10 foot tree on wood truss roof.

[diegotorres2020]

Hey everyone. I'm seeking guidance on design loads for a roof patio. The structure is existing and this is part of a tenant improvement design, and the roof is pre-engineered wood trusses at 2ft o.c. and about 3 inches of roof material. The architect is calling for a 26ft Dia "zen garden" probably 3 inches of sand, and then a glass floor over it which will be the flooring for the bar area. In the middle of that "Zen Garden" they are also calling a 10 foot tall tree in a 3 feet dia planter. I'm having issues estimating the weight that's going to go on this roof. The roof was previously designed for a 50 psf DL and your typical 100 LL for assembly space. I have been all over the internet trying to get an idea of what the weight of the glass, and the weight of the tree will be. Would you also assume that the tree has wind loads affecting the MWFRS. Any advice or idea where i can find more info, let me know. Thanks!

 

[palk7 EIT]

Attached the glass weights, but highly recommend you get that info. from whoever the glass floor manufacturer is as that's the system that would be going in. With regards to rooftop gardenings again that saturated weight of the garden could be obtained from the system supplier, I remember long time ago I got the info. for one of the projects, they provided us with two systems one was a lighter version which was a 25 psf saturated D.L and the other was around 45 psf saturated D.L. So that would most probably be the D.L's in your case unless there are some other finishes or miscellaneous attachments(not taken into account the weight of that tree), maybe you might have to contact someone in that field to see how much does that particular species or type of tree weighs. With regards to wind load from the tree to structure it depends on how much surface area or a big chunk pieces is there to grab the wind or I might be wrong there, as the other half I think that the tree wind load will be taken up by the soil itself and will not transfer it to the roof deck as there is no positive connection between them. Need to have senior gentlemen's opinion/ advice

on that.

 

[DBronson]

diegotorres2020:

I think you need to get the landscape architect to specify the tree type, size and weight at maturity: trees grow. Make them assume responsibility for that data. The nursery supplying the tree will have to know its weight for shipping. A couple of things you need to consider: 1) the LA should also give you the volume and density of the planting medium; this can be substantial - I'd guess a 10' tree would require a soil depth of 36"-48". 2) the tree will almost certainly need to be irrigated. If the valve sticks in the open position it could flood the planter. This weight should be accounted for.

ASTM has several standards that address green roofs: ASTM E-2397 Standard Practice for Determination of Dead Loads and Live Loads Associated with Green Roof Systems. I haven't seen this document so I can't offer any comments on it. Also, apparently some codes treat the plant materials as live loads and other codes treat them as dead loads, so you may want to check the local practice.

For the glass floor the Architects need to get off their butts and specify the floor system they want. These are proprietary systems. No point in guessing.

Regards,

DB

 

[Ron]

Trees grow. As they grow, they get heavier.

 

[Settingsun]

DBronson is right about trying to get the landscape architect to give you a number, but they probably don't know and will refuse if they're smart. I did once see equations from the USDA but can't find them now - you might have better luck. However, when I looked into it, the planter and wet soil was easily the majority of the gravity load. Although trees do grow as they get older, they are limited by the size of the pot. If you end up having to guess the design load, make the weight and wind load the agreed design criteria, with the client responsible for remaining within what you can reasonably use as your design basis - not something nebulous like "10-foot tree".

Edit: Here are the tree weight equations plus some other useful info.

https://mgase.weebly.com/uploads/6/...s_terraces_and_walls_by_seaosc_sdc_7-7-08.pdf

 

[bones206]

I just planted a 6 ft pine tree in my yard. The clay root ball weighed at least 500 lbs.