How to Retrofit Insulation in an Existing Property
Want to keep your energy bills down while helping the planet? Start by upgrading your insulation
Professional advice from: Phil Wontner-Smith of PWS Architecture + Design; Kieran Hawkins of Cairn Architects; Nimi Attanayake of Nimtim Architects
The word ‘retrofit’ might throw you, but it’s really just another way of explaining the process of improving insulation in a home you already live in. “It means insulation that’s added to an existing building structure after its construction, not to a new house or extension,” Kieran Hawkins says.
Many in the UK live in older buildings, such as Edwardian, Victorian or Georgian properties. It’s estimated that around 24 million homes in the UK are in need of a retrofit solution.
The Climate Change Act of 2008 set a legal target to cut greenhouse gas emissions by 80% below 1990 levels by 2050. How we heat our homes plays a big part in this.
There are various ways to solve the problem of heat escaping. “External insulation is like adding a cosy extra blanket over your home,” Phil Wontner-Smith says. “Internal or cavity insulation [where you insulate walls] is a bit like that extra layer of weight you put on in winter that helps to keep you warm. Roof insulation is like wearing a fluffy hat and floor insulation is like your boots.”
If that tired layer of yellow blanket insulation you’ve had in your attic for several decades isn’t stopping the heat from escaping, it might be time to replace it with something more effective.
Find the right local professional for you project in the Houzz Professionals Directory.
For most people, cutting heating costs and being greener will be key reasons to retrofit insulation.
“The main driver for most of our clients is controlling their bills over a long period of occupancy, wanting a warm feeling in the house, and wanting to reduce their carbon footprint,” Phil says.
“Improving insulation will reduce the amount of heat leaking out of your house,” Kieran says. “For example, a boiler will burn less gas to maintain the target thermostat temperature. This decreases what is known as the operational energy, or operational carbon, of the building.
“Using less gas is important, because it’s a contributing factor to the climate crisis,” he continues. “This has a significant impact on the cost of living. Most people in the UK aren’t going to build a new house. We need to improve the efficiency of existing buildings or be prepared to live in colder homes.”
While it might feel like a less glamorous use of your funds than, say, a new bathroom, insulating wisely should make a difference to your home’s longevity.
“Ultimately, the most positive outcome is that clients are able to stay in a neighbourhood and community they love in a house that’s designed to suit their needs for many years to come,” Nimi Attanayake says.
Let’s start with walls…
Internal wall insulation This is where you fit rigid insulation boards to existing walls. You can also create stud walls filled with an insulation material such as mineral wool fibre or sheep’s wool, for example.
As you might expect, this can be disruptive, as you’ll need to clear rooms, remove skirting boards and fitted cupboards, and redecorate.
If you have a newer home with cavity walls (an existing space within them), these can be filled with insulating materials that are injected or blown into place through small holes. This is generally only possible in houses built after the 1920s.
The pros of exterior insulation are that fitting it is potentially less disruptive to daily life than with interior wall insulation, and it won’t shrink your living space. It can also protect brickwork from the elements and stop damp getting in.
However, it can be pricy, running into many thousands of pounds. It might also require Planning Permission, so always check.
It will be easier, less invasive and cheaper to install the above types of insulation when you’re having other work done – for example, a new kitchen or roof (meaning scaffolding is already up), or gutting a whole property.
“These are often easier to tackle than walls,” Kieran says. “Insulating under a draughty suspended timber floor can make a big difference, for example.”
Roof insulation Around 25% of the heat in your home is lost through the roof. Roof insulation can include options such as putting mineral wool fibre between floor joists or fitting rigid insulated boards between rafters.
Floor insulation Another 10% of heat is lost through the floor. Older homes with ‘suspended’ floors (with a gap underneath) usually lose more heat.
Floor insulation involves fitting insulation, such as mineral or glass wool, under boards. If you have carpet, you can add insulating underlay. Simply sealing gaps up between boards will also help.
When it comes to materials, “The optimal solution will vary hugely from house to house based on the construction. There’s no ‘one size fits all’ answer,” Kieran says.
More: Which Type of Loft Insulation Should I Choose?
Most experts agree it’s especially crucial to deal with any damp or condensation issues before going ahead with retrofitting insulation.
“Damp should be dealt with anyway,” Phil says. “Vapour control layers [which control moisture and reduce condensation] may need to be considered.
“Also think about things such as windows and doors,” he adds. “I’ve known people replace a roof but leave in a rotting old timber window, where the wind and heat can get in and out. The more air- and heat-tight your home is, the better.”
More: How to Deal With Penetrating and Rising Damp
Check your walls. If they’re solid (which they will be in most period homes), you probably won’t be able to install cavity wall insulation, so you’d need to add insulation boards.
“Internal insulation will inevitably mean you lose space in a room and will require any wall finishes to be removed,” Phil says. “Often, they end up discarded rather than being put back, which is heartbreaking – think beautiful period wall panelling or coving. If you have a listed building, check none of the features are listed.
“External insulation on period properties can be difficult, depending on the finish,” he continues. “If you’re cladding externally or rendering, you can use a system to insulate behind the cladding or render, but this can be a huge issue for listed buildings or ones in conservation areas, where planners will want the building to maintain a certain visual appearance.
“For roofs, it’s important to assess the breathability or whether it’s a warm or cold roof construction,” Phil says. “For floors, again features such as a tiled floor would need to be removed and relaid. It’s not so bad with timber suspended floors, but a floor on solid earth would need to be dug out and a new one installed. Concrete floors would need to be taken up to get insulation down then a new screed added.
“You can also insulate over the top and lose the floor you have, shorten all your doors and so on, as the floor level rises,” he adds.
Inevitably, budget is a factor for most people, Nimi says, so think about what’s realistic for you.
“Often, clients can’t stretch to upgrading the whole fabric of the house, so it’s important to focus on improving key elements,” she says. “As well as retrofitting wall insulation, we can look at replacing the roof and ground floor slab with a high-performance insulation, which would vastly improve the thermal performance of the ‘external envelope’.”
Kieran agrees. “When deciding where to insulate, choose areas that give the most value and savings in operational energy,” he says. “First repair the existing building, particularly any cracks or gaps around doors and windows. ”
“PAS 2035 is a British Standard document giving guidance on retrofitting homes,” Kieran says. “It contains some useful information and acts as a framework and a Code of Best Practice for professionals, but homeowners don’t need this themselves if they’re employing a suitably qualified professional who’ll be able to give advice tailored to the specific house.”
Retrofitting can be a challenge, so getting professional help is always a sensible idea. “I’d recommend employing an expert rather than trying to determine what is or isn’t relevant for a particular property,” Kieran says.
More options are becoming available for homeowners who want to choose green insulation. “Where possible, natural insulation materials, such as wood fibre, should be used,” Kieran advises.
Nimi says sustainable insulating materials, such as hempcrete, are gaining visibility. Also consider cork (seen here), wool or recycled newspaper.
It would also be worth getting advice on sustainable living and running costs and information on tax-free government subsidies before committing to a retrofit.
More: Which Alternative Materials Could I Use to Insulate My Extension?
Did you retrofit insulation, and are you happy with the result? Share your thoughts and advice in the Comments.