So you are going to build a new home or have one built. That’s great! There are a lot of challenges but also a lot of rewards.
This blog is about one of the challenges you will face when you start your new home or addition. It’s also about one of the biggest mistakes made by seasoned builders as well as “do it yourselfers." It has to do with your foundation and what you are going to put it on.
We’ve all heard the old clichés about cornerstones and foundations being the most important key to a successful build. I won’t re-hash those here. We all know it to be true.
One of the most common mistakes made in foundation work is to put the foundation on unacceptable ground or fill.
I was asked once to build a concrete foundation for a house on crappy fill dirt. The property was sloped. The contractor had cut into the slope and then used that cut fill to level a building spot. Cut and fill to balance a site is okay, we did some of that here, but not if the fill is non compactable or unacceptable to carry a load without future settling. I refused to do the job because eventually that foundation was going to fail. One half of it was on good sub grade but the other half was going to be on poor load carrying topsoil. Where the two type soils meet there was going to be a break in the concrete foundation and settlement of one half of the house.
I have been hired to repair this exact type of damage. One half of the house settled and the other half stayed where it should. First we had to jack the sagging half of the house back up to level. Then we had to go under the sagging foundation and dig down until we hit good soil and put new foundation piers in to hold it up. It was very expensive and entirely avoidable.
In our case on our homestead, we were somewhat horrified to find that our topsoil was 4’ deep in the location we wanted to build. Most of our acreage has topsoil that averages 14” deep. It cost us more excavation money to move the topsoil off the building site but it had to be done. We had to get down to the native clay/gravel mixture you find here that is suitable to build on. We had to completely change our plans for grades around our home but again, it had to be done. It cost more than I had budgeted but not near as much as it would have if we had ignored the problem. We ended up with a completely different “look” of the grades around our house but it’s what we had to do.
I would guess most of these decisions are about money. Sometimes it just costs more up front to do it right but I can guarantee you it will be less expensive in the long run. It always costs more to come back and do a job in a “finished” environment. In the above example of the home repair, we didn’t have access for equipment due to property lines and existing landscaping etc. Everything had to be done by hand and it took several weeks. The homeowners had to access their house through mud and over ditches. It was no fun for them; let alone what they had to pay for it.
I was talking to my neighbor this past weekend and he was sharing a story about his pole barn he built at his last residence. He had the excavator on site three times longer than he had anticipated because they ran into poor soils. He had to bring in 15 truckloads (150 cubic yards @ $15.00) of good fill to build on after the garbage dirt (also 159 cubic yards) had been hauled away. He did exactly what he was supposed to do.
You can build the best foundation in the world but if it isn’t sitting on good soil it will fail. Click on this illustration (PDF) to see a picture of a proper cut and fill job. This plan was drawn by a civil engineer for our home which was built on a slope. Notice the tiered “cuts” that were made to accommodate the approved fill. You never want to put good fill on a slope.
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