How To Set Out Your Building Foundation, Stage 1
Setting out your building foundation will require alot of checking and re-checking and a few tools you will need are:
Long Tape Measures
Timber for profiles
Now we have cleared the site and are ready to start setting out the build. Now we have to position your building in the exact position shown on your plans. Great emphasis should be put on this especially if your building has required planning permission, your local authority building inspector will certainly check this and if found to be in the wrong position, you stand a good chance that the whole building may have to be moved in future. This obviously would not be a good thing, so you have been warned!
This stage is to establish the dig, this will be wider than the size of your specified structural wall to allow for enough concrete to get a good bearing, it essential you centre your wall on the concrete and will be checked by your building inspector.
Establish Parallel Line
The first thing we need to establish is a parallel lines, we will assume for the sake of this article that we have an existing building close to the proposed new structure. Shown as AA-AA / BB-BB. These lines should be off set from the building to prevent any possible snagging of the string lines, in this case i have off set the lines 500mm. This line should then be established with the use of a stake at each end and the line should be fixed at each point. Pleasue ensure the line is very tight as this will prevent a false reading if the weather conditions are very windy, (it is very difficult to measure from a moving line).
Step 1: First Corner A
Now we have the parallel lines established we can refer to the drawing to find the distance required from these lines to comply with your planning permission and we can put in our first pin at position A
Step 2: Second Corner B
Now we can measure out along our parallel line using the off set of 500mm to establish position B and we can put in another pin.
Step 3: Third Corner C
Now we have a little more work to establish point C. For this we will need our 2 tapes, you will need to work out the diagonal measurement from point A to point B this would be done using the Pythagorean Theorem which you can find an example of this HERE. Once you have this measurement established you can extend your tape from position A to position B until you reach the measurement, then extend your other tape from position B until the 2 tapes exactly cross at the required measurements, this will establish position C and a pin should be driven into the ground.
Step 4: Fourth Corner D
Now we have to repeat the process of stage 3. Using the diagonal measurement you have established take your tapes and run them out from position B and C until they exactly cross on your tapes at the established measurements and drive a pin in at position D. Now we have a box which is bigger than an actual building to allow for a concrete toe which is explained in the picture below.
Step 5: Establishing Your Profiles
Now we have 4 pins in the ground establishing the outside of our dig, you should get these lines very close to the ground without being snagged and either run a line of sand on the lines or use a ground spray paint, this is to help the excavator dig in a straight line. The next thing we need to to is set up our profiles, these should be about 500mm away and be about 300mm about the finished level. I have made a graphic to explain how they should look.
You should then plumb up your pins and mark the line on top of your profiles and put in a nail and write on the profile something like “outside of dig” from this point we can mark the centre of our dig, which will also be the centre of our structural wall. As we know this measurement we can then establish on the profile our actual building line, i would write this on the profile “outside structural wall” and the inside. Put in small nails and repeat this on each profile.
Please go to Stage 2