Ever suffered a burst pipe? It's no fun at all – if the pipes from your water storage tanks rupture, a tank can empty itself unchecked. Even worse – if a mains pipe bursts, water can cascade down through your house until someone turns off the stopcock. If you're away, or even just at work, that may take a while…..
On the continent they tend to do it differently, but for decades here in Britain we have cheerfully adopted the practice of installing insulation above our ceilings, not to the underside of the roof. We then run our pipes above the insulation. This keeps our bedrooms nice and toasty, but leaves our water pipes out in the cold zone of our lofts. We often expose our tanks and associated pipes up high on a nice raised frame, well away from any residual heat penetrating through the ceiling into the loft. Just to flirt with danger further, we often run pipes close to the eaves, where an icy wind can whip-in through cracks and gaps.
Things are now changing, but if your house is more than a few years old, it is likely your attic will resemble the description above. Make sure your pipes and tanks are lagged – tubular pipe lagging is inexpensive and available at DIY stores. Pay special attention to joins and corners – if two bits of lagging run up to a corner, but the corner is exposed, you may as well not bother. Ideally all joins to the lagging should be taped to ensure continuity and prevent separation, leading to an exposed section of pipe. Where possible, run loft insulation over any pipes so they are effectively in the 'warm zone'. Remove insulation from below storage tanks to allow warmth from the rooms below to reduce the risk of freezing. And consider leaving your central heating on low when the temperatures fall below zero; it may not sound very 'eco', but it's a lot more environmentally-friendly than replacing everything, down to the plaster.