Digging and laying footings questions?

[Gedburnell]

Just got a quote of £60,000 for a 30m2 ground floor + 10.5m2 upstairs extension, which I think is a bit steep! I'll get more quotes but even so I've decided to dig my own foundations by hand and lay the concrete, to save money.

My existing house is built in the bottom of a former limestone quarry. The top-soil/clay is relatively shallow approximately 500mm, below that you hit solid limestone bedrock. So it's quite good for building solid foundations on.

Digging the trench I think will be relatively straight forward (architect's plan state strip foundation 600mm x 200mm)

I have a number of questions and concerns:- My biggest concern is making sure the concrete will be level and uniformly at the same depth (digging the trench to a uniform depth is relatively easy). I've read about knocking wooden pegs in to the trench bottom so you can easily gauge concrete levels. But won't they weaken the foundation if left in which I'm told you do? How about using Steel pins, where do you purchase them, are they the ones used for steel reinforcing?

-How do you tamp the concrete easily without sideboards do you use a "vibrating poker"?

- Should I measure concrete depth to coincide with brick/block measurements, so that the once the bricks are built up to ground level they coincide with the existing house brick level?

Any tips websites, books that can give me a full insight into what is required would be most appreciated.

[Gedburnell]

Thanks for all the advice so far

Here is a prelimanary plan of the new extension (left of existing house), dimensions (red lines) are approximate:

There is a 4" soil drain which will go under the rear wall of the extension. Do I run the footings to either side of the pipe leaving approx 6" gap and then the brickies will place a lintel to bridge the pipe?

[The Natural Philosopher]

Yes. That is one way. Another, after you have checked your levels, is to run the pipe OVER the footings and construct a brick and lintel arch over it.

In general bricks should go from perhaps a couple of courses below ground level to a couple or three above it, before you insert the DPC, which is usually at or about finished floor level.

The higher your soil pipes can exit the steeper the run they will have outside. Conversely the shallower they will have inside..so its a fine point as to where they should go,

BUT try always to get to 1:60 drop. You *can* get away with less, but thats a good target to aim for.

You should gravel it up as well

[Hugo Nebula]

On 23 May 2006 09:23:01 -0700, a particular chimpanzee named " [e-mail]" randomly hit the keyboard and produced:

No. You will need to excavate below the pipe, making sure that if the footings are stepped down, the concrete overlaps by twice its thickness, and leave at least 50mm clear between the pipe and the concrete. The wall is then lintelled over as you describe.