ᐅ Is Additional Insulation of the Attic Useful in New Construction?
Created on: 3 Nov 2019 14:25
H
hausbauer
Hello,
we are building a house with two full stories and a pitched roof above, constructed according to the Energy Saving Ordinance standard. The construction company includes an insulated attic space (insulation between rafters with 200 mm (8 inches) thick mineral wool insulation (thermal conductivity 0.035 W/mK), with a vapor retarder foil, sealed airtight). The concrete ceiling above the upper floor (i.e., the attic floor) remains uninsulated.
Now I am considering whether it would be beneficial for summer heat protection and winter heating costs to additionally lay insulation boards on the attic floor, for example, EPS insulation boards. Is this sensible or just a waste of money? Can this be done well as a DIY project, and what should I pay attention to? Do the boards need to be placed tightly together/glued, or is a little gap acceptable?
I am somewhat concerned about the ventilation of the attic during the first year or two after construction, as the attic will not be connected to the central mechanical ventilation system (I will probably have to leave the attic windows open occasionally in weather with low dew points). Should I wait some time before insulating the attic floor for this reason? Or can I do it right away without any issues?
Or would you recommend a thicker insulation between the rafters instead of working on the attic floor? The latter would have the advantage that I could avoid the very high prices charged by the general contractor by doing it myself.
we are building a house with two full stories and a pitched roof above, constructed according to the Energy Saving Ordinance standard. The construction company includes an insulated attic space (insulation between rafters with 200 mm (8 inches) thick mineral wool insulation (thermal conductivity 0.035 W/mK), with a vapor retarder foil, sealed airtight). The concrete ceiling above the upper floor (i.e., the attic floor) remains uninsulated.
Now I am considering whether it would be beneficial for summer heat protection and winter heating costs to additionally lay insulation boards on the attic floor, for example, EPS insulation boards. Is this sensible or just a waste of money? Can this be done well as a DIY project, and what should I pay attention to? Do the boards need to be placed tightly together/glued, or is a little gap acceptable?
I am somewhat concerned about the ventilation of the attic during the first year or two after construction, as the attic will not be connected to the central mechanical ventilation system (I will probably have to leave the attic windows open occasionally in weather with low dew points). Should I wait some time before insulating the attic floor for this reason? Or can I do it right away without any issues?
Or would you recommend a thicker insulation between the rafters instead of working on the attic floor? The latter would have the advantage that I could avoid the very high prices charged by the general contractor by doing it myself.
H
hausbauer4 Nov 2019 08:24Joedreck schrieb:
I don’t have it in mind. How do you plan to heat? With an air-source heat pump, a model that has a relatively above-average annual performance factor for air-source heat pumps.
Joedreck schrieb:
So the attic might be heated after all? No, it should just stay between 35°C (95°F) and 0°C (32°F) year-round.
Which insulation material would you recommend?
H
hausbauer4 Nov 2019 08:37I have now done a rough calculation. According to the U-value calculator, the U-value of the roof is 0.20 W/m²K without additional insulation and 0.125 W/m²K with the insulation. The transmission losses to heat the house are estimated to cost me around 500 euros per year (losses due to ventilation and heating costs for domestic hot water are additional). The roof area accounts for 26% of the building envelope, and I reduce the energy transmission of the roof by 38%. Therefore, I save about 10% of the total transmission losses of the entire house through the additional insulation, which amounts to around 50 euros per year.
If the insulation mats for the area already cost 1500 euros, it will take 30 years to break even, assuming zero percent financing. So, in fact, the measure doesn’t make much financial sense.
However, I might do it anyway, also because of heat protection in summer. And I would probably have installed some kind of flooring in the attic anyway (chipboard or something similar), so the insulation can just be included in that layer.
If the insulation mats for the area already cost 1500 euros, it will take 30 years to break even, assuming zero percent financing. So, in fact, the measure doesn’t make much financial sense.
However, I might do it anyway, also because of heat protection in summer. And I would probably have installed some kind of flooring in the attic anyway (chipboard or something similar), so the insulation can just be included in that layer.
I would need to study the calculations myself. I assume there is a mistake in the reasoning, but I currently have little time.
Still, you are right for now—it will take a long time to pay off.
However, the efficiency of the heat pump should not be overlooked. Every degree higher supply temperature costs 2.5%. By indirectly conditioning the attic, additional costs will also arise here.
For now, I stick to my advice: try going without it for a year. I don’t believe energy costs will skyrocket.
You can also check whether the ceiling gets heated in the summer.
Such a measure can be implemented quite easily afterward.
By the way, this is not my personal conviction. I think the attic is mostly used for items that are needed once or twice a year. You probably wouldn’t want to use that staircase more often—at least I wouldn’t.
These items are often resistant to both cold and heat.
If it were my house, I would leave out insulation between the rafters and insulate the floor/ceiling assembly to the maximum extent possible.
But that is entirely your decision and should be considered individually.
Still, you are right for now—it will take a long time to pay off.
However, the efficiency of the heat pump should not be overlooked. Every degree higher supply temperature costs 2.5%. By indirectly conditioning the attic, additional costs will also arise here.
For now, I stick to my advice: try going without it for a year. I don’t believe energy costs will skyrocket.
You can also check whether the ceiling gets heated in the summer.
Such a measure can be implemented quite easily afterward.
By the way, this is not my personal conviction. I think the attic is mostly used for items that are needed once or twice a year. You probably wouldn’t want to use that staircase more often—at least I wouldn’t.
These items are often resistant to both cold and heat.
If it were my house, I would leave out insulation between the rafters and insulate the floor/ceiling assembly to the maximum extent possible.
But that is entirely your decision and should be considered individually.
Hausbauer schrieb:
What would you suggest? Cheaper and a bit more labor-intensive installation is also fine. Rolling out mats and placing stepping stones on top? Other materials? It shouldn’t be much thicker than 10-15cm (4-6 inches), otherwise I won’t be able to walk stooped in the attic. We don’t have a basement, so the attic is an important storage space. Also, the temperature range in the attic shouldn’t differ too much from the rest of the house during the coldest winter and hottest summer, so should the insulation of the attic floor perhaps be a bit less than the insulation between the rafters? The ceiling insulation is the real thermal barrier for the heated area – it should be well done. The insulation between the rafters above is the one that keeps your replacement cellar frost-free and is sufficient at a satisfactory level.
H
hausbauer4 Nov 2019 09:43Joedreck schrieb:
But for now, I’ll stick to the advice: try it for a year without doing itGood advice, but I know myself. Either I do it right away, or realistically, I’ll never do it...If you find a calculation error, please let me know. The 23-degree (23°) pitch of the gable roof is already implicitly included in the numbers (it only makes about a 10% difference).
H
hausbauer4 Nov 2019 09:47Nordlys schrieb:
The ceiling insulation is the real deal for the heated area—it needs to be good quality. The insulation between the rafters above is what keeps your crawl space frost-free, and a satisfactory level is sufficient there.Did you insulate both the floor and between the rafters? What material did you choose for the walkable floor insulation, and roughly how much did it cost? Have you experienced any issues with moisture in the attic?Similar topics