Breaking the "Thickness Myth": Why 10mm Aerogel is the Only Viable Protocol for UK Heritage Retrofit

The UK retrofit industry is currently debating a critical question: "Space vs. Efficiency."

In a recent discussion with leading European building physicists and Retrofit Coordinators, we tackled the "150mm Strawman." The consensus is clear. Attempting to achieve Passivhaus U-values (0.15 W/m²K) using 150mm of Mineral Wool on a Victorian solid wall is not just impractical, it is architecturally destructive.

For Grade I & II listed buildings, or tight London terrace homes, we don't need thicker insulation. We need smarter density.

Here is the data-driven case for why 10mm Silica Aerogel is the calculated "Space-Age" solution for "Stone-Age" walls.

1. The Physics of Thickness: 10mm > 50mm

The first rule of Heritage Retrofit is simple: Don't steal the resident's floor space.

Traditional Rock Wool or Glass Wool relies on trapped air, requiring bulk to resist heat flow. Our latest lab testing (Report No. ZX240415-C111104) confirms that our Silica Aerogel Blanket operates on a different level of physics known as the Knudsen Effect.

• Aerogel Tested Thermal Conductivity (Lambda): 0.020 W/(m·K) (at 25°C)

• Traditional Mineral Wool Typical Lambda: ≈ 0.035 - 0.040 W/(m·K)

The Real Estate Reality:As Derek Forsyth rightly asked in our recent discussion regarding the "Total System Cost," we must look at asset value. In a city like London where property prices average £10,000 per sqm, losing 100mm of depth along a 10m wall costs the homeowner £10,000 in asset value. By using 10mm Aerogel to replace bulky PIR or wool, we are preserving the property's financial value.

2. Solving the "Dead Zone": The Window Reveal Strategy

As architect Patrick Osborne highlighted in our forum, the Window Reveal (Jamb) is the weak point of every retrofit. If you insulate the wall but leave the reveal bare due to lack of space, you create a severe Thermal Bridge.

This leads to "Radiation Asymmetry". The cold reveal (surface temp ~12°C) sucks heat from the body, creating a 50-80cm uncomfortable "Dead Zone" near the window where no one wants to sit.

The 22mm "Gold Standard" Solution:We have engineered a composite laminate specifically for this detail:

1. Core: 10mm Aerogel Blanket (High Tensile Strength: 1255 kPa).

2. Barrier: Integrated Aluminum Foil (Vapour Control Layer).

3. Finish: 9.5mm - 12.5mm Gypsum Board (or our PVC-faced board with surface resistance 5.2 x 10^8 Ohms).

Total Thickness: ~22mm.

This fits perfectly within standard Victorian window frame profiles, raising the surface temperature to 19°C and reclaiming the "Dead Zone" for comfortable living.

3. The "Gore-Tex" Effect: Managing Moisture Risk

Moisture accumulation is the "Silent Killer" of Internal Wall Insulation (IWI). This is where the Hydrophobic vs. Permeable paradox matters.

Our lab data confirms two critical characteristics of our Aerogel:

1. Hydrophobic Rate: 99.7% (GB/T 10299-2011). It repels liquid water. If the external brickwork leaks, the insulation will not become a soggy sponge.

2. Vapour Permeability: mu ≈ 5. It is highly breathable for water vapour.

Think of it like a Gore-Tex jacket for the house. It stops liquid water from entering the structure but allows the damp masonry to "breathe" and dry inwards. This eliminates the condensation risk that typically plagues impermeable foam retrofits.

Invitation to Collaborate:If you are a Retrofit Coordinator with access to dynamic simulation tools like WUFI, we welcome collaboration to validate these assemblies for specific UK climate zones. Contact us for our raw material data files.

4. Fire Safety: The Non-Negotiable A1 Standard

In the post-Grenfell era, combustible insulation is a liability.

While many PIR/PUR boards struggle to reach Class B, our inorganic Aerogel Blanket achieves Class A1 (Non-combustible).

• Sustained Burning Time: 0 seconds (Test result).

• Furnace Temperature Rise: Only 2°C.

• Combustion Calorific Value: 1.9 MJ/kg (Standard requires ≤2.0).

For Housing Associations and high-rise retrofits, this provides the ultimate peace of mind.

5. The Hidden Detail: Joist Ends

A common failure point raised by expert Roger Emmerson is the Joist End. When internal insulation is applied, the timber joist ends embedded in the cold wall can rot.

Because our Aerogel Blanket is flexible and ultra-thin (10mm), it can be carefully packed around the joist ends without requiring massive masonry surgery. This creates a thermal break that keeps the timber above the dew point, preserving the structural integrity of the floor.

Conclusion: A New Protocol

We must stop judging insulation by its thickness. In Heritage Retrofit, Less is More.

By utilizing material with Lambda = 0.020, we respect the architecture, protect the asset value, and ensure the health of the building fabric.

This article was inspired by a technical discussion on LinkedIn regarding the "Space vs. Efficiency" paradox. Special thanks to the industry experts who contributed valuable insights and challenged the status quo. [Read the original discussion here]

Ready to validate the data?

Don't just take our word for it.

1. Request a sample kit for your material library.

2. Test the 0.020 W/(m·K) against your own calculations.

3. Better yet—run it through your WUFI model. Then tell us if the data holds up.

[Request Your Sample Kit Here]