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We want to add a second story to our house, how do I know if my foundation can hold the extra weight?

Answered by Jeffrey ~ July 27, 2010 ~ No Comments » | Respond to this question

We have a house that has a daylight basement. The basement walls are cement blocks and we're wondering if it is strong enough to hold a full second story or if we have to go through the hassle of raising the house and putting in a new foundation like I have been told I will have to do by two different contractors. They have never answered my questions about if I can test the strength of it.

Audrey T. ~ Talkeetna, Alaska

Jeffrey Anderson

Hi Audrey, A typical 8 inch concrete block foundation with an appropriate concrete footing should be sufficient to support most 2 story homes. The fact that 2 separate contractors have indicated that your foundation needs improvement before you can add a second story addition makes me think there might be something out of the ordinary going on there.

There is a possibility that there is a special soil condition in that area of Alaska which dictates that homes over 1 story have a strengthened foundation. I have built in areas before where soil conditions determined that we had to use a custom foundation design.

However, I think that a stronger possibility is that your foundation might not meet present day building codes. You don't mention how old your house is, but I know that in many areas of the country, including where I live, older homes were built on foundations that were slightly questionable. In some cases those foundations did fine over the years, but in other cases the homes have settled in places and acquired "character" with their sloping floors. Building inspections didn't exist in many areas and even when an inspection took place it was often lenient.

When you do an addition the building inspectors in Talkeetna are going to require that your foundation be substantial enough to meet modern code, so my guess is that is what is going on with the 2 contractors stating that your foundation is going to need to be replaced.

I suggest that you get an architect or structural engineer involved. They can take a look at your existing foundation and your planned second story addition and make an educated determination if your foundation is going to need to be improved. If they state that it is fine and are willing to give you a report with their seal on it, that is usually enough for local building departments to approve the planned addition.

Even if they find that the foundation is not sufficient to support the second story addition, they may be able to come up with some ideas that are a little more economical than raising the house and putting in a new foundation. It may be possible to pump some concrete into the block cores or add some rebar or something of that nature.

Raising a house, tearing out the existing foundation, and putting in a new foundation is a very big project that can be somewhat costly. However, it is possible that is the only way that you are going to be able to add a second story addition. If that is the case, you might want to think about adding on horizontally rather than vertically if you have room on your property.

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