Roof Insulation Guide

Investing in insulating your roof can improve your home's energy efficiency and reduce your carbon footprint: your investment will be recouped over time, and you will enjoy the benefits for years to come.

This article will guide you through everything you need to know when considering roof insulation, including costs, timeframes, design ideas, hiring tradespersons, doing it yourself, and the pros and cons of each type.

What Is Roof Insulation?

Roof insulation provides a barrier of material between your home and the outside world. It can be laid between the joists (the beams across the attic floor) or the rafters (the beams that support the roof of your home).

Regardless of which you choose, insulation slows down the transfer of heat between your home and outside, keeping your rooms cooler in the summer and warmer in the winter.

An uninsulated home can lose up to a quarter of its heat through the roof, making your house colder and increasing your heating bills. Insulating your roof and attic is a great way to reduce this, being effective for at least 40 years and saving you even more money than initially spent.

Find Tradespeople, compare up to 3 quotes!

It's FREE and there are no obligations

Get started

Types of Roof Insulation

There are two main types of loft insulation. The first is typically known as 'cold roof' insulation. It basically means that the insulation is fitted directly onto the floor in the loft, which will trap the heat in the main section of your home and prevent it from escaping through the loft.

The second type of roof insulation is known as 'warm roof' insulation and follows the slope of the roof at rafter level. Now, this type of insulation uses a different form of insulation to the aforementioned 'cold roof' insulation and is primarily used when the loft is to be used as a habitable space.

Pricing can vary wherever you choose to place the insulation, with the variation usually being in the type of materials used and the contractors' fees.

What Are the Pros and Cons of Installing Roof Insulation?

Insulating your roof has an abundance of perks, but it is important to make sure you choose the right method suited to you and your home.

Blanket and Batt Insulation

Batts of fibreglass, cotton or wool provide solid insulation properties. Pre-cut pieces fit easily into standard constructions and lofts. It will require extra care to fit around pipes and wires, although minor compression is usually less of a problem than gaps.

Pros

• ✔ Cost-effective and easy-to-install.
• ✔ Optional facing acts to support vapour barrier.

Cons

• ✖ Glass fibres can cause health issues and irritate lungs, eyes and skin.
• ✖ Poor installation will result in tears, open spaces and rips.
• ✖ Heat can be conducted through structural elements.

Spray Foam Insulation

Closed-cell spray foam offers high levels of insulation, but spray foam generally costs more than other options. For most lofts, mineral wool laid between and over the floor joists is simpler to install and carries fewer risks.

Open-cell foam allows water vapour to pass through, reducing the risk of trapped moisture damaging roof timbers compared with closed-cell foam. However, it needs a thicker layer to provide the same level of insulation.

Closed-cell foam provides effective insulation but can trap moisture against roof timbers, making it harder for them to dry out.

Pros

• ✔ Can reach awkward areas in roofs, walls and floors.
• ✔ Closed-cell foam provides strong insulation even in a relatively thin layer.

Cons

• ✖ Toxic gases are released during installation.
• ✖ A highly qualified subcontractor is needed.
• ✖ Much more expensive than other materials.
• ✖ Closed-cell foam can trap water from leaks or condensation against roof timbers, increasing the risk of rot.

Blown Insulation

Blown insulation, usually composed of fibreglass or cellulose, is flexible and extremely easy to install.

Blown insulation contains small particles which mould to any space. You can use this type of insulation to fill existing walls with minimal damage.

Settling can be a disadvantage in walls but an advantage in attics.

Pros

• ✔ Most affordable option.
• ✔ Can sometimes be topped up and reused.
• ✔ Suitable for lofts with awkward access or limited space to work.

Cons

• ✖ Dust may irritate lungs, eyes and skin.
• ✖ Weight of cellulose can be too heavy for some ceiling styles.
• ✖ Holds moisture which can affect performance and cause mould.

How Much Does Roof Insulation Cost?

The average cost of installing roof insulation in the UK depends on the extent and area of the project.

There are many cost-affecting factors to consider when calculating the cost of installing roof insulation to your property:

• The type of roof you have.
• The materials used.
• The method of insulation.
• The size of area to be insulated.
• How difficult or easy it is to access.
• The existing condition of your loft.
• Which region you live in.

In the UK, the majority of homes have what's known as a pitched roof. A pitched roof consists of two sloped sides that run downwards, away from the central ridge of the roof.

To class a roof as a pitched roof, some regulations state that the angle of the slope needs to exceed 10 degrees.

How to Insulate a Roof

If your loft is dry and easy to access, you may be able to fit insulation between and over the floor joists yourself. Insulating a sloping or flat roof is more complex and should be carried out by a professional, as is any work where damp is present.

With MyJobQuote, you can request multiple quotes from roof insulation installers near you. It's fast, free, and there is no obligation to go ahead.

Here's the typical process of installing roof insulation.

Lay Loft Floor

Before the Job Starts

• Prepare the Loft Space — Ensure the loft is safe to work in and adequately lit. Check for signs of rot or cracking before walking on the joists. Remove objects from the space and clear dust and debris by vacuuming or sweeping.
• Cover Light Fittings — If light fittings from rooms below protrude into the loft, cover them with downlight caps which sit atop the fixture.
• Use Crawling Boards — When moving around the loft space, use crawling boards placed firmly onto the supporting joists. Loft panels work well for this. Never step between the joists as this risks falling through the ceiling.
• Measure the Space — Take your tape measure and carefully measure the entire area you'll need to insulate by taking the length of the floor and multiplying it by the width. Next, measure the distance between the joists in the loft, then measure the actual joists' height.
• Choose Insulation Material and Thickness — Decide which type of loft insulation material you want. The measurements from the previous step will help determine what thickness you'll need. For example, if your joists measure 100mm, you'll need insulation that matches it before adding additional insulation to meet the recommended government standard.

During the Job

• Insulate Between the Joists — Insulate between the joists until you have a strong layer around 100mm in thickness.
• Lay Insulation Over Base Layer — Add insulation over the top at as close to a 90-degree angle as possible to reach the recommended depth of 270mm set by government guidelines. Start from the farthest point from the loft opening and work to spread the material over the joists, ensuring no gaps are left between strips. When starting a new roll, place edges tight together without overlapping or pressing too tightly.

After the Job

• Insulate the Loft Hatch — Fit insulation to the back of the loft hatch to help reduce heat loss. You can also add draught-proofing strips around the edges to stop cold air getting through.
• Insulate Water Tanks and Pipes — Insulating the joists risks pipes and tanks freezing due to lack of heat reaching the loft space. Fit pipe insulation by cutting to fit and taping onto pipes. For cold water tanks, purchase a tank jacket.

Warm Roof

A professional installer should carry out this work and insulate any gable walls, party walls and chimneys within the loft to prevent heat escaping around the roof insulation.

Before the Job Starts

• Clear the Loft and Check Safety — Ensure the area is safe by installing adequate lighting. If your loft doesn't have floorboards, use crawling boards to make getting around safer and easier. Thoroughly inspect rafters and joists for signs of rot or cracking. If you spot damage, call in help to fix this first.
• Measure the Space — Calculate the distance from the top of the roof down the joists, then multiply by the width of the space. If planning to put insulation on the underside of joists, measure that also. Calculate the distance between rafters for use later.

During the Job

• Insulate the Rafters — Your installer will choose suitable insulation and make sure the roof has the ventilation it needs to prevent moisture building up.
• Install Rigid Boards — If you opt for rigid insulation boards, work out how you'll cover the space, then trim the boards to fit. Using nails, fix the boards to the underside of rafters.
• Install Insulation Foil — Foil is easier than boards but less effective for heat retention. Simply staple the foil to the underside of rafters throughout to ensure no gaps between.

Ask a Trade

Got a question that only a tradesperson can answer? We have thousands of trades ready to answer any question you may have.

Ask your question

How Long Does It Take to Insulate a Roof?

It can take up to around 2 to 4 hours to install loft insulation throughout an average three-bedroom house. Some larger homes and bungalows may take more as there is a much larger surface area to cover.

Planning Permission Approval for Roof Insulation

Planning permission is not normally required for fitting insulation (where there is no change in external appearance). However, if the building is listed or is in a conservation area, you should consult your local planning authority.

Questions to Ask When Hiring a Roof Insulation Specialist

Consider the following points before hiring a roof insulation installer.

• Are they registered with a recognised scheme? Look for a TrustMark-registered installer. If the work is being funded through a government scheme such as the Energy Company Obligation (ECO), check that they also hold PAS 2030 certification. Some installers may also provide guarantees through organisations such as the Insulation Assurance Authority (IAA).
• Do they have experience? Make sure the installer you are hiring has experience in roof insulation. Ask them to provide evidence of their work.
• Are they insured? Check they have public liability insurance to cover any accidental damage or injury while working in your home.
• Do they offer any guarantees? If they offer a guarantee with their work, check what this covers and if they fix any issues that arise.
• Have you been given an itemised quote? Ask for a cost breakdown, so that you're aware of what is covered in your quote, and if there are any additional costs.
• Do they have positive reviews? Check their MyJobQuote profile to see what feedback they have from other homeowners.

FAQs