Modern Roof Truss Design Loads

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Hi,

I live in a modern house with 'W' shaped roof trusses and timbers approx. 75mm x 35mm.

I've been boarding the loft for fairly light storage use by installing some 4" x 2" CLS timber cross batons to the joists, then 22mm chipboard flooring.

I've just had one of those uneasy moments where I've wondered whether I am doing the right thing. The boarding out is probably adding an extra 12kg/mtr. sq. and then some storage on top.

I would imagine that the truss design and loadings are very individual for the property (inc. wind, snow, etc) but wondered on whether anyone add any indicative views on what capacity may be built into the design and which will accommodate boarding/storage.

I know there is a water tank spread across several trusts in part of the roof space I am not boarding but I'm not sure whether this is getting any support from one of the internal (non-load bearing) walls. Certainly one option I thought would be to fix a support between the joists and the top of the internal walls in case the existing joists started to sag to allow the internal walls to give added support.

Any views appreciated - I guess I should probably get a Structural Engineer in to give a view if I want top be absolutely sure.

Many thanks,

Damian
 
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You fill be hard pressed to overload a trussed roof with chipboard and boxes of stuff

Come and have a look at my loft for proof ... if you can get in past all the stuff

The trusses work in a load sharing way so that it is very difficult for individual trusses to sag. They are normally designed to span across the external walls and get no support from your internal partitions
 
Bottom chord would have been designed for a live loading of 0.25kN/m2 or 25kg/m2..
Still gives you a fair amount of allowance.. also there is a factor of safety allowing you a little extra before your get any cracks in the ceilings..

Also as said the cross battening will spread the load over more than one truss, just spread stuff out and dont heap it all in one spot
 

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