ᐅ Is additional insulation of the upper floor ceiling necessary or beneficial when there is a heated attic space?
Created on: 4 Feb 2022 09:32
E
erazorlll
Good evening,
we are currently building a solid (masonry) house and I have a question regarding the insulation of the roof.
We are constructing a pitched roof with an attic and both exterior rafter insulation and cavity (between-rafter) insulation. The cavity insulation will be done using blown-in insulation. The insulation is applied on the roof slopes, so the attic will be conditioned (warm). There is a vapor retarder both on the ceiling of the attic and below the ceiling of the upper floor.
For better understanding, here is a simplified structure from bottom to top:
Upper floor -> Vapor retarder -> Collar beam -> Wood fiber boards (floor of the attic)
Attic -> Vapor retarder -> Between-rafter insulation (blown-in insulation) -> Exterior rafter insulation -> vapor-permeable underlay membrane
Now we have two options for implementation and I would like your opinion:
1) As described above. The insulation is only applied on the roof slopes and in the conditioned attic. The ceiling between the upper floor and attic has a vapor retarder but is not insulated.
2) Same as option 1, but the floor/ceiling between the upper floor and attic is additionally filled with blown-in insulation. This would involve an extra cost.
We were told that option 2 is recommended. The reasoning was that in the "warm" but unheated attic, the temperature is significantly lower than in the living space. This can cause warm air, especially from humid rooms (e.g. bathroom), to rise, condense on the "cold" ceiling, and over time, lead to mold growth. Also, the cold ceiling can transmit cold to the rooms below. With the additional insulation, it would be cooler in summer and warmer in winter.
Now I would like to hear the forum’s opinion. Is it worthwhile to insulate the ceiling/floor between upper floor and attic and pay the additional cost (amount still unknown)?
Does it provide a noticeable and significant improvement in summer and winter? Is this ceiling really "cold" or "colder" if you don’t insulate it?
Thanks a lot.
we are currently building a solid (masonry) house and I have a question regarding the insulation of the roof.
We are constructing a pitched roof with an attic and both exterior rafter insulation and cavity (between-rafter) insulation. The cavity insulation will be done using blown-in insulation. The insulation is applied on the roof slopes, so the attic will be conditioned (warm). There is a vapor retarder both on the ceiling of the attic and below the ceiling of the upper floor.
For better understanding, here is a simplified structure from bottom to top:
Upper floor -> Vapor retarder -> Collar beam -> Wood fiber boards (floor of the attic)
Attic -> Vapor retarder -> Between-rafter insulation (blown-in insulation) -> Exterior rafter insulation -> vapor-permeable underlay membrane
Now we have two options for implementation and I would like your opinion:
1) As described above. The insulation is only applied on the roof slopes and in the conditioned attic. The ceiling between the upper floor and attic has a vapor retarder but is not insulated.
2) Same as option 1, but the floor/ceiling between the upper floor and attic is additionally filled with blown-in insulation. This would involve an extra cost.
We were told that option 2 is recommended. The reasoning was that in the "warm" but unheated attic, the temperature is significantly lower than in the living space. This can cause warm air, especially from humid rooms (e.g. bathroom), to rise, condense on the "cold" ceiling, and over time, lead to mold growth. Also, the cold ceiling can transmit cold to the rooms below. With the additional insulation, it would be cooler in summer and warmer in winter.
Now I would like to hear the forum’s opinion. Is it worthwhile to insulate the ceiling/floor between upper floor and attic and pay the additional cost (amount still unknown)?
Does it provide a noticeable and significant improvement in summer and winter? Is this ceiling really "cold" or "colder" if you don’t insulate it?
Thanks a lot.
P
Pumpernickel14 Mar 2022 22:54Tarnari schrieb:
That’s exactly how we did it. We installed two low-temperature radiators integrated into the underfloor heating circuit. It’s working great so far.May I ask which brand the radiators are? I’m not very familiar with this. Also, are the radiators somewhat noisy because of the fans?
O
Oetzberger5 Mar 2022 07:54erazorlll schrieb:
So I now have several options:
a) Insulated attic space - no insulation on the intermediate ceiling -> as currently planned, but probably not the best solution? a) is less critical in terms of mold compared to c), but the temperature up there will be around 18 to 19°C (64 to 66°F) in the coldest winter months. At least that’s how it is for me; I implemented option a). Should the attic be ventilated via a mechanical ventilation system with heat recovery or not? Is a future installation of an enthalpy exchanger planned for the ventilation system? Or will ventilation be done through windows? I placed a wireless thermometer with a dew point display in the attic and regularly air the space during the cold season. The air up there needs to be drier than in the living areas, especially early on while there is still construction moisture.
erazorlll schrieb:
b) Insulated attic space - additional insulation on the intermediate ceiling -> incurs extra cost, but probably a sensible solution to balance the temperature difference Beware of mold risk! This is possible and doable, but you need to carefully think this through and know what you’re doing. The attic may have air temperatures between 8 and 13°C (46 to 55°F) with comparatively high relative humidity, rising due to air leakage from the living space or initially from construction moisture. The dew point of 10°C (50°F) can be quickly exceeded when it gets cold outside. You need to ventilate either via a mechanical ventilation system with heat recovery or very frequently by manual window ventilation. However, ventilation through a central mechanical ventilation system is somewhat counterproductive, since it blows warm air into the attic. And an enthalpy exchanger would pose a huge mold risk!
Alternatively, a decentralized ventilation unit can be installed in the wall structure of the attic (e.g., a wall ventilator). In addition, airtightness between the attic and the living space must be very well ensured.
I might upgrade from a) to b) sometime soon as a hobby project; it won’t really save much heating energy. But it’s important to me that construction moisture is allowed to dry out over two winters first.
erazorlll schrieb:
c) Insulated attic space - no insulation on intermediate ceiling, but radiators in the attic -> I would have to discuss with the plumbing contractor how feasible this still is. Does it make sense to heat the attic continuously if it’s only used for storage? Best regarding mold prevention and more efficient heating costs than option a), because you can run the overall heating system at lower flow temperatures. Also, you avoid cold ceilings on the upper floor.
The simplest is option d), insulation on the top floor ceiling and cold roof only. Proven thousands of times, no risk of mold, by far the cheapest. But expect deep freezes in winter and high peak temperatures in summer in the storage space.
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Pitiglianio5 Mar 2022 08:43That storage space is not worth it to me—I mean, the effort involved in insulating and heating the attic. As @Oetzberger already suggested, I would also recommend making it a cold roof. That initially saves you the effort and cost of insulation, the effort and cost of heating, and ultimately, no one can even guarantee that you won’t still have mold problems despite all the effort.
Oetzberger schrieb:
Beware of mold risk! …Although ventilation via centralized mechanical ventilation with heat recovery seems contradictory, since it blows warm air back upstairs. And an enthalpy exchanger would pose a huge mold risk!
I can confirm this from my own experience. During the first winter with construction moisture, it was only manageable using a dehumidifier without any other measures.
In summer, I’m considering a ventilation strategy for upstairs and sealing some areas more tightly.
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Oetzberger5 Mar 2022 10:07@OWLer How exactly was it installed in your case? What building materials and U-values were used for the top floor ceiling, and what type of roof insulation? Is the top floor ceiling a concrete slab or a wooden beam ceiling?
In my case, the top floor ceiling is a concrete slab. I’m still uncertain whether I should add additional insulation. The downside of my current uninsulated concrete ceiling is that some rooms on the first floor feel a bit cold because the concrete ceiling is somewhat cold.
In my case, the top floor ceiling is a concrete slab. I’m still uncertain whether I should add additional insulation. The downside of my current uninsulated concrete ceiling is that some rooms on the first floor feel a bit cold because the concrete ceiling is somewhat cold.
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