Solid wall insulation

Why insulate your solid walls?

Solid wall insulation is an effective way to stop wasting energy and money at home. In winter, a well insulated house keeps warmth exactly where you need it – indoors.

So, insulating your walls will help to heat your home more efficiently. Using less energy reduces carbon dioxide (CO₂): one of the biggest causes of climate change. It will help you to stop wasting money on your energy bills too.

What could you save?

Solid walls can be insulated in two different ways: with internal insulation (from the inside) or external insulation (from the outside). Both options can make your home warmer and more comfortable, and greatly reduce your heating bills at the same time.

In fact, by insulating your solid walls you could cut your heating costs by up to 40%. By using less energy, your household will produce less CO₂. So, insulating your walls is a great way to help fight climate change.

Cavity walled properties can also benefit from the same kind of solid wall insulation, especially if the cavities are not suitable for filling – always check the best option with your installer.

Let’s do the maths

*Estimated figures based on insulating a gas-heated, semi-detached home with three bedrooms.
The figures given above are for the whole installation however if you are going to be renovating the individual walls of your home, you can make some big savings by insulating them at the same time.

Is solid wall insulation suitable for your home?

Internal wall insulation is best carried out when you are re-plastering your walls or you’re changing major fittings in your bathroom or kitchen. External wall insulation will be more cost effective if your external walls need re-rendering; you may need planning permission if your property is listed or located within a conservation area. Each approach has its own pros and cons; conditions when it’s ideal or which make it unsuitable.

Did you know…? 1 in 4 homes in the UK has solid walls

How do you get solid wall insulation?

Internal solid wall insulation is usually installed professionally, and should not be attempted by the average DIY-er; only the very experienced should install it themselves. Approach an installer that provides dry lining or plastering and ask them to show you:

1. examples of previously completed internal wall insulation work
Ask them what internal wall installations they have done previously and if they have any photos of the work before, during and after.

2. what is the best way of insulating your walls to achieve a good energy performance (it should be to a U-value of around 0.35W/m2K)
The U-value of a wall is a measure of the rate at which heat passes through the wall and so is a measure of how well insulated the wall is and is expressed in terms of “Watts per meter squared-Kelvin” (W/m2K). The lower the U-value, the better the performance of the insulation and the less it will cost to heat your home.

3. what measures can be taken to prevent condensation forming on the wall structure once it is insulated.
Condensation occurs when warm air meets a cold surface. This means that when internal wall insulation is fitted heat is prevented from reaching the wall of your home, which whilst good news in terms of preventing energy from being wasted, also means there is a risk of unwanted condensation. To prevent this from happening a special seal, which prevents warm moist air from reaching the wall, is fitted as part of the solid wall installation process.

If you’re thinking about external solid wall insulation, you’ll definitely need to employ a specialist installer trained by approved system designers – to find such an installer visit the Insulated Render & Cladding Association (INCA) website.

How does solid wall insulation work?

Heat will always flow from a warm area to a cold one. In winter, the colder it is outside, the faster heat from your home will escape into the surrounding air.

Solid wall insulation slows down the rate at which it escapes, keeping as much of it as possible inside your home for as long as possible. How? Insulation works by coating or filling walls with a layer of material that only allows heat to pass through it very slowly. This reduces what is known as the U value of the walls – the rate at which heat can flow through them. The lower the U value, the more slowly heat is lost – and the more money you will save on your fuel bill to keep your home warm.

Solid wall insulation also helps prevent “cold bridging”. Cold bridging occurs when a material that is a good conductor of heat makes a “bridge” between the warm interior and the cold exterior. They are a significant source of heat loss and can lead to condensation and mould forming in buildings. An example of a cold bridge would be the party wall separating two semi-detached homes and spanning the length of the building. Warmth from both homes is conducted along the length of this wall and escapes into the air.

You may on occasion also see references to the “thermal conductivity” of the insulation material. This is often known as the “lambda (λ) value” and is measured in “watts per meter-kelvin” (W/mK). The thermal conductivity of a material describes how easily heat passes through it. The best insulation materials have a low lambda value as a material with a low thermal conductivity will need a thinner layer than a material with a high thermal conductivity.

External wall insulation can also renew the appearance of the house, improve weatherproofing, air tightness and sound resistance.

How to identify whether I have solid walls?

If your home has solid walls, then it should be suitable for either external or internal insulation. That said, each measure comes with its own pros and cons; conditions when it’s ideal or which make it unsuitable. To find out what might be suitable for you read the section on ‘ How do internal and external solid wall insulation compare?’. Once you have decided on the type of insulation, speak to your installer about whether this is the most suitable option for your home.

Does your home have solid walls?

Solid walls are mainly made of brick or stone and are found in most houses built before the 1920s. So, if your house dates back to Edwardian, Victorian or Georgian times – and is built of brick or stone – its walls are likely to be solid.

The easiest way to tell is from the pattern of the bricks on the outside of your house.

If your home has solid walls, the bricks will tend to be placed head-on and lengthways in an alternating pattern like this.

If your home has cavity walls, the bricks will tend to have a regular pattern like this.

However, an installer will be able to tell you whether you have solid walls or not.

If the brickwork has been covered, you may be able to tell a solid wall by measuring its thickness. Go to a window or door on one of your outer walls, and take a measurement there. If the wall is more than 25.4cm thick then it probably has a cavity; solid brick walls are usually around 22cm thick; solid stone walls are just a little thicker.

You can also contact your local authority’s building control department, which might know if your house has solid walls.

Solid wall insulation can also work for properties with cavity walls that are not suitable for cavity wall insulation and other non-traditional housing types.

How do internal and external solid wall insulation compare?

Both internal and external solid wall insulation substantially reduce a home’s heating costs and CO₂ emissions. However they are quite different in terms of the effect they have on your home:

Internal Wall Insulation

• Generally cheaper to install than external wall insulation
• Doesn’t alter the appearance of outside walls but it will slightly reduce the floor area of any rooms in which it is applied (the thickness of the insulation is typically around 100mm).
• Is ideally installed at the same time as internal renovation work and re-plastering as this will reduce the costs of the installation.
• As work is being done to the interior of the house, there will be some disruption but the disruption can be minimised by doing it room by room.
• Skirting boards, door frames and external fittings need to be removed and reattached to the new wall surface.
• Can make it difficult to fix heavy items to inside walls – although special fixings are available to help.
• If there are unresolved problems with penetrating or rising damp, these should be resolved before installation.

External wall insulation

• Can be applied without disruption to the household and does not reduce the floor area of your home.
• Renews the appearance of ageing outer walls. Planning permission may be required so check with your local council before undertaking any work.
• Fills cracks and gaps in the brickwork, which will reduce draughts.
• Increases the lifetime of a home’s wall by protecting the brickwork.
• Reduces condensation on internal walls and can help prevent damp, although it will not solve rising or penetration damp which must be resolved prior to insulating the walls
• Is ideally installed at the same time as other refurbishment work to outer walls as this will save you a lot of money
• Requires good access to the outer walls so that the installers can apply the insulation
• Not recommended if the outer walls are structurally unsound and can not be repaired.

How are solid walls insulated from the inside?

There are two main ways to insulate a solid wall internally – either with rigid insulation boards, or a stud wall. Neither of these methods should be attempted by the average DIY-er. So, unless you’re very experienced in DIY, ask a contractor/installer that provides dry lining or plastering and to show you:

1. examples of previously completed internal wall insulation work

Ask them what internal wall installations they have done previously and if they have any photos of the work before, during and after.

2. what is the best way of insulating your walls to achieve a good energy performance (it should be to a U-value of around 0.35W/m2K)

The U-value of a wall is a measure of the rate at which heat passes through the wall and so is a measure of how well insulated the wall is and it is expressed in terms of “Watts per meter squared-Kelvin” (W/m2K). The lower the U-value, the better the performance of the insulation and the less it will cost to heat your home.

3. what measures can be taken to prevent condensation forming on the wall structure once it is insulated

Condensation occurs when warm air from inside your home meets a cold surface and when you fit internal wall insulation it stops the heat from your home reaching the wall so it will be a lot cooler. When insulation is applied on the inside of your external wall, a vapour barrier is applied to prevent moisture from the air in your home forming on the cold exterior wall.

The first step is to assess the condition of your existing indoor walls; repairs must take place before installing insulation. Any problems with penetrating or rising damp must be resolved in advance as these both arise from defects within the building structure. Insulation should not in any circumstances be used to cover, hide or isolate damp. This could lead to more serious problems in the future. An installer will be able to advise on this.

Next, will the insulated walls be supporting heavy fixtures like kitchen units, radiators or wash basins? If the answer is no, then you can fit rigid insulation boards. If the answer is yes, you may be best installing a stud wall.

How are rigid insulation boards installed?

This insulation technique involves fitting plasterboard backed with rigid insulation onto the inside of walls. Typically the insulation will be made of either expanded or extruded polystyrene (EPS or XPS), polyurethane or phenolic foam.

The insulation should be at least 60mm deep to meet recommended standards, and can be anything up to 100mmm deep.

Before installation, it’s crucial to prepare the wall that’s to be insulated; its surface needs to be even. Where existing plaster has been removed and the brickwork is uneven, the wall must be levelled using a layer of plaster or render. Ask your installer if they do it as part of the job.

Once the wall is even, the insulation boards can be fixed straight to it using continuous ribbons of plaster or adhesive. Additional fixings should be used to hold the boards firm, and the joints between each board should be sealed to prevent air leaking out through the solid wall.

How is a stud wall installed?

With this technique, a metal or wooden studwork frame is attached to the wall and filled in with mineral wool fibre. It can then be plastered over, ready for redecoration.

Mineral wool insulation, which is also used to insulate lofts, is a less powerful insulator than rigid insulation boards. So, to provide the recommended level of insulation, the mineral wool ‘filling’ needs to be at least 120mm deep.

This makes stud wall insulation thicker than rigid insulation boards, which means it will affect the size of your room a little more. But on the plus side, a stud wall is strong enough to hold heavy fittings. Rigid insulation boards, by contrast, would need lengthy mechanical fixings that reach all the way from the cupboard to the outer solid wall.

Are there any other ways to insulate from the inside?

Rather than finishing off a stud wall with plasterwork, rigid insulation boards can be added at the final stage instead.

This combination of techniques will boost the performance of your insulation and reduce your running costs and risk of condensation even further. It is also a good idea if the wall is very uneven; putting a stud wall on first will reduce the time spent preparing the surface.

Is there a lot of upheaval when insulating from the inside?

If you’re planning to insulate your walls from the inside with insulation boards or a stud wall, then it needs to be clear of any objects – including radiators – so that the entire space can be insulated. Only external walls need to be cleared of objects, not internal partitions.

Light fittings and pipe work will probably also need to be removed and reattached, so that they are flush with your new ‘wall’.

Skirting boards and door frames on external walls will also need to be removed and replaced on the new wall and areas round windows must be insulated at the same time as the walls, to prevent condensation.

These points explain why internal wall insulation is most cost effective when major renovation works are being carried out, the walls are being re-plastered or major wall fixings are being replaced in bathrooms or kitchens.

This is especially true for properties with lots of indoor period features like coving and cornices, which will all need relocating. Simple modern interiors will generally cause less upheaval.

How is a solid wall insulated from the outside?

External wall insulation must be fitted by a specialist installer trained by approved system designers – to find such an installer visit the Insulated Render & Cladding Association (INCA) website. The installer will need full access to your walls from the outside. It is not recommended for homes with structurally unsound outer walls that can not be repaired.

A layer of insulation material is fixed to the walls with mechanical fixings and adhesive, then covered with a special type of render (plasterwork) or cladding. The finished look can be smooth or textured and painted, tiled, panelled, pebble-dashed (for easy maintenance) or finished with brick slips to provide a real masonry brick finish.

As they will cover the whole of the outside of your property, any of these finishes are likely to change its appearance – and will cover existing brickwork. So, you must ask your local council whether you need planning permission. For information on planning permission in England and Wales visit the Planning Portal website, for Scotland, visit the Scottish Building Standards Agency website, and for Northern Ireland visit the Planning Service Website.

To prevent condensation, recessed areas around windows must be insulated as well as the walls – with the depth of insulation depending on the width of the window frame.

Which is better – cladding or render?

It’s all down to personal taste. Some people prefer the look of cladding, which can come in a variety of attractive colours and forms: timber panels or shingles, stone or clay tiles, aluminium panels or brick finish.

Render can take the form of either a thick sand or cement applied over a wire mesh – or a thinner, lighter cement over a strong fibre mesh. Render is generally a less expensive option.

What type of insulation is used?

Your installer will know the most suitable type of insulation for you but ask if they are using Energy Saving Trust Recommended insulation, this means it has been tested by independent experts and it complies to BSI’s British standards scheme.

The Landlords Energy Saving Allowance
Tax allowances of up to £1,500 are available until 2015 for Landlords through the Landlords Energy Saving Allowance. This allowance can be used on each of the properties a landlord owns, enabling landlords to claim the costs for cavity wall insulation, loft insulation, solid wall insulation, draught proofing, hot water tank insulation and floor insulation. Visit the Directgov website for more information.

VAT

A reduced rate VAT is applicable for the professional installation of certain energy saving materials (including the materials themselves) - provided their primary purpose is to save energy - in residential accommodation or buildings used solely for a relevant charitable purpose. The reduced rate covers any incidental work that is undertaken as part of the installation process. This reduced rate includes the installation of insulation for solid walled properties, but does not cover materials that are installed primarily for decoration. More information can be found on the HM Revenue & Customs website.