Foundations / Substructure

The foundations will be carried out by a groundwork contractor or your builder.

• There are a number of different ways to construct foundations, and we will explain them here. The budget costs that are given, are based on strip foundations, with a concrete strip foundation, and the floor and damp proof course (DPC), where concrete blocks are used to build the wall up in the inside to support the floor joists, and the outside, to just below ground level, where bricks are then used as they are more visual.
• The cavity of a foundation wall should be filled with a lean mix concrete.
• The budgeted price includes for carting away, and the elements shown in the detailed specification.

         Typical Strip foundation                            Typical trenchfill detail  

  

 

• This is generally the preferred method and most cost effective way to construct your foundation. However, until you can get your project to dpc level, and ‘out of the ground’ until you know what the ground condition is like, the final design of your foundation will not be finalised.

 

• It will be the building inspectors recommendation and approval that you will need to satisfy! If you don’t, he can make you dig it up and start again until he is happy with the depth, of excavation, concrete etc.

 

• Other methods of foundation is always likely to increase costs, but you should sill ensure that your builder explains things, and try to be there when the building inspector makes his visit and explains why things need to be done a certain way. This will help you understand why, the builder may require extra payments, deeper excavations, means more material to be disposed off whether on site or offsite, more concrete to fill the foundation, and possibly a saving on blocks and bricks. When the full extent of the foundation work is known (agreed with the building inspector) talk them through with your builder and always try and get the builder to agree the extra costs before he starts the work.

 

• The oversite – this is the ‘sub-surface’ that finishes the structural element of the floor. It is not the finished surface, but the one that will be insulated and screeded or or another alternative method of flooring to be used. On a timber type of suspended floor, the oversite can also refer to the covering of the ‘natural ground’ between that and your building.
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• Floor beams and blocks, are suspended on structural walls, depending on the size of your extension or building, internal supporting structural walls maybe required not only to support these concrete beams, but structural internal walls aswell. There will also be a requirement to provide ventilation inder the floor structure to allow any moisture from the ground to evaporate out. This will avoid any long term dampness rising through the structure, and with the insulation available today for floors, cold floors are not too much of a problem.

         Suspended concret block floor                     

 

• Drainage- - the 2 main types of drainage that you need are surface, and foul water drainage.

 

• Foul drainage will normally run into an existing drain to be taken eventually into the main drain network for treatment, or in situations where this si not possible, a cesspool or septic tank can be used. This is where the water from your toilets etc will go.

 

• Storm drainage, is the water that collects in your guttering, and can run into storm water drainage system or into soakaways. Water from sinks or basins can also run into storm water drains.

 

 

• In both cases the pipes need to be laid into an excavated trench, on a good level bed of pea shingle and will usually be required to be surround in concrete, the proximity to your existing or new building may dictate the strength of concrete required.