18th Nov 2022 -

Walls, windows, and doors are a major source of heat loss in homes, with up to 35% of escaped heat passing through them. Cavity wall insulation has taken hold as the popular method for insulating the walls of a house, but there are several circumstances where it is not applicable, such as older houses, or houses with damaged walls. 

The most effective alternative is external wall insulation, affixing insulation to the exterior of your house to prevent heat from escaping. External wall insulation will greatly improve the thermal performance of your house, saving you money on heating bills and helping the environment.

In this guide we’ll take a look at the best method for external thermal wall insulation, affixing solid boards to the brickwork, covered with a visually striking render. We’ll look at the efficacy of this type of insulation, the best choice for an exterior insulation board, and some of the benefits and drawbacks when compared to internal wall insulation.

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Who Needs External Wall Insulation?

External solid wall insulation is the most thermally efficient way to add an insulation system to a house with solid walls. Many houses built before 1920 do not have cavity walls, built instead with either brick or stone walls, so choosing internal or external wall insulation is a must in order to reduce heat loss. Another reason to opt for external wall insulation is if you are in a location with a high level of wind-driven rain, which can cause dampness in houses with cavity wall insulation. Cavity wall insulation is also not encouraged in houses where an external brick wall is damaged.

An external insulation cladding system has some key benefits over internal wall insulation, the key one being that it typically provides a better level of thermal insulation. Another benefit is that the installation will leave the interior of your house intact, not requiring you to lose any floor space.

A drawback of external thermal wall insulation is that it will usually cost more, and will be very difficult to install yourself if you do not possess near-professional levels of experience. Another issue with external wall insulation is that in certain cases you may not be allowed to install it on your home, such as if you live in a listed building, or if your house is within a protected area, such as conservation areas. External wall insulation will permanently change the look of your house, and if you are adding a coloured render over a bare brick-walled property you may need to apply for planning permission. You should always contact your local planning authority to alert them before making exterior alterations to your house.

How is External Wall Insulation installed?

The first stage depends on if your external wall's facing is solid brick, or if it has a coating of render. If the facing is rendered, a render test will need to be carried out to ensure that your walls will support the weight of the insulation. If your wall fails the render test, all render will need to be removed. Next, all pipework must be removed from the wall, to be reapplied at the end of the installation.

Your choice of insulation panel will be attached to the wall using adhesive mortar. Next, the panels will then be secured into your wall around their perimeter with plastic or mechanical fixings. Another coat of mortar will then be applied over the panels, into which an insulating mesh will be sunk. The mortar will then be sanded down to perfectly flatten it, and given a coat of primer. This will then be covered by a render such as a silicone render to finish. There are alternatives to render, including textured paint, tiles, and brick slips. If looking to replicate the look of a brick wall, then brick slips can be a great choice. Each of these stages requires the materials to be left to dry, so the building process is extremely weather dependent.

What Insulation Board Should You Use?

You should look for an insulation board of 50mm to  100mm thickness for your wall insulation cladding. An industry standard for external wall insulation board is the Kingspan Kooltherm K5 External Board, which comes in thicknesses of 50mm through to 80mm. This insulation board is designed specifically for external walls, and is resistant to air infiltration and the passage of water vapour, helping to minimise the chances of dampness and condensation. They are affordable, costing about £5 per m2 before VAT.

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Is External Wall Insulation Good?

External wall insulation provides excellent thermal insulation, the best available for houses with solid walls. A 3-bedroom semi-detached house could save up to £300 a year by installing external wall insulation, and the energy saved in a detached house could be up to £700. With a layer of waterproofing, it can reduce the condensation on internal walls. External wall insulation can also reduce draughts in your home. While installation can be costly, there will be no disruption to your internal rooms. Unlike internal wall insulation, the interior of your house will remain unchanged. Another benefit is that it provides acoustic insulation, which can be useful if you live in a noisy area such as a busy street or under a flight path.

The drawbacks are both visual and financial. Installing external thermal wall insulation yourself is a very challenging job, and getting it installed by professionals will come with a hefty price tag. Even if planning permission isn’t an issue, external wall insulation will change the look of your house and can cause issues with eaves, windows, and windowsills. If you need to add insulation to your house with solid walls, you will need to weigh up which of the two is right for you.

What Does External Wall Insulation Cost?

External wall insulation is rarely undertaken by a homeowner, due to the scale and complexity of the process. According to estimates by the Energy Savings Trust, a government-funded body, the costs of installing external thermal wall insulation in a 3-bed semi-detached house are likely to be around £10,000. This may seem costly but your house will save money on heating bills for many decades to come, and will also be warmer throughout the year. As external wall insulation is essentially a small building project, it comes with a far higher price tag than cavity wall insulation.

When opting for a provider, it’s important to ensure that they will use both adhesive mortar and fixings to secure your insulation panels. Many reputable builders will also offer 25-year guarantees on their work, ensuring your peace of mind. It is worth checking with both your local council and your energy supplier to see if there are any grants available, such as the discontinued Green Homes Grant.

If you are looking to do the work yourself, the largest expense will be the insulated boards, used as wall insulation cladding. As stated, the Kingspan Kooltherm K5 board will cost about £5 per m2 before VAT. You will also have to buy mortarinsulating mesh, and render or brick slips. You will need to install scaffolding if you live in a larger house. A single 10m scaffold can cost about £625 a week.

Our Wide Range of External Wall Insulation Supplies

Building Materials Nationwide offers a wide range of products that can be used within an external wall insulation project. We have solid insulation boards such as the Kooltherm K5 for sale, perfect for wall insulation cladding. We offer a range of mortarinsulating mesh, and renders available. If you are looking to complete your own external wall insulation project or to source materials for a professional installation, we have a comprehensive range of products. Our insulation supplies can be delivered across the UK.

For our customers in the trades, we offer trade accounts. Our trade account holders gain access to their own dedicated account manager, who’ll be able to help organise large or unusual orders. This includes sourcing products not listed on our website through our network of suppliers. Sign up for a trade account through our website today, or tell us what you need through the contact form below.

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