Tiled floors with underfloor heating: A guide to minimising and repairing cracking

BRE (Building Research Establishment) is an independent, research-based consultancy, testing and training organisation, operating in the built environment and associated industries.

On 22 May 2015, BRE published Tiled floors with underfloor heating: A guide to minimising and repairing cracking (IP 6/15), by Rupert Pool and Tony Yates.

Warm-water underfloor heating (UFH) has become more widely used in the last 10–15 years. It provides background heat in large spaces and makes tiled floors much more comfortable to walk on in houses. Compared with traditional radiators, UFH provides a number of operational benefits because of the lower temperature of the circulating water. This can improve the efficiency of the boiler supplying the heat and allows the use of renewable energy sources such as ground source heat pumps.

However, cracking, associated with underfloor heating is a common cause of problems in rigid tiled flooring. BRE has investigated many cases where stone or ceramic tiles have been laid on screed only for cracks to appear in the tiles and along grouted joints within weeks of the heating system being operated. This is almost always caused by movement of the screed at a pre-existing crack or, in some instances, a ‘day’ joint in the screed. Even though this movement is just a fraction of a millimetre, it is sufficient to crack thick granite slabs. These cracks are normally the result of a poorly-designed floor screed (ie badly coordinated movement joints) or failure to properly commission the heating system before the tiles are laid.

This 8-page information paper sets out BRE’s experience of screeds that contain warm-water underfloor heating systems and describes how the risk of cracking can be minimised and how repairs can be undertaken. It is intended for architects and specifiers.

Its contents are:

• Introduction.
• Description of underfloor heating systems.
• Screed.
• Design of screed to incorporate underfloor heating.
• Problems that can occur.
• Crack-isolation systems.
• Commissioning the heating system.
• Checking a screed before the tiles are laid.
• Conclusions.
• References.
• Further reading.

Electric ‘undertile’ heating and proprietary ‘thin-screed’ underfloor heating systems are not dealt with.

--BRE Group

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