Weight on garage ceiling

[bagofjuice]

I have a pitched roof double garage with roof truss timber size of 70 x 35mm only. They span 5.4m across the ceiling using metal connector plates for joins.

I would like to plasterboard the ceiling, insulate with Kingspan or similar in the 70mm gap and board the top for storage.

I won't be storing anything particularly heavy (at the moment just empty boxes, old paint tins, some timber, chairs etc.) but want to be able to walk around it safely.

Does it look safe, or would new ceiling joists be required?

Untitled

• bagofjuice
• 29 Nov 2012
• 1

 

[dormermike]

I have similar so watching with interest.. i suspect the joists will need beefing up - i've stored some oak on mine and there was creaking, doubt it would take walking around up there.

 

[catlad]

Trusses unless designed otherwise are made for plasterboard only not for boarding out and storage.

 

[theoldun]

Ceiling ties for standard Fink trusses such as yours are designed as follows.
Long term load.
Plasterboard and skim 175N/m2
Light imposed storage load 250N/m2
Short term man load.
At a point to produce the highest stress 675N/m2
Note these are metre square loads
If you do not understand kN and Newtons we list explanation below.
1 N = 100 g
10 N = 1 kg
--------------
KiloNewtons
--------------
1 kN = 1000 N = 100 kg
10 kN = 10000 N = 1000 kg
--------------
Kilograms are always for one 0 less than Newtons.
Kilo' increases a value x1000 times.
If there are 12 N, then there are 1,2 kg.
---------------
That is only an estimation. A kiloNewton (kN) is a measure of force while a kilogram (kg) is a measure of mass.
F=ma. F=force, m=mass, a=acceleration
When talking about weight, weight is a force. So if something weighs 1kN then it will have a mass of 102kg. Get this by dividing this force by the gravitational constant.
The acceleration gravitational constant is around 9.81m/s2.
If you still do not understand, then come back and will explain in old money.
Regards oldun

 

[Deluks]

Does it look safe, or would new ceiling joists be required?

 

[bagofjuice]

Ceiling ties for standard Fink trusses such as yours are designed as follows.
Long term load.
Plasterboard and skim 175N/m2
Light imposed storage load 250N/m2
Short term man load.
At a point to produce the highest stress 675N/m2
Note these are metre square loads

Thanks, that's very useful.

Is the Light imposed storage load in addition to the plasterboard and skim load?

I will be plaster-boarding the ceiling and laying fibreglass type insulation, and your figures read to me like I will be ok storing some general junk up there too, max 25Kg per m2 if I've read that right (?).

Thanks

 

[theoldun]

Is the Light imposed storage load in addition to the plasterboard and skim load?

Yes

if I've read that right (?).

Yes
Regards oldun

 

[bagofjuice]

I'm thinking about doubling up the joists for piece of mind before the ceiling goes up. However I don't think it will be easy to remove and replace the joist hangers easily.

Any ideas?

 

[bagofjuice]

Or to rephrase: I am thinking it would be wiser to put additional larger joists in between the existing roof trusses (currently 600mm centres) to hold the new ceiling.

The span is 5.4 meters with single skin brickwork after that. So about 5.7m timber span required. One of the supporting walls is the garage door side (2 lintels supporting the weight.)

Assuming 12.5mm plasterboard, 18mm chipboard flooring and 100kg per m2 load bearing requirement, what size and grade timber joists would be required?

 

[RonnyRaygun]

Assuming 12.5mm plasterboard, 18mm chipboard flooring and 100kg per m2 load bearing requirement, what size and grade timber joists would be required?

At a 5.7m span you will struggle to get anything sensible to work.

You will be looking at 47x245mm C16, or 47x220mm C24 timbers at 300mm centres (so two between each truss).

Are you planning to install them below the ceiling tie brace that can be seen in the picture? You will lose quite a bit of headroom if so, especially once the plasterboard goes on.

It's the right decision though to ignore the capacity of the existing trusses. They're unlikely they have anywhere near enough spare capacity for what you want, and you can't really just beef up the ceiling tie as you will also put considerably more stress onto the web braces, top chords, and connections too.

 

[freddiemercurystwin]

Oh FFS I've been in more garages and houses like this with piddly trusses just like these whereby the owner has stored all manner of junk timber, paint pots, ladders, lawnmowers etc etc etc than I've had hot dinners! Low and behold they even step on the joists when they're up there and shock horror the roofs haven't collapsed either! Really if the trusses can cope with a couple of gorilla size builders stepping on them when they build'em they can cope with some chipboard and the kinda stuff the OP is talking about!

Just get on an do it and ignore the tiresome meaningless posts some seem to right.

 

[RonnyRaygun]

blah blah blah

He's talking about 100kg/m2...

Paint pots no problem, 100kg/m2 more of an issue...

 

[freddiemercurystwin]

Doubt he'll ever get anywhere even approaching that.

 

[bagofjuice]

That's a bit of an arbitrary figure. I just quadrupled what I thought was a realistic max load for plenty of headroom.

If there are too many obstacles and/or costs to increase the load bearing to 3-4 times then I will just board up as is and limit the paint pots.

 

[RonnyRaygun]

Doubt he'll ever get anywhere even approaching that.

I agree, unless he decides to store thousands of books up there...

Not likely I admit...

If it was my garage, I'd be chucking all sorts up there! Just wouldn't tell someone else to do it...

As I said though, if he wants to put new properly designed joists in then nothing sensible will work.