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Green Home Improvements: Why “Fabric First” is the Only Way
Green Home Improvements: Why “Fabric First” is the Only Way
📌 The “Fabric First” Rule
- Order Matters: Insulate first, generate later. Installing a Heat Pump in a draughty home is throwing money away.
- The Weakest Link: Windows are typically the poorest insulated part of a home (5x worse than a solid wall).
- The Goal: Reduce your home’s energy demand before buying expensive eco-tech like Solar or Heat Pumps.
The UK is in the middle of a green renovation boom. Homeowners are rushing to install Heat Pumps, Solar Panels, and Battery Storage systems. While this enthusiasm is fantastic, many people are doing it in the wrong order.
At KJM Group, we advocate for the “Fabric First” approach. This simple engineering principle states that before you change how you heat your home, you must first minimize the heat you lose.
Table of Contents
1. What is “Fabric First”?
Imagine trying to fill a bucket with water that has holes in the bottom. You have two choices: turn the tap on harder (install a bigger heating system), or plug the holes (insulate the fabric).
“Fabric First” prioritises the structural envelope of your home—walls, roof, windows, and doors—over “bolt-on” technologies.
2. The Heat Pump “Efficiency Trap”
Air Source Heat Pumps (ASHPs) are fantastic technology, but they operate differently from gas boilers. A gas boiler blasts out heat at 70°C. A heat pump operates most efficiently at a steady, low flow temperature of 35°C – 45°C.
⚠️ Why Draughts Kill Efficiency
If your windows have a high U-value (poor insulation) or draughty seals, this low-grade heat escapes faster than the pump can replenish it. The pump then has to work overdrive, running on high-power electricity to boost the temperature. This can result in higher bills than your old gas boiler.
3. Where is Your Heat Going? (The Data)
It is easy to assume “my walls are cold,” but the data shows that glass is often the biggest offender. Here is how the thermal performance (U-Value) of different parts of your home compares. Remember: Lower is Better.
Thermal Weak Points (U-Values)
Solid Brick
~2.1 W/m²K
Insulated Cavity
~0.3 W/m²K
Verdict
Insulation works wonders.
Single Glazing
~5.8 W/m²K
Old Double Glazing
~2.8 W/m²K
Verdict
Major Heat Leak.
Modern A-Rated
~1.2 W/m²K
Triple Glazing
~0.8 W/m²K
Verdict
Heat Pump Ready.
4. The Green Renovation Roadmap
If you have a limited budget, what should you do first? Here is the KJM recommended order of works for maximum ROI.
- Phase 1: Draft Proofing & Windows. Replace blown units or upgrade to Triple Glazing. Seal the envelope.
- Phase 2: Insulation. Loft insulation (270mm+) and cavity wall insulation.
- Phase 3: Ventilation. Ensure you have trickle vents or PIV systems to manage moisture (see below).
- Phase 4: Heat Source. Only now should you install a Heat Pump or Solar PV.
5. Don’t Forget Ventilation!
There is an old builder’s saying: “Build tight, ventilate right.”
If you seal up all the draughts with new windows and insulation but don’t provide controlled ventilation, you will trap moisture. This leads to black mould and poor air quality.
All new KJM windows come with discreet Trickle Vents as standard (compliant with Part F Building Regulations). These allow stale, damp air to escape without letting all your heat out, keeping your fabric-first home healthy.
📚 Related Green Guides
- Finance: Can New Windows Lower Your Mortgage Rate?
- The Science: Understanding U-Values & Energy Ratings
- Product: Explore our Triple Glazing Range
6. Frequently Asked Questions
Always windows. Reducing the amount of energy you need (by insulating) is cheaper than generating energy yourself. Once your home is sealed and efficient, you can install a smaller, cheaper solar/battery system because your demand is lower.
No, provided you choose the right glass. Modern triple glazing keeps heat in during winter but can be specified with Solar Control coatings to keep heat out during summer. Read our U-Value Guide for more on this.
Currently, widespread grants for windows are limited to specific low-income schemes (like ECO4). However, many mortgage lenders offer “Green Additional Borrowing” at 0% or low interest to fund energy efficiency improvements like glazing.
Mark Pearce is a highly experienced specialist in the double glazing industry, having built his knowledge from the ground up through hands-on experience in installation, manufacturing, sales, and business management. Beyond his role at KJM, Mark is a keen blogger, writer, and traveller, often sharing insights on the latest innovations in the home improvement industry.
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