Why Rooflight Performance Matters: Air, Water & Wind Testing Explained
When Performance is a Priority, Have You Checked the Spec?
Choosing a rooflight isn’t just about aesthetics — it’s about performance. But understanding how a rooflight performs can be tricky, especially if you’re not an engineer or don’t read British Standards in your spare time.
What does something like ±2000 Pa serviceability actually mean? Do you even need a performance-tested rooflight for your project?
Let’s cut through the jargon and look at what really matters: weathertightness, which includes:
- Air Permeability
- Water Tightness
- Wind Resistance
1. Air Permeability: How Drafty Is Your Rooflight?
Ever felt a cold breeze through a poorly sealed door in an older house? That’s essentially what air permeability measures — how much air leaks through your rooflight when it’s shut.
How we test Air Permeability:
A full-size rooflight is sealed into a chamber. It’s then subjected to:
- A vacuum, simulating air being pulled into the building (positive pressure)
- A fan, simulating air being pushed out (negative pressure)
The result is a pressure rating, such as ±900 Pa. The higher the pressure a unit withstands without leaking, the better its performance.
Rooflights are also given a Class from 1 (worst) to 4 (best). Our Next Generation Rooflights Slide Over Fixed Rooflight, tested in April 2019, achieved Class 4 — the highest rating.
2. Water Tightness: Keeping the Rain Out!
Nobody wants to wake up to water dripping from the ceiling. Testing for watertightness ensures your rooflight won’t leak in heavy rain or under pressure from high winds.
How we test Air Watertightness:
The rooflight is soaked with water for 15 minutes using multiple nozzles
- A vacuum is applied while the water continues to flow
- When water finally penetrates, the test stops, and the product is graded based on the last pressure it withstood
Most high-quality rooflights achieve Class 8A or 9A (450 Pa to 600 Pa). If a product exceeds this, it’s classified using an E-rating, such as E1050.
Our sliding rooflights reached E1050 Pa, without failing — limited only by the test chamber’s capability!
3. Wind Resistance: Will Your Rooflight Stay Put in a Storm?
Rooflights must not only resist air and water but also withstand extreme winds without breaking or flying off.
There are two key wind resistance tests:
a) Serviceability Test
This simulates repeated wind gusts, applying both high positive and negative pressures. It measures how much the rooflight bends or flexes (deflection).
- Class C = best deflection performance
- Class 5 = highest pressure tested
b) Safety Test
This test ignores deflection and focuses on structural integrity under extreme, short bursts of pressure.
We tested our units to ±3000 Pa, equivalent to wind gusts of around 156 mph. That’s peace of mind.
4. Why Does These Tests Matter?
Air Permeability, Weathertightness and Wind Resistance aren’t “nice-to-haves” for your Rooflight – they are essential.
- Poor Air Permeability = heat loss + higher energy bills
- Poor Water Tightness = damage, stress, and expensive repairs
- Poor Wind Resistance = safety risks
We go above and beyond with our testing because you deserve a rooflight that performs in real-world conditions, not just on paper.
Remember Not ALL Rooflights Are Tested — So Always Ask!
Unfortunately, not every rooflight on the market — even from big-name suppliers — undergoes our rigorous performance testing.
At Next Generation Rooflights, we test every major product line. We believe that when you’re installing glass and metal above your head, safety and performance should be non-negotiable.
Ask this one key question before you buy:
“What is the weathertightness performance of this rooflight?”
If the answer isn’t clear — or the supplier says, “We’ve been doing this for years” — it’s time to think again.
Speak to our Trusted Advisors
If you need help choosing a fully tested rooflight for your project, get in touch with one of team of trusted advisors who specialise in helping architects and contractors specify the right rooflight solutions for both commercial and high-end residential projects.
You can call us on 01223 792 244 or email us at [email protected]