Civil Engineering Reference
In-Depth Information
The question of restricted headroom must be considered when deciding upon the location
of the tanks within the roof. The tank will normally be supported about the centre line of
the roof truss, this generally being the largest clear void within a trussed rafter roof. Low
pitched roofs bring their own problems of restricted headroom, likewise the numerous
timber members in a hip end roof generally prevent tanks being placed within the hip area.
Not only must access to the tanks be considered, but also reasonable space must be left
around the tank for initial installation and maintenance thereafter. Do not forget the addi-
tional thickness of tank insulation. NHBC NHB standards pitched roof clause 7.2/S14 ad-
vises on this subject.
General Considerations
Where showers are installed in rooms below, it is often required to raise the level of the
tank as high as practical to afford head of water for the shower. The tank platform indic-
ated in Fig. 7.19 can still be used, but modified by building a rigid ply clad box-like struc-
ture around the above supports C. On the top of this box the normal water tank platform
itself may be securely fixed.
Do not nail supports B to the sides of the trussed rafter webs
,
they are not designed to carry such loads and the results could eventually be disastrous.
In refurbishment work, where the plumbing system is often renewed, the designer and/or
installer must make sure that adequate ventilation is provided for the roof space to prevent
condensation occurring on pipes to, and the tank itself. This condensation can be a cause
of seriously wetting the tank platform structure, causing degradation of both platform and
supporting bearers. If chipboard is used for the platform then it should be of the moisture
resisting grade.
Ventilation of Roof Voids
The ever increasing need to conserve the energy used for home heating has led to higher
insulation standards in recent years, and further improvements in these standards can be
anticipated in years to come. The insulation is usually placed between ceiling joists, res-
ulting in what is known as a cold roof space, as against a warm roof space, which would
be the case with insulation placed within the rafters. The following discussion assumes a
cold roof space situation.
