I am going to build an addition for my house in spring. The addition is 24' X 26' behind the garage attached to the house. Addition drawings call for non-monolithic slab on grade foundation. I need to build standard 16” wide X 8” deep footings 3' below grade, 8” thick slab walls and then pour 4” slab itself. I want to DIY the project as much as it is economical and practical.

I have several questions that I would be glad to get answers for. Especially I am interested in opinions of folks who did DIY foundations or at least portion of it.

1. Backyard where the addition will be built slopes slightly away from the house. Currently grade of outer edge of future addition is approximately 1 1/2' below the back wall of the garage that forms opposite wall of the addition.

Do I need to grade foundation area first and then dig trenches for footings or build footings, foundation walls and then grade slab area?

2. Can someone describe me as detailed as possible sequence of steps of building my type of foundation?

As far as I understand I need to do the following:

- grade foundation area to level it
- dig trenches for footings
- build footings
- build walls
- put 4" perforated drain pipe next to footings running to some drywell
- insulate walls with closed cell foam insulation (I intend to insulate walls both inside and outside)
- back fill the trenches
- compact soil for slab
- add 4" of gravel
- add 2" of sand
- put Styrofoam or other closed cell foam insulation under slab
- put rebar and pour the slab

Hopefully I did not miss anything.

3. What excavating equipment do I need to rent and at which stages of addition construction?

4. How deep do I need to dig trenches for the footings 3’ which are below grade? How wide the trenches should be to comfortable build cinder block walls?

5. My architect advises me to build cinder block walls. Is this the best way to build walls in my case?

6. What parts of foundation construction I can reasonably do myself and what I should hire pro? I will obviously order concrete for footings and slab.

Any other advise for DIYer would be appreciated.

 

I suggest getting some bids from contractors. In my area a lot of contractors are hungry for work and the prices are competitive.

When I built my addition my intent was 100% DIY. I started pricing materials for the foundation/slab (fill, concrete, forms, rebar, tools etc.) and rapidly concluded that the time saved by hiring a pro more than made up for whatever I would have saved by DIYing it.

I was framing walls in a week where if I had done the work myself it probably would have taken a month. A couple of years later when I built a new garage/shop I didn't even consider doing the foundation.

 

I agree with Wayne!
Pouring and finishing a slab is hard work! Given a choice I would always hire it out. There is a lot of skill involved in finishing concrete, if you use a wetter mix to combat lack of experience you stand a good chance of having weaker concrete

You might save some $ by doing all the site work yourself but you would want to do that talking to the concrete finisher to make sure it's done correctly so you can get a good concrete job at the agreed upon price.

 

Just to clarify. I am not considering pouring slab myself. This is the part of building foundation that I will absolutely hire help to do. But what about pouring footings and other steps like grading area, excavation, building forms for footings, building cinder block walls and others? In area where I live all services are very expensive though I will certainly try to get quotes for different parts of foundation process and overall.

 

Do not put sand down over the gravel. It will only cause moisture problems. You should be putting plastic sheeting down over the gravel so the concrete sits on top of it.

http://www.buildingscience.com/docum...ience-insights

That explains why.

 

ISAG02 - I had the same thought process. What part of this can I do?

I ended up letting a pro do the whole thing. He came in with an excavator and a crew and professional forms and was in and out in a couple of days. And most importantly the job was done right. I paid just a bit more but I got a guy that knew what he was doing. We wrote the contract off the drawing and he did exactly what I wanted.

 

I forgot to mention plastic sheathing. Regarding layer of sand both my architect and several very reliable books I read strongly advise putting 2" of sand in addition to 4" gravel.

 

Thank you for the info. I will certainly get several quotes and will talk to pros. I have no doubt they will do work way faster then I will and probably with less problems though it is not guaranteed. However, for me the cost is very important, I may simply not be able to afford hiring pro to do all work. If hiring a pro to do all work will turn out to be $1K more expensive then for me to pay for all materials and equipment rentals I will certainly hire a pro. However if the difference will be $10K I may decide to do at least some of the work myself. From my past experience any project I was planning I talked to pros. Every time the quotes they gave me were outrageously expensive so I had to learn myself new things and ended up doing almost all work myself.

 

The most economical way to build an addition is to -
purchase all the permits yourself .
get quotes for all trades , and save all the commission that a contractor would make .
make a materials list of everything you need , and submit them to all of the local home improvements stores , the will be happy to beat any prices out there . ( you will save a ton of money ) . .........thousands.
make sure all sub-contractors have general liability and workers comp.
this will protect you in case of an accident.
get written estimates from all , and choose the right one.
be sure to write some type of waiver saying as long as payments are made as follows , there shall be no legal action taken such as liens .
and that you are not responsible for any injuries occured on this project.
and all payments are based on performance and quality.
This will be a great experience .

 

In short, be the general contractor.

 

You are making yourself the General Contractor that hires sub contractors and assume the liability if they are not supervised/administered properly by you.

That is the cost and liability that you assumed. One person hiring a contractor to do a specific job is a different and simpler situation that that taking individual bids that are usually not comparable because there are few written requirements.

Micro-managing and construction does not work unless you are there supervising the details and co-ordination.

Dick

Dick

 

Thank you for all advice. I am going to be GC for overall addition project. I never did this but I am very well aware of all pitfalls and dangers involved. Moreover, not only I will be GC, I will be doing good portion of work myself. This is the only attainable way for me to build this addition.

I am at the stage of working with architect so once I will have construction drawings completed I will apply for all permits, write detailed project requirements and start talking to contractors. I already got several references from my friends.

My plans including hiring contractors to put up the frame, sheathing and roof and maybe install windows if this will be not too expensive. Hopefully the same guys can both put frame and roof. I will do myself all interior work, fiber glass insulation, drywall, all wiring (except main panel upgrade), plumbing, siding and hopefully at least some portion of HVAC. I have both plumbing and wiring experience, basically re-wired entire house, change 100% of all pipes in my existing house, built two bathrooms, including one in basement with underslab plumbing and sewage ejector. I also replaced myself all windows in my house.

I was not sure about foundation but after considering all pros and cons I will probably hire a pro to do all foundation work.

Absolute requirement for the contractor to be hired by me is to be willing to work and cooperate with me both as GC and as another contractor. I also intend buying all construction materials (lumber, subfloor plywood, sheathing, house wrap, insulation) myself unless contractor can buy it cheaper than I can.

Yes, it is a challenge for me. But I have no choice and quite frankly I enjoy building. I intend to write down as detailed contract as possible what he will do what I will do, what stages, all materials, tools, resposibilities, deliveries, penalties, etc. My architect said he would help me and I will probably go to an attorney to review it.