it is probably the air gap that is above the beam and above it some kind of board... no, I haven't asked about the deflection but trust that the designer and the person responsible for control have a handle on the situation.. They say that one layer of gypsum in the ceiling should be enough. It meets the fire requirements, providing enough time for evacuation. I could possibly check the cost of having two layers of gypsum instead... need to consider the cost. The risk of cracks etc. in the joints is probably less if I have two layers of gypsum ...
I would ask how they determined that one gypsum board is enough. The requirement should be R30, which is normally achieved with, for example, 2 gypsum boards. Depending on the type and thickness of insulation, it may be sufficient with one board. If 2 boards are required, then you should not pay extra for it since the beam replacement prompted the requirement for two layers of gypsum.
A question regarding the insulation. In the construction drawings, 400 mm of loose-fill is specified, but we plan to use Knauf's brown eco-friendly insulation (ecobat & ecoblanket), and according to Knauf, 340 mm of their insulation corresponds to 400 mm of loose-fill.
I can imagine that the amount of insulation in the sloping ceiling also affects the risk of condensation, etc. - I'm thinking again about the steel beam (which already has 70 mm of rock wool on top). Is it wise to stick to 340 mm of Knauf's glass wool, or is there an advantage (besides saving energy) to having thicker insulation?
According to rumor, loose wool compacts, which leads to an uninsulated gap closest to the steel beam, which if true, is not good.
No, there is no other advantage that I know of that is relevant.
However, you should check with the designer regarding the change in insulation thickness, as the roof is built for 400 mm insulation, and changing it would create a 60 mm void.
It's probably true that there are no beams that suffice; a quick test with Moelven's dimensioning program showed that they didn't have any that could handle an 11m span on a 10m wide house in snow zone 1.5.
For an 8m span, concrete tiles on the roof required a 630mm high beam (their largest).
One thing to remember, when calculating load on a beam that has only two supports (one at each end), the load depends on the length raised to the power of 4, so it increases quite quickly, and a meter matters more than you might think. That's why there are load-bearing walls near the center of the house.
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