Overlaying a bitumen roof means we apply a fresh bitumen layer directly over the existing roof covering. This is possible when the substrate is dry and stable and not too many layers are already present. It is faster and more economical than full replacement, while improving insulation and waterproofing.
What does overlaying a bitumen roof mean?
Overlaying a bitumen roof means applying a completely new layer of bitumen over the existing roof covering, rather than removing the old roof first. The old layer stays in place and serves as the substrate for the new, waterproof top layer. This is the signature specialty of Dakservice van Belzen: we have applied it for years on flat roofs across North Holland and know exactly when it is, and when it is not, the right solution.
An overlay is a form of renovation, not an emergency repair. It is intended for roofs whose existing bitumen layer is reaching the end of its life, but where the structure underneath is still sound. In that case you give your roof many more years in a single job, without the cost and mess of a full replacement.
When can a roof be overlaid, and when not?
Not every roof qualifies. We always assess this first on site during a roof inspection. Three factors are decisive:
- The number of existing layers. A flat roof cannot carry an endless stack of layers. If two bitumen layers are already present, we usually advise against adding a third, because weight and adhesion then become a risk.
- The condition of the substrate. The existing layer must be firmly attached. Loose, blistered or powdery bitumen offers no proper adhesion and must first be repaired or removed.
- Moisture beneath the covering. This is the most important check. If moisture is trapped between the layers or in the insulation, you must never work over it: the moisture stays sealed in and causes blistering and later roof leaks. We check this carefully before we start.
If any of these points is not in order, we tell you honestly and recommend a partial or complete roof renovation. With us you are not a number; we only do what is technically responsible.
How does the overlay process work?
Our method follows fixed steps, so the result stays waterproof for years:
- Inspection and moisture measurement. We assess the substrate, count the existing layers and check for trapped moisture.
- Preparation. Loose sections, blisters and damage are repaired. The roof is cleaned and, where needed, treated with a bonding primer.
- Detailing. Upstands, roof edges, penetrations, skylights and connections are carefully prepared; this is exactly where most leaks otherwise begin.
- Applying the new layer. We torch or bond a new bitumen layer. For a durable result we often choose a double-layer system with a mineralised top layer.
- Finishing and inspection. All edges, seams and details are sealed watertight and the entire roof is checked.
What are the benefits of overlaying?
An overlay has clear advantages over a completely new roof:
| Aspect | Overlay | Full replacement |
|---|---|---|
| Project duration | Shorter | Longer |
| Demolition and disposal of old layer | Not needed | Needed |
| Disruption | Limited | Greater |
| Added insulation value | Possible | Possible |
| Suitable with ≥2 existing layers | Usually not | Always |
Because the old layer stays in place, there is no demolition or disposal of the old covering. That saves time, work and cost, and it adds an extra layer that improves insulation and waterproofing. For many flat roofs, an overlay is therefore the smartest choice. To learn more about the options for your type of roof, read our page on flat roofs and our article on bitumen, EPDM or PVC.
A real example: Pijnacker
In Pijnacker we overlaid a 615 m² flat roof with a double-layer mineralised bitumen system. The existing covering was still stable and dry, which made an overlay technically responsible. The result: a large roof made fully waterproof and well insulated again in a short time, without demolishing it for a completely new roof. You can see more of our work on our projects page.
Free quote
Whether an overlay is the right choice for your roof is something we can only say after we have seen it. That is why we come by for a roof inspection and then prepare a free, no-obligation quote. We respond within 2 hours via WhatsApp, and on our work we offer up to 15 years of warranty. Get in touch and we will gladly think along with you.
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Frequently asked questions
On a sound, dry substrate, an overlay is a full and durable solution that makes your roof waterproof again for many years, often with an added insulation benefit. It is simply not suitable when too many layers are already present or when moisture is trapped under the covering. That is why we always assess it first during a roof inspection.
In practice we usually work up to a maximum of two layers. If two layers are already present, we generally advise against adding a third, because the weight and adhesion then become unreliable. In that case a full replacement is the wiser choice.
With expert workmanship and a good substrate, a newly applied bitumen system lasts many years. On our roofing work we offer up to 15 years of warranty. The exact lifespan depends on the system, the detailing and the maintenance.
Overlaying is a bitumen technique for existing bitumen roofs. An EPDM roof requires a different approach. We are happy to come and see which solution suits your roof; also read our article on bitumen, EPDM or PVC for a comparison of the materials.