The Underfloor Heating Manufacturers Association (UHMA) is working with Junckers to promote better understanding of the natural synergy between the two products. UHMA’s Chairman Mike Lamb explains why
A BEAUTIFUL floor of natural wood; the invisible comfort of an integrated heating system - what could be more desirable?

Timber floors and underfloor heating are current must-have features of projects across the UK.

So, with demand so high, why is UHMA working with one of the best-known suppliers of hardwood floors to improve the information flow? Because it could be so much better. If awareness among architects and builders of the kinds of problems facing the underfloor heating designer and the timber floor supplier were higher, many projects could run more smoothly.

Timber floor constructions come in two basic types. There are the intermediate timber floors so popular in domestic settings and the structural wooden floors set on concrete in schools, sports halls and commercial buildings. Each presents its own potential hazards for the designer which could be avoided with co-operation.

Traditionally, installing underfloor heating systems for use in association with an intermediate timber floor has involved cross battening. This means laying battens across the joists to create a supporting surface for the aluminium heat diffusion plates, or whichever method is preferred. However, modern lightweight joists aren't suitable for this technique - they can't be notched either. So, underfloor heating specialists had to develop a 'counter battening' method. Battens the same thickness as the diameter of the heating pipes are fixed along each joist.

The designer also has to take into account whether loops may need to be laid at closer centres and will need to be shorter than in a concrete floor. Otherwise there is a risk of a pipe jam beneath the floor with the problems of local heat gains near the manifold.

Acoustics also have to be taken into account. In the case of intermediate timber floors an increase of the mineral wool insulation layer to around 100mm should meet Part E requirements. However each case must be considered individually.

The architect and/or the builder need to make room for a number of simpler manifolds rather than one with 15 circuits! And there must be a 20mm zone allowed in the floor depth to make room for the battens - and an allowance for the extra insulation needed for acoustic requirements.

Wooden floors used in association with a concrete base offer a different set of potential problems.

First the floor must be tamped and level and 'biscuit dry' before the underfloor heating is installed.

A dry floor is essential as there is a damp-proof membrane below the slab and the only way for moisture to escape is into the timber floor.

It is also crucial to know what type of timber floor is being used.

Some manufacturers use a base layer of T&G or plywood beneath the hardwood surface and the UFH designer needs to know the floor detail. Which timber is being used? Has it been properly cured to give the appropriate moisture content recommended in BS 8201:1987: Unheated rooms (15% to 19%); Intermittently heated (10% to 14%); Continuously heated (9% to 11%); and Underfloor heated (6% to 8%)?

In his turn the heating system designer must bear in mind that wood is a living material. Flow temperatures must be set to achieve UHMA's recommended maximum surface temperature of 270C for timber floors. In sensitive woods it may be desirable to install limiting sensors in the floor so that this maximum is not exceeded.

An accurate heat loss calculation is very important. No timber floor is likely safely to produce an output of more than 70W/m2 (other types of floor will happily produce up to 100W/m2). If this isn't enough then it may be better to think again.

Function is critical. If the project is a hall which is going to be used only for sports, a heat output of just 40 to 50 W/m2 should be adequate. But, if it is a school hall which is to be used for exams and by the wider community, a higher output may be required. These kind of decisions need to be made early.