A storm or fire can devastate a large part of a house, but leave the foundation intact. If the wood-framed structure of the home is not repairable or if it’s just old and dilapidated, it may be possible to rebuild on the original foundation. In many cases, however, it’s not a good idea to do so, especially if the foundation isn’t nearly new. This is one area where recycling may not be in your best interest.
If you have the original house plans, your best bet is to build an identical house on the foundation. The foundation was designed to support that specific house. If you want to build a different home, say, a two-story in place of the original one-story home, the foundation’s load-bearing capacity may be inadequate. It is possible to build another style of home on a structurally sound foundation, but it requires an assessment by a structural engineer and new architectural plans. Foundation reinforcement may be necessary to support the new house.
Just because a foundation survived a fire that damaged the rest of the house doesn’t mean the intense heat didn’t compromise its integrity. While concrete walls don’t burn, intensely high temperatures can weaken them. This is also true for block walls. In a historic stone foundation, the stones will survive the heat, but the mortar holding them together can suffer. If the foundation has historic value, the stones can be removed and reset, but weakened concrete or block foundations are not suitable for rebuilding.
An old home can sit for a hundred years in the same place and no one will pay attention to code violations that occurred during original construction. Start building a new house on an existing foundation, however, and the code inspectors will be crawling the site. That’s because today’s building codes are much stricter than they used to be. Your old foundation must be brought up to code before you can start framing. This may require any number of repairs called for by your local building authority, such as re-pouring some walls, reinforcing others, and excavating to the footers to install drain tile.
If the existing foundation is in good shape, only a few years old and it wasn’t damaged or weakened by the event that destroyed the house, you may save a few bucks by rebuilding if you use the same plans. The bottom line is that if you’re going to fork out the money for a new house, it only makes sense to put it on a strong foundation. The money you save now by using the old foundation could reduce the resell value of your home. A brand-new home on a new foundation is probably going to bring a higher price than a brand-new home on a 60-year-old foundation. By the time you pay an engineer and an architect and bring the old foundation up to code, there may not be much cost difference between rebuilding on the old foundation or pouring a new one.
- Code Check Building: A Field Guide to the Building Codes; Michael Casey
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