How can I strengthen my roof?

[Peter500]

I've just finished a truss roof. I used queen post trusses so that I could store loads of stuff up there. I've now discovered that it won't actually take the weight. Plasterboard + chipboard may just about leave me with enough weight to support my garage door, which makes the storage area pointless if I can't put anything up there.

I'm now wondering how I can increase the weight capacity

I'm considering running matching timbers parallel to the bottom chords (72mm thick), but on a 3.4m span, I think I would need quite a few of them, and they would be quite hard to squeeze in. Another option I've considered is something like steel box sections (maybe 40mm) instead, which can take the weight of the ceiling and garage door, but I'm not certain how well they would cope with that span. Fixing plasterboard to steel could also be a pain.

Does anybody have any thoughts/ideas?

 

[noseall]

I've just finished a truss roof.

Can you post a piccie?

 

[Peter500]

Here are a couple of pictures. The front and back (timber wall plate and steel beam with timber). The OSB is where it transitions to a flat roof.

I'm thinking of cutting a square out of the insulation, pushing steel through and then pulling it through to put the other end on timber.

 

[stevie888]

Those look like fairly normal gangnail trusses. A few dimensions and a sketch or 2 would clarify things

 

[Peter500]

I believe it has been designed so that the bottom chord will only take 250N/m2.

 

[freddiemercurystwin]

They'll cope with some storage, not engine blocks but certainly a few lengths of timber. They'll be designed to have a ceiling hanging off them no problem and some fat builders hoofing around on them whilst they're installed.

 

[Peter500]

They'll cope with some storage, not engine blocks but certainly a few lengths of timber. They'll be designed to have a ceiling hanging off them no problem and some fat builders hoofing around on them whilst they're installed.

I spoke with a truss designer person and he believed that they were only designed for 250N/m2, which is what my designs seem to say. I think they were designed for a chipboard deck and minimal storage. Chipboard + plasterboard isn't far off 250N/m2.

I believe trusses are also spec'ed to allow a 'fat builder' (900N), but that's based on it being a temporary load. I wouldn't be able to store any fat builders up there long-term. I think we can assume that the garage door is a short term load (only there when open), so that would probably be ok as long as I don't have a person in the loft at the same time.

 

[Peter500]

I think I know what I'm going to do now...

I will support the garage door with uni strut (or similar). This may be off the walls at the sides, but I'll use the wall plates if that doesn't work out.

For the ceiling, I'll use PVC panels, which I believe are a little under 4kg/m2. If I combine this weight with the loft boards and a few lights, then it should leave around 12-13kg/m2 for storage. Not as much as I would have liked, but I can work with that.