Types of Foundations

The foundations of a modular home transfer the weight of the building to the land it is placed on. Since our homes are manufactured from shipping containers the foundation requirement is generally very cost efficient as a container home usually weighs less than a traditional brick house and the structure is also load bearing, however the foundation still needs to support their overall weight and there is no standard requirement for the foundations, it depends on the soil (or rock) the home is placed on. Engineers will need to study the properties of the soil to ensure that it can withstand the load of the buildings. It is common practice for an engineer to carry out a soil test to determine the safe bearing capacity of the soil. As an example, the SBC (safe bearing capacity) could be determined as 18 T/m2 (tonnes per square metre) this would be the maximum figure that the soil could hold per square metre of that land. This capacity also can change at different depths of the soil, usually the greater someone digs the greater the Soil Bearing Capacity.

 


Strip Foundations

Standard practice in the trenchfill method is to place as little solid concrete as possible into trenches, then blockwork will be used to build up to ground level. Single storey modular buildings will typically allow for concrete measurements of 450mm wide and at least 200mm deep, two storey modulars will allow for 600mm wide and 200mm deep.  

Deep Strip Foundations: When the soil bearing capacity is found at a lower level the trench can be dug deeper and wider, the concrete is poured and then masonry is used to bring the fooundation to ground level.

Wide Strip Foundations - Soil can sometimes be soft or of a low bearing capacity, wide strip foundations can be used to spread the modular load over a greater area and also reinforced with steel so that the loading per m2 is reduced.

 

Piled Foundations

Costs are very predictable with piled foundations which go hand in hand with modular building logic. The piles are driven into the ground and then filled with concrete.

The short bore pile and beam method involves typically a 2-3m long pile reinforced with concrete, a suspended slab can then be placed on top of the piles. This slab is not necessarily needed with our modular buildings as the piles can attach directly to the container, however the slab method does help with energy efficiency under the floor of the building.

Friction Piles are a similar concept to short bore but are used where the soil bearing structure is low even at low depths, piles in this method rely on the skin resistance against the soil.

 


Trenchfill Foundations

Trenchfill is a widely used alternative, trenches are dug out and simply filled with ready mixed concrete. Where trees are close, steel reinforcement can also be added. The foundation is then covered with a damp proof course, ready for modulars to be loaded on.

In comparison to deep strip foundations, trench fill minimises the width of the dig and the labour and materials required for building masonry below ground level, offsetting the cost of the additional concrete.

 

Raft Foundations

A concrete raft is produced which is designed to "float" on the soil underneath. A large area is dug out and an extra thick floor slab which is strengthened by steel reinforcing is put in. This raft provides a base for a ground floor of a building but they are not ideal as are very complex to construct.

A raft is generally used where soil requires a large bearing area and wide strip foundations are required to spread too far, so it would be more economical to pour a large reinforced concrete slab.

 

Pad Foundations

Pad foundations are used when an isolated load needs to be supported, these are ideal for container homes as the steel structure is load bearing. Each load is concentrated in a small area where concrete pads will be placed, these pads can be rectangular or square. This method is the most cost efficient solution for modular home foundations.