Floor joist sizing

[O.M]

Planning to extend the house with a garage on the basement level, a living room on the entrance level, and a bedroom on the upper floor.

The garage has external dimensions of 7.4m long and 5.5m wide with a ceiling height of 2.1m.

Does anyone know what dimension I need for the floor joists? Since I don't want to lose too much ceiling height, maybe c/c 300 is recommended?

Grateful for responses.

 

[O.M]

Doesn't anyone know if 45x220 with c/c 300 seems reasonable without it sagging too much?

The floor will just be a living room without particularly heavy objects.

 

[injonil]

If you use 70x220 (a local sawmill can arrange this, you have end-year problems getting the right length at the builders' merchant) with cc300 and screw-glue the floor chipboard, it MIGHT be enough, but it's on the edge, I would say.

 

[anaitis]

if you have a span of 5.5 m you might need to reconsider.
It won't work with the timber dimensions mentioned.
Either you need support in the middle or significantly stronger beams.

 

[injonil]

Yes, that's probably correct.

I’m going to extend 4.8m and plan to use approximately 75x220, cc300 and screw-limed floor chipboard. It’s on the edge, and a 70cm longer span is quite a lot.

 

[anaitis]

Keep in mind that the deflection (=sag) increases with the fourth power of the length!

 

[O.M]

Thank you for the answers!
I would prefer not to have posts in the garage, but I understand the span is quite long.

I saw on moelven.se that according to their calculations, a glulam beam 56x270 cc600 would suffice.

What size might be needed if using a steel beam instead?