Unit Overview
Traditional Cavity Wall and Strip Foundation
Raft Foundations and Timber Frame Construction

Raft Foundations and Timber Frame Construction

Raft Foundation

A raft foundation spreads the load of the building over a large area, it is formed of a continuous ‘raft’ of concrete. The edge of the raft generally steps downwards forming a lip, this helps to prevent lateral movement.


The raft is poured into formwork that needs to be set to the correct height and braced to prevent the concrete breaking out of the formwork. A metal rebar mesh is supported on rebar chairs, which ensure the steel cannot come into contact with the underlying soil.


Concrete is poured into the formwork and raked into place, before being leveled off with in line with the height of the formwork. The concrete is then smoothed over by

hand, if a smooth finish is required a power float can be used.

Services such a sewage and mains water can be piped through the foundation if the pipes are set in place before the concrete is poured.


Timber Frame

Timber frame buildings consist of a prefabricated timber walls made up of studs attached to a plywood sheet. The walls are prefabricated in a factory where a higher degree of accuracy can be achieved, window and door openings are added at the factory stage.


The timber walls have a waterproof membrane stapled to the outside.


The lower floor walls are bolted to the foundation with expansion bolts, wedges can be used to help level the walls to compensate for any inaccuracies in the raft foundation.


The first floor is generally placed on top of the lower wall, with the upper floor being constructed by the same method as the lower floor.


Prefabricated roofing trusses are commonly used to create a pitched roof.


Bricks can be used to clad the building to help with weather proofing and to give the appearance of a brick built house, L shaped brick ties are used to form lateral stability between the inner timber wall and the out brick wall. As the window and door openings are already in place there is far less likely to be mistakes in the brick laying or the size of the windows.


The internal finish is normally plasterboard, with normal first and second fix for plumbing and electrical.


A Key feature of timber frame construction is that the timber frame supports the load of the building.


Timber frame buildings are generally quicker to construct on site and are very popular in residential construction.