Foundation for addition full basement vs pier or post and beam construction
Hey hope all is well. In the planning stages of an addition, meeting with an architect next month to draw up plans. The idea from architect is to extend the rear of home 12-14 feet out across entire length of house and extend it 6 feet past the left side of original footprint. So basically a 12×22 feet addition with a full basement, first and second floor above attached to rear of house. Original house has same floors so it would attach to all 3 levels. The rear of house is on the bottom of a hill so with a full basement the house will need some additional work to control water, maybe a few dry wells. I guess my question here is if this is built on piers will the overcall cost and complexity drop or am I creating a bigger project? Do people build this is a cold climate like NY because I haven’t seen it maybe because it’s not possible. I’m imagining an open patio below surrounded by piers. It would create more outdoor space and less basement space. Between current patio and first floor is about 6’4’ feet so the entire back yard would need to be lowered slightly unless new addition is higher than original first floor. I guess also from personal preference would you guys rather have more basement than outdoor space? Back yard is small so you don’t have a lot to work with. Of course cost is more important than preference, I would go with the cheaper option.
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What you have and the options you are proposing are a bit hard to follow. You might find you'll get more responses if you attach a couple of simple sketches.
My preference - In general basements are overrated. If I didn't really need the basement space I would opt for the cheapest foundation alternative, which depends on your site. I would definitely prioritize more outdoor space over a basement.
To determine the cheapest foundation approach you will definitely need the input of an architect or engineer who has visited the site and inspected the existing foundation you will be attaching to. The cost calculation should also consider ground water drainage approaches for the various foundation configurations.
I attached a sketch, not a professional drawing but just to see. The addition is going to connect to the old part of house. The rear of house has a shorter 2nd floor, I’m going to use that space to expand the second floor with the new addition. Not sure if a post and beam could support the weight of 2 floors above it. The rear of house where the addition will be is at the bottom of a driveway/hill.
I also attached a second picture where I circled a small area to expand the basement to help support the addition. I’m thinking the hardest part to support would be the part that is out in space. This would require a smaller basement addition.
This may just require a full basement either way, just trying to see if I can save money/outside space