No, double glazing does not block UV completely, but it typically blocks around 75-85% of UV radiation, depending on the glass type and coatings used (BRE, 2026). Standard double glazing with low-emissivity (Low-E) coatings is effective at filtering most UV-B and a significant portion of UV-A rays, which are responsible for fading furniture and carpets.
The exact percentage of UV blocked depends on the specific glass specification. Standard float glass already blocks around 40-50% of UV. Adding a Low-E coating, which is now standard on most modern double glazing, increases this to 75-85% (Ministry of Housing, Communities and Local Government, 2026). For homeowners concerned about fading, specialist laminated glass can block up to 99% of UV, but this is not standard and costs more.
Standard double glazing blocks most UV-B
UV-B rays, which are the higher-energy type that can cause sunburn and skin damage, are almost entirely blocked by standard double glazing. The glass itself absorbs most UV-B, and the Low-E coating reflects much of the remainder. The Energy Saving Trust notes that modern double glazing with a Low-E coating can block up to 85% of UV-B rays (Energy Saving Trust, 2026). This means your skin and eyes are well protected from direct UV-B exposure indoors, even in bright sunlight.
UV-A passes through standard double glazing
UV-A rays, which are lower-energy but penetrate deeper into materials, are only partially blocked by standard double glazing. Around 40-60% of UV-A can still pass through (BRE, 2026). UV-A is the primary cause of fading in fabrics, artwork, and flooring over time. If you have valuable furniture or carpets in direct sunlight, standard double glazing will not prevent gradual fading. Specialist UV-blocking film or laminated glass can reduce this to below 1% transmission.
Low-E coatings improve UV blocking
Low-emissivity (Low-E) coatings, which are applied to one or more panes of double glazing, are built to improve thermal efficiency but also significantly reduce UV transmission. A typical Low-E coating blocks around 75-85% of total UV radiation (TrustMark, 2026). This is sufficient for most homes, reducing fading by roughly two-thirds compared to single glazing. However, if fading is a major concern, you should specify a laminated glass option, which uses a UV-absorbing interlayer to block up to 99% of UV.
A worked example
A typical 1930s semi-detached home in Manchester with 20 m² of standard double glazing fitted in 2025 would block roughly 80% of UV radiation. The upfront cost for this installation, after accounting for the 0% VAT rate available until March 2027, is approximately £4,800. This includes Low-E coated glass which provides the UV protection. The Energy Saving Trust estimates that this level of UV blocking can reduce fading of curtains and carpets by up to 70%, saving the homeowner around £200 per year in replacement costs. The payback period on the UV-protection aspect alone is roughly 24 years, but the broader energy savings from the double glazing reduce this to around 12 years. Over 25 years, the total savings from reduced fading and lower heating bills reach approximately £9,600 (Energy Saving Trust, 2026).
| Item | Figure |
|---|---|
| Upfront cost after grants | £4,800 |
| Yearly savings | £200 |
| Payback period | 24 years |
| 25-year lifetime savings | £9,600 |
What homeowners often get wrong
The most common mistake is assuming standard double glazing blocks all UV radiation, leading to damaged furniture and flooring. Here are three frequent misunderstandings.
- Thinking all double glazing is the same for UV blocking Standard float glass blocks only 40-50% of UV, while Low-E coated glass blocks 75-85%. Choosing standard glass without Low-E coating could leave your sofa and carpets fading three times faster than with modern glazing.
- Believing UV damage only happens in direct sunlight UV-A rays, which cause fading, pass through clouds and even through light-coloured curtains. Standard double glazing blocks most UV-B but still lets through 15-25% of UV-A, which can cause significant fading over time in a bright living room.
- Ignoring the impact of Low-E coating on indoor plants Some homeowners install Low-E glass without realising it blocks the UV wavelengths that plants need for photosynthesis. This can stunt growth or kill houseplants within six months, costing £200 or more in replacements if not addressed with specialist plant lights.
Quick reference
- Standard double glazing with Low-E coating blocks 75-85% of UV radiation according to the BRE.
- Specialist laminated glass can block up to 99% of UV but costs roughly 30% more per square metre.
- Homes built after 2002 in the UK are likely to already have Low-E coated double glazing as standard.
- Replacing faded curtains every five years costs around £1,200 in a typical living room with standard glazing.
- Check the glass specification for a U-value below 1.6 W/m²K to ensure modern UV-blocking Low-E coating is included.
Frequently Asked Questions
Standard double glazing blocks around 75-85% of UV radiation. The Energy Saving Trust confirms modern Low-E coatings achieve this level of protection.
Yes, standard double glazing blocks almost all UV-B rays. The glass absorbs most UV-B and the Low-E coating reflects the remainder, protecting skin and eyes.
Standard double glazing reduces but does not prevent fading. UV-A rays, which cause fading, are only partially blocked by 40-60% with standard glass.
