Warm up and keep Cost down with wall insulation

Save money and energy by insulating the outside walls of your home

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In an uninsulated home, a third of the heat you’re paying for is escaping. You heard that right: a third. Insulating the walls is a major step towards saving money and energy.

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What are your walls made of?

Different walls in different homes are made up of different stuff. Houses in the UK are generally either single-skin (solid) or cavity walls. First step is to find out which you have.

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• Cavity walls. These are made up of two layers with a gap between them. Since the 1920s, many homes have been built with cavity walls - a design that helps prevent rain from soaking through to the inside. If you have these kinds of walls, you can fill that gap with insulation.
• Single-skin brick walls (also called solid walls). As you’ve probably guessed, single-skin brick walls don’t have that gap. This is typical in older buildings and means you have to put your insulation on the outside or inside of the walls. 

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Cavity wall insulation

If you have cavity walls, you can insulate them by injecting insulation material from the outside in. Insulation is typically injected through holes drilled in a diamond formation. After the work is finished, the holes are covered in cement – you wouldn’t know they were ever there. 

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It’s a job you can’t do yourself, but an average house shouldn’t take a registered installer more than a couple of hours. 

Solid wall insulation

Insulating solid walls is a bigger job. You can get external or internal wall insulation – meaning you can insulate the outside or the inside of your wall.

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Internal solid wall insulation

This involves layering material (like plasterboard) over your wall inside. This internal option will slightly eat into the space inside the room, but it has a few advantages:

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• It’s less expensive than external solid wall insulation
• It doesn’t ruin the look of period properties or other beautiful buildings
• It works in conservation areas or for listed buildings
• It works for flats or maisonettes where you can’t use external insulation for one level of the building

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External solid wall insulation

This means fixing insulation to the outside of the building. If your wall is old or cracked it’ll have to be repaired first. Here are the advantages:

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• It doesn’t reduce the size of your rooms or eat into square footage
• It’s less disruptive (other than your garden being messy while it’s done!)
• It helps to reduce outside noise and makes your home more weather resistant

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How much can you save?

The price depends on the condition of the walls and of course, your property size. 

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Cavity wall insulation costs around £2,700 for a semi-detached house. It will save £240 a year in energy bills, according to the Energy Saving Trust.

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Solid wall insulation is more expensive. Internal wall insulation for a three-bedroom semi costs £7,500 and external wall insulation would be around £11,000.

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There’s no denying that solid wall insulation comes with a hefty price tag, but savings can be as high as £320 a year for a semi. Both costs and savings are higher for a detached home, and lower for a mid-terrace.

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What about other types of insulation?

Glad you asked. Loft insulation can also save you a packet since a quarter of heat in an uninsulated home goes straight through the roof. So we wrote a guide about that, too.

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Getting a mortgage for a home with single-skin brick walls 

Mortgage lenders view properties with single-skin brick walls as “non-standard”, which means that they can be less keen to lend, and will place a lot of weight on what a surveyor says as part of the valuation process. 

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This is because of the potential risks, such as water getting into the property. 

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If you’re thinking about getting a home with single-skin brick walls, it’s wise to speak with a mortgage expert first.

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Can you get a better mortgage on an energy efficient home?

Most lenders offer “green mortgages” which are designed to reward you for having things like solar panels and good insulation. The incentives come in the form of lower rates, larger loans or cashback.

You could consider a green mortgage if you’re remortgaging after making energy-saving improvements to your current home, but while the rates are competitive, they aren’t always the cheapest deal. 

You can find out more in our guide to green mortgages, or chat to a mortgage expert.