Cost of home addition

We know that at some point we will need to add onto our 860 square foot 2 bedroom 1 bathroom house. We are a family of four and while our kids are young, we think that as they get older they will need their own space, especially since they are different genders. 

We recently completed a 300 square foot in law cottage that cost about $115,000 total (a prefab build) but are wondering about the cost of building up, lifting the house and building underneath, or building out. My hope is to be able to either build up or lift the house to be able to take advantage of the Golden Gate Bridge views in a way we couldn’t building out unless we went out and up. At the very least, we would like to add another bedroom and bathroom, probably a master suite.  

Has anyone done a similar project recently and how much did it cost? Any other tips? We are probably a few years away from actually doing this but need to get our ducks in a row. 

Parent Replies

New responses are no longer being accepted.

RE: Cost of home addition ()

Thanks for sharing about your experience. There are a lot of factors that go into determining the costs of doing additions. I recommend speaking with at least three contractors.

RE: Cost of home addition ()

The short answer would be to budget $500/square foot. 

We recently build a second storey and renovated the existing kitchen and bath in our 2/1 in Albany. It ended up around the above-quoted number, though of course details will matter. In terms of your options, building out and up is a cost-effective way to achieve what you want. We've seen 3 homes in our area where they extended the kitchen out to create an open kitchen/family area, with stairs leading up to a master suite. This way you get air and views, without having to significantly modify and reinforce your existing structure and foundation (that's what we had to do for a strictly on-top addition). I've heard arguments for lifting up and building under, but unless the lower storey is still well above grade, it's likely to be darker/basement-ish, which I find unappealing. Building out would also (typically) allow you to stay in your home during construction, which could save $10-15k on rent. You lose yard space, of course, which is the downside. 

For more specific pricing you'd need (at the least) a floor plan sketch, which many architects will do for minimum cost. There are several recommendations here on BPN, my only tip is to choose someone local (who knows your city permitting quirks). Good luck!

RE: Cost of home addition ()

In our experience, building up will cost you substantially more than building out - and depending on your neighborhood you may have to have to go through an additionally approval process if you will potentially block another's view by building up. The costs will depend on so many things, will you lift up or build up (i.e. will you keep your existing roof or need a new one - $50k alone)  will you need to reinforce or actually replace your foundation, how much square footage you want to add, whether you hire a design/build or a GC or manage it yourself - the costs could vary by over 100k - with your total costs being between 200-400k or more. Definitely MUCH more complicated than a pre-fab cottage in your yard, but it can be done with patience and the right planning - good luck!