How much will adding loft insulation cost?

While loft insulation costs are inevitable when it comes to improving the thermal efficiency and comfort levels of your home, they need to be looked at in relation to the savings you are likely to make in the longer term on your heating bills. 

Home insulation really should be a priority, both for those renovating or extending as well as anyone self building a new home. That said, you will no doubt be keen to ensure that you understand how to insulate your home effectively without spending a fortune or going over budget. 

In this guide, with the help of the experts, we take a look at how much different types of insulation cost as well as how much you will need to buy.

Why add loft insulation?

While paying out for areas of our homes that we can't actually see – pipework, insulation, wiring and so on – can be frustrating, it is often these elements of buildings that ensure the whole house works well and is a pleasure to live in.

It is also important to bear in mind that by spending money on good loft insulation and researching how to insulate a loft properly, you will actually be able to reduce your outgoings over time. 

"In the long run, effective insulation can significantly reduce heat loss therefore helping to save money on energy bills," explains to Nick Fisher, director of sales and customer service at home and self build online retail destination Good Build Superstore. "But it’s easy to feel overwhelmed with the different types of insulation available. From boards and rolls to slabs (also known as batt insulation) and insulated plasterboards, there are plenty of options."

Why building regulations are important

Before you start your loft insulation project, it's worth researching the building regulations relating to insulation.

"Adhering to building regulations is incredibly important when undertaking home renovations or self build projects — so it’s vital people don’t cut costs when it comes to fire-resistant insulation," says Nick Fisher. "There are two types available: non-combustible insulation, which retains energy while reducing the risk of fire, and fire-resistant boards, which create a solid barrier and help to prevent the spread of fire. 

"A roll of Class B fire rated reflective vapour control layer starts at approximately £215 for a 75m2, while 2.44m x 1.22m x 9mm fire resistant boards start at £199.32.

"Equally, it’s imperative that lofts are insulated to help homes retain heat. Glass wool, mineral wool and sheep’s wool are all popular choices for roof spaces as they trap air which gives them their thermal insulating properties."

How much does loft insulation cost?

Different types of insulation work better for different areas of the home and also for various styles of property. For example, when insulating a wall, a very different product with a very different price will be called for than when insulating pipes. 

The type of insulation and the material it is made up from will also affect how much it is priced at — as well as how much it is likely to cost to install as some insulation products are not suitable for DIY fitting. 

"Loft insulation can vary from £37.06 for 6.84m2 to £115.55 for 6.84m2 for more premium sheep's wool insulation," advises Nick.

1) Insulation boards

"Insulation boards are often the lowest cost, with cavity wall insulation boards starting at £62.50 for 7.56m2 — these are an ideal solution to partial fill insulation for masonry cavity walls on new and existing buildings, as well as extensions. High-performance rigid polyisocyanurate (PIR) is amongst the best performing insulation materials available and offers long-term savings on energy bills.

Homebuilding & Renovating's sustainable building methods and energy efficiency expert Tim Pullen adds: "The polyurethanes and polystyrenes are usually sold as boards [and] can be used in any application, but are particularly good under floors. Boards are often fitted in sloping roofs but this requires a lot of cutting"

2) Multifoil insulation

Multifoil insulation can be an easier option for homeowners to add as a loft insulation material due to how thin it is as well as being easy to install. 

"Multifoil insulation continues to grow in popularity thanks to its long lifespan of over 50 years and ease of installation," continues Nick. "Available as a very thin layer which can be easily cut with scissors or a knife, reducing overall wastage, it’s the ideal choice for self build projects and areas such as roof spacers and cellars. It’s extra effective as it has radiation, conduction and convection properties while traditional insulation only concentrates on the latter two. Rolls of 1.5m x 10m cost approximately £140."

3) Mineral wool insulation

Mineral wool can be inexpensive options when insulating your loft space but often require a greater thickness in material to get the same insulation quality as other insulation options. The most common types of mineral wool insulation, which you can buy fairly inexpensively at Wickes, are glass and rock.

"The wool-type insulations (often sold in rolls) are the cheapest," explains Tim Pullen.  "Mineral wool will cost around £5/m² plus installation."

He adds: "Insulating the floor can be achieved by a mineral fibre quilt laid between the joists. Use the heavier, denser sound insulation quilt."

4) Spray foam insulation

Spray foam insulation tends to lie at the more expensive end of the price scale. 

"The Energy Saving Trust estimates it costs around £300 to insulate the loft of a semi-detached three bedroom house, but it could cost over £1,000 to insulate the same home with SFI," says Tim.

"£20/m² will buy a 100mm-thick SFI, which includes installation. A 100mm-thick rigid foam insulation board will cost around £15/m² plus the cost of installation. But the K value of SFI is closer to that of mineral wool insulation than it is to rigid foam."

How much insulation will I need?

'How much loft insulation do I need?' It is a common question and the answer will obviously affect how much you end up paying. 

"When choosing insulation types, be mindful of building regulations," says Nick Fisher. "Currently, they stipulate a need for at least 270mm of loft insulation at the required U-value of less than 0.16w/m2k.

"You'll need 170mm PIR (made from polyisocyanurate and often sold in rigid board form)," points out Tim Pullen. "Interestingly, they are the same requirements as for Passivhaus, indicating that any more than that is probably not worth the investment.

"To achieve these values using spray-form insulation, a depth of 125mm is usually required although this will vary."

It is important to realise that these insulation levels only apply to new builds. If you are upgrading your existing loft insulation, you won't be required to meet this depth.

"If you’re looking to refresh the insulation in your loft space, you may find you have as little as 25mm, which was the recommended amount in the 1980s," says Olivia Byrne from Roofing Megastore. "New insulation simply can be laid over existing insulation to achieve the required thickness, provided it isn’t damaged in some way."