Setting out a Building.
1.Once the foundation is excavated, the formwork supporting the sides of foundation is marked as per the dimensions shown in the architectural foundation floor plan.
2.Nails are nailed on the formwork, measured out exactly as shown in the drawing.
- Nylon strings are tied from one end to the extreme opposite for all sides of the foundation.
The nails on the formwork should be in the same exact dimensions as in the drawings. The wall thickness dimensions should also be captured. This is a very critical dimensioning since the rest of the walls after the ground floor slab is done will be dimensioned the same way. Wall structural loading should be very accurate , where the top floor wallings sit exactly on top of the foundation wallings as marked in the seting out.
- In the drawings above, notice the wall thickness marked 0.150, meaning the wall is 150mm thick. This dimension should be captured in the setting out where the nails supporting the nylon strings on the timber formwork are located.
Procedure for transferring measurements.
1.Using the architectural drawing, starting from one end of the edge, note the wall thickness and mark it on the wooden support formwork erected at the edge of the foundation.
- Mark it using nails, from which later on the nylon strings will support from.
3.Continue noting the dimensions from the drawings and marking them out progressively from one end towards the farthest end.
- Tie the nylon string to the nails and using a builders square to ensure the strings are at 90 degrees to the edge, pull the strings to the opposite side and after positioning it, nail to the timber formwork.
5.Repeat this procedure for all the sides and countercheck again to ensure all dimensions are matching as in the drawings.
6.Using the structural engineer’s drawings, use same procedure to set out for column foundation bases.
See the structural engineering drawing above.
- Measure out form one end and take the dimensions in the drawings to position them in the timber formwork and mark them using mails and nylon rope as in the procedures described above.
- Using a builders square, strings are re adjusted to ensure they are 90 degrees to the formwork.
Care should be taken to ensure that the strings attached to the wooden formwork are protruding at 90 degrees angle from the timber formwork towards the opposite end.
- The longer type of builders square , with the short end held on the wooden edge, and the long edge along the string, is best placed to ensure that the string protrudes at 90 degrees.
3 4 5 method of triangulation.
Check above images to see a demonstration of the 3 4 5 method used to recheck if the corners are at right angles together.
- Using one end of a corner where the 2 end walls meet, measure out 3 meters from one side and mark on the string.
- Measure out 4 meters on the other right angle side and mark on the string.
- The diagonal distance between the 2 points should be 5 meters.
- If the distance is not 5 meters, this means the corners are not at right angles and the strings will need to be adjusted to be 90 degrees protruding from one edge.
Diagonals method for checking right angles.
- Measure out the distance diagonally from one end of a corner to the other.
- Measurue out the diagonal distance of the opposite side.
- These 2 measurements should be the same.
- If the distances are not equal, this means there is a problem with the overall measurement and setting out so the procedures ofr setting out should be repeated again until the diagonal measurement s are all equal.
On the foundation corners, the diagonal ends are measured to ensure that they are of the same size, meaning the foundation is rectangular or square, not hexagonal.
Also, on the edge of the foundation, use of the 3 4 5 method can be done to quickly confirm that the corners are at 90 degrees.
Marking the wall trenches.
Using lime powder, mark the foundation walling trenches then start excavation as per structural engineer’s specifications.
Screeding should then follow suit in readiness for foundation walling and beams.
Architect Francis Gichuhi Kamau.