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Bauwiesel8 Oct 2019 19:13Hello,
we have purchased an old house where the roof is currently insulated with aluminum-coated insulation wool placed between the rafters.
The roof tiles are laid on wooden battens. In the upper roof area, there is a ventilation tile installed in each rafter bay.
We would like to re-insulate the roof from the inside because the old insulation is partly falling out and torn.
However, the roof will only be re-covered in 5-8 years.
My question is whether it makes sense to install 120mm (5 inches) of insulation batts between the rafters (rafter height is 140mm (5.5 inches)) plus an additional 50mm (2 inches) of insulation below the rafters,
or if it would be better to double the rafters and install 180mm (7 inches) of insulation batts from the inside.
In both cases, of course, with an interior vapor control layer and an appropriate finish with drywall/plasterboard (Rigips/Fermacell).
The idea would then be to add further insulation from the outside later with a wood fiberboard when the roof is replaced.
Thank you very much in advance. Best regards from the North
we have purchased an old house where the roof is currently insulated with aluminum-coated insulation wool placed between the rafters.
The roof tiles are laid on wooden battens. In the upper roof area, there is a ventilation tile installed in each rafter bay.
We would like to re-insulate the roof from the inside because the old insulation is partly falling out and torn.
However, the roof will only be re-covered in 5-8 years.
My question is whether it makes sense to install 120mm (5 inches) of insulation batts between the rafters (rafter height is 140mm (5.5 inches)) plus an additional 50mm (2 inches) of insulation below the rafters,
or if it would be better to double the rafters and install 180mm (7 inches) of insulation batts from the inside.
In both cases, of course, with an interior vapor control layer and an appropriate finish with drywall/plasterboard (Rigips/Fermacell).
The idea would then be to add further insulation from the outside later with a wood fiberboard when the roof is replaced.
Thank you very much in advance. Best regards from the North
How does it work with tar paper battens? A modern roof has a vapor-permeable underlay membrane, like delta Max or similar. You can install insulation and a membrane; the interior side is sealed, and the exterior side is ventilated. But if you also install tar paper battens, using the membrane might be a bad idea.
As long as air can flow behind the roof tiles, I don’t see any problem.
I personally think the idea is good, and both methods are common. Installing insulation perpendicular to the insulation between the rafters reduces thermal bridges. Make sure to follow the principle of airtightness on the room side and vapor permeability on the outside. I assume that the roof is not airtight on the underside, allowing air to flow from bottom to top through the ventilation tiles. This then helps dry the insulation.
I personally think the idea is good, and both methods are common. Installing insulation perpendicular to the insulation between the rafters reduces thermal bridges. Make sure to follow the principle of airtightness on the room side and vapor permeability on the outside. I assume that the roof is not airtight on the underside, allowing air to flow from bottom to top through the ventilation tiles. This then helps dry the insulation.
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Mottenhausen8 Oct 2019 20:15Do not increase the rafter thickness to add more insulation mineral wool. It’s not worth the effort. Instead, apply a continuous layer beneath the rafters.
One option for this could be gypsum board–polystyrene composite panels installed perpendicular to the rafters (i.e., horizontally). This way, you achieve an additional thermal bridge–free insulation layer in a single step, which is then finished directly from the inside. Of course, attach a vapor barrier to the rafters beforehand to keep the polystyrene boards on the warmer side of the insulation and prevent any condensation.
One option for this could be gypsum board–polystyrene composite panels installed perpendicular to the rafters (i.e., horizontally). This way, you achieve an additional thermal bridge–free insulation layer in a single step, which is then finished directly from the inside. Of course, attach a vapor barrier to the rafters beforehand to keep the polystyrene boards on the warmer side of the insulation and prevent any condensation.
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Bauwiesel8 Oct 2019 20:50@Joedreck....I'm glad my idea wasn't completely off. And yes, the air can flow from the gutter to the ridge.
@Mottenhausen.....you would have skipped the insulation beneath the rafters here and stapled a membrane directly onto the rafters, then added battens and screwed on, for example,
Gypsum board composite panel with EPS KNAUF GKB 2500x1250x12.5+40mm?
Or would you omit the battens between the membrane and the composite panel in this case?
Regards
@Mottenhausen.....you would have skipped the insulation beneath the rafters here and stapled a membrane directly onto the rafters, then added battens and screwed on, for example,
Gypsum board composite panel with EPS KNAUF GKB 2500x1250x12.5+40mm?
Or would you omit the battens between the membrane and the composite panel in this case?
Regards
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borderpuschl9 Oct 2019 09:04Just don’t use Styrofoam. It doesn’t allow any breathability.
Use insulated batt between rafters with a low thermal conductivity value (WLG).
Then install a proper vapor retarder (e.g., Siga Majpell).
After that, add battens and then drywall/wooden ceiling/etc.
When you do the roof later, you can add wood fiber insulation above the roof deck (e.g., from Steico) and a breathable underlay membrane.
Use insulated batt between rafters with a low thermal conductivity value (WLG).
Then install a proper vapor retarder (e.g., Siga Majpell).
After that, add battens and then drywall/wooden ceiling/etc.
When you do the roof later, you can add wood fiber insulation above the roof deck (e.g., from Steico) and a breathable underlay membrane.
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