CAVITY WALLS AT EAVES LEVEL

The term ‘eaves’ refers to the lower edge of the roof and includes the soffit and fascia boards. The most structurally sound treatment for termination of a cavity wall at eaves level is to seal the cavity with blockwork laid flat. This gives

the wall greater stability, by tying the two leaves together, and improved load distribution over both leaves of the cavity wall (see Fig 192). As there is a risk of cold bridging at this point, aerated concrete blocks of the appropriate thermal grade should be used.

CAVITY WALLS AT EAVES LEVEL

Fig. 192 Termination of a cavity wall at eaves level.

The timber wall plate (typically 100mm x 75mm sectional size) is bedded on mortar in order to compensate for any deviation along its length. It is then held down and secured to the inside face of blockwork with ‘L’-shaped galvanized steel straps.

Ventilation into the roof space is achieved by vents left in the soffit board and plastic ventilation trays fixed between the timber rafters.

A simpler alternative treatment for the termination of a cavity wall at eaves level, which also eliminates the risk of cold bridging, is to omit the sealing course of blocks. The cavity is, therefore, left open at the top, with a timber wall plate positioned on top of the last course of blockwork upon which the roof timbers are fixed. This allows the loft roll insulation to be effectively joined up with the cavity-wall insulation, making a complete thermal barrier. The downside is that the top of the wall is not as structurally stable as a result of omitting the blockwork sealing course.