Retrofitting Historic Homes: A Guide to Preventing Damp and Mould

Modernising an old house sounds simple… until you end up with black mould behind the wardrobe.

Older homes were built differently, which means that they need a different approach to retrofit. If you don’t consider the whole building, your well-meaning upgrade could cause lasting damage.

Why can retrofitting go wrong in older homes?

Traditional homes (typically pre-1919) were designed to breathe.

Materials like lime render and solid brick allowed moisture to pass through and evaporate. These homes weren’t airtight, but they rarely suffered from damp in the same way modern buildings do.

That delicate balance is easily disrupted. If you block the air flow, add insulation without ventilation, or use impermeable materials, moisture can quickly become trapped inside the building. This trapped moisture builds up as condensation. Over time, it leads to damp patches, mould growth, and eventually timber rot.

What did people do before insulation?

Before modern insulation, houses were designed to keep specific areas warm: thick curtains, timber shutters, internal doors, and canopy beds. These helped create heat zones and trap warmth where it mattered most.

It wasn’t energy efficient by today’s standards, but it worked in harmony with the building fabric.

Modern standards of living demand more. Thanks to advances in technology, we now expect our entire home to be warm, not just the bed. Most of us don’t have the time, or the staff, to stoke fires, boil water for a fortnightly bath, or pre-warm the sheets with a coal-filled bedpan. And even if we did, the health and safety risks alone would rule it out.

We also don’t accept having to go to bed simply because the rest of the house is too cold to sit in. Instead, we’re used to heating that works at the push of a button, hot water on demand, and a consistent temperature from room to room. That level of comfort has become the baseline. For historic homes to remain liveable, they need to adapt to meet it. Nobody should need to don a Wee Willie Winkie-style nightcap just to stay warm in the 21st century.

How can heritage glazing help?

Upgrading to energy-efficient glazing can make a real difference if you choose the right product.

Our Heritage Range offers outstanding thermal performance while preserving the authentic look of period windows. Whole window U-values range from 1.09 W/m²K for sliding sash windows to 1.06 W/m²K for flush casements. Heritage doors in the range achieve values as low as 1.03 W/m²K. This means lower energy bills, greater comfort, and no compromise on appearance.

Although trickle ventilation is not required for heritage windows under current building regulations, we offer a discreet alternative. Our concealed trickle vents are available as an option across the Heritage Range. They provide additional airflow where needed, without affecting the appearance of the window.

In some cases, it is also possible to retrofit vacuum glazing into existing timber frames. This improves insulation while retaining the original joinery and historic features.

Even so, glazing alone cannot deliver a successful retrofit. Without other complementary measures, the building may still be at risk.

What other retrofit measures should you consider?

A successful retrofit isn’t just a checklist. It’s about how each change interacts with the rest of the building. Treat one area in isolation, and you risk damaging another.

Here are key areas to think about, along with practical examples of how to get them right.

Ventilation

When you insulate or seal up draughts, you reduce air movement. That sounds helpful, but without proper ventilation, it can trap moisture indoors and cause condensation on walls, windows, and floors.

What to do instead:

  • Install mechanical ventilation with heat recovery (MVHR) where possible, especially in airtight homes
  • In smaller projects, consider humidity-controlled extractor fans in kitchens and bathrooms
  • Don’t block traditional air bricks or chimney flues unless you’ve provided alternative ventilation

Moisture management

Older buildings rely on moisture vapour moving in and out through the walls. Sealing them with cement render, plastic paints or non-breathable insulation can trap that moisture inside the wall, leading to damp and rot.

What to do instead:

  • Use lime plaster, clay paints, and natural insulation such as wood fibre or sheep’s wool
  • For internal insulation, avoid foil-backed boards and choose breathable systems
  • Maintain good external drainage, including gutters, soakaways, and using soft landscaping where possible

Insulation

Insulating a historic home can be hugely beneficial, but it must suit the wall and roof type. If done poorly, it can create thermal bridges or trap moisture.

What to do instead:

  • For solid brick or stone walls, internal wall insulation is often appropriate, using breathable materials to avoid damp
  • For timber-framed buildings, external insulation may be safer and helps preserve internal features
  • In the roof, allow ventilation between rafters. Avoid sealing the loft completely, which can lead to timber decay

Heating systems

Old homes weren’t designed for central heating, let alone underfloor systems or heat pumps. That doesn’t mean they can’t be used, but they do need careful planning.

What to do instead:

  • If using a heat pump, make sure your home is well insulated and adapt radiator sizes or layout
  • Zone your heating to control temperatures in different rooms and reduce energy use
  • Review radiator placement, especially if upgrading the glazing, to avoid unnecessary heat loss

What tools can help guide your retrofit?

Before starting any work, we recommend using the Responsible Retrofit Guidance Wheel.

This free tool from the Sustainable Traditional Buildings Alliance (STBA) helps you:

  • Understand how retrofit measures interact
  • Identify potential risks like trapped moisture or structural damage
  • Balance thermal upgrades with heritage protection

It’s a practical resource for homeowners, designers, and professionals working with older buildings.

Retrofitting done right

Retrofitting a historic home isn’t about applying modern upgrades at random. It’s about understanding the building’s history, structure, and materials. Then choosing solutions that support and protect them.

With a thoughtful approach, you can make your home warmer, healthier, and more efficient. And you can do it without sacrificing what makes it special.