Tying into existing foundation (residential) 1

[DEW29]

I am putting an addition onto southern New Jersey house. The house is single story with full basement. I do not plan on doing the work myself, however I would like to be sure it is being done properly. My question is what the common practice to tying into the existing foundation when adding onto the house. The existing wall is concrete masonry block. I feel I only need a crawlspace however information on how it is done with both crawl space and full basement would be greatly appreciated.

 

[pmkPE]

The important consideration is the depth of the frost zone in your particular location and the soil types and their bearing capacities. The reason homes have basements in the northeast is to get the foundation down below the often times deep frost zone. (If they didn't the freezing water in the soil would literally lift the house differently resulting in tilted floors and jambed doors and windows.) Since they have to dig deep in the first place they went ahead and constructed basements and made use of the area. Often times they were referred to as fruit cellers, that were naturally cool in the summer yet not freezing cold in the winter.

Why do you want a crawl space. Are you originally from that part of NJ? If you are, are crawl spaces common there?

 

[DEW29]

pmkPE,

I have not yet priced out the difference in cost between a full basement and a crawl, however I don't think a full basement would benefit anymore than the crawl space. Being from South Jersey, I have noticed that crawl spaces are or have been very common in many homes in this area. I do not know for sure at this time, but I believe the frost line is approximately 3' below existing grade.

 

[pmkPE]

That sounds shallow to me and would make the crawl space attractive from a cost perspective. Do you know anyone who has a crawl space? If so ask what, if any kinds of problems or concerns that they have with them. Such as ventilation, moisture entrapment etc.

 

[cdh61]

pmkPE,

You will have to look at the stresses from the footings (if used) of the new addition and how they impact on the block wall. Just placing footings a few feet down adjacent the old block foundation wall may not be acceptable. In some cause like this you may have to place the new footings at approximately the same depth as the old ones to prevent excess stress on the wall, depending on design of addition (etc). Alternatively, you may want addition to be independent on say a piled foundation.

Depth of grade beam for frost action will also have to be addressed. For moisture problems I feel the best is always to heat, and create an opening in the new to old for ventilation. You should also look at the amount of potential movement of old verse new, you do not want old:new to have significant differential movements.

regards

 

[DEW29]

pmkPE,

To answer an earlier question, I spoke with someone who has a crawlspace and they said that they have never had any moisture related problems (the house is approx. 7 yrs. old). Their crawl is ventilated periodically along the perimeter of the block wall. I also recall being in the basement of an older home (approx. 100 yrs. old) with a more recent addition built over a crawlspace. Like cdh61 suggests, the full basement and crawlspace were linked through the common wall with a moderate opening. I am not aware if there was any additional ventilation in the crawl space.

 

[pmkPE]

cdh61 is correct regarding the need to evaluate the resultant loads from a new wall/footing located next to a full depth basement wall. It would help if you had deisgn plans of the original to determine the amount of reinforcement, if any exists in the existing wall.