Hello!
I intend to create an opening in the exterior wall (2800 mm) for a bay window in my house with a timber frame from 1932. The house has a mansard roof with angles of 67 degrees and 42 degrees. The house's width is 9200 mm.
I'm considering using glulam, and there are at least two different applications from manufacturers like Moelven and Svenskt Trä that can help with the dimensioning. If I go to Svenskt Trä and choose 1.5-story house and input my values, it shows that 45x195 in C24 quality is sufficient to meet the requirement of L/300 in deflection. It's worth noting that I entered a roof angle of 60 degrees since a mansard roof is not an option in the application. I have a tiled bathroom above the opening and want larger margins. To achieve L/600, however, 56x225 glulam is enough. Moelven indicates that 140x225 glulam is needed to reach L/600. Here, I can’t choose a higher roof angle than 45 degrees.
To check the reasonableness, I also looked at calculations for a two-story house, which is only available on Svenskt Trä. Entering my values (42-degree roof slope), I get 90x405 instead. The difference between 1.5 stories and 2 stories on Svenskt Trä is therefore enormous. I can somewhat understand that there is a higher load from the upper floor slab since it equals the ground floor when calculating 2 stories, but it shouldn't differ that much.
Interestingly, the support reaction in all 3 cases is about 40 kN, slightly lower for 1.5 stories compared to 2 stories, which seems logical. With the same support reaction, the deflection should be the same at the same span, or is there something else I’ve missed?
Kind regards,
Björn Widarsson
