Why Use Block and Beam?
Some builders will tell you that block and beam (also known as "Bison beam") is the way to go, that you put in the beams and blocks one day and you are ready to start building the walls the next. It isn't as simple or as quick as that!
Apart from the fact that some builders and architects may prefer that construction, there are a couple of reasons for going for block and beam over a concrete slab floor, although these are not cast iron reasons:
- the void between the ground and the underside of the floor is more than 600mm
- the terrain or access means it would be hard to get sub-base and or plant to the area
The first of these reasons can be overcome in that synthetic fibres can be added, by the readymix company, to the concrete mix for a slab. The second reason - a difficult terrain will also make it difficult for handling the beams.
As with a concrete slab, the walls are built up from the foundations according to the architects plans, taking into account the optimum arrangement for the beams. It is worth noting here that, although the decision on whether to go for slab or beam can be made later, a better beam design will usually be produced if factored into the design stage. If not, a beam design can be done later but it may involve a bit more work in getting the beams to work, and more cutting of blocks.
Installing a Block and Beam Floor
Click on all photos for a larger view
Preparing for the Beams
The walls are up to level to receive beams. The cavity of the external walls has been filled with concrete and, for the internal walls, we have used blocks laid flat. Excess spoil has been put between the walls, but leaving an air gap of at least 6 inches to the underside of the beams - to provide ventilation.
DPM is laid on top of the soil to suppress the growth of weeds. The DPM must be held down by rocks, bits of block etc, to prevent the circulating air from raising it up.