Insulating your loft or attic is essential in the present era of high energy costs. According to the Energy Saving Trust, we lose 25% of our home heat through an uninsulated roof. Therefore, we should make our homes more energy-efficient, thus reducing our heating bills.
In the UK, the average cost of insulating a loft varies with materials. But, a fibreglass blanket costs £8/m2 for 3-layers, or £360 in a semi-detached house, and £250/day for labour. The prices of other insulation vary, and we’ll discuss these later.
As you probably already know, heat rises. Therefore, warmth from your radiators rises into the loft space, where it’s lost through the roof. This makes your heating system work harder to maintain an acceptable temperature
Suppose you intend to build a house extension, conversion or replace your heating system. In that case, the local authority building control inspector will ask about existing insulation and compare it to the requirements recommended by the Building Regulations. If there’s a shortfall, you must upgrade the loft’s insulation thickness as part of the project. You can do this yourself with some insulation types. But, it’s better to hire a professional loft insulation company having the manpower, equipment, and safety knowledge to insulate your loft to comply with the regulations. However, if you can’t afford the loft insulation prices when upgrading insulation, government grants are available if your circumstances meet the criteria.
This guide explains why we need loft insulation, how much to install, how to do the job and what regulations apply. Finally, we’ll talk about the government grants available for financial help.
How Much Does Loft Insulation Cost?*
The table below compares various sized properties, loft insulation types, and estimated prices. Use it as a cost calculator to compare against professional quotations.
|House Type & Loft Area||Insulation Type||Estimated Purchase Price|
|4-Bed Detached 75m2||Fibreglass Blanket (3 layers) @ £8/m2||£600|
|Loose-fill @ £9/m2||£675|
|Sheet @ £30/m2||£2,250|
|Spray-foam @ £35/m2||£2,625|
|3-Bed Semi-Detached 45m2||Fibreglass Blanket (3 layers) @ £8/m2||£360|
|Loose-fill @ £9/m2||£405|
|Sheet @ £30/m2||£1,350|
|Spray-foam @ £35/m2||£1,575|
|2-Bed Terraced 32m2||Fibreglass Blanket (3 layers) @ £8/m2||£256|
|Loose-fill @ £9/m2||£288|
|Sheet @ £30/m2||£960|
|Spray-foam @ £35/m2||£1,120|
|3-Bed Bungalow 75m2||Fibreglass Blanket (3 layers) @ £8/m2||£600|
|Loose-fill @ £9/m2||£675|
|Sheet @ £30/m2||£2,250|
|Spray-foam @ £35/m2||£2,625|
* Disclaimer – We compiled these estimated costs from various sources. Therefore, use them as benchmarks for your research. Furthermore, they also depend on several factors we’ll discuss later. For accurate quotations, contact a qualified insulation company. Alternatively, use the form on this page.
The above table excludes VAT and labour at £250/day per person. Remember, the house loft area is estimated and varies depending on room configuration.
Loft Insulation Price Factors
As you’d expect, various factors affect the insulation installation costs. These include:
We’ll talk about these in more detail later. However, here’s some basic information.
- Blanket insulation – There are various types. But, they’re easy to install and are some of the most affordable. Typically, basic 300mm thick fibreglass blankets cost around £8/m2.
- Loose-fill insulation – Granular or fibrous material poured or blown into the gaps between joists. The cheapest costs around £9/m2.
- Sheet insulation – Usually, they’re expanded polystyrene batts fitted between the rafters. Various thicknesses and quality are available, but typically, the correct thickness costs around £30/m2.
- Spray-foam insulation – This needs professional installation because of the necessary equipment and training. Spray-foam adheres to the underside of the roof between the rafters and costs about £40/m2.
How much insulation?
Your loft size governs how much insulation you need. Although you pay more to insulate a large area, you might get a bulk buy discount, which reduces the cost per m2. Furthermore, how much insulation you need depends on the amount you’ve already got. If you live in an older house that hasn’t been upgraded, you’ve probably noticed the fibreglass insulation is 25-100mm thick. Furthermore, recently built homes may have 200mm thick fibreglass. The current Building Regulations Part L ensure those houses with recent extensions, conversions, or heating systems have 270mm thick insulation. However, other materials have different recommended thicknesses, and you should follow the manufacturer’s guidelines.
Is old insulation present?
You don’t have to remove old insulation unless it’s water damaged or compressed. If the insulation looks damp, find the leak and fix it before continuing. Alternatively, the insulation won’t have the correct air gaps within the structure if crushed. Generally, if the existing layer is okay to use, you’ll save the expense of buying that thickness insulation.
Remember, you can mix and match most insulation types. However, you can’t put spray-foam onto granular or blanket insulation because there’s nothing rigid to support it and adhere to.
Removing old insulation
If possible, always leave the existing insulation in place as it saves on removal labour costs, which is difficult and produces a lot of dust. Furthermore, you must pay to have the insulation sent to landfill, as most types aren’t biodegradable. Typically, hiring waste skips cost £120-£400, depending on their size. Additionally, you’ll need a council permit to leave it on a public road.
Loft accessibility is a big problem if you live in an old house. Standard sized loft hatches have been around since the 1970s so that older properties might have access hatches too small for a fibreglass roll or polystyrene batts.
Once in the loft, there might not be enough room to stand up or easily move around during installation. And if the building has a flat roof, it’s almost certain there won’t be enough room for most insulation types anyway.
Either choose an insulation method suited to the hatch size or hire a carpenter and install a larger access point. Depending on the region, carpenters charge £125-£250/day, with an average of around £200/day. A new loft ladder and hatch costs £500-£700 and takes 4-8 hours.
There are grants available to help with installing loft insulation. Later in this guide, we’ll discuss the current grant system, the ECO System.
After insulating a loft floor, you immediately make the space much colder than before. Therefore, protect water pipes in the loft from freezing and bursting in the winter. Simply insulate the water pipes with lagging to remove this risk. You can buy lengths of foam pipe lagging from any builder’s merchants or DIY store. Typically, 22mm thick by 1m long foam lagging costs around £1.50, and you can buy it in bundles. They’re easy to install using simple DIY skills.
Depending on where the electrical wires run in the loft, they might need relocating for better access. You need a qualified Part P electrician who is certified to work on domestic properties and do all electrical work before installing the insulation. You can find a local authority certified Part P electrician in the government approved Competent Person Register. Typically, electricians charge around £40/hr plus materials.
Loft board installation
Most people keep rarely used household items in the loft, such as Christmas decorations or empty suitcases. If this sounds familiar, you must fix boards onto the joists to spread the weight. However, don’t allow the boards to compress the insulation; otherwise, it’ll lose its insulating properties. Instead, support them with a gap beneath. You can raise the boards with timber spacers, or better still, use Loft Legs which you can buy from all DIY stores and online. These increase the gap by 175mm and cost around £15 for a pack of 12.
Many lofts suffer from dampness caused by broken tiles or flashing. Because it’s not a space visited every day, you might overlook damp insulation and rotten wood for many months. Therefore, before installing new insulation, repair the rotten wood. A carpenter charges around £200/day plus materials.
Labour costs vary depending on where you live in the UK. London and southeast England usually cost up to 15% more than elsewhere.
Insulating the loft hatch
Generally, you can lose up to 5% of the heat in your home if you don’t insulate the loft hatch. Simply glue a piece of expanded polystyrene foam to the hatch’s top surface using PVA glue. Finally, add draught strips around the hatch’s edge.
Loft Insulation Benefits
Insulating your loft provides substantial benefits.
Saving on energy bills
The main reason for insulating the loft is to save money on your energy bills by losing less heat through the roof.
Keeping the warmth in your home reduces the risk of dampness and subsequent mould growth. Also, a warmer house is healthier for everyone, especially children and seniors who feel the cold more than able-bodied adults.
Many people forget that insulating the loft reduces their carbon footprint by reducing energy consumption. Thus, they contribute to a greener, more sustainable world.
Types of Loft Insulation
We’ve already mentioned the various types of insulation available for our lofts. Now we’ll discuss them in more detail.
Blanket insulation is commonly sold in a roll, although it’s also available as a batt. It comes in various materials such as mineral-wool, fibreglass or flameproofed sheep’s wool.
- Mineral-wool and fibreglass are sold in thicknesses to comply with the Building Regulations.
- Their widths are the same as the standard gap between joists.
- Sheep’s wool is a natural material.
- They’re easily carried and handled.
- Easily installed as a DIY project.
- Mineral-wool and fibreglass are fireproof and don’t attract rats or other rodents.
- Mineral-wool and fibreglass produce sharp dust particles when handled. Use protective clothing and a suitable dust mask.
- Sheep’s wool doesn’t have a standard thickness or width. Therefore, it needs cutting to size.
- Sheep’s wool might attract rodents and other pests into the loft.
- You must cut all blanket insulation around obstacles and in small spaces.
- Sheep’s wool is more expensive than other blanket insulation.
Usually, loose-fill insulation is mineral-fibre, cellulose or cork granules.
- Cellulose and cork are greener alternatives than mineral-wool.
- It fits into the smallest space to cover the entire area.
- Fibres irritate, so protect the skin and wear a suitable dust mask.
- Granules or fibres will move around in a draughty loft.
- Needs professionals and specialist equipment to install correctly.
Usually, sheet insulation is expanded polystyrene foam, sometimes with reflective foil on one face. However, there are greener options, such as fibreboard.
- Ideal for fitting between rafters on sloping roofs.
- Place behind plasterboard in loft conversions.
- Often has a bespoke attachment system.
- More expensive to produce.
- Needs solid DIY skills or a professional to install.
Polyurethane foam applied via a hose sticks to the surface between the rafters.
- Quick to install, light to handle and trim after curing.
- Ideal for difficult-to-reach and small areas.
- Produces no dust or fibres during handling.
- More expensive than other options.
- Needs specialist equipment and professional knowledge.
- Produces fumes during installation.
- Technicians must wear protective clothing.
Should I remove old loft insulation?
We can only answer this question after inspecting the existing insulation. Remove the old insulation if:
- It’s damp or water-stained. If so, find the cause and remedy it before adding new insulation. Otherwise, the problem will damage the new insulation and wood, causing mould, rot, and fungal or pest infestations leading to structural issues.
- Remove the insulation if it’s compressed. To adequately insulate your home, the material must contain air gaps. Compressing the insulation removes air gaps and reduces its insulating properties.
- If the insulation is old vermiculite, it may contain asbestos. Don’t disturb the insulation, or you’ll produce hazardous dust. Instead, contact a registered asbestos removal company that can dispose of it safely. You can find information on asbestos disposal in this government database.
Can you put new insulation over old?
We’ve discussed the removal of old insulation in the previous section. If those situations don’t apply to you, you can safely place new insulation onto existing. However, the R-Value of the total insulation thickness must comply with the Approved Document L1B of the UK Building Regulations.
- New blanket insulation must not have a vapour barrier against existing insulation. A vapour barrier must only contact the plasterboard surface. Otherwise, it traps moisture, causing mould growth and rot. Therefore, use blanket insulation without a vapour barrier.
- You can install a non-vapour barrier blanket or loose-fill insulation over existing insulation.
- Don’t tack down blanket insulation to keep it in place. Compressed insulation reduces its R-value, which reduces its insulating properties.
How long does attic insulation last?
As long as you haven’t damaged the insulation, loft insulation should last 40 years. Over this lifespan, the energy you’ve saved will more than pay for the outlay regardless of the insulation type.
How thick should my loft insulation be?
The necessary insulation thickness depends on its thermal conductivity. The various insulating materials have unique conductivities, meaning they can be of different thicknesses. For example, the minimum required thickness for fibreglass insulation blankets is 270mm.
UK Regulations & Compliance
The current regulations state that loft insulation must have an R-Value of between 6.1-7.0 m2K/W.
To explain where this comes from, let’s calculate the required fibreglass thickness necessary to give this R-Value.
- Standard rolls of 100mm (0.1m) thick fibreglass insulation have a thermal conductivity of 0.044W/mK.
- Therefore its R-Value would be 0.1 / 0.044 = 2.27 m2K/W.
- To reach the required R-Value needs 3-rolls of this thickness laid on top of each other: 3 x 2.27=6.82 m2K/W
- This value is within the required range of 6.1-7.0 m2K/W.
The regulations state that you need at least 270mm of fibreglass to comply. This thickness gives an R-Value of 6.13 m2K/W.
The UK government currently provides financial assistance for loft insulation through the ECO scheme (Energy Company Obligation). To qualify for the grant:
- The loft must be accessible.
- Existing insulation must be less than 100mm thick.
Check your eligibility on the ECO Grants website, and find information about other energy-saving solutions. Alternatively, look on Simple Energy Advice, a website providing government-endorsed advice and information on home energy grants.
Loft Insulation Installation Steps
As most insulation requires specialist equipment or knowledge, we’ll concentrate on how to install fibreglass insulating blankets.
- You need a safe place to work. Therefore, ensure the loft is well lit, with no damaged joists. If the wood is damaged, it might collapse. Therefore, hire a professional carpenter for repairs.
- Remove old insulation now and vacuum the remaining dust.
- If necessary, call in an electrician to re-route cables.
- Supported by at least three joists, Crawling boards provide a safe working platform.
Calculate the amount of insulation
Calculate the area of the loft floor by multiplying the length by width.
Measure the distance between joists. Most insulation rolls are 370mm or 580mm and should be approximately the same as the gap. So, it’s worthwhile checking the size.
Choose the preferred brand of insulation. Then, inspect the label to find the roll’s coverage, width, and thickness.
Select the roll width nearest to the joist gap size. Usually, the blanket is 100mm thick. But, to comply with the Building Regulations, you need three times this thickness. Therefore, buy three times the calculated floor area.
When laying fibreglass rolls, you need a Stanley knife, large scissors and a tape measure. Also, you need protective equipment such as a dust mask, goggles, and overalls.
Lay 1st insulation layer
Most joists are 100mm high. Therefore, lay one roll thickness (also 100mm) between them, filling the gap to the top of the beam.
Lay 2nd and 3rd insulation layers
Lay the subsequent two layers at 90⁰ to the first, ensuring they cover all the gaps and joists. Butt the end of a new roll next to the old roll without overlapping or compressing the fibreglass.
Insulate the loft hatch
Don’t forget to insulate the loft hatch, as you can lose up to 5% of the heat through that small area. Using PVA glue, fix a rectangle of expanded polystyrene foam onto its upper surface. Finally, add draught excluders around the hatch’s edge.
Insulate water pipes and tank
Usually, most water pipes will be safely tucked under the fibreglass blanket. However, there will inevitably be some that run above the insulation. Use lengths of pipe lagging to protect these from freezing during cold weather. And don’t forget to lag the cold water tank, if you have one, with a correct sized jacket.
Assuming you don’t need joist repairs or re-routing electrical cables, most insulation work takes under a day.
If you want to save money on your heating bills and keep your home cosy and warm, get your loft insulation upgraded without delay. There are several different materials you can choose from as insulation, and a few of them are relatively affordable. Also, if you’re eligible, government grants are available to help with finance.
Complete the form on this page, and we’ll ensure you get up to four local professional loft insulation quotes from competent insulation installers.