Residential floor finishes

Service pipes buried in floor screeds are never a good idea and are best kept above floor level. The theory that buried pipes are disturbed less and so less prone to damage is persuasive up to a point. However, like many aspects of construction, workmanship can let down the best theoretical plans and it may be some time before any significant problems emerge.

If there is insufficient cover of pipes, screeds can crack due to excessive heat. BS 8204 suggests that the screed depth should be no less than 25 mm and should be reinforced where pipes run underneath. The Water Regulations 1999 require copper supply pipes to be set in trunking with access lids, when running through concrete floors. BS 8000 Pt 15 requires all pipes to be in chases or ducts.

Since 1995 underfloor heating has gained in popularity. While there does not appear to be an apparent problem, the fundamental risk that an entire floor may have to be broken up to replace a defective system still remains. Early systems used steel, copper or polypropylene pipes, and there have been cases of corrosion of steel pipe walls caused by copper ions in systems installed in the late 1990s, seeming to stem from the inclusion of copper fittings in the system. This thinning of the pipe wall can lead to leaks and a drop in pressure. Pipes have been known to be punctured by mechanical fixings, and where care has not been taken to spread floor loads through insulation mats.

Newer polypropylene pipes designed after 1995 have anti-oxidising barriers in them to reduce the oxidisation risk. The coverings over underfloor heating systems should not have high thermal insulation properties. Carpets and underlays should not exceed 2.5 tog, and screeds should be lightweight. Timber flooring is potentially problematic if shrinkage is not accounted for or the delivery moisture content is too high. The running temperature of an underfloor heating system should not be hotter than 28 degrees centigrade. When underfloor heating is fitted under a screed, it is inadvisable to run the system before the screed has fully dried, or to initially run the system at full capacity, as this will cause the screed to crack.