Building Methods & Construction Technology

Hollow Ground Floors

Hollow Ground FloorsThis type of floor consists of a series of timber joists laid at stipulated centres and supported on dwarf sleeper walls sometimes called honeycomb walls because they have holes or gaps built into the walls to allow a constant circulation of air to pass throughout the floor.Timber joists always span the shortest distance and need to be supported at regular intervals by sleeper walls

Sleeper walls are built straight on top of the oversite concrete, and timber wall plates are laid on top of the sleeper walls to support the joists.

External brickwork

Cavity insulation Internal blockwork

Joist ends treated with preservativeJoistWall plate with DPC underSleeper wall

Oversite concreteDP membrane

Hardcore

DPCAir brick and liner

Cavity fill

Foundation

Section through a traditional timber hollow floor.

Modern innovations have made it possible for timber floors to be supported on metal joist hangers built into the inner leaf of the brickwork or blockwork.

Section through a hollow floor supported by metal joist hangers

External brickwork

Internal blockworkCavity insulation

Air brick and linerDPC

Joist

DPC membraneOversite concrete

HardcoreCavity fill

Foundation

Joist ends treated with preservative

Mild steel galvanised joist hanger

The ends of the joists are positioned so that they are never in contact with the inner leaf of the brickwork or blockwork.

To promote a continuous circulation of air under the floor, a series of air bricks are built into the walls of the building.

InsulationThe Building Regulations require all ground floors to be insulated to prevent heat loss. Hollow ground floors may be insulated in a number of ways. One way is to insulate the floor using glass fibre quilt which can be supported under the joists with metal wire mesh.The most common method is to insulate the floor by installing the insulation on top of the joist but under the flooring material.