Green Roof

[staceydsf]

Hello All, some advice please if possible. We are building a garden room 6meters by 3 meters with a flat roof. The building is constructed from 4"x2" C16 @ 400 Centers with a double plate at the top, on a 3 coarse brick foundation and a concrete footing of 6". The Roof is constructed from 6"x2" C16 timber at 600 Centers with 12MM plywood.

The loading of the green roof is approx 150KG per Sq Meter. Would the roof we've build be strong enough to cope with this loading?

We'll be using a seedum plant mix

Thanks

Stacey

 

[doitall]

I think you should get a strutural engineer to do some sums.

At nearly 3 tonne I'm not sure even the footings would take it unless they're on rock

Not an expert by the way.

 

[garyo]

Is the 150KG a worst case scenario - taking in to account rain soaked soil and a couple of feet of snow?

 

[theoldun]

Hello All, some advice please if possible.
Thanks Stacey

Never built a Green Roof, never read up on them, and no wish to do so.
Advice. Little good news, so will jump straight to bad news.
12mm plywood is undersized for 600 centre roof joists.
Your wall studs are at 450 centres and even with a double top plate your roof joists should have been the same centres and sat directly above wall studs. However if you only have light roof covering, you will be okay.
150kg/m2 equates to 0.15 kn/m2 dead load. Would suggest that you check your loading as this is a very light load.
Working on the above dead load you will have an imposed snow load of 0.75kn.m2.
C16 47x145 at 600 centres will suffice for 3 metre span for that loading but will only give you access for maintenance and repair. Thats the little good news.
For unlimited access you will need 47x170 C16.
Without knowing ground conditions, width and depth of foundation ,150mm concrete is suspect to heave and shrinkage.
Regards oldun.

 

[staceydsf]

Is the 150KG a worst case scenario - taking in to account rain soaked soil and a couple of feet of snow?

Yes

 

[staceydsf]

Hello All, some advice please if possible.
Thanks Stacey

Never built a Green Roof, never read up on them, and no wish to do so.
Advice. Little good news, so will jump straight to bad news.
12mm plywood is undersized for 600 centre roof joists.
Your wall studs are at 450 centres and even with a double top plate your roof joists should have been the same centres and sat directly above wall studs. However if you only have light roof covering, you will be okay.
150kg/m2 equates to 0.15 kn/m2 dead load. Would suggest that you check your loading as this is a very light load.
Working on the above dead load you will have an imposed snow load of 0.75kn.m2.
C16 47x145 at 600 centres will suffice for 3 metre span for that loading but will only give you access for maintenance and repair. Thats the little good news.
For unlimited access you will need 47x170 C16.
Without knowing ground conditions, width and depth of foundation ,150mm concrete is suspect to heave and shrinkage.
Regards oldun.

My wall studs are at 400 Centres at the rear and sides of the building, and at 300 Centres at the front, but we do have two windows at the front and a door opening. The Door is 1.5m in the centre and the windows are 750mm one each side of the door.

The rear of the building is approx 2.2 Meters High, the front approx 2.5 meters high, the pitch of the roof is defiantly 5Degrees.

We only need access for maintenance to the roof. If 12 ply is undersized, what dou you recommend?

The foundation is a 150mm concrete steel reinforced slab 6meters by 3 meters. The ground conditions are sandy. The slab has been there before we owned the property so at least 7 years

Hope this helps answer some of your questions

Thanks

 

[catlad]

Your roof will deflect too much with that loading and eventually fail.

 

[staceydsf]

Your roof will deflect too much with that loading and eventually fail.

I assume you mean the extra loading for the green roof?

 

[tony1851]

150kg/m2 equates to 0.15 kn/m2 dead load.

You must have been away when they did maths!

 

[theoldun]

You must have been away when they did maths!

Tony and OP,
Hold our hands up, will squeeze our nuts and humbly appologise for our mistake.
On the strength of new loading 1.5kn/m2, nothing in the tables go up to that weight, and we can only guess that you would need C16 75x220.
Regards oldun

 

[tony1851]

You must have been away when they did maths!

will squeeze our nuts and humbly appologise for our mistake.

Ouch! No need to go quite that far