Garage Truss - boarding celing & load query?

Hi,

I have a detached single garage, approx internal dimensions of 6.4 x 3.5m.

I'm wanting to board the ceiling off, as I'm turning part of the garage into a small gym. The garage is built from single blocks, rendered on the outside.

The trusses are approx 47 x 100mm that span the width of the garage and are spaced approx 50-57cm apart (they're not equal). 12 in total, the two ends are closer together.

I do not plan on putting much up in the "loft" area, if I do at all, it'll be very light weight (upvc pipes, bamboo canes -- anything long that I don't have floor space for really - lightweight DIY/garden things).

My thoughts are that I'd like to board it out with 11mm OSB, and put some insulation (new polyester rolls, similar to the old glass fibre wool like you get in house lofts).

I'm wondering if the trusses will take the weight of 11mm OSB? I'm planning on having 6 x LED panel lights - again lightweight, but 11mm OSB boards seem to be around 20kg each. Approx 9 boards would be needed I believe - call it 10, as I'll need to box in my roller garage door housing - so that's approx 200Kg, at least pulling down on the width-running trusses.

The garage has a pitched roof, with tiles on - trusses, as expected I guess as tied together with some boards that run the length of the garage.

I'm fairly handy, DIY wise - but roof loads etc is out of my knowledge - is this something I really should be talking to a structural engineer or similar for? My thoughts are that 11mm OSB shouldn't sag, but if it does I'll put some support noggins in between the trusses.

I've added a few photos in so you can see the make up of the garage. Thanks for any advice/insights into if my plan is viable!

They're not trusses, there is nothing supporting the ridge, preventing the roof from spreading, except a few nails connecting the ends of the joists to the rafters, that said it doesn't seem to be sagging. You may want to consider adding some struts. Anyway do you mean OSB on the underside of the joists?

Ah! Thank you, I wasn't too sure of the terminology - initially I thought to call them joists, but wasn't sure about that either.
Can you please explain what struts are - wood to brace the joists between them?

I do mean OSB underside of the joists yes - basically to close off the ceiling area of the garage - I do plan on have a small hatch to access the top parts for any lightweight storage.

Thanks so much for your reply

Thinking too... would it be worth my adding some diagonal timber - almost emulating the typical 'W' or 'V' style (trusses?) you see in loft roofs for houses?
Edit: I think now, quickly reading up about roof supporting systems that this is what you mean by struts

My gut feeling is that the present structure is a little on the flimsy side to take the OSB weight. Maybe think of something you could use instead of OSB that is lighter. I'm not an expert though, this is just from looking at it.

Qusetion .. what is the roof covering for a rough weight calculation? My sight cannot distinguish.

It's tiles - from what I can tell, standard tiles that go on a house roof (the wavey-interlocking type )

Garage looks to be about 3.6m wide. I would be happy to fix 9mm osb to the underside of those joist if I wasn't putting any heavy in the roof space.

OSB is a dense material with an unknown mixture of various chips of wood, so weight cannot be calculated properly. With that roof that you have, I would not like to be under any ceiling material thicker that say 5.5mm, so decent ply sheets. This is just my opinion and others might say thicker.

Weight is less than plasterboard.

ajstoneservices said:

Weight is less than plasterboard.

Click to expand...

It is indeed and I would also recommend an extra annular nail in each joist end.

chris29 said:

I've added a few photos in so you can see the make up of the garage. Thanks for any advice/insights into if my plan is viable!

Click to expand...

My suggestion, would be to look at reinforcing what you have at the moment, before adding any weight. I notice the joist ends, seem to be just nailed with a couple of nails. I would drll through the end of the rafter, joist, and add an 8mm bolt, plus large washers either side, to prevent the roof spread.

Then to give the 3.5m joist extra support, track down some U brackets, three for each joist (3x 12 = 36), again, bolted in place to both rafters and middle of the joists. You would then need some galv steel wire rope, 3mm should be more than adequate, and some wire rope clamps, to suit - this type of thing - https://www.amazon.co.uk/Wire-Rope-Clamps/b?ie=UTF8&node=10257040031

The brackets, and the wire rope, form a Y, suspended on the brackets, bolted on the rafters, and joists. That would allow you to board the space out, as a usable loft space, board laid on top the joists.

Thanks all.

Harry, I don't need to have the loft space as something I can walk around on, but I'm intruiged by your reply. If what I'm envisaging from your reply is correct, the steel wire would prevent me from boarding on top of the joists unless cut outs were made? (I'm guessing you're implying tying the joists to the mid point, or higher in the rafters?)

I will bolt / nail through the joist ends, that's a good shout -- how would this prevent roof spread though? The joists have some timber on top of them, tying them all together to stop any lateral movement from what I can understand... although the person we bought the house off built the garage himself, there's been no movement or sagging of the roof (yet!), however if I'm going to the expense of putting a workshop/gym in the garage I'd rather do this prep work now!

My main aim is to close off the loft space to keep some heat in, when I heat the garage to use the gym during the winter months.

chris29 said:

I will bolt / nail through the joist ends, that's a good shout -- how would this prevent roof spread though?

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The joists, are under tension, presenting the spread of roof, fixed by what looks like a couple of thin nails. If you hang support, more weight on the roof timber, it will be more inclined to spread. Improving on the nails, is essential.

chris29 said:

Thanks all.

Harry, I don't need to have the loft space as something I can walk around on, but I'm intruiged by your reply. If what I'm envisaging from your reply is correct, the steel wire would prevent me from boarding on top of the joists unless cut outs were made? (I'm guessing you're implying tying the joists to the mid point, or higher in the rafters?)

I will bolt / nail through the joist ends, that's a good shout -- how would this prevent roof spread though? The joists have some timber on top of them, tying them all together to stop any lateral movement from what I can understand... although the person we bought the house off built the garage himself, there's been no movement or sagging of the roof (yet!), however if I'm going to the expense of putting a workshop/gym in the garage I'd rather do this prep work now!

My main aim is to close off the loft space to keep some heat in, when I heat the garage to use the gym during the winter months.

Click to expand...

Don't worry about roof spread as long as the joists are adequately fixed.

Adding the ply to the joists will help stiffen the structure in any case. Loading the ply with modestly weighted stuff won't make a jot a difference.