DOOR AND WINDOW REVEALS
The term ‘reveal’ refers to the vertical inside face of openings against which door and window frames are fixed. Cavities are closed at reveals by returning the internal blockwork across the cavity into the back of the external leaf of brickwork (see Fig 182). A vertical DPC felt (150mm wide) is inserted at the back of the brickwork, projecting into the cavity by 25mm and out of the reveal by 25mm. It is folded forward and ‘trapped’ between the reveal and the door or window frame. The length of felt must be sufficient that it projects 150mm below sill level and overlaps with any DPC felt or tray positioned in the sill construction. In addition, the felt must project above the reveal by at least 25mm so it can be folded forward and ‘trapped’ under the bearing end of the lintel used to bridge over the door/ window opening.
Fig. 182 Simple reveal detail – uninsulated, resulting in ‘cold bridging’.
Fig. 183 Simple reveal detail – insulated.
Again, this form of construction is not regarded as good practice today because of the risk of ‘cold bridging’, unless aerated concrete blocks of the correct thermal grade are used. To prevent cold bridging, insulation board or insulated DPC is introduced at the point where the blockwork seals across the cavity at the reveal.
A more recent development is the insulated plastic cavity closer, which comes in a variety of widths to suit different sizes of cavity and is easily cut to length on site (see Fig 184). Cavities are left
open at sills and reveals to allow the cavity closer to be inserted. Not only does the closer prevent cold bridging and seal the cavity, its extruded plastic construction acts as a DPC. This is a much more efficient and speedy form of construction, which eliminates complex masonry detailing and the insertion of DPC felt.