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[Tensketch]

Hi,

I have a detached garage that I'm gonna turn into a workshop/hobby space and I'm going to put some insulation in there to make things a little more comfortable. First thing I'm going to be doing is the ceiling. The roof space is a trussed pitched roof with the joists of the trusses running the length of the garage (about 5.4m). I can't get a definitive answer to this, but every topic in this area seems to have their fair share of people saying that I can fix a ceiling to the trusses or people saying if I touch the trusses I'll bring the whole garage down. So I am opting to not touch the trusses.

So my plan is to get some timber fixed to the walls across the width of the garage (about 2.8m) just below the trusses (I won't fix them to the trusses either) and from there, add noggings, loft insulation and finally a ceiling.

I have a few questions about this.
1) does this approach sound OK? I can probably get some wood long enough to run the length of the garage and have the new timber for the ceiling fixed to that for extra support.
2) I'm still a bit concerned about weight. What is a reasonable material to use for the ceiling itself? I was thinking 9mm plasterboard as its a little more affordable now but looking around it seems a single board is about 24kg. Are there better options?

Thanks for your time.

[stoneyboy]

Hi tensketch,
If you use 100x50mm joists across the 2.8m width this will be more than adequate to support 9mm plasterboard. Don’t bother with a central reinforcing joist.
Regards S

[Tensketch]

Hi,

Thanks for getting back to me.
I have 50x75mm to hand, would that do the trick or would it be better to go and get 50x100mm as you recommend?

Thanks

[stoneyboy]

Hi tensketch,
50x75 is probably too small. The only load the new ceiling will have is the plasterboard even so go for the larger size. You could strengthen the new joists using saddle brackets and strap then to the trussed rafters.
Regards S

[Tensketch]

Hi stoneyboy,

Thanks again for the info. Genuinely appreciate it. One final thing before I go and source some 50x100, if I went ahead with my original plan of running extra timber parallel to the trusses to create a central reinforcing joist, would the 50x75 work?

It's fine if not. If anything, I wanna educate myself to understand why 50x100 is correct.

Also, if weight is a concern, is there any alternative material I could use that is lighter?

Thanks again.

[stoneyboy]

Hi tensketch,
I hope I understand your description correctly:
Trussed rafters running the length of the garage ie a span of 5.4m. Trussed rafters not running across the garage a span of 2.8m.
Allowing for there to be a load on each of your new joists of around 15kg, 50x75 timbers would not be adequate. With a spacing of 400mm each 1.2x2.4m plasterboard sheet would be supported by 3 100x50 joists.
If you were to add a beam centrally up the length of the garage the yes your 50x75s would be ok but you would need a very large beam to support over 5.4m. Also this would need bearers both ends - one end would be in the middle of the door.
Regards S

[Tensketch]

Hi,

Thank you so much for the explanation. This DIY project is the biggest I've undertaken and I'm researching a lot of new stuff. So explanations like this are extremely valuable.

Your understanding is correct. I have a mockup that you can see here: .
The existing truss joists span the length of the garage and sit on wall plates at the front (above the door) and the back wall. Hopefully this helps illustrate what I'm dealing with.

Thanks