Suggested design loads for loft conversion

[alfatom]

Hello all.
First post on here but a long time reader.
I am currently preparing my calcs for building control for a loft conversion but am struggling to get a definitive set of loads to use.
I can work out the actual loads of each material and use that to calculate loads, but for the design of the floor and roof, what live loads should I apply.
In summary, the loft will contain a bedroom and a bathroom.
floor construction will be/is timber joists with lathe and plaster ceiling attached below with plaster board below that. I will be putting a T+G chipboard covering and then carpet in the bedroom and tiles in the bathroom. The roof itself is standard clay tiles (10mm?) on top of 12mm sarking board. Rafters and floor/ceiling joists are 100x50 @350 ctrs.
Any advice on sensible loads to use would be much appreciated.

I am hoping to prove that the existing ceiling/floor joists in the loft are already strong enough to be used as the floor for the new room and therefore avoid putting in steels and duplicating exactly the same floor again over the steels.

 

[rou]

Hello
From you discription it looks like the new floor is about 0.6-0.7Kn/m^2 and the roof 1-1,5kN/m^2.
You will need to allow a live load of 1.5kN/m^2 in addition to the self-weight to the floor and 0.6kN/m^2 for the roof. The roof load can be reduced depending on the slope and location of the property(wind, snow loads).
It is very unlickely that the existing joists will be strong enough as they would have been designed to support only ceiling load which is substantially less. The maximum allowable deflection for domestic floor joists is the lower of 0.003xspan or 14mm.
Strengthening the floor does not necessarely require steels to be added.
I would recommend to employ a structural engineer to do the calculation for you. Doing them yourself might save some money but it will defenatelly cause problems with future insurance and when it come on selling the property.

 

[freddiemercurystwin]

I am hoping to prove that the existing ceiling/floor joists in the loft are already strong enough to be used as the floor for the new room and therefore avoid putting in steels and duplicating exactly the same floor again over the steels.

Not a hope in hell unless the spans are about 1.8m or less! If you want usefull advice you'll need to provide more info such as the spans required and some photos etc, how is the roof supported etc.

 

[Shytalkz]

You have absolutely no chance in providing a calculation to do what you are proposing. Don't even waste your time.

And get someone who is a qualified SE to do the design. You know it makes sense.

 

[freddiemercurystwin]

Is that........

Shytalkz! There must be ahint of some work in the air!

 

[Shytalkz]

Lol, the wanderer returns...possibly.