Cost guide
How much does loft insulation cost in London?
What actually sets the price in London — and how to compare three quotes without being fooled by the cheapest headline.
Advice
Loft insulation guides
Straight answers to the questions homeowners ask before they spend money — written by the people who survey London lofts rather than by a marketing department.
Insulation is an unusually opaque purchase. The product disappears the moment it is fitted, the performance is invisible, and the numbers quoted in advertising are often measured under laboratory conditions that have very little to do with a draughty Victorian roof in February. These guides are our attempt to make the decision legible.
Each one is written by the people who carry out the surveys, and each is updated when the guidance or the market moves — building regulation depths, the state of the grant schemes, and what materials actually cost this year rather than three years ago. Where we are uncertain, we say so, and where a figure is a national average rather than something we can promise for your house, we label it as one. You should be able to read these and then argue with us competently on site, which is exactly the conversation we want to have.
Four guides
Everything worth knowing before you spend
Materials compared
SuperQuilt vs mineral wool
Two products that are constantly compared and rarely competitors. Which one your roof needs, and why.
Funding
Loft insulation grants and funding
How the schemes really work, who tends to qualify, and how to check without handing your details to a cold caller.
Damp and airflow
Loft condensation and ventilation
The problem we find most often on survey, and the one homeowners most often blame on the wrong thing.
Where to start
If you are simply trying to work out whether the job is worth doing at all, read the cost guide first. It sets out what drives the price in London specifically — access, joist depth, the amount of old material that has to come out — and what a realistic payback period looks like at current energy prices.
If you are choosing between materials
The SuperQuilt versus mineral wool comparison is the one to read. The short version is that they are not really competitors: one is a thick, cheap, extremely effective floor-level insulator and the other is a thin, higher-priced product that solves a specific problem — depth. Which you need depends entirely on whether the loft is a room or a roof space.
If you are worried about damp
Read loft condensation and ventilation before you insulate anything. Adding insulation to a loft that is already condensing will make the condensation worse, not better, because you are making the roof space colder. That is a solvable problem, but it needs solving first, and it is the single most common thing we find on survey that the homeowner did not know about.
If you think you might qualify for help paying
The grants and funding guide explains how the main government schemes work, who tends to qualify, and — importantly — how to spot the scams that cluster around them. We are not a grant-funded installer, so we have no commercial reason to talk the schemes up or down.
A note on the numbers you will see online
Savings figures for loft insulation are national averages calculated on a standard, gas-heated, detached property. Your house is not that house. A mid-terrace with neighbours on both sides loses far less heat than a detached bungalow with the same roof area, and a heat-pump home behaves differently again. Treat every published saving figure — including the ones in these guides — as an order of magnitude rather than a promise.
The five mistakes we see most often
Almost every survey we carry out on a loft that has been insulated before turns up at least one of these. None of them are exotic, and all of them are avoidable.
- Insulation pushed hard into the eaves. It feels thorough. It blocks the only ventilation path the roof has, and it is the single most common cause of the damp that homeowners later blame on the insulation itself.
- Boards laid straight onto the joists. A 270mm layer compressed to 100mm performs roughly like a 100mm layer. The homeowner paid for the deeper number and is living with the shallower one.
- The hatch ignored. A metre-square uninsulated, un-draughtstripped panel in the middle of an otherwise sealed ceiling undoes a surprising amount of the work around it.
- Downlighters buried. Covering recessed lights with wool is both a fire risk and a route for warm, moist air to be driven straight into the roof space. They need clearance or proper fire hoods.
- The cold water tank insulated underneath. The warmth rising from the house is what stops it freezing. Insulate the sides and lid, never the base.
Why these guides exist
We write them because the alternative — homeowners making a four-figure decision on the basis of a doorstep pitch — produces exactly the sort of work described above. A customer who understands what they are buying asks better questions, gets a better installation and is less likely to be sold something they do not need. That is worth more to us over ten years than a few extra jobs sold to people who did not know any better.
In the loft
What the guides are about
Three of the situations these pages were written to explain.
Read enough? Book the survey
We will measure what is actually up there and give you real numbers for your roof, not an average for somebody else's.