Roof loading

[Russell griffiths]

Evening all

i have had a couple of roof designs done by timber i joist companies, now both companies have specified that they have designed with these roof loads in mind. 

0.8kn/m live load

0.6kn/m dead load

do these loads look fairly standard, I spoke with one company and said I wanted the best they could offer and was willing to pay more to close the joist spacing up to provide a :better roof:  two blokes looked at me like I was a nutter and said it far exceeded any spec needed and to stop worrying as it was all well inside deflection criteria. 

 

Anybody know what sort of load was specific to their roof

for your information my roof is mono pitch at 15 degrees. 

[PeterW]

Dead load is the weight of the roof which given this is probably sarking and steel sheet is fine. Live load is normally the snow load which used to be 0.75 or 1.0 depending on location, so 0.8 seems to be a variation on this. 

[mvincentd]

for my flat green roof posijoist co' states the following;

top chord live 1.5 kn/m2

top chord dead 1.42

bottom chord dead 0.25

They were asked to design them by my SE who would have given them his calcs as below;

 

[Russell griffiths]

Looking at @mvincentd post with his roof loadings if I give a run down of my roof buildup can anybody point me in the right direction as to the loading we should allow for in the design. Hope that makes sense. 

From the top down. 

Raised seam steel roof sheets 

18mm osb

50x50batten 

220x69 I joists

75mm service batten 

19mm softwood ceiling 

i have left out vcl and roof membrane and insulation, also mvhr ducting in the service void. 

Any thoughts anybody. 

[Mr Punter]

I think you need to just give this to an engineer as Building Control will want the structure signed off by an engineer in any case.  Why not just supply BC with a full set of drawings and spec then you can be sure that as long as you do what is on there it will be 100%.

[Russell griffiths]

Hi @Mr Punter if you have a quick look at my first post you will see It has all been given to a local timber engineering company and they have done all the calcs and design. 

The problem is me being me I asked if it could be improved upon, this was deemed to be a strange request and both designers thought I was silly wanting to spend more money than was needed. 

They both said it met all design requirements and deflection criteria so why would I want it any stronger. 

 

Now if this was a floor I would without doubt be insisting that joist spacing be tightened up to 400 instead of 600 centres as I would want a bounce free floor, however being a roof is there any point in over engineering it, I can’t see me ever up there with 20 mates dancing to the latest chart topper. 

Confused as usual. I might send it to my structural engineer to look at, it’s just another £100 to add to his bill I would like to avoid. 

[Mr Punter]

OK I misunderstood having read that you were doing the BC application bit by bit.

 

It is mainly snow loadings with a roof.

 

For you I would not rule out the 20 mate scenario though.