Underfloor Heating for Conservatories, Extensions and Garden Rooms: The Complete Guide

Underfloor heating works in conservatories, extensions, garden rooms and loft conversions. What changes from one to the next is how hard the system has to work, and that comes down almost entirely to how the room is built.

That's the idea this guide is built around. Rather than treating "adding a room" as one job, it looks at each type of space in turn: how it holds heat, what that means for an electric underfloor heating system, and what to sort out before any work starts. Where we've covered a topic in more depth, you'll find a link to the full article.

Why the type of room matters more than the heating

Electric underfloor heating warms the floor surface, which then radiates heat gently up into the room. In a well-insulated space, that heat stays put. In a poorly insulated one, it escapes through the walls, roof and glazing, and the system has to run for longer to keep up.

So the construction of the room sets the limit on how well any heating system can perform. Broadly, the four spaces in this guide line up like this:

• Extensions. Built to current Building Regulations, including the insulation standards in Part L, so they generally behave like any other room in the house.

• Garden rooms. A well-built garden room with an insulated floor, walls and roof can perform as well as an extension, although quality varies a lot between suppliers.

• Loft conversions. Performance depends heavily on how the roof has been insulated, and lofts have their own quirks when it comes to floor construction and head height.

• Conservatories. The most glazing and the most heat loss, which makes them the hardest of the four to heat, although far from impossible.

That ranking isn't fixed, mind you. A conservatory with a tiled roof can close much of the gap on an extension, and a cheaply built garden room can be colder than you'd expect.

Conservatories

Conservatories are where most people start, usually because they've got one that's too cold to use from October onwards (and too hot to sit in by July). The glazing is the problem. Glass and polycarbonate lose heat far faster than an insulated wall, so a conservatory will always ask more of its heating than a brick-built room of the same size.

That being said, it's very rarely a lost cause. With a correctly specified electric system, laid on proper insulation boards and run from its own thermostat, a cold conservatory can become a room you actually use in winter. We cover the thermal side of this in detail in Conservatory vs Garden Room: Which Gets Better Underfloor Heating Results?

There are three things worth knowing before you commit:

• The roof makes the biggest difference. A tiled or solid roof cuts heat loss dramatically compared with polycarbonate, and underfloor heating performs much closer to extension standards underneath one. It isn't the only upgrade worth considering, though, and our guide to 7 essential conservatory upgrades ranks the options by their effect on comfort.

• The heating needs independent controls. Conservatories under 30m² that are separated from the house by external-quality doors or windows are generally exempt from building regulations, but one of the conditions is that the heating has its own separate temperature and on/off controls. Extending the house's central heating into the conservatory without that separation can put the exemption at risk, whereas electric underfloor heating with its own thermostat meets the requirement directly. Our article on planning permission for heated conservatories explains the rules in full.

• Insulation boards aren't optional. Without them, you're heating the slab underneath as much as the room above, which pushes up running costs and slows warm-up times.

If your conservatory is already built and you're retrofitting heating, the floor height and door thresholds are usually the main constraint. Electric systems are slim, so it's normally manageable, but it always needs checking on site. You can find out more about our underfloor heating for conservatories service.

Extensions

Of all four spaces, a new extension is the easiest to heat well. It's built to modern insulation standards from the outset, so the heating system isn't fighting the structure, and running costs tend to be predictable.

The catch with extensions is timing rather than performance. Underfloor heating is simplest to design in while the floor build-up is still being planned, because that's when heights, insulation and floor finishes can all be set to suit the system. Leave it until the builder has finished the floor and it's still possible, but you're working around decisions that have already been made.

A couple of things are worth thinking about early:

• Open-plan extensions. Many kitchen extensions knock through into the existing house, so the new space and the old one become a single room. Electric underfloor heating can be zoned with its own thermostat, which makes it easier to heat the area you actually use without relying on the older part of the house to do the work.

• Floor finishes. Large-format tiles and stone are popular in extensions and work very well with underfloor heating. If you're considering engineered wood, LVT or carpet in part of the space, it's worth checking the TOG rating of the floor covering, as more insulating materials reduce how efficiently heat reaches the room.

For extensions being built from scratch, see our new build underfloor heating service. If the project involves reworking existing rooms too, our refurbishment underfloor heating service covers low-profile systems designed to go over existing subfloors.

Garden rooms

Garden rooms have become a popular alternative to conservatories, often as a home office, a gym or somewhere to get away from the rest of the house. Because they're built more like a conventional building, with insulation in the floor, walls and roof, a good one holds heat well and electric underfloor heating tends to perform very efficiently in it.

"A good one" is doing a lot of work in that sentence, however. Specifications vary widely between suppliers, and the insulation in the floor in particular has a big bearing on how the heating performs. It's worth asking your garden room supplier exactly what's going into the floor before you choose a heating system.

The other practical point is power. A garden room needs a suitable electrical supply from the house, and any fixed electrical work has to comply with Part P of the Building Regulations. If you're adding underfloor heating, the heating load needs factoring into that supply, so it's best to agree early on who's handling the electrics rather than discovering a problem once the room is built.

If you're still deciding between a garden room and a conservatory, our side-by-side comparison covers how each performs with underfloor heating.

Loft conversions

Loft conversions are the odd one out, and not only because they're upstairs. They can often be built under permitted development, but they'll almost always need building regulations approval, and the finished room's comfort depends heavily on how well the roof has been insulated.

From a heating point of view, two things stand out. The first is head height. Lofts rarely have much to spare, so a heating system that adds very little to the floor is a real advantage, and that's where slim electric systems suit the space well. The second is floor construction. Loft floors are usually timber rather than a concrete slab, which changes the board and build-up choices, so it's something we'd always assess on site.

What every project has in common

Whichever space you're heating, the same handful of decisions determine whether the system performs as it should:

• Insulation beneath the heating. Insulation boards direct heat upwards into the room rather than down into the subfloor. In a conservatory they're essential, and in any other space they're still the difference between a responsive system and a sluggish one.

• Floor build-up. Modern electric heating mats are only a few millimetres thick, and with a slim insulation board the overall build-up can often be kept to around 15 to 20mm. Door clearances and thresholds still need checking on site.

• The floor covering. Porcelain, ceramic and stone are the most efficient finishes. Wood, LVT and carpet can all work, but they need to be rated for underfloor heating and chosen with their TOG rating in mind.

• Thermostat control. Conservatories, garden rooms and lofts are often used intermittently, so a programmable or smart thermostat that only heats the room when you need it makes a real difference to running costs. In a conservatory, a thermostat with an air sensor gives a more accurate reading of comfort than a floor sensor alone.

The honest bit: running costs

Electric underfloor heating is the simplest system to install in all four of these spaces. It doesn't need connecting to your boiler, it sits in a thin layer under the floor, and each room gets its own controls. For most of these projects, that makes it the most practical choice by some distance.

Still, electricity costs more per unit than gas, so electric heating earns its keep through efficiency rather than cheap energy. In a well-insulated extension or garden room with sensible thermostat settings, that works very much in your favour. In a conservatory with a polycarbonate roof, the same system will cost noticeably more to run, and no amount of careful installation changes the physics. That isn't a reason to avoid it. It's a reason to be realistic about it, and to deal with the biggest sources of heat loss where you can. Our guide to electric underfloor heating running costs goes through the numbers in more detail.

Planning and building regulations at a glance

Adding heating to a room rarely needs planning permission on its own. The building regulations side is where it gets more nuanced:

• Conservatories. Generally exempt from building regulations if they meet the conditions, including independent heating controls. Our planning permission guide covers this in detail.

• Extensions and loft conversions. These need building regulations approval as part of the wider project, so the heating should be planned in alongside everything else.

• Garden rooms. The rules depend on the size and use of the building, so check with your local authority or the Planning Portal before you start.

• Electrical work. All fixed electrical work must comply with Part P, which means using a registered installer or notifying building control.

These rules apply to England. Scotland and Wales have their own systems, so check locally if your property is there.

Getting the timing right

Whatever the room, the best time to plan underfloor heating is before the floor is finished. For extensions and loft conversions, that means early in the build. For conservatories and garden rooms, it's worth knowing that installers get much busier from September onwards as the weather turns, so spring and summer are usually the easier times to book work in. If you've left it later than that, our article on heating a conservatory in autumn covers what's still achievable.

Which brings us back to where we started. Underfloor heating will work in any of these rooms, but the heating itself is rarely the deciding factor. Get the room right, meaning the roof, the insulation and the floor, and the system has an easy job. Get it wrong, and even a well-specified system spends the winter making up for the building around it.

Talk to Comfort Floors

Comfort Floors has over 25 years of experience designing and installing bespoke electric underfloor heating, and we're an authorised partner and certified installer for Speedheat systems. Every installation is designed around the specific space, and every system comes with a 10-year warranty.

We offer free site visits and no-obligation quotes across Milton Keynes and the surrounding area. We'll look at the construction, the insulation, the floor height and your choice of floor covering, and recommend a system that suits the room rather than a generic package. To book a visit, get in touch or call 01908 562211.