Friday, 16 November 2018

Underfloor Heating FAQ: Floor types, screed options, the latest products & more

Underfloor heating (UFH), both wet and dry, is loved by homeowners for its even heat distribution, energy efficiency and compatibility with green methods of heating.

But while the idea is simple, the practicalities might not be quite so straightforward. What are the implications for flooring? How long does it take? Can I extend the system later?

Here we answer reader’s questions about installing UFH in new build or renovation projects.

What flooring type should I choose for underfloor heating?

A: The best flooring for any underfloor heating system system is solid, such as ceramic tiles, slate, or stone flags, as they have the best thermal conductivity, and will provide the best heat output. But bear in mind that a screeded construction will expand and contract with the heat.

Underfloor heating & tiles

In the screed, this is absorbed by an expansion gap and edge insulation, so any tiles fitted on top – which may well expand at a different rate to the screed – should also be laid with an expansion gap around the perimeter of the room (the bigger the room, the bigger the gap should be). This gap can usually be covered by a skirting board. Flexible adhesive and grout must be used, or you’ll be taking up your tiles again in six months.

Suspended timber floors, by their nature, are more prone to movement than screed, but tiles can still be used by covering the joists with a minimum of 18mm (although 22mm is the recommended measurement) staggered chipboard or ply panels with glued joints screwed down securely. Once again, you’ll need to use flexible tile adhesive and grout.

Underfloor heating & timber floors

Wood flooring also goes fine with UFH, providing that it is less than 22mm thick, the boards have a width-to-thickness ratio of no more than 4:1, it has a moisture content of six to eight per cent, and that the floor temperature does not exceed 28°C.

When it comes to timber flooring and UFH, the most suitable type is engineered board, which is made of several layers laminated together, often with the wood grain running in opposite directions in each layer, and finished with a thick hardwood surface. As it is an inherently stable material, expansion and contraction will be minimal.

Solid timber is also suitable, although narrower boards are recommended as they expand and contract less with atmospheric changes than wide boards.

Underfloor heating & laminate flooring

Thin laminate flooring is less suitable, and will need a chipboard or ply sub-deck to ensure stability. Good-quality laminate floors and engineered boards will probably have their moisture content corrected before lamination, but care should always be taken to acclimatise any timber floor.

To avoid excessive movement of the finished floor, the screed, timber flooring and internal construction (wall and ceiling plaster) must all be moisture-free, which may mean leaving boards unpacked in a dry room for several weeks to acclimatise.

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Article reference Underfloor Heating FAQ: Floor types, screed options, the latest products & more

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