the foundation. The lengths of the foundation walls should be measured and multiplied by this square footage to give you the amount of soil required. Soil is normally sold by the yard or metre, which is roughly one cubic yard or metre. Divide your total number by 27 to give you the number of yards of topsoil to order.
If the soil height is uneven between the foundation wall and yard, there are a few other items to consider before proceeding. If the height of the new soil will be near or above the bottom of the basement windows, window wells should be installed to prevent moisture damage to the windows. If the overall grade of the yard is sloping slightly toward the house, additional soil may be required after filling next to the foundation. This may be necessary to create a swale that will drain the water toward the front street or back lane and away from the home.
Once in place, the new topsoil can be covered with sod or seeded with grass seed. This will help prevent erosion and hold the new soil together. Regular maintenance will be required to maintain this slope, but if kept up, it should provide considerable added protection for your basement from seepage.