How much does conservatory insulation cost? Here’s how you’ll need to budget

There are various ways to tackle the problem of keeping a conservatory snug, come rain or shine – from insulating the roof and even swapping it for a solid tiled version, to insulating the floor and any exposed brickwork. There are lots of ways to improve a conservatory, without starting from scratch.

What you can expect to pay will vary depending on the size and shape of your conservatory and what options you choose. A thermal window film added to your existing glass roof could cost around £10 for 6 sq m (64.6 sq ft), for example, whereas a replacement solid roof that’s insulated would set you back at least £2,000.

So before you fork out more than you need to, we take you through the insulation options available, from the roof to the floor, and how much they’ll cost so you can choose what’s suitable for your conservatory type and budget.

It’s no surprise the cost to insulate your conservatory roof will depend on its size, the materials you need and how long it takes to complete the work.

Polycarbonate is the most affordable material for conservatories, although according to The Eco Experts, it’s the least thermal efficient. So, if you do have a polycarbonate roof it’s worth improving its insulation value.

So, what are the options when it comes to insulating your conservatory roof and how much will it cost?

Applying a window film is the least expensive method. Stormguard offers a Seasonal Double-Glazing Film that’s available for just over £10 for 6 sq m (64.6 sq ft).

Window film can be applied to both polycarbonate and glazed roofs, but be sure to check that you purchase the correct version for your roof type. It can also be done as a DIY job, although you may find it tricky to apply yourself. Window film specialist Purlfrost suggests it’s a two-person task. However, it’s readily available from specialist companies and DIY stores.

Greenmatch explains that window film “provides an added layer of thermal insulation that will make a massive difference in the comfort of your home”, and that it improves “heat retention in your home leading to less wasted energy and reduced energy bills”.

If you want to avoid replacing the whole roof, one option is to install lightweight internal roof insulation. Checkatrade estimates that it will cost in the region of £2,000-£4,500 for a 9 sq m (96.9 sq ft) conservatory. This cost includes battens fixed to the underside of the existing roof, the addition of insulation and an internal roof finish.

The insulation used will depend on your chosen system but can range from panels including foil-backed insulation or high-density foam insulation. It can work for both polycarbonate and glass roofs.

Thomas Goodman at MyJobQuote says: “You can add insulation to a glass roof. This is usually done by applying aluminium foil and thermal wadding to the underside of the roof. The contractor will then add a plastic or plaster finish over the insulation to act as the ceiling internally.”

Insulation can also be applied to replace the glazed panels, which is done externally. Rather than fitting a solid tiled roof, the glazed or polycarbonate panels are taken out, from the outside, and replaced with insulated panels that fit the shape and size of the original slots. This is how Green Space UK Conservatory Roofs do it.

Nick Johnson, owner at Sun-Room Conservatory Ceilings says approximate costs to have external roof insulation fitted would be from £15 per sq m for a lean-to, and from £20 per sq m for other conservatory roof styles. According to Sun-Room, its insulated panel system is similar in weight to polycarbonate panels and is lighter than double-glazed glass units, meaning your current roof system would not need strengthening to support the weight.

If your budget goes beyond this amount, the next alternative is to replace the roof. Goodman, estimates a conservatory roof replacement will cost in the region of £4,000-£20,000, with the upper end covering larger roofs, with complex angles and more expensive materials, in areas of the country where labour is pricier.

Steve Rawdings, sales and marketing director at home improvement company SEH BAC agrees: “Typical costs for a replacement roof depend on the size. Up to 10 sq m (107.6 sq ft) would be from £12,000; up to 12.5 sq m (134.5 sq ft) from £15,000; and above 15 sq m (161.5 sq ft) from £18,000. But it’s important to remember this does depend on the design and complexity of the roof and specifications required.”

Despite the high cost, replacing the roof for a solid tiled version is the most effective way to insulate your conservatory, keeping the draught out and the heat in.

Some conservatories will have bare brickwork that is not plastered. Goodman points out: “As dwarf walls only make up a small portion of your conservatory, insulating them won’t make as much difference in terms of heat retention as insulating the roof would. But it may be worth insulating them if they’re made from a single skin of bare brick.” He adds: “One of the easiest ways to do this is to use insulating plasterboard.”

Tim Phillips, senior quantity surveyor at HiiGuru, says to do this you can use a 50mm (2in) Celotex GA4050 General Purpose PIR Insulation Board, measuring 2400 x 1200 x 50mm (95 x 47 x 2in) – estimating that a typical 6m x 4m (20ft x 13ft) conservatory with 1m (3.3ft) high dwarf walls will cost £137 to insulate.

“Alternatively, you could use external wall insulation (EWI),” says Phillips. “This is fitted on the outside of dwarf walls and mechanically fixed, and then sealed with a thin render coat.” He estimates that you should expect to budget for £80 per sq m for supply and installations, meaning an area measuring 16 sq m (172.2 sq ft) will cost £1,280 to insulate.

“Unsurprisingly, the easiest time to insulate a conservatory floor is during its initial construction,” says Abbas Youssefi, director at Porcelain Superstore. And the insulation available will depend on whether your build includes a concrete base or floor joists, although most conservatories are built on a concrete base.

“The best way to create a well-insulated floor is to use a rigid PIR insulation board underneath the concrete slab,” he says. “This will help the concrete retain heat generated during the day, helping to keep the room warmer at night.”

So, how much does it cost to insulate a conservatory floor at this stage? As a guide, Phillips suggests budgeting for £25 per sq m for the supply and installation of PIR insulation. However, he says: “For cost effectiveness, most conservatories are built by conservatory companies who supply, design and construct the conservatory, so the cost wouldn’t be broken down into detail.”

Phillips explains why PIR board is the most used material to insulate conservatory floors, rather than insulation material such as wool: “The material needs to withstand the aggregate and concrete which will be placed on top of it to build up the construction to the finished floor level. Wool insulation wouldn’t be able to take this weight, hence rigid PIR board is most used.”

As Youssefi mentions above, the ideal time to fit floor insulation is at the outset, because doing it after the event is extremely costly. Phillips warns that the cost of insulating an existing concrete slab conservatory floor could cost more in the long run than what you’d gain in insulation value – and is purely down to the amount of work involved. He explains that the floor would need removing to give a depth of 200mm (8in), before a dampproof membrane is laid, followed by a layer of stone and 125mm (5in) of insulation material. This then needs to be topped with a 100mm (4in) concrete slab, before your final choice of ceramic or porcelain tiles.

But while Phillips estimates insulating a 6m x 4m (20ft x 13ft) conservatory floor will cost a minimum of £1,500, there is a cheaper alternative: you can install the insulation yourself. “If your floor is made up of timber joists and floorboards, and you have DIY skills, you can simply remove and replace the existing floorboards,” he says.

He suggests then fitting a Celotex GA4100 General Purpose PIR Insulation Board, measuring 2400 x 1200 x 100mm (95 x 47 x 4in). “The board can be cut and friction fitted between the joists,” he adds, “and you could possibly carry this out yourself for up to £400.”

If you’ve invested in a conservatory but find you only use if for a few months each year, as it’s too hot during peak summer but too cold in winter, you may be feeling short changed. However, with the correct insulation you could enjoy your conservatory all year round.

Although it’s best to focus on getting the insulation right at the beginning of a project, it’s still possible to retrofit insulation, you just might not what to go the whole hog with insulating the roof, walls and floor.

Depending on what you are planning to do, some tasks can be completed yourself. Goodman says: “Insulating kits and easy-to-use materials, such as thermal foil, are widely available. So competent DIYers can insulate their conservatories. However, to be sure your installation is as efficient as possible and has adequate ventilation to avoid damp, you’re best hiring professionals to carry out the work.”