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RENOVATION­S: CAN I INSTALL UNDERFLOOR HEATING?

Rebecca Foster lays out the options for retrofit scenarios, highlighti­ng the main factors to consider when choosing the best underfloor heating system for your property

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Rebecca Foster examines how and when to add UFH to your home improvemen­t project

Often considered the de facto choice for new builds, underfloor heating (UFH) works by transformi­ng your home’s floor surface into an ambient heat emitter. As well as delivering a cosy warmth underfoot, UFH allows for clutter-free walls with no radiators. In some scenarios, it’s also more costeffect­ive to run than a traditiona­l heating setup.

While a renovation project doesn’t offer the same clean slate as a self build, it doesn’t mean UFH is beyond the realms of possibilit­y. There’s a selection of water-based and electric systems to suit various applicatio­ns – a lot depends on the heat source that will power the setup, the type of subfloor you have and the overall thermal efficiency of the house. “Usually heat loss (insulation/airtightne­ss) is one of the biggest factors that would limit the use of UFH,” says Chris Holt, managing director at CDI Innovative Constructi­on Materials. “The next factor to consider is the amount of disruption it will bring to the building, as it is potentiall­y a major process that may require the building to be stripped right back to allow the work to happen.”

It’s also worth bearing your lifestyle goals in mind before charging ahead and installing UFH – a key aspect to consider is the amount of time it takes for the system to warm up once it’s been switched on. Radiators have quicker response times, so in areas of the house where you’re looking for a quick burst of heat (eg bedrooms), a convention­al setup might be the preferable option.

The options

UFH systems can be divided into two categories – waterbased and electric. A ‘wet’ setup comprises a network of pipes laid beneath the floor finish. When switched on, warm water (around 35°C) is circulated through the system to heat the surface above. In the past, retrofitti­ng this type of underfloor heating was only really worth it on major projects, as the height build-up brought about by the pipework and screed layer often called for the removal of skirting boards and shortening of doors. However, there are now many low-profile systems that can be laid in existing homes without too much disruption.

There are two types of water-based arrangemen­t: those that don’t require a screed and those that do. The latter solution is typically what you’d find in most self build scenarios, with tubes sealed into a sand and cement floor screed. In a new house, this layer would generally be around 75mm thick. However, many manufactur­ers offer slim, low profile systems designed to keep increases in floor height to a minimum – a huge plus in a renovation scenario. For example, Nu-heat’s Lopromax uses castellate­d trays to hold the pipes in place. These are laid directly above the existing floor finish before a self-levelling compound is poured on top. This layer cures within eight hours and is ready for your choice of floor covering in as little as three days (so much quicker than traditiona­l screed), adding just 22mm to the overall floor height.

Water-based systems without a layer of screed are also known as ‘dry’. This can be confusing, as UFH powered by heated electric cables can also be referred to as ‘dry’ because it doesn’t have any water – it’s important not to confuse the two. A non-screeded setup features prerouted tubes laid into a panel, often with a foil layer that helps distribute heat across the floor finish above. This is often the preferred choice for homes without the space for the self-levelling compound to be poured. However, they typically offer a lower heat output, so are therefore better suited to houses that are well insulated.

Electric underfloor heating systems come in two forms; either as a sticky mat with self-adhesive backing or as loose wires that can be shaped to fit the area you are covering. Both are cheaper and easier to install than waterbased UFH – some products can even be fitted on a DIY basis. However, the running costs will be more. “Electric UFH is best used in small, wet rooms that require short bursts of heat,” says Mark Dowdeswell, senior category manager at Uponor. “The setup has such a slim profile that the finished floor level is similar to what it was before.”

Key considerat­ions

Floor type This is often one of the biggest issues you’ll face when installing UFH as part of a renovation. Even if you’re not planning to rip out the entire floor structure and

start again from scratch, there are still systems that will enable you to install UFH. Most older houses come with suspended timber floors. In this scenario, one option is to take up the floorboard­s and lay the heated tubes suspended between the joists, above a mineral wool or rigid insulation. “This would be supported by battens so that the space that includes the pipe is around 25mm deep. A sand and cement mix is then installed around the pipes on top of the joists,” says Simon Currie, director at Borders Underfloor Heating. “The joists need to be notched at either end, as required, for the pipe to pass from one space to the other.”

If the additional weight of a screed layer is going to cause problems, it may be better to use a dry system with an insulated backing board pre-grooved to accept UFH tubes. This can be laid on top of the existing floorboard­s. Installing an electric setup within a suspended timber floor shouldn’t present too much of an issue. “They can be applied to most floor bases,” says Mark. “The UFH mats are fixed under the finished floor (tiles/laminates/wood) and wired into the home’s electric circuit with their own spur.”

If your house has a concrete slab floor, installing the UFH tubing will be less labour intensive as everything can be laid directly over the top. However, this does mean that things can get trickier when it comes to managing the build-up in floor height, which is where modern slimline systems come into their own. “A concrete slab plus screed floor will give a better heat output and thermal efficiency per m² compared to a suspended timber floor,” says Simon.

Insulation Underfloor heating runs at a lower flow temperatur­e than radiators, which isn’t a problem if you live in a snug, airtight home. However, you might hit a snag if you live in a poorly insulated house with single glazed windows. In addition to protective thermal barriers in the walls and roof, you’ll need something in the floors to prevent heat from escaping downwards. “Whichever method you choose for your UFH, the most important aspect is the installati­on of sufficient quantities of insulation either beneath the concrete screed or between the joists,” says Pauline Currie, director at Borders Underfloor Heating. “With suspended timber floors, you may be governed by having to retain your existing floor levels, and the depth of your joists will determine the amount of insulation that can be installed.” If you have a solid concrete floor, a layer of rigid insulation can be added – but you’ll need to factor it into the height build-up. Controls If you’re installing UFH on the ground floor and combining it with radiators upstairs, you’ll need to be able to operate the two systems independen­tly of one another, as they warm up at different rates. You can split the two feeds up at the boiler by using a blending valve, so the UFH is able to run on a cooler supply of water than the radiators.

Common pitfalls

Careful planning and adequate preparatio­n are essential, especially if you’re working with suspended timber floors where fitting is more labour intensive. “Avoid pre-installed services such as electric cabling and pipework,” says Pauline. If you’re restoring a period property, it’s important to work sensitivel­y if you want to retain original traits that give the house it’s character. “Special features such as mosaic or tiled floors, delicate skirting boards and door thresholds and architrave­s can sometimes be the deciding factor as to whether or not to fit UFH,” says Pauline.

Calculatin­g the cost

A renovation will always come with more unknowns than a new build. The extra considerat­ions you’ll need to take into account when installing UFH will likely mean that costs are greater on a per m² basis. However, this reflects all aspects of the scheme – not just the heating system. “Budget around £50 per m² for a property of approximat­ely 175m2, including the supply of materials with individual time and temperatur­e control for each zone, installati­on, anti-freeze and the electrical connection of control components,” says Simon. “The actual price will vary depending on the size of the project, due to economies of scale and the floor constructi­on.” As it’s easier to install, electric UFH has a lower initial outlay, though running costs will be greater.

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 ??  ?? Above: As part of the restoratio­n of this 16th century mill, CDI’S Lewis Deck system was installed to create a screeded underfloor heating setup on the ground and first floors. The dovetailed metal decking works alongside joisted floors, and has allowed for the new timber beams on the ground floor ceiling to be left exposed
Above: As part of the restoratio­n of this 16th century mill, CDI’S Lewis Deck system was installed to create a screeded underfloor heating setup on the ground and first floors. The dovetailed metal decking works alongside joisted floors, and has allowed for the new timber beams on the ground floor ceiling to be left exposed
 ??  ?? Right: Here, insulation and underfloor heating pipes have been laid between timber floor joists, ready for the screed to be poured over the top. This installati­on was carried out by Borders Underfloor Heating
Right: Here, insulation and underfloor heating pipes have been laid between timber floor joists, ready for the screed to be poured over the top. This installati­on was carried out by Borders Underfloor Heating

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