Roof trusses - strong enough?

[RzB]

I want to attach some sound insulation material to the bottom of the main ties of the roof trusses in my garage. There is no ceiling there at the moment see picture..

plan is to use Maxi board to make a ceiling...

is a product specifically designed with sound insulation in mind. However it is quite heavy - 26.3 Kg/sq M.

My problem is loading of the roof trusses. Can they take the weight, or will the whole thing sag?

The garage is about 5.3M x 7M. The roof trusses...

the 5.3M width. There are 13 (including the two at each end) trusses spaced about 600mm apart. They are constructed throughout with 72mm x 35mm timber.

The tiles on the roof are Redland Stonewold. They are a concrete tile and are about 380 x 435. They weigh about .35kg each.

I have scoured the web to find resources that will help me with the calculations, but have found nothing helpful.

Have I got to call in an engineer to do some calculations ? If so what should I expect to pay for something like this?

Any thoughts would be most welcome..

Thanks, Roy

[Michael Mcneil]

and a thick wad of glass wool.

I imagine that rthe boarding you are thinking of will match that. Why can't the suppliers tell you about the tech side?

[N. Thornton]

should take it, but may sag a bit. I wouldnt think it would be the ideal choice, 26kg/m2 is pretty OTT. If youre putting something as beefy as that up its pointless to put it on springy bendy joists like

3x1.5.

How much work you do depends on what results you need and why.

One workable example might be... 12mm PB with all joints filled. Run lines of exanding foam along the space between the joists on the back of the board to act as a stiffener and absorber. Keep it off the woodwork. Fill space between joists with glass wool. Chipboard on top of joists as well adds more sound deadening. Use TnG and pay attention to filling all gaps everywhere.

If youre looking at studio quality sound proofing, its probably going to include uprating the joists. 5m spans of 3x 1.5 is not very rigid.

NT

[RzB]

Michael, Many thanks for your response.

To be fair the suppliers are being very helpful. They just are a not willing to accept the risk of telling me it will be OK.

I think I'm going to have to find an engineer...

Thanks, Roy

[RzB]

N, Thanks for your response...

Yes - I wonder if I could just reinforce the main ties with something a little heavier. Add some extra stiffness.

The reason for the sound proofing is that I'm converting the garage into a workshop. It will have noisy things like routers and planers screaming away... Mostly high frequency - not so worried about the low frequency stuff. No booming bass loudspeakers to worry about...

Being a "good" neighbour I want to do the best job I can, even if it costs a little more cash.. Hence the purpose designed Maxi board.

I think I'm going to have to get an engineer involved.

Many thanks for your help.. Roy

[RzB]

BTW - I did get and engineer to do the calculations.

No strengthening required. Good news.

Cost of calculations - 3hrs at £40 / hr - £120 + Vat.

Roy