House addition questions

I am planning an addition to my 2 story colonial. The addition is actually extending first floor along the side facing backyard. The addition will be narrow 50 ft long by 6 ft wide and will not create any additional room rather extend existing kitchen and office. I want to do as much as I can myself leaving to pro only that part of the job that I absolutely cannot do or make no sense to do myself. I have moderate experience in framing, plumbing, electrical, insulation, drywalling and have all necessary power tools to do the job. I do not have any experience in building foundation or putting joist beam floor system. I am weighing two options for the addition foundation: crawl space and full basement. Here I have several questions:

1. While I realize that every project has it many specifics what the approximate cost would be to excavate hole for the 50 ft x 6X ft addition foundation, build the foundation walls and slab, backfill and put the floor with no subfloor? I line in Central NJ.

2. What's the approximate cost difference of building full basement vs. crawl space? Frost line in my area is 3 ft so trenches for the footings must be dug 3 ft at least. If building full basement is not considerably more expensive then crawl space I want to build sauna and additional storage in extra basement space under the addition. It will also be connected to rest of the basement through door opening I plan to create by extending current basement window. Existing basement height is slightly more then 7 ft.

3. What's the approximate cost and benefits difference of concrete monolithic vs. cinder block foundation? My house (55 years old) foundation is built using cinder block with I believe no rebar reinforcement.

4. Is it feasible both economically and from time perspective trying to do some of foundation work myself? Could you advise me if any of the following foundation tasks I can do myself or I should forget about them and leave them to pro:

- building footing forms and put rebar in them

- renting gas powered concrete mixer or get ready mixed concrete and build footings myself

- building foundation walls using cinder blocks

Is above what I can really do myself or it is not worth it? I have limited experience with concrete (redoing parts of basement slab after installing underslab plumbing).


I believe having foundation built and floor put I can take over enlisting my Dad's and friend's help to put frame, siding, roof, plumbing, electrical and internal finish.

Any comments and advise would be greatly appreciated.

 

i'm doing a similiar job myself although not as big. i too have experience in foundation work. what it came down for me in the end was time of year, available time to do the work, etc. i found it would be easier to have a mason come out and do the work and when he was done i could begin the framing. as it was he still took longer than expected but he did a good job. if i had to lay the block i would still be laying it. since then i have finished most of the framing and have the house extension and garage roofed. not completely water tight but now i can work with out getting wet. personally for me having the full basement was more important as far as storage and such. there is definately a price diference for full bsmt vs crawl space my basement was 8' x 24' x 7' deep. plus a 42"d foundation wall for a 24x30 garage. excavation, walls, slab, etc........13,500. done in about 5 weeks (way more than the 2 he said it would be. weather did play a small part) if i did a crawl space it would have been about 8500. i think the shear size of your job would make doing it yourself a tough time. thats a lot of concrete to mix, would be better having the concrete delivered. and i believe the frost line in nj is 42" might be 3' in extreme south jersey though. i live in northern jersey myself.
in the end i think the foundation is better left to a pro for a couple of reasons:
they will get it done probably quicker than you could.
while you have some experience this is the foundation of you home. if this is off, not square, etc... it will only propagate the problems up to the framing, flooring and the roof. not to say the contractor can be off but you are paying him to get it right and if it isnt that you can have him back out to fix his work.

hope this helps