Hear how others have tackled the job for this winter.

How to insulate your loft the DIY way 

John Moule shares his first-hand experience of insulating his loft himself, including top tips on the tools, materials and approach he used.

The 55-year-old software engineer had insulated a loft once before in a previous home when he decided to repeat the process at his 1930s, three-bedroom semi-detached house in Bristol, this summer.

“I’ve got kids, two sons aged 15 and 18, so I wanted to set a good example to them, encouraging them to try to conserve energy where they can, and also from a financial perspective, if you can stop heat losses then you will spend less on energy”

“I’ve got kids, two sons aged 15 and 18, so I wanted to set a good example to them, encouraging them to try to conserve energy where they can, and also from a financial perspective, if you can stop heat losses then you will spend less on energy,” says John.

A renovation of the house a few years ago required wiring to go through the loft, which had disturbed the existing insulation, so John was keen to put back the missing elements and bring it up to current standards.

“Loft insulation is an important part of the mix when it comes to making your home more energy-efficient,” says John, who has had other upgrades made to his home including solar panels on the garage, external wall insulation and double glazing throughout.

So, where did he begin? “First off, I had to spend about a day clearing the loft out, which included moving a few water tanks that had been decommissioned.

“The insulation that existed already on the floor of the loft, between the ceiling joists, was about 100mm. So, the approach I decided upon was to straighten out and relay the existing insulation, and then where there were gaps, to add new stuff in, as well as lay an additional layer perpendicular to what was there to bring it up to about 300mm.”

Insulation rolls were “easy to use, easy to fit and reasonably cheap”

John made the decision to use Knauf insulation space loft roll, at 200mm, which is a glass mineral wool roll. He chose this material because it was “easy to use, easy to fit and reasonably cheap” plus widely recommended.

John carried out some online research with DIY stores like B&Q and Wickes to find the most competitive price for the new insulation, landing on Wickes where he bought 12 rolls, for £25 each, which totalled £300 including delivery. His entire loft space is 6.3 x 9.5m, which is 60 sq m.

“They gave you the area each roll would cover, so I divided the area I needed by that figure, which told me the number of rolls I needed to order,” says John. He also bought some overalls and a mask, which cost him about £35, but already had gloves.

All kitted out, John enlisted the help of his son on the day of the installation. His son lifted each roll up the loft ladder to John, who used a flat piece of wood, placed across the ceiling joists – the loft floor – as a platform from which to work.

“The roll is wrapped in a thin plastic, so you get the roll in the position where you want to lay it, then cut the plastic off, before rolling it out. Then you get the next roll and repeat,” says John.

He would highly recommend making use of the pole normally used to push the loft hatch up, if you have one. “I used that to help me push out the rolls. You’re sat on the platform you’re working on, and you don’t want to move from there, so you want as much reach as possible. Having a stick to move the rolls into position is really useful.”

John started as far away from the loft hatch as possible, over in the far corner of the roof, and worked his way closer and closer to the loft hatch.

“The width of each roll is about 1.5m, so ideally you want to roll that whole length out. However, sometimes you need to get it into a small place, for example where there’s a chimney breast, at which point you can just cut these rolls up using a normal wood saw very easily.”

It’s important not to plug up the gaps in the eaves, where the roof meets the floor of the loft, to allow ventilation, explains John. The whole process took John about 4 to 6 hours.

Has he noticed a difference to energy usage or the temperature of the house since installation? It’s a bit early to say in terms of the bills. However, John has noticed that the bedroom is warmer.

“There’s definitely a temperature gradient as you come from the first floor to the ground floor, more pronounced than I remember in previous years, so I’m sure more heat is staying in the bedroom.

“I’ve also been doing lots of small DIY jobs around the house, filling up gaps, draught proofing and so on,” explained John.

His parting words to anyone thinking of trying their hand at DIY loft insulation: “Have a go, it’s not difficult. If you’re reasonably fit and healthy, it should be quite achievable.”

Insulating your loft with the help of a professional   

Are you thinking of hiring a loft insulation installer? Tony shares his insights into getting the work done successfully.

The 71-year-old, who is semi-retired, had a loft conversion done on his three-bedroom home in Bristol, 30 years ago, turning it into an office and additional living space.

However, there was a small area left under the eaves, at the apex on the front of the house, which didn’t form part of the conversion and remained without insulation.

“I’d been meaning to get it done for years…”

“I’d been meaning to get it done for years, and then of course with energy prices going up, I thought now would be a good opportunity to do it,” says Tony. “Having said that, I’ve not necessarily done it in order to save energy costs, it’s largely for comfort.”

The office could become quite cold, particularly in the winter months, even when the rest of the house was warm, so Tony would use an electric radiator.

Describing the small area left after the renovation, Tony says: “It was just open joists on the floor, with plasterboard of the rooms below visible, and open rafters in the roof section, showing the felt on which the slate is placed.”

He had originally considered doing the job himself, but with the space so limited, he felt his back wouldn’t be up to it. So, in summer 2022, Tony asked his daughter, who was having an extension done, if her builder would consider doing a loft insulation job and he was interested.

“Before I contacted the builder, I did research online to learn about which type of insulation would be most appropriate”

“Before I contacted the builder, I did research online to learn about which type of insulation would be most appropriate. I looked up spray on foam but after reading up online, I was concerned about the possibility of the timber retaining moisture,” explains Tony.

He couldn’t use rock wool insulation, as he’s allergic to it, so Tony settled upon Celotex polyisocyanurate (PIR) insulation, even though it was a more expensive option. “It’s effectively expanded foam with a thin metal covering,” explains Tony.

“I decided to fill the void between the beams on the floor, which is approximately 100mm, and to have the roof space insulated at the same time. Imagine the arrow where the floor meets the gradient of the roof, so the horizontal and the 45 degrees, all that triangle of the roof space.”

Tony was also keen to have the area floored with chipboard, with the insulation underneath. In total, the project required 110 sqm of floor and roof insulation to fill the void. The total size of the loft room, for context, is around 225 sqm.

The builder sourced the materials, prepared the area for the work, which involved removing items stored under the eaves, carried out the insulation installation in the loft floor and roof space and installed the chipboard flooring. The total cost was £2,400 and it took around 10 days.

“A lot of that time was because the builder did all the cutting of the Celotex under the eaves, so as not to make a mess in the loft room. He was very good.”

“Do your research on what type of insulation suits you…pick a reputable company…look at some of the work they’ve done previously…ask the people who have had work done by them to hear their first-hand experiences”

One important aspect of the approach was that it was essential not to seal off the air vents that had been created as part of the original conversion. The material used is also breathable, says Tony, mitigating any potential ventilation issues.

Tony’s parting words for those considering hiring a loft installer: “Do your research on what type of insulation suits you and pick a reputable company. Go and look at some of the work they’ve done previously, and physically go and ask the people who have had work done by them to hear their first-hand experiences.”

Tony’s installation was a more complicated job than rolling mineral wool or fibreglass between the joists and he used a more expensive product. This accounts for the greater cost and duration of the work.

Join the conversation

twitter logo  instagram logo  facebook logo

Get involved

In partnership with:

Energy Saving Trust logo     TrustMark logo


This information is provided for guidance only. Please see the full disclaimer in our terms and conditions.

DIY cost estimates include VAT. Professional installer estimates exclude VAT as this is not applied to insulation services.