Leveling and sealing a bitumen roof

Hello everyone,

my house and the roof were built in 1991 and are therefore 34 years old. A small part of my roof surface is covered with bitumen sheets. The pitch angle is rather low, max. 2°. In addition, it is uneven, which causes standing puddles to form after rain.

When I bought the house two years ago, I quickly noticed that the bitumen roof is leaking. During heavy rainfalls, moisture penetrates into the underlying structure. A triple insulating coat last year provided temporary relief. Now in spring, the bitumen roof has become leaky again due to the frosty nights.

What would you recommend to provide a permanent solution? Is there something like a leveling compound for bitumen roofs that eliminates unevenness and at the same time seals the roof?

Since you are looking for a permanent solution and the roof obviously has a few problem areas (low slope, standing water, age of the bitumen membrane), you will probably not be happy with further coatings. Here are a few practical considerations:

If the roof is only minimally inclined (as you say: max. 2°), it is no longer a classic pitched roof but tends toward a flat roof. And here applies: standing water is always problematic in the long term, regardless of which coating or sealing is applied. Bitumen (especially old) can only handle this for a limited time, then there will be cracks, blisters, or it becomes brittle in frost.

You have two options:

Either reconstruction with slope compensation: You can apply slope insulation panels, for example, on such surfaces (usually made of EPS or PU), which create a functional slope. Then comes a new sealing – either classic multilayer bitumen or more modern: an EPDM or plastic membrane. This is more complex but technically clean and permanently tight.
Or liquid plastic: If you cannot or do not want to sacrifice build-up height, sealing with liquid plastic (e.g., Triflex, Kemperol, or comparable) would also be conceivable. This also compensates for small unevennesses somewhat; however, it does not replace proper slope correction. Advantage: permanently elastic, resistant to standing water (depending on the product), and easy to apply at edges, penetrations, etc.

It is important to really clean the surface thoroughly beforehand (remove moss, loose bitumen pieces, etc.) and use a suitable primer.

If you want peace of mind in the long term, honestly, I would not “paint around” again but rather renovate properly once, with functioning slope and permanent sealing.

Have you already obtained quotes or are you still in the exploratory phase?

Hello Lüftermax,

thank you for your response. I have already considered using liquid plastic. I have set my sights on MEM Wasserstop from Bauhaus.

I plan to get an offer for a proper renovation with a reasonable slope and substrate soon. If the offer is in the lower four-digit range, I will probably go for it. If it becomes too expensive, I will reconsider a coating with liquid plastic. If it lasts a few years, I would be satisfied, then I just have to do preventive repainting every few years.