Insulation of collar beam layer vs. between rafters - mold formation?

Good evening everyone,

Currently, we are building a single-family house with approximately 180 m², one and a half stories, masonry made of calcium silicate bricks, roof pitch 45° with a Frisian gable (60°). Our house will have an attic of about 60 m², which is not intended to be inhabited.

Our site manager has recommended, in addition to the insulation between rafters with mineral wool WLG035 (200 mm) and a vapor retarder, also considering insulating the collar beam layer between the rafters with mineral wool WLG 035 and 120 mm.

So far, everything is okay, it’s not a huge cost factor (you somehow lose perspective on large amounts of money during construction, that’s my feeling...).

So, bar conversation last Sunday, I’ll summarize briefly: Nowadays, in new buildings, attics not intended for living are no longer insulated between the rafters; only the intermediate ceiling between the upper floor and the attic is insulated. The reasoning is that if you insulate the attic, there is a risk of mold growth in the attic because there is no longer any airflow.

It goes without saying that we do not want to cause unnecessary heat loss in our house. But what is the truth of the above statement? Does insulation as described above promote "mold growth" (no food is to be stored there!), or is it advisable to carry out the insulation recommended by our site manager?

Thank you in advance for your responses!

Hello,

Our site manager recommended, in addition to the mineral wool WLG035 (200 mm) insulation between the rafters with a vapor barrier, also considering insulating the collar beam layer between the rafters with mineral wool WLG 035 and 120 mm.

Why is insulation between the rafters preferred at all if you only want to use the attic for storage purposes? Standard according to the construction description or is this your wish?

@ €uro,

In other words: With the insulation of the OGD, there should be a credit for the heating system if the project is a general contractor project!

Realistically only in the case where the heating system – as purchased – is already designed now for _later_ heating after construction-side completion of the SPIBOS

Kind regards

...@ €uro Realistisch betrachtet nur in dem Fall, wo die Heizungsanlage - wie gekauft - auch jetzt schon zum _späteren_ beheizen nach bauseitigem Ausbau des SPIBOS ausgelegt ist

Mistake! The intermediate rafter insulation was purchased together with the accordingly properly sized heating system!
If the thermal insulation of the upper floor is improved, the heating system must become cheaper, because the heating loads in the upper floor/attic become lower!

Best regards