MarkW1981
2020-08-12 17:40:56
- #1
Hello everyone,
10 years ago we built a garage and black spots (mold?) are forming on the inside of the ceiling on the OSB 3 panels. The problem appeared only after a few years and was treated once with a product against mold and mildew, after which it was basically fine again. I thought the garage was not ventilated enough (8 ventilation holes with a diameter of 8 cm are present), since then we have mostly kept the sectional door in ventilation mode during the summer. However, the problem has slowly reappeared and always starts in the summer and improves over the winter. The sun shines directly on it from sunrise to sunset; where the garage (which is directly attached to the house) is shaded by the roof overhang of the house, the problem does not exist. In summer, the heat builds up extremely under the roof. My suspicion is the high temperature difference between inside and outside, at night when the outside temperature drops and condensation forms. The top side of the OSB panels is dry and no spots are visible. The spots run in streaks along the roof, exactly where the deep rib directly touches. Back then, we had a company from which we ordered the sheet metal put together a package with everything we needed, and everything was built according to the assembly instructions. I now also know that the construction is not optimal. I took some pictures so that you can better imagine the whole thing and see the problem. Building permit and structural engineering are of course available. I wanted to insulate the garage from the inside between the rafters because of the heat buildup in summer. But I’m afraid that I might make the whole thing worse because then no air could get to the OSB panels at all. So, what to do?
The garage data and construction are as follows:
9 m x 7 m garage or carport directly on the house wall, and the open sides partially closed with bricks and wood.
Flat roof with 3% slope – according to the instructions at that time, trapezoidal sheet metal is possible from 2.5 cm per 1 m slope – water drains well, only small puddles form at the roof end where it flows into the gutter.
160 mm rafters – on them boarding with 18 mm OSB 3 panels (suitable for moist rooms) – directly on that steel trapezoidal sheet S35/207 – according to the instructions, when screwed on directly without ventilation, no condensation can form because there is no distance (deep rib) or only 35 mm (high rib) – roof closed with rib filler (so no rear ventilation).
Overlaps were sealed with sealing tape.
Thanks in advance for the help!
In another forum I have already received some help, but I still have no solution proposal with thermal insulation. The problem is probably the following:
The relatively high water vapor diffusion resistance of the OSB 3 panels is probably also a reason.
Possible solutions with thermal insulation (main goal: to slow down the heating by the roof in summer), if I understood correctly:
1. Ventilated insulation with already existing OSB panels: trapezoidal sheet with "anti-drip coating" – battens with ventilation – OSB panels on battens with ventilation – vapor open underlay membrane on rafters to protect the insulation – cavity insulation of glass wool 100 - 160 mm – impregnated gypsum board as bottom finish on the rafters.
The whole thing would be vapor open from the inside, ventilated, and I would have better protection against summer heat buildup. I would use the OSB panels because I already have them and they create insulation/protection between the trapezoidal sheet and the "under roof."
2. Ventilated insulation without already existing OSB panels: trapezoidal sheet with "anti-drip coating" – battens with ventilation – vapor open underlay membrane on rafters to protect the insulation – cavity insulation of glass wool 100 - 160 mm – impregnated gypsum board as bottom finish on the rafters.
This would also be vapor open from the inside, ventilated, and I would have better protection against summer heat buildup. I would omit the OSB panels to avoid possible problems like the current ones.
3. Trapezoidal sheet with ventilation: trapezoidal sheet with "anti-drip coating" – battens with ventilation – vapor open wall and roof board (DWD), e.g. 40 mm directly on rafters. This would be vapor open from the inside, ventilated, and I would have better protection against summer heat buildup. The DWD boards are supposed to protect very well against heat. Optionally, one could subsequently add cavity insulation of glass wool – impregnated gypsum board as bottom finish on the rafters if the DWD boards are not sufficient.
Please feel free to correct me.
Or should I rather work with Styrodur rigid foam boards (suggestion from an acquaintance from construction) instead of glass wool / DWD boards? I just don’t know how I would then make the roof construction, since Styrodur rigid foam boards are not vapor open.
10 years ago we built a garage and black spots (mold?) are forming on the inside of the ceiling on the OSB 3 panels. The problem appeared only after a few years and was treated once with a product against mold and mildew, after which it was basically fine again. I thought the garage was not ventilated enough (8 ventilation holes with a diameter of 8 cm are present), since then we have mostly kept the sectional door in ventilation mode during the summer. However, the problem has slowly reappeared and always starts in the summer and improves over the winter. The sun shines directly on it from sunrise to sunset; where the garage (which is directly attached to the house) is shaded by the roof overhang of the house, the problem does not exist. In summer, the heat builds up extremely under the roof. My suspicion is the high temperature difference between inside and outside, at night when the outside temperature drops and condensation forms. The top side of the OSB panels is dry and no spots are visible. The spots run in streaks along the roof, exactly where the deep rib directly touches. Back then, we had a company from which we ordered the sheet metal put together a package with everything we needed, and everything was built according to the assembly instructions. I now also know that the construction is not optimal. I took some pictures so that you can better imagine the whole thing and see the problem. Building permit and structural engineering are of course available. I wanted to insulate the garage from the inside between the rafters because of the heat buildup in summer. But I’m afraid that I might make the whole thing worse because then no air could get to the OSB panels at all. So, what to do?
The garage data and construction are as follows:
9 m x 7 m garage or carport directly on the house wall, and the open sides partially closed with bricks and wood.
Flat roof with 3% slope – according to the instructions at that time, trapezoidal sheet metal is possible from 2.5 cm per 1 m slope – water drains well, only small puddles form at the roof end where it flows into the gutter.
160 mm rafters – on them boarding with 18 mm OSB 3 panels (suitable for moist rooms) – directly on that steel trapezoidal sheet S35/207 – according to the instructions, when screwed on directly without ventilation, no condensation can form because there is no distance (deep rib) or only 35 mm (high rib) – roof closed with rib filler (so no rear ventilation).
Overlaps were sealed with sealing tape.
Thanks in advance for the help!
In another forum I have already received some help, but I still have no solution proposal with thermal insulation. The problem is probably the following:
[*]Trapezoidal sheet cools at night due to heat radiation to the sky
[*]OSB cools down, especially under the contact strips to the trapezoidal sheet
[*]warmer air under the roof construction cools down and condensation occurs on the coldest strips of the OSB layer
[*]gradual moistening causes the OSB panel to become a substrate for mold growth,
[*]which becomes visible as black spots
The relatively high water vapor diffusion resistance of the OSB 3 panels is probably also a reason.
Possible solutions with thermal insulation (main goal: to slow down the heating by the roof in summer), if I understood correctly:
1. Ventilated insulation with already existing OSB panels: trapezoidal sheet with "anti-drip coating" – battens with ventilation – OSB panels on battens with ventilation – vapor open underlay membrane on rafters to protect the insulation – cavity insulation of glass wool 100 - 160 mm – impregnated gypsum board as bottom finish on the rafters.
The whole thing would be vapor open from the inside, ventilated, and I would have better protection against summer heat buildup. I would use the OSB panels because I already have them and they create insulation/protection between the trapezoidal sheet and the "under roof."
2. Ventilated insulation without already existing OSB panels: trapezoidal sheet with "anti-drip coating" – battens with ventilation – vapor open underlay membrane on rafters to protect the insulation – cavity insulation of glass wool 100 - 160 mm – impregnated gypsum board as bottom finish on the rafters.
This would also be vapor open from the inside, ventilated, and I would have better protection against summer heat buildup. I would omit the OSB panels to avoid possible problems like the current ones.
3. Trapezoidal sheet with ventilation: trapezoidal sheet with "anti-drip coating" – battens with ventilation – vapor open wall and roof board (DWD), e.g. 40 mm directly on rafters. This would be vapor open from the inside, ventilated, and I would have better protection against summer heat buildup. The DWD boards are supposed to protect very well against heat. Optionally, one could subsequently add cavity insulation of glass wool – impregnated gypsum board as bottom finish on the rafters if the DWD boards are not sufficient.
Please feel free to correct me.
Or should I rather work with Styrodur rigid foam boards (suggestion from an acquaintance from construction) instead of glass wool / DWD boards? I just don’t know how I would then make the roof construction, since Styrodur rigid foam boards are not vapor open.