If a loft or roof space has been properly insulated, it will be a lot colder than it was before because the warmth is staying down below where you need it. That leaves a problem: the roof space can now become cold enough for pipes and cisterns to freeze in winter, even if the rest of the house is cosy and warm. If the water in your supply pipe freezes you’ll temporarily lose your supply, and since water expands when it freezes, it may burst the pipes.
As long as no insulation is placed directly under any cisterns in the roof, they will still get a small amount of warmth from below. Cisterns and pipes should be wrapped, and there are several ways to do this. Make a note of where the stopcocks are fitted: in an emergency, your quick action can save a great deal of time, money and trouble repairing water damage to coving and decorations below.
In addition to purpose-made cistern ‘jackets’ that are easy to install, thick slabs – at least 25mm (1 in) – of expanded polystyrene make the ideal insulation for cisterns. The material is light and easy to cut to size and shape. The slabs – and the cut-out sections to accommodate fitting round pipes – are held together by taping round the sides of the cistern. Remember, don’t cover the bottom of the cistern even if it is accessible. The slight amount of warm air rising from rooms below is needed to keep it freeze-free.
Circular cisterns or those with awkwardly placed pipes which make slab insulation difficult can be insulated with mineral wool or glass-fibre blankets sandwiched between two plastic covers. Before fitting, make sure the cistern is fitted with a water-resistant cover. Water will form on the underside of the cover and it should not be airtight. Specially moulded plastic lids are available, or you can make one from a sheet of expanded polystyrene.