Floor structure sizing

[c_vette]

What an unfathomable jungle one ends up in when building/expanding a house.

Depending on who you ask, you get different answers, but who should you trust?

I plan to have truss rafters and a finished 1 1/2 story "attic" floor, and according to the truss rafter book, among others, the floor like the lower frame beam on the truss should be covered with a K24 45x195.

But today I came across a person who should have expertise in this, and according to him, 45x195 wouldn't be enough; it should be at least 45x220 to meet the deflection regulations.

Sigh, as an enthusiastic amateur, you just end up confused...who the heck should you believe?

 

[Mats]

Take 45X220 just to be safe. The price difference for the timber isn't that significant, and in the worst-case scenario, you have what you need. In the best-case scenario, you have good margins.

 

[c_vette]

Go for 45X220 just to be safe. The price difference in the timber isn't that bad and at worst you'll have what's required. At best, you'll have good margins

If I go with 220 instead of 195, there will be a level difference between the old part of the house and the new one since the intermediate supports and outer walls (wall plates) are set for a height of 195. The contractor I got hold of seemed very *confused* and we didn't discuss quality, so maybe he was thinking of k12 timber instead of k24, which I am using?! The attic floor structure, including the lower frame of the trusses, will be at cc 40 and with cross bracing in between, I doubt that 195 k24 will be too weak since the length in the longest direction between the wall plate and the center support is barely 3.5 meters.

So I have decided to ignore the *confused* contractor and instead follow the other carpenters, knowledgeable people, including documentation and professional truss manufacturers who say that k24 45x195 is more than sufficient.

 

[Mats]

There is a small detail. That thing with 3.5 meters between supports.

I have a single-story house, but I have about 4 meters between my supports, and it's standard 45X195. It has been standing for 8 winters now, so it looks good.