ᐅ Insulation between rafters is already installed. Should the floor also be insulated?
Created on: 11 Jan 2024 15:01
L
lzw011995L
lzw01199511 Jan 2024 15:01Hello!
We have a house built in 2022. Recently, I finished the insulation between the rafters together with a roofer I know, and then loosely stapled a vapor retarder over it without sealing it (neither the seams nor at the base). The chimney and ridge are also not airtight and not sealed at the base. My acquaintance said that if we don’t receive any blower door test subsidies, it would only cost money. He recommended insulating the floor and leaving the rafter insulation as it is. It is not windproof, but since the hipped roof attic is only suitable as storage space, this will be sufficient.
The house is solid construction, with an upper ceiling made of concrete, but it is not insulated. Roof structure: tiles, underlayment membrane, 4cm (1.6 inches) air gap, insulation, foil.
We now have 20cm (8 inches) of glass wool insulation with a thermal conductivity of 0.032 W/mK, tightly fitted between the rafters. On top is the vapor retarder with a single-digit SD value (I don’t know the exact value at the moment). I have a smart meter in the attic, and since the foil was installed, the temperature up there has been about 18°C (64°F) ± 0.5 and the humidity around 25% ± 3% with current outdoor temperatures between 0 and -10°C (32 and 14°F).
Since we don’t need a (passively) heated attic for storage, I think this approach is not bad. I am planning to simply lay and glue Styrodur boards on the floor (2 layers of 6cm (2.4 inches) each?). Since the foil is vapor permeable and not sealed—so it is wind-permeable—shouldn’t everything be well ventilated and any condensation quickly evaporate?
I don’t think you can calculate this precisely; to be frank, the work here is not done to standard. With a complete airtight seal, I am more worried that there might be a small gap somewhere where condensation could build up and not dry out quickly enough, or moisture might rise from below (through the attic hatch) and not diffuse out fast enough, causing condensation. The goal of insulating the roof was to create usable storage space (otherwise, it would be around 50°C (122°F) in summer and 0°C (32°F) in winter in a cold attic). The goal of the additional ceiling insulation is to save heating costs (calculated over 60+ years) and provide comfortable warmth in the upper floor.
Does anyone have a similar setup and can share their experience?
We have a house built in 2022. Recently, I finished the insulation between the rafters together with a roofer I know, and then loosely stapled a vapor retarder over it without sealing it (neither the seams nor at the base). The chimney and ridge are also not airtight and not sealed at the base. My acquaintance said that if we don’t receive any blower door test subsidies, it would only cost money. He recommended insulating the floor and leaving the rafter insulation as it is. It is not windproof, but since the hipped roof attic is only suitable as storage space, this will be sufficient.
The house is solid construction, with an upper ceiling made of concrete, but it is not insulated. Roof structure: tiles, underlayment membrane, 4cm (1.6 inches) air gap, insulation, foil.
We now have 20cm (8 inches) of glass wool insulation with a thermal conductivity of 0.032 W/mK, tightly fitted between the rafters. On top is the vapor retarder with a single-digit SD value (I don’t know the exact value at the moment). I have a smart meter in the attic, and since the foil was installed, the temperature up there has been about 18°C (64°F) ± 0.5 and the humidity around 25% ± 3% with current outdoor temperatures between 0 and -10°C (32 and 14°F).
Since we don’t need a (passively) heated attic for storage, I think this approach is not bad. I am planning to simply lay and glue Styrodur boards on the floor (2 layers of 6cm (2.4 inches) each?). Since the foil is vapor permeable and not sealed—so it is wind-permeable—shouldn’t everything be well ventilated and any condensation quickly evaporate?
I don’t think you can calculate this precisely; to be frank, the work here is not done to standard. With a complete airtight seal, I am more worried that there might be a small gap somewhere where condensation could build up and not dry out quickly enough, or moisture might rise from below (through the attic hatch) and not diffuse out fast enough, causing condensation. The goal of insulating the roof was to create usable storage space (otherwise, it would be around 50°C (122°F) in summer and 0°C (32°F) in winter in a cold attic). The goal of the additional ceiling insulation is to save heating costs (calculated over 60+ years) and provide comfortable warmth in the upper floor.
Does anyone have a similar setup and can share their experience?
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