Suspended Timber Floor - How to Build a Hollow Timber Floor Suspended on Joists

Summary: Buiding and understanding a suspended or hollow timber floor.

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Ground Floor - Hollow or Timber Floor

Hollow floors, also known as suspended or timber floors, are simply timber joists suspended across and supported by load bearing walls under the floor. The ends of these timber joists are built into, or suspended by joist hangers from the external walls of the property.

The internal load bearing walls are called sleeper walls and are very often built with gaps in between the bricks to allow a free flow of air under the floor. This stops any build up of condensation and is assisted by building in air bricks through the external walls. More can be seen about air bricks and underfloor ventilation by using the related project links on the left of this page.

Sleeper walls are built on small foundations and hold up the joists at regular intervals or spans. The width of these spans depends on the size of the timber used for the floor joists and more can be seen about joist spans in our loadbearing walls project.

There are many problems associated with hollow or timber floors, not least that they can be very drafty with air sometimes whistling up through the gap between floor boards. This can be overcome these days by installing draught excluder between the floorboards. Have a look at our project on filling gaps in floorboards. This problem is very much alleviated by using tongue and grooved floorboards. Since 1990, when a modern timber floor is constructed, insulation is required by the Building Regulations. This insulation is placed between the floor joists. If the insulation is soft insulation it can be suspended on netting fixed between the joists whereas rigid insulation can be sat on battens nailed to the side of the joists.

Suspended, hollow or timber floors also have a tendency to creak as the nails work loose over time. The answer to this problem can also be found in our related projects. Creaking floors and stairs.

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