SIP Panel U-Values Explained: Meeting UK Building Regulations 2025
U-values determine whether your building complies with UK Building Regulations. Understanding them is essential for anyone planning extensions, new builds, or garden rooms using SIP panels.
What Is a U-Value?
A U-value measures thermal performance in W/m²K (watts per square metre Kelvin). The principle is simple: lower values indicate better insulation and reduced heating costs.
U-Value Rating Scale
- 0.15 or less: Excellent
- 0.15-0.20: Very Good
- 0.20-0.30: Good
- 0.30-0.40: Adequate
- 0.40+: Poor
UK Building Regulations Part L 2021
The regulations specify maximum U-values for different building elements:
| Element | Maximum U-Value |
|---|---|
| Walls | ≤0.18 W/m²K |
| Roofs | ≤0.16-0.18 W/m²K |
| Floors | ≤0.18 W/m²K |
SIP Panel U-Value Specifications
| Panel Size | U-Value | Compliance |
|---|---|---|
| 72mm | 0.396 W/m²K | Non-compliant |
| 97mm | 0.264 W/m²K | Non-compliant |
| 122mm | 0.209 W/m²K | Borderline |
| 142mm | 0.179 W/m²K | Compliant |
| 172mm | 0.144 W/m²K | Exceeds requirements |
Garden Rooms and Building Regulations
Garden rooms under 15m² floor area and more than 1m from boundaries often fall outside full Building Regulations. However, we still recommend using properly insulated panels for comfort and energy efficiency.
Why Exceed Minimum Standards?
- Lower heating costs for the life of the building
- More comfortable internal environment
- Future-proofing against tightening regulations
- Higher property value
Frequently Asked Questions
Can I use 122mm panels for an extension?
Yes, but you may need to demonstrate compliance through a SAP calculation showing overall building performance.
What about thermal bridging?
Our PIR splines eliminate thermal bridging at panel joints, maintaining consistent U-values across the structure.