RENOVATING OLD PROPERTIES: WHAT TO KNOW ABOUT SINGLE SKIN WALLS, INSULATION AND EPCS
Don’t panic.
If you’re looking at older properties to flip, chances are you’ll come across one with single skin walls—especially Victorian terraces.
If you’re looking at older properties to flip, chances are you’ll come across one with single skin walls—especially Victorian terraces.
Don’t panic.
This doesn’t automatically mean the property is un-mortgageable or a major problem.
I once had an estate agent tell me a house was “unmortgageable” because of single skin construction. But I knew the area—it was a row of Victorian railway cottages. And when I saw the property, it turned out to be exactly that: a typical Victorian mid-terrace, solid-walled, but not non-standard construction.
Here’s the important part:
Solid wall construction (with no cavity for insulation or damp protection) is the norm for most homes built before 1920.
These homes aren’t unusual. They’re everywhere, and they sell.
So why does this matter when flipping for profit?
Because insulation and EPC ratings now affect saleability and valuation.
And if you want your flip to be taken seriously, especially by mortgage buyers, you need to know what’s possible, what’s allowed, and what’s worth doing.
INSULATING SINGLE-SKIN WALLS
Improving insulation on a single skin property isn’t as complicated or scary as it sounds.
You’ve got two main options:
1. Internal Wall Insulation
This involves adding rigid boards or insulated stud walls inside the external walls.
Yes, you lose a bit of room depth, but in return, you gain:
Better EPC rating
Warmer rooms
Lower energy bills
Less outside noise
A smoother resale
2. External Wall Insulation
This means wrapping the outside of the house in insulation (mineral wool, rigid foam, or similar), then applying render or cladding.
It’s more noticeable and can affect the appearance of period properties, so it may not be suitable for listed buildings or conservation areas.
But be careful:
Insulation done badly can cause major issues.
So, make sure whoever installs it knows how to:
Handle vapour control properly
Avoid thermal bridging
Work around existing windows and finishes
CHOOSING INSULATION MATERIALS
When flipping, you’re always balancing cost, performance, and buyer appeal.
Here’s a quick breakdown:
Mineral Wool – High performance, fire-resistant, more expensive but reliable
Rigid Foam – Great for tight spaces, strong barrier against heat and moisture
Natural Fibres – Eco-friendly options like sheep’s wool or recycled cotton
Cellulose – Recycled newspaper, low cost, sustainable, but trickier to install
Tip: Even insulating one less-exposed wall can make a difference. Combine that with draught-proofing and smart heating controls, and you’ll see a boost in EPC and comfort.
WHY THIS MATTERS FOR FLIPPING
Legally, you can sell a house with a poor EPC.
But will it sell well? Not always.
Buyers today are more aware of running costs and efficiency.
According to government data, improving a home’s EPC can raise its value by up to 14%. That’s a figure worth remembering when planning your renovation budget.
You can read the full report here:
https://www.gov.uk/government/publications/an-investigation-of-the-effect-of-epcs-on-house-prices
THE BOTTOM LINE
If you're looking at a property with solid walls, don’t write it off.
Yes, it may need more thought around insulation and resale—but it could also be the kind of project where smart upgrades bring real profit.
Just make sure you renovate with clarity and purpose, not fear.
(And in case you’re wondering, that “unmortgageable” house I mentioned?
The real issue wasn’t the walls.
It was a missing fire break in the loft party wall - something fixable, and very common.)