ᐅ Is a screed necessary? Unfinished but insulated attic space

Created on: 3 Aug 2017 13:07

Hello community,

We are currently planning a semi-detached house with a developer and I need some advice on one question.
It’s about the attic, which is not living space and not heated, but will be used for storage.
The roof will be insulated with 240mm (9.4 inches) of mineral wool and OSB boards, and the floor consists of a 20mm (0.8 inches) concrete slab.

My question: Is it necessary to seal the floor with screed, or can this be omitted for a purely storage area? The costs seem relatively high, so I’m asking about the benefit.
According to the developer, the screed would of course contribute to thermal insulation; without screed, the upper floor would help heat the attic. But since I have insulated the roof, no heat should be lost.
Is it possible to estimate how many degrees the attic would heat up more without screed compared to with screed?
Is it really necessary to install screed, or would floor coverings be sufficient? I just want to store cabinets and boxes there.

Thank you very much for your help and support,
Best regards
Holleradhiho

Holleradhiho3 Aug 2017 18:49

#13

11ant schrieb:
That should be about right. The screed is denser than concrete. It doesn’t primarily provide insulation—that’s not its purpose, nor what it’s designed for. It doesn’t make a significant difference. It certainly can’t fix insulation applied in the wrong place—although better than nothing, the ceiling would have been more appropriate. The screed changes this by such a microscopic amount that it won’t justify the difference. The mistake was made elsewhere and cannot be corrected here (mitigating it is only possible to such a minor extent that it would be pointless).

Why do you think this building method is a mistake?
Isn’t it more sensible to insulate the building envelope rather than an intermediate floor, which would leave the enclosed space cold?
The floor between the ground floor and upper floor is also not insulated, but the entire building envelope (walls and roof of the house) is insulated.

The concrete slab is, of course, 20cm (8 inches) thick; sorry for the mistake.

My thought was: Instead of insulating the top-floor ceiling (in the attic) and then insulating the pitched roof afterwards, the pitched roof would be professionally insulated right away, and that would be sufficient.
I hoped this would allow me to save on insulation.

Bieber08153 Aug 2017 19:43

#14

In the end, you are also heating the attic, but in my opinion, that is irrelevant. I would rather ask how the ventilation concept looks up there and whether a (small) heater should be installed.

Holleradhiho schrieb:
The floor between the ground floor and the upper floor is also not insulated,

Do you have underfloor heating?

Holleradhiho3 Aug 2017 20:30

#15

The attic will be used as an insulated storage room; it is not intended to be a living space. Therefore, I will not install any heating there.

Yes, underfloor heating on the ground floor and upper floor.

11ant3 Aug 2017 20:35

#16

Holleradhiho schrieb:
Why do you think this construction method is a mistake?
Isn’t it more sensible to insulate the building envelope instead of an intermediate floor, which would leave the enclosed space cold?

That’s exactly the mistake (not meaning entirely wrong, but less practical): insulation should separate warm from cold, not enclose ambient air. For a living roof, insulating the building envelope is beneficial; for a storage room ceiling, the top floor ceiling is the more appropriate boundary.

Holleradhiho schrieb:
The floor between the ground floor and the upper floor is also not insulated,

According to the explanation above, it only makes sense to insulate this if the upper floor remains unused for a long time.

Holleradhiho schrieb:
My thought was: instead of insulating the top floor ceiling (in the attic) and then retrofitting the roof slopes, why not professionally insulate the roof slope right away?
I hoped to save on insulation that way.

You didn’t save anything there: insulating the roof surface instead of the top floor ceiling, for example with a 40° roof pitch, increases the insulated area by about 30%. Only if the attic is going to be permanently used as living space would that be a cost-effective approach.

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77.willo3 Aug 2017 20:49

#17

In my opinion, there should be a heating system installed there, or the insulation should be applied to the ceiling of the upper floor. Additionally, a window or a controlled residential ventilation system should be installed.

Joedreck3 Aug 2017 20:54

#18

There are basically two reasonable options:

1.: Insulate only the topmost floor ceiling and leave the other sloped ceilings uninsulated, since they are not heated.

2.: If the attic is heated, insulate both the screed and the sloped roof surfaces.

Otherwise, you end up inefficiently heating the attic with a higher supply temperature.
In my opinion, that doesn’t make much sense.

ᐅ Is a screed necessary? Unfinished but insulated attic space

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