How To Set Out Your Building Foundation, Stage 2
Now we have established your profiles and the lines we require to move on. Before any work can be carried out we have to have a good understand of “what lies below“The next step is to get your foundations excavated to the correct levels. We have to establish the ground conditions for your structure, a good understand of the subsoil strata on your site is required. Depending on the type of structure you are building, this will determine what type of foundation you will require. Hopefully you will soon have a good idea of how to set out your building foundation. Your local building prefessional should be consulted if you have any doubts.
Having a ground survey is always a good idea as many things can affect the type of foundation you will need.
Construction near Trees
If there are trees near your proposed build it could have a dramatic affect on your foundations, mainly due to the trees sucking moisture out of the soil in very hot weather, which may lead to subsidence.
Manholes and Sewers
Your drainage should be checked in case they are interfering with your build, if manholes or pipes are found within your build boundaries, they may have to be moved and re-positioned, which will have an affect on costs.
Clay soils will contain fine particles, these can often have huge impact, because the silt and sand particles will change their volume depending on moisture. A way of avoiding these problems is to dig your foundation to a level were the moisture content becomes stable. If the soil remains unstable to an impractible level then you may have to consult an engineer who will give you guidance on this and a way to go forward.
A good tip when concreting this type of ground condition is to concrete the foundations as soon as possible, never let the foundation dry out or you could find yourself digging even deeper, this will avoid any shrinkage problems. There are main types of foundations which i have listed….
Trenchfill foundations are were the concrete is poured to all the full depth of your foundation. This type of foundation could be used were the ground is loose or there are many different trees. These type of foundations can be taken to a depth were the soild moisture is stable, also there is no need to actually have someone in the trench to level out the concrete as they can be poured directly from the surface and made good.
Raft foundations would used were you have fairly stable ground near the surface, but you are in an area were mining has taken place in the past, which may lead to ground movement at some point in the future. The raft is reinforced with steel mesh and is normally made deeper around the edges to allow both skins of your construction to be placed on the raft edge.
Piled foundations would be used when ground conditions are such that good bearing ground can only be found at impracticable levels and make using traditional foundations impossible. The piles are mainly driven or bored into the ground. These piles will then be used to support a concrete ringbeam or groundbeam which then bears from pile to pile. This type of work is not for the amateur and should only be done in consultation with your engineer.
Now hopefully we have our foundations concreted and we are at a stage were we can start to set out for the structural walls.
This article is meant as a guideline only and your should always consult your local building professional for advice.
As always keep checking your lines and measurements.