Hello house building experts,
I have been silently following for some time and would like to ask my first question.
We are currently planning a two-story house with a shed roof. The roof will cover a base area of 10.75m x 8.40m (35.3 ft x 27.6 ft) plus a 1.0m (3.3 ft) continuous roof overhang, resulting in a total roof area of 130 m² (1,399 sq ft). The roof is oriented approximately 10 degrees to the south, sloping upwards toward the north, and will be constructed as an insulated roof without an additional intermediate ceiling or attic space. Our structural engineer has designed the roof with bitumen roofing membranes covered by slates. His reasons are the low costs and the reduced noise during rain compared to metal roofing. However, we are now questioning whether bitumen membranes make sense in terms of durability.
We are also planning a photovoltaic system, and ideally the roofing should last at least as long as the solar panel system so that replacement can be done simultaneously. Flat roofs are often made with bitumen membranes, so what are the arguments against using it here? Is bitumen an unsuitable substrate for photovoltaic systems? What do the experts recommend?
- Bitumen membrane as currently planned
- Synthetic membrane/EPDM membrane (I was recommended the Alwitra membrane)
- Metal roofing (corrugated or standing seam?)
- Tile roofing (probably not practical given the low roof slope)
Like most homeowners, we are of course very concerned about not having excessively high construction costs due to the current price increases.
Best regards,
Kevin
I have been silently following for some time and would like to ask my first question.
We are currently planning a two-story house with a shed roof. The roof will cover a base area of 10.75m x 8.40m (35.3 ft x 27.6 ft) plus a 1.0m (3.3 ft) continuous roof overhang, resulting in a total roof area of 130 m² (1,399 sq ft). The roof is oriented approximately 10 degrees to the south, sloping upwards toward the north, and will be constructed as an insulated roof without an additional intermediate ceiling or attic space. Our structural engineer has designed the roof with bitumen roofing membranes covered by slates. His reasons are the low costs and the reduced noise during rain compared to metal roofing. However, we are now questioning whether bitumen membranes make sense in terms of durability.
We are also planning a photovoltaic system, and ideally the roofing should last at least as long as the solar panel system so that replacement can be done simultaneously. Flat roofs are often made with bitumen membranes, so what are the arguments against using it here? Is bitumen an unsuitable substrate for photovoltaic systems? What do the experts recommend?
- Bitumen membrane as currently planned
- Synthetic membrane/EPDM membrane (I was recommended the Alwitra membrane)
- Metal roofing (corrugated or standing seam?)
- Tile roofing (probably not practical given the low roof slope)
Like most homeowners, we are of course very concerned about not having excessively high construction costs due to the current price increases.
Best regards,
Kevin
Kevke93 schrieb:
- Plastic sheeting/EPDM membrane (I was recommended the Alwitra membrane)
I installed this on a flat garage roof with a very slight slope of about 1° (degree). I can definitely recommend it; so far, I haven’t heard of anyone having issues with it. If I remember correctly, it comes with a 50-year warranty.
The membrane was fully glued over the wooden decking.
H
Hausbau e.K.14 Apr 2022 13:47With an 8° roof pitch, I can only recommend a flat roof waterproofing system.
As with all bitumen membranes, there are different quality levels. The lowest quality is the PYE used as a top layer. After about 10 years, cracks often appear or the mineral granules start to detach. This is related to the quality of the bitumen.
High-quality membranes from manufacturers have no problem lasting several decades. This is also reflected in the product warranties offered by the manufacturers. The standard system usually comes with a 5-year warranty, while high-quality systems offer 10 years. Of course, a high-quality top layer costs about €5 more per square meter (approximately $5 per square yard), but considering the lifespan, this is a small price to pay.
The situation is similar with plastic membranes. PVC is the lowest standard. FPO or EVA membranes are significantly higher quality as they use different plastics. However, plastic membranes can have issues with plasticizers. UV radiation can cause these to escape, leading to cracks. This happens especially often with PVC membranes.
Another important point: PVC membranes are installed in a single layer, usually with a thickness of 1.5–1.8 mm (0.06–0.07 inches). However, about one-third of this is filler material, so the actual waterproofing layer is reduced to 1.0 to 1.3 mm (0.04–0.05 inches).
Bitumen membranes are installed in two layers. The first layer is 3 or 4 mm (0.12–0.16 inches) depending on the build-up, and the top layer is 5 mm (0.20 inches). This results in 8–9 mm (0.31–0.35 inches) of waterproofing across two layers. Using two layers also minimizes the risk of a leaking seam, as there is an additional protective layer.
A bituminous build-up requires applying two layers, which means higher labor costs.
Plastic waterproofing requires only one layer and fewer joints, which reduces labor costs.
From an expert’s point of view, in this case I would recommend a two-layer high-quality bituminous waterproofing system.
The 7° roof from Braas is an interesting idea, but it is only approved with Braas system components. Because it is system-approved, the costs should not be underestimated.
If you have any questions, feel free to ask.
Greetings from Cologne
As with all bitumen membranes, there are different quality levels. The lowest quality is the PYE used as a top layer. After about 10 years, cracks often appear or the mineral granules start to detach. This is related to the quality of the bitumen.
High-quality membranes from manufacturers have no problem lasting several decades. This is also reflected in the product warranties offered by the manufacturers. The standard system usually comes with a 5-year warranty, while high-quality systems offer 10 years. Of course, a high-quality top layer costs about €5 more per square meter (approximately $5 per square yard), but considering the lifespan, this is a small price to pay.
The situation is similar with plastic membranes. PVC is the lowest standard. FPO or EVA membranes are significantly higher quality as they use different plastics. However, plastic membranes can have issues with plasticizers. UV radiation can cause these to escape, leading to cracks. This happens especially often with PVC membranes.
Another important point: PVC membranes are installed in a single layer, usually with a thickness of 1.5–1.8 mm (0.06–0.07 inches). However, about one-third of this is filler material, so the actual waterproofing layer is reduced to 1.0 to 1.3 mm (0.04–0.05 inches).
Bitumen membranes are installed in two layers. The first layer is 3 or 4 mm (0.12–0.16 inches) depending on the build-up, and the top layer is 5 mm (0.20 inches). This results in 8–9 mm (0.31–0.35 inches) of waterproofing across two layers. Using two layers also minimizes the risk of a leaking seam, as there is an additional protective layer.
A bituminous build-up requires applying two layers, which means higher labor costs.
Plastic waterproofing requires only one layer and fewer joints, which reduces labor costs.
From an expert’s point of view, in this case I would recommend a two-layer high-quality bituminous waterproofing system.
The 7° roof from Braas is an interesting idea, but it is only approved with Braas system components. Because it is system-approved, the costs should not be underestimated.
If you have any questions, feel free to ask.
Greetings from Cologne
TmMike_2 schrieb:
I installed it on a garage flat roof with very little slope, maybe 1°.
I can only recommend it; so far, I haven’t heard of anyone having problems with it. I mean, there’s a 50-year warranty?
The membrane is fully glued to the tongue-and-groove decking. Did you use some type of membrane or exactly this membrane (Alwitra)? A 50-year warranty sounds very interesting. The only remaining question is how the photovoltaic system is attached.
lastdrop schrieb:
Roof tiles on such low-sloped roofs are basically just decoration and protection. In any case, a waterproof underlay is required, as I have read several times as a layperson.
I really like double standing seam metal roofing. It’s built to last forever. Probably, tiles really just mean extra costs without added value.
Hausbau e.K. schrieb:
For an 8° roof pitch, I can only recommend a flat roof waterproofing membrane.
With bitumen sheets, as with everything, there are different quality levels. The lowest tier is the PYE as the top layer. Often after about 10 years, cracks appear or the mineral granule layer slips off. This is related to the quality of the bitumen.
With the premium sheets from manufacturers, a lifespan of several decades is no problem. This is also reflected in the product warranty given by manufacturers. The standard build usually has a 5-year warranty, while the premium build has a 10-year warranty. Of course, a premium top layer costs about 5€ more per square meter (around 0.50 USD), but compared to the lifespan, this is a small price to pay.
It’s similar with plastic membranes. PVC is the lowest standard. FPO or EVA membranes are clearly higher quality because they use different plastics. However, plastic membranes can have issues with plasticizers. UV radiation can cause these to evaporate, which can lead to cracks. This especially happens with PVC membranes.
What you should also know: PVC membranes are installed in a single layer. Usually, they are 1.5–1.8 mm (0.06–0.07 inches) thick. About one-third of this thickness is filler, so the actual waterproofing layer is reduced to 1.0 to 1.3 mm (0.04–0.05 inches).
Bitumen sheets are applied in two layers. The first layer is 3 or 4 mm (0.12–0.16 inches), depending on the build, and the top layer is 5 mm (0.2 inches). So, with bitumen, you get 8–9 mm (0.3–0.35 inches) of waterproofing in two layers. Using two layers also reduces the risk of leaks at seams because there is an additional protective layer.
With bituminous waterproofing, two layers must be applied = higher labor costs.
With plastic membranes, a single layer is applied with fewer seams = lower labor costs.
From an expert’s point of view, I would recommend a two-layer premium bitumen waterproofing in this case.
The 7° roof pitch from Braas is an interesting idea but only approved with Braas system components. Since it is only approved as a system, the costs should not be underestimated.
Feel free to ask if you have any questions.
Regards from Cologne Thank you very much for this very detailed answer! This makes me lean more and more towards bitumen sheets.
You mention a possible lifespan of several decades for bituminous waterproofing but then product warranties of 5 or 10 years. How do these fit together? Even compared to the previously mentioned 50-year warranty for Alwitra, that would rather speak in favor of a membrane waterproofing, wouldn't it?
H
Hausbau e.K.19 Apr 2022 15:00Kevke93 schrieb:
Thank you very much for this very detailed answer! It definitely makes the option of bitumen membranes more attractive.
You mention a possible lifespan of several decades for a bituminous waterproofing, but then you refer to product warranties of 5 or 10 years. How does that fit together? Even when I compare that to the 50-year product warranty mentioned earlier for Alwitra, wouldn’t that rather favor a membrane waterproofing? I am not aware of a 50-year product warranty.
Alwitra provides a 6-year product warranty.
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