Minimum Paint LRV Requirements for Weatherboard Cladding
Key Lesson Learned
My chosen paint colour had an LRV of 30, which is too dark for weatherboard (timber) cladding. Many manufacturers and systems require a minimum LRV of 45 (some specify ≥40%).
What is LRV?
Light Reflectance Value (LRV) measures the percentage of visible light a painted surface reflects (scale: 0 = pure black/absorbs all light → 100 = pure white/reflects all light).
- Lower LRV = darker colour → absorbs more solar heat
- Higher LRV = lighter colour → reflects more heat
Why the Minimum LRV Requirement Exists
Dark colours on timber weatherboards absorb excessive heat → core timber temperature rises → problems include:
- Excessive timber movement / expansion & contraction
- Increased risk of resin bleed (especially in radiata pine / finger-jointed timber)
- Faster paint degradation, cracking, or peeling
- Potential voiding of product warranty / guarantee
Many pre-primed or treated timber weatherboard suppliers (e.g. common NZ/AU systems like EnviroPine, JSC, Niagara/Envira, OTC, etc.) explicitly state in their technical guidelines:
Use only paints with LRV ≥ 45% (and often gloss ≥10% for durability)
Some fibre-cement or insulated systems allow down to 40% or even 25% with special "CoolColour" technology, but standard timber weatherboards are stricter (usually 45%).
NZ Building Code Context
The NZBC itself does not mandate a specific LRV for timber cladding (it's not a direct code clause).
The minimum LRV requirements come from manufacturer specifications and product appraisals / warranties / CodeMark certifications.
Practical Takeaways for Future Projects
- Always check the specific cladding manufacturer's technical data sheet for LRV limits before selecting colour.
- LRV < 45 almost always disqualifies very dark / near-black shades on standard timber weatherboards.
- For darker looks, consider:
- Specialised timber products designed for low-LRV colours (e.g. thermally modified timber)
- "CoolColour" / infrared-reflective paint technology (still check if accepted by cladding supplier)
- Non-timber cladding options (some allow LRV 25–40%)
- Paint suppliers (e.g. Resene) publish LRV values for each colour — verify before purchase.
Personal note: My LRV 30 colour was rejected — next selection must be ≥45 LRV to stay within warranty and performance guidelines.