How long does a roof membrane last?
This is the question we get the most, and it is also the hardest to answer briefly. A roof membrane does not last a certain number of years, it lasts as long as the substrate and application allow. Here is what the two numbers on the bucket mean, and what in practice determines whether you hit one or the other.
The two numbers and the difference between them
Luna Roof roof membrane has 25-year product warranty and one lifespan of up to 40 years when applied correctly. These are not two ways of saying the same thing.
- The guarantee covers the product. It states that the membrane will not fail on its own within the 25 years.
- Lifespan is what the membrane can actually withstand on a roof, and it depends on the roof it is on and how it was laid.
A roof that was dry and clean when the membrane was applied, and where enough material was used, is at the high end. A roof where the amount was skimped on, or where there was moisture on the surface, is not.
What wears down a roof membrane?
Three things work on the roof all year round:
- UV. Sunlight degrades most roofing materials over time. The membrane has enhanced UV protection, and this is the property that contributes most to the lifespan of a flat roof where the sun shines directly on the surface.
- Temperature change. The roof expands and contracts every day. The membrane is resistant from minus 40 to plus 90 degrees and remains elastic, so it follows instead of cracking.
- Water that remains. A flat roof always has depressions. Because the membrane is seamless, there are no joints for water to work its way into, and this is the difference that matters most compared to sheets and tiles.
It's the substrate that determines the rest.
The membrane is never better than what it is stuck to. The mistakes we see repeated are the same every time:
- The roof was not completely dry. Moisture on the surface means that the membrane can come off, and then the work will have to be redone.
- Too little was used. Consumption is approximately 1.5 kg per m², and a layer that is too thin will not last 40 years regardless of what is written on the bucket.
- Joints, flashings and edges were treated like the rest of the surface. These are the places where the roof leaks first and need extra.
How to keep an eye on it
Check the roof once a year, preferably in the fall before winter. You look for three things: whether water remains for a long time after rain, whether there are cracks or holes in flashings and penetrations, and whether the surface feels hard and brittle instead of elastic.
If you find something, it can be fixed. The membrane is seamless, so you can apply a new layer on top of the old one without tearing anything off. It's the same reason a roof can be extended again in 20 years instead of being re-laid.
What you need for your own roof
A 20 kg bucket covers up to 13.3 m² in one layer, so a 100 m² roof corresponds to 8 buckets. The membrane can be laid directly on top of roofing felt, eternit, concrete, slate, zinc, roofing foil, metal and wood, so in most cases nothing needs to be torn off first.