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Setting Concrete Foundations

The foundation for your new home or addition is perhaps the most critical step in the building/remodel process. A good, solid, structurally sound foundation will provide you with years of worry-free living in your new home. Or master bedroom! That being said, it cannot be stressed enough how important it is to get your foundation done correctly. What may seem cheaper now can cost you much more than peace of mind later. Therefore, unless you are an experienced builder, I recommend seeking out a good, knowledgeable contractor to do the work.

Nonetheless, here are some important factors to keep in mind when setting up your foundation or discussing it with your contractor. A foundation consists of footings and the foundation walls. Footings will be placed directly on the soil and the walls will be built up from there. Therefore, the first important step in building any new structure is excavation. Your footings will need to be placed on bedrock or good, well-compacted soil, so you’ll want to make sure you dig deep enough to bypass soft, water-prone topsoil or sand. Doing this will prevent your foundation from settling under the weight of the house, which can cause cracks in the foundation and present some very expensive problems.

Another factor regarding the depth of the foundation walls is the frost line. Before you break ground on your new home or addition, be aware of the frost line for your area. This information should be readily available and factored into the building codes for your city or county. If your footings are set above the frost line you most likely will develop flex in your walls as the soil (due to freeze/thaw and water saturation) pushes up and down on your foundation. This is a much more powerful force than you might think and can cause cracks and failures that will be detrimental to your structure.

Now that you’ve established the depth of your footings and the hole for your foundation is dug and compacted well, there are two more variables to consider before forming up the walls: height and thickness. Height depends on the level of finish grade. Thickness depends on the height of the walls and the amount of soil to be backfilled against it. Now, you will want the top of your foundation to be a good amount above grade (the level of the topsoil after the foundation is finished and soil removed in excavation has been replaced). Building codes for foundation height usually require between 6-8” above grade (sometimes less, sometimes more depending on your climate). Remember that these are minimum standards and it never hurts to go above and beyond the call of duty. Pushing your wall height to one foot or even two feet may very well be worth your while. Negative draining (water running toward your home not away from it) can cause a lot of problems later. Landscaping or improper grading are common causes of poor drainage. A good, safe foundation height not only protects you from water issues but also helps to stave off pests and rodents that would love to make their own home inside yours.

Thickness of wall depends on two factors: the height of your wall and the amount of fill dirt that will be pressing against it. The average foundation wall is 8” thick and less than 8’ tall. Footings are usually two to three times wider than the width of the foundation wall. If your walls will be quite tall (i.e., you have a basement or your home is on a steep slope), then you may want to go with a 10”-12” wall, especially if the bulk of wall height will be backfilled. There are also more complex structural issues involving foundations (such as the necessary amount of steel reinforcement needed in your walls/footings), and it is a good idea to contact a structural engineer in preparation for pouring footers and constructing walls. Your contractor should already have prior knowledge of requirements for your situation or have an engineer with whom he/she regularly works.

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