Thoughts on taking existing first floor and building a new first floor beneath it
bseiden
| Posted in Construction Techniques on
Hi everyone. Just looking for some thoughts or experiences about a remodel like this. We like our current area in south sf bay and are curious about an addition by going up.
Thanks for your thoughts.
Regards,
Ben
Replies
It's essentially the same as moving a house or jacking one up to put a new foundation under it, though with some additional cost/risk since the house must be jacked up so high, and workers must work under it to build the new level. Expensive and not worth it except when building codes, et al, prevent total reconstruction or when the existing structure has some exceptional value.
A lot cheaper/simpler to add a new floor on top, in most cases.
Your's is a perfectly acceptable method for increasing one's house size. Of course it is not without risk, but these sorts of things are done safely all the time. I don't think, raising a house is necessarily more costly than adding a second floor. You should talk to a competant local architect and/or design-build contractor. There are a lot of seismic considerations involved (especially in SF) that could put the project out of financial or practical reach.
I think it would be a difficult task for the workers to build a new floor beneath the existing one compared to constructing one above it. You should employ a good architect for the purpose so that the new floor is built without any damage to the existing one.
" You should employ a good architect "
What exactly is this good architect going to do that makes the building of a new floor devoid of damage to the existing one?
Just curious.
Actually, in SF I would think you'd WANT to build underneith, as it would allow you to redo things like foundations and shearwalls.
This is another Can You/ Should You question.
Almost 100% of the time the answer to can you is "Yes" given enough time and money, you CAN do almost anything.
The answer to "should you" is always open ended but there is point at which the balance tips to the negative.
In this case, what is driving the desire to raise the entire home rather than rip off the roof and build on top? There must be some percreived or assumed advantage because the second method is the accepted norm.
house lift and build-out underneith
Hogwash, it's a great idea. I'm doing that to my house right now in Oakland. So far so good. We are half-way through the project and under budjet. 19 times out of 20 it is cheaper to lift and build under than add a story above. Why? How do you add a second story onto a one-story foundation? Building underneith you get to build a new foundation (probably a good idea) and get new seismic shear-walls, so you are improving your upper story a lot, and simultaneously building a new story underneith. It cost me $5500 to lift the house and stack it on cribbing. That's a lot cheaper than a new roof.
The practicality of the project has to do with the state of the existing structure, naturally. I wouldn't do it if it was new construction on an updated foundation. Otherwise it's the cheapest and easiest way to add a new floor to a house.
Some tips:
- for the lift, Use phil joy, he is amazing. Seriously, the best lifting contractor in the bay area.
- hang your top-plates first to the existing house and use a lazer to plumb down and set your form boards. That way when you drop the house down it sets right in place. The existing house may not be square or straight. You might have to make some compromising decisions about how to build the floor below. Easiest way, I think is build the floor below perfectly square and let any slop from the story above be taken up by a trim board at the seam between floors.
- yes you'll want to get a good architect, duh.
- with the house up high and the beams and cribbing on the interior, you will have plenty of room to bring in a bobcat to demo the old stuff and bring in an excavator to dig the foundation trench. But make sure you plan for that in terms of cribbing placement and stuff.
- depending on how level the house is, you will probably get plaster cracking and will have to re-work doors in the story above. This presents a pain in the butt, but in the long run it will be healthier for the house to be leveled out.
-todd