How to improve airtightness in older homes without causing damp issues

Airtightness is one of the most overlooked — yet essential — aspects of energy efficiency. While most people focus on insulation or heating systems, airtightness plays a critical role in reducing heat loss, improving comfort, and lowering energy bills. But in older UK homes, especially those built before 1919 with traditional solid wall construction, improving airtightness can be a delicate balancing act.

Do it wrong, and you risk condensation, mould, and even structural damage. Do it right, and you’ll have a warmer, healthier, and more efficient home.

So how do you improve airtightness in a traditional home without introducing damp problems? Let’s break it down.

Why Airtightness Matters

Airtightness refers to how well a building prevents uncontrolled air leakage through gaps, cracks, and holes in the building envelope. In older homes, these gaps are everywhere — under skirting boards, around doors and windows, through floorboards, chimneys, and service penetrations.

Uncontrolled airflow:

• Wastes heat (and money)

• Causes draughts and discomfort

• Pulls moist air into cold spaces, increasing condensation risk

  
  

That’s why improving airtightness is a key part of whole-house retrofit strategies. But older homes were never designed to be airtight — and sealing them up without proper planning can cause serious issues.

The Risk: Moisture & Damp

Traditional buildings are typically made from moisture-permeable materials like lime mortar, stone, or solid brick. These homes “breathe” — they allow moisture to pass through the structure, gradually drying out.

If you make a home more airtight without adding ventilation or moisture control, you can trap warm, moist air inside. This air condenses on cold surfaces, leading to:

• Black mould in corners and behind furniture

• Condensation on windows

• Timber decay and plaster damage

  
  

The key is to improve airtightness in tandem with proper ventilation and moisture management.

How to Improve Airtightness the Right Way

1. Start with a Whole-House Assessment

A Retrofit Assessor can evaluate the building and identify key areas of air leakage. This might include:

• Around loft hatches

• Floorboard gaps

• Window and door frames

• Service penetrations (pipes, wiring, extractor fans)

They’ll also check the condition of the building fabric, existing insulation, and ventilation systems.

2. Seal Gaps — But Selectively

Focus on sealing areas that contribute to heat loss without blocking necessary airflow. Consider:

• Draught-proofing doors and windows with brush seals or foam strips

• Caulking or mastic around skirting boards and architraves

• Air-tightness tapes or grommets around pipes and cables

• Chimney balloons or covers (only if not in use)

Avoid sealing off vents or breathable airbricks unless they’re being replaced by a mechanical system.

3. Use Breathable Materials Where Needed

In older buildings, avoid using vapour barriers or impermeable materials that could trap moisture. Instead, opt for:

• Lime plaster instead of gypsum

• Breathable insulation (like wood fibre, hemp, or mineral wool)

• Vapour-open airtightness membranes in roof spaces or walls

These allow moisture to migrate out of the building gradually while still reducing unwanted draughts.

4. Pair Airtightness with Adequate Ventilation

This is non-negotiable. As you reduce draughts, you must introduce controlled ventilation to replace the airflow you’re removing. That could mean:

• Background ventilation via trickle vents or air bricks

• Mechanical Extract Ventilation (MEV) in wet rooms

• Positive Input Ventilation (PIV) systems for whole-house air movement

• MVHR (Mechanical Ventilation with Heat Recovery) in airtight or deep retrofit homes

Your ventilation strategy should align with Building Regulations Part F and PAS 2035 guidance.

5. Test and Adjust

Consider an air pressure test (blower door test) to measure the building’s airtightness before and after work. This helps identify remaining problem areas and ensures the building remains safe and functional.

Final Thoughts

Improving airtightness in older homes doesn’t mean turning them into sealed boxes. It’s about carefully managing the flow of air and moisture to create a home that is warm, dry, and efficient.

At Target Green, we specialise in PAS 2035:2023 compliant retrofit design that balances insulation, ventilation, and airtightness, especially in heritage and traditional properties.

Thinking of making your home more energy efficient? Get in touch for expert advice and a free consultation.