. DAMP PROOF COURSES IN BOUNDARY WALLS
While it is not required for the purpose of any statutory obligation, it is considered good practice to include a horizontal damp proof course at the base of a boundary wall and/or isolated pier. The inclusion of a DPC, typically positioned around 150mm above finished ground level, prevents groundwater from rising that would ordinarily cause staining to the facing brickwork and/or efflorescence from soluble salts contained in the groundwater. In addition, frost damage may occur in winter to the brickwork at the base of the wall resulting from groundwater in the brickwork expanding on freezing and causing the bricks and/or mortar to crack and spall. For boundary walls, a layer of DPC felt incorporated into a bed joint 100-150mm above finished ground level, or two courses of solid Staffordshire Blue engineering bricks, will provide a sufficient barrier to prevent the rise of groundwater. For more detail on materials for DPCs and their installation, see Chapter 11.
An ideal boundary wall construction (see Fig 243) includes all of the key features required by
good practice. Specifically, and working upwards from ground level, the masonry below ground level will have been constructed of common bricks or concrete blocks of a quality designated as suitable for use below ground. The wall has a two-course solid blue-brick DPC, which is an ideal moisture barrier and also forms an attractive feature.
Brickwork from ground level up to DPC is constructed in engineering bricks of special quality that are also water – and frost-resistant, making them capable of remaining in a saturated condition (either from groundwater or rainwater ‘splash-up’ from the pavement) with little risk of frost damage in winter. Engineering bricks are also more resistant to the dirt and staining that are associated with rainwater splash-up. In addition, the low water absorbency of engineering bricks will minimize the possibility of efflorescence – ordinarily, any soluble salts present in the
ground will be absorbed during periods of wet weather, resulting in white salt deposits forming on the face of lower-quality bricks during dry weather.
The wall incorporates a plentiful number of double attached piers for maximum stability, which terminate higher than the main wall. This is both attractive and further increases stability. The brick-on-edge copings and caps to the wall and attached piers respectively are constructed in Staffordshire Blue engineering bricks for maximum weather resistance. Oversailing courses with a mortar fillet have been included to the tops of the wall and all piers to provide a weathering under the brick-on-edge coping. Closer inspection of the brickwork shows that a half-round joint finish has been applied; this is one of the more compact and weather-resistant joint finishes available.