structural calcs

[FRAN1870]

hi all,

I'm trying to do my loft conversion with as little steel as possible so the SE has spec'd two c24 10x3's bolted together.

The calcs are attached but I think he's missed / not considered that the original purlins are staying in ?

So 2 X 10x3's seems huge for a 4m span ?

Any thoughts ?

 

[tony1851]

Can't really tell - there is 'additional roof load'(?) of 0.25kN/m2 - but that seems v. low for a roof;

Also, is it only supporting 0.8m width of floor? - seems on the low side?

 

[FRAN1870]

I don't understand it so really have no idea ..... Maybe he has considered the existing purlins then ?

I assume the additional roof load is additional though, so the insulation etc ?

 

[FRAN1870]

The floor span is about 1.5m to the central wall .... Let me post my full plan

 

[FRAN1870]

Joist layout

 

[CambridgeBrummie]

Partition allowance looks high at 1kN/sq.m. This is unlikely and could be reduced. Have you got any partitions loading the floor?
Not sure where the "Additional roof load" is coming from based on your sketch.
Span is going to be the issue as the timber size will be driven by deflexion.

You could consider using an engineered timber beam such as Kerto LVL instead (not sure on price differential).

 

[tony1851]

Or an insitu concrete beam might be cheaper.........?