With over 30 years in the builders’ merchant trade, Andrew brings deep knowledge of everything from civils to timber. Now part of the Gilmore team, he helps customers make the right choices with advice built on decades of hands-on experience.
Nearly 1 in 3 cavity-wall homes in Great Britain still have no insulation. That’s around 6.2 million properties left exposed as of the end of 2024.
Source: UK Department for Energy Security & Net Zero (DESNZ), 2024.
Cavity wall insulation is a requirement under UK Building Regulations for all new construction work, with few exceptions. But is it worth the time, expense, and trouble required to retrofit existing buildings?
Building Control will want to see evidence of cavity wall insulation compliance for your new extension, or garage conversion, but there’s no requirement to fit it to existing, previously built cavity walls.
This may leave the rest of the property without cavity wall insulation. Is this a problem?
The UK Building Regulations have been updated over the years in order to optimise the levels of insulation that go into new construction. Cavity wall insulation matters, as without it, heating and cooling bills will be higher.
Part L of the UK Building Regs sets out exactly what is required for all new construction work.
Cavity wall insulation is an essential part of your home’s thermal envelope, the continuous wrap-around strategy that eliminates cold spots, cold-bridging, and condensation issues.
According to the Energy Saving Trust 33% of heat is lost through uninsulated walls. If installing cavity wall insulation is combined with upgrading the condition of the walls, gutters and drainage, it can make a huge difference to drafts and damp too.
The easy way to tell if your brick built home has cavity walls is to check out the brick bond pattern on the outside of the house. The rule of thumb is that if your walls have a nice even pattern with all of the bricks laid lengthways, then you likely have a cavity wall.
For houses built after 1990 it is almost certain that your home was built with insulation in the cavity wall. This doesn’t mean that it can’t be added to!
Don’t despair, you can still insulate your solid walls either by adding insulation to the outside of the building, or to the inside by constructing either a metal or timber stud wall.
Chances are that your property will be an older dwelling, so will likely require a survey and assessment by a surveyor or other expert.
If you are putting up your own extension, then installing cavity wall insulation is pretty straightforward.
Fitting insulation board is easy, and has a tongue and groove edging joint that helps to provide continuous insulation with no gaps.
Insulation board is a great choice when you are working with a narrow cavity as it has a high level of thermal resistance.
Mineral wool insulation works well at moderating moisture, mould won’t grow on it, and it is incredibly fire resistant.
When working on a new project it is great to use, light and easy to fit as you go. It dries out quickly if exposed to moisture and is designed to fit snugly in the cavity.
There are a couple of good choices for retrofitting cavity wall insulation, using insulating liquid foam, or blown fibre. Both have advantages and disadvantages, and it may come down to availability of equipment for hire.
Make sure you have clear access to the eaves in your loft so you can see the top of the cavity wall. From here, you can top up blown fibre, or spot foam when it expands out of the cavity.
Remember that you must maintain ventilation to the structural timbers of your roof to prevent condensation, rot and damp.
The benefit of using a professional insulation installation company is that you will be paying for their experience. A firm will have the tools, equipment and product required to carry out the work in the most efficient way.
The work will also be underwritten with a warranty and be compliant with all legislation and manufacturer’s guarantees.
Blown wood fibre cavity wall insulation scores highly for eco-friendliness as it is made from recycled paper and cardboard packaging. It’s treated to make it fire retardant, and insect repellent. Basically, it tastes nasty so you won’t be inviting pests into your home.
Foam has been used to retrofit cavity walls for decades. You can hire the equipment and DIY install. Don’t skimp on the holes required to pump the material in, and be mindful of any vents for sub-floor airflow.
Sometimes cavity wall insulation is not the best way to address energy conservation in a home. Here are some things you may have to take into account:
If your home is a listed building, or has to conform to conservation area regulations, you may need to take professional advice. At the very least, any making good to mortar, render or other external finishes will have to be taken into account.
Your extension, or other new build project will have to pass a certain level of compliance when it comes to energy conservation. Choosing thermally efficient blocks can help deliver what is required as part of an overall strategy.
Gilmore has been supporting builders, contractors and the public for many years. As legislation changes and regulations are tightened we make sure we have what you need to comply, save time, save energy and save money.
Call us on 01902 366620 or email us today, for expert advice from industry specialists at Gilmore Building Supplies. Find out how we can help you hit your energy efficiency targets today.
Please note: The information provided on this website is for general guidance only and should not be relied upon as professional advice.
Building methods, material specifications, and regulations can vary depending on location, project design, and site conditions.
Always refer to the latest Building Regulations, manufacturer data sheets, and consult with a qualified structural engineer, surveyor, or building control officer before starting any construction work or making design decisions.
Gilmore Building Supplies accepts no responsibility for loss, damage, or injury resulting from reliance on the information provided.
