Richard Renouf highlights problems with UFH that still arise – and not necessarily because of new technologies.

UNDERFLOOR heating (UFH) is becoming more common and most flooring professionals are keeping up with developments in materials and advice to customers so that problems can be avoided.

Two recent inspections, however, highlighted that problems still arise and they’re not necessarily the result of the new technologies.

I was asked to inspect a 300sq m installation of LVT flooring in a property that had been adapted for mobility purposes.

The project had been overseen by an architect who specialised in this kind of refurbishment and the detailed plans included specifying what flooring – range and colour – was to be laid.

There were some hiccups – the flooring had been discontinued and so an identical product with a different backing from the same manufacturer had to be used for part of the project. Both were fitted by a sub-contractor and as they were click-together tiles they were fitted as a floating flooring with door bars to hide the height difference between the two products.

When the homeowners moved in to the property they immediately complained. The flooring did not look flat. The tiles were cupping and the header joints were peaking throughout the property. The architect approached the floor layers but was rebuffed because they’d fitted ‘hundreds of floors like this without a problem.’ In their view it couldn’t be anything but a manufacturing defect in the flooring so they suggested the architect should speak to the manufacturer.

It wasn’t long before the architect contacted me. In the brief he admitted that there had been a fault with the underfloor heating system when it had been commissioned, but this had been put right, so he was ruling it out as a factor.

I was given a warm welcome by the customer. She spoke to me only briefly as she needed to attend to her family, but the temperature in the home more than made up for her brevity. A quick scan with a thermal camera showed the UFH was running with a surface temperature on the flooring of well over 30deg C so the floor surface was clearly well above 27deg C. This would be causing a lot of expansion, and this in turn would be magnified because the fitted area had continuous runs of more than 21 linear metres in places, and the product maximum was nine metres.

If that wasn’t enough, the edges had been sealed with silicone sealant. This may be flexible, but it’s a powerful adhesive and it prevents the flooring moving laterally under the skirting boards.
The result? The expanded flooring could only ripple and lift. The architect would need to take all these issues up with the relevant people, including their own specifiers who determined the heat output of the UFH and the flooring product as well.

It wasn’t long before I found myself in a traditional country house that dwarfed the bungalow in terms of floor area. This time the rooms had been carpeted with a prestigious wool twist, but when the homeowner went on holiday and switched off the UFH he returned to find the carpet creased and rippling in one of the three reception rooms.

The retailer restretched the carpet, but the rippling returned, so he did it again, this time double-banking the gripper and using a power stretcher (as he should have done from the outset if he had been familiar with BS 5325: 2021 which requires this tool to be used on any stretch-fitted carpet over 4 metres long or wide).

When the rippling returned the complaint was taken up again. A carpet inspector was sent to the site and then a moisture expert, because the carpet inspector had suggested the issue was due to high moisture levels in the subfloor in combination with the varying temperatures of the UFH. The moisture expert completely contradicted the carpet inspector, so the issue became a stand-off.
In this case the UFH was running at a moderate temperature in spite of the frost outside, and my own moisture readings confirmed those of the moisture surveyor rather than the carpet inspector.

So, what was the issue?
The carpet was 11 mm thick, the gripper gully was 10-11 mm wide. This is not enough to pinch the carpet and hold it tightly where it is tucked in, and it does not form a tight gully to trap the tucked in carpet edge.

BS 5325: 2021 states that the gripper should be two-thirds of the thickness of the carpet away from the skirting boards. In this case, double-banking the gripper made no difference to the lack of hold so the carpet continued to work loose. Sadly, this was the case in another room where the rippling had gone unnoticed but which I spotted in passing and had to point out.

Keeping up with industry developments is hard work. All CFA consultants have to maintain ‘continuing professional development’ as a condition of their ongoing registration, and this gives us access to some of the best instruction available. These cases remined me it’s all very well learning the ‘new stuff’, but you mustn’t overlook the basics.
www.richard-renouf.com
Richard Renouf is an independent
flooring consultant