When in the year can you apply roof membrane?
The question we get most often during late summer is the same every year: can I make it this year, or should I wait until spring? The answer doesn't depend on the calendar, but on three things you can check yourself before you go up to the roof.
The three requirements, in brief
- The roof must be dry, not just dry on the surface
- It should remain dry throughout the drying period.
- The temperature must be above 5 degrees
If all three are met, it doesn't matter whether it's May or October. If just one of them is missing, you have to wait, no matter how nice the weather forecast looks that day.
Therefore, late summer is the best period
August and September are usually the best window in Denmark. The days are still long enough for the membrane to dry before evening, and the humidity is lower than in early spring, when the roof may be dry to the touch and still have moisture lying on the surface.
From mid-October it becomes difficult. Not because it is too cold during the day, but because the nights are. If the temperature drops below 5 degrees at night, or if dew forms on the roof before the membrane is dry, you have spent a day and a bucket for nothing.
How to read the weather forecast correctly
Don't just look at the daytime temperature. What you need is:
- Night temperature the next few days, not just today's highest
- Precipitation throughout the drying time, not just while you are working
- Whether the roof has been wet the previous days. A flat roof with roofing felt retains water in joints and depressions long after it appears dry
If you are unsure whether the roof is dry enough, wait an extra day. The membrane adheres to a dry surface and will stay in place for decades. If you apply it to dampness, it may come off and the work will have to be redone.
If you don't make it this year
A leaky roof can't wait until April. If you have an active leak, temporarily seal it and make the right seal when the weather permits. It's better than applying the membrane to a damp roof in November and having to do it all over again.
If the roof just needs maintenance, and there is no water inside, it costs nothing to wait for the right window.
How much do you need?
A 20 kg bucket covers up to 13.3 m² in one layer, so a roof of 100 m² corresponds to 8 buckets. You can enter your m² on the product page and see the price immediately.