I want to build a ceiling in an old barn, where inside there is a room with brick walls but no ceiling. The room is about 13 x 11 meters in size.
I plan to attach two 45x195mm joists (A) on either side of 95x95mm posts (D) in the middle of the room. On the center joists, I will attach 45x195 with joist hangers, which at the other end rest on the masonry walls (B), and in these, I will screw battens with 40 cm centers (C) which I will then screw plasterboard onto.
How can I calculate the required distance between the posts (D), distance between the joists (B), and the dimensions of joists A, B? The ceiling should not support any upper floor but only be able to support itself and possibly some insulation on top.
The drawing is exemplary! It says everything needed. Gypsum plus battens weigh about 15 kg/sqm. Add a 195 mm mineral wool board at 8 kg, and you're up to 23 kg/sqm. If you use 45x195 C 24 for "B" at c/c 600 mm, the distributed load (on the main beams) including the weight of the beam itself is about 18 kg/m. This results in a maximum deflection of 9 mm, which is good considering the span. If you use two 45x195 C 24 for "A," the post spacing should be about 3.6 meters, resulting in a deflection on each beam of 7 mm. You can use 45x170 for "B," but the deflection will be greater. If you go up to 45x220 C 24 for "A," you can manage with just two posts in total.
The drawing is exemplary! It says everything needed. Gypsum plus battens weigh about 15 kg/sqm. Add a 195 mm stone wool slab at 8 kg and you reach 23 kg/sqm. If you use 45x195 C 24 for "B" at c/c 600 mm, the distributed load (on the middle supports), including the weight of the beam itself, will be about 18 kg/m. This gives a maximum deflection of 9 mm, which is good considering the span. If you use two 45x195 C 24 for "A," the post spacing should be about 3.6 meters, resulting in a deflection of each beam by 7 mm. You can use 45x170 for "B," but the deflection will be greater. If you upgrade to 45x220 C 24 for "A," you can manage with just two posts in total.
Absolutely fantastic that one can receive such a competent and detailed response to a vaguely posed question late on a Wednesday evening. Thank you so much!
What I'm considering is that if it requires c/c 600 mm between joists (B), it might be just as well to place them at c/c 400 mm instead and skip the supporting battens. I thought I could place them (B) further apart.
The battens require c/c 600 mm spacing between (B). I would keep that solution because it's significantly easier to mount the plasterboards that way and it provides better support for the boards' joints.
The purlins require c/c 600 mm apart (B). I would keep that solution as it makes it significantly easier to mount the gypsum boards and provides better support for the board joints.
Do you mean 60 cm between studs (B) and 40 cm between purlins (C)?
