Minimum Snow Load on Fabric Structures
Minimum Snow Load on Fabric Structures
(OP)
I am looking for some guidance on the minimum snow loads required on fabric structures. My question really relates to the Cs (roof slope factor) and I am more concerned about the National Building Code of Canada although I welcome any commentary from other code users.
I know both NBCC and ASCE have similar equations for Cs where it is a function of roof slope and slippery vs non-slippery surfaces. Essentially for a slippery surface with a roof slope of less than 60 degrees the Cs will be > 0 and therefore the structure must be designed for some value of snow load.
I am wondering if there is any reference or code commentary that suggest that a lower snow load value could be used for fabric roofs. I beleive ASCE has one but I can't find anything on NBCC. These companies have been building these structures for years in cold climates and I am wondering how they justify it to meet code?
Thanks in advance for your help.
I know both NBCC and ASCE have similar equations for Cs where it is a function of roof slope and slippery vs non-slippery surfaces. Essentially for a slippery surface with a roof slope of less than 60 degrees the Cs will be > 0 and therefore the structure must be designed for some value of snow load.
I am wondering if there is any reference or code commentary that suggest that a lower snow load value could be used for fabric roofs. I beleive ASCE has one but I can't find anything on NBCC. These companies have been building these structures for years in cold climates and I am wondering how they justify it to meet code?
Thanks in advance for your help.






RE: Minimum Snow Load on Fabric Structures
BA
RE: Minimum Snow Load on Fabric Structures
I completely agree but how is that these structures are built here in Canada? Does someone at the municipal level approve of their use? Since municipalities can choose to adopt the National Building Code or not, does that give them the authority to allow this type of construction?
The explanation I was given from a Fabric strcuture manufacturer is apparently from the commentary for ASCE-7-02 where it says "Glass, plastic, and fabric roofs of continuously heated structures are seldom subjected to much snow load because of their heat loss causing snow to melt and sliding. For specialty roofs, knowledgeable manufacturers and designers should be consulted".
According to this manufacturer a snow load of 6psf is the maximum load any structure will have to resist. This is 10 times less than the normal roof snow load in my City.
RE: Minimum Snow Load on Fabric Structures
6 psf is not an adequate wind load, much less snow.
RE: Minimum Snow Load on Fabric Structures
RE: Minimum Snow Load on Fabric Structures
RE: Minimum Snow Load on Fabric Structures
How do you deal with the degredation of the fabric, and it's strength, with time due to UV radiation? Special coating, or recommended replacement time of the fabric?
Seems like this would be a real issue with snow loads of any magnitude.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Minimum Snow Load on Fabric Structures
Because the fabric does degrade over time, all the more reason to not reduce the snow load any more than is acceptable per the ASCE 7. Really not much different than a metal buidling roof as they degrade in their slippery factor over time as well. Type of fabric, special coatings, location in country will all affect the lifetime of the fabric.
RE: Minimum Snow Load on Fabric Structures
I wouldn't reduce anything. In fact, I'd be worried about localized sagging leading to some kind of collection of snow if the geometry and fabric tension allows it.
RE: Minimum Snow Load on Fabric Structures
I have attached a short paper which explains why this company believes 6psf is a maximum load these structures need to resist. If you have a few minutes please read through it and let me know what you think.
RE: Minimum Snow Load on Fabric Structures
I remember seeing some conversation about the old Cover-All sheds being under-designed to the NBC around the time they went bankrupt. If you can find any reliable sources it may provide some insight to the big picture.
RE: Minimum Snow Load on Fabric Structures
RE: Minimum Snow Load on Fabric Structures
RE: Minimum Snow Load on Fabric Structures
RE: Minimum Snow Load on Fabric Structures
As an EOR, I would be telling them what loads to use. If they wanted to lower those loads, I would require documentation of where it is allowed in the codes with the calculations and test for it.
As an sub-engineer, I would calculate the loads to the foundations. Compare my loads to theirs. Use the higher loads for my design. (Unless I get their calculations and documentation for a lower loading.)
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Minimum Snow Load on Fabric Structures
So the OP is the EOR for the foundation, and the other engineer is the EOR for the fabric structure. This is the same situation as for many PEMB's where there is no designated EOR for the project, only parts of it.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Minimum Snow Load on Fabric Structures
2009 IBC Section 107.3.4 “...The registered design professional in responsible charge shall be responsible for reviewing and coordinating submittal documents prepared by others, including phased and deferred submittal items, for compatibility with the design of the building.”
If you are not doing this you are a sub-engineer responsible only for what you are sealing.
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Minimum Snow Load on Fabric Structures
In the Province of Alberta, municipalities do not have the option of choosing the building code. They are required to use the Alberta Building Code (ABC) which is identical to the National Building Code (NBC) insofar as structural design is concerned. Climatic and seismic information for various municipalities is given in Appendix C of the ABC.
The Engineer of Record does not have the option of varying the snow load unless he obtains a variance from the authority having jurisdiction.
BA
RE: Minimum Snow Load on Fabric Structures
RE: Minimum Snow Load on Fabric Structures
BA
RE: Minimum Snow Load on Fabric Structures
After reviewing your file on the structures built by Sprung Structures, I tend to believe that, for the type of structures illustrated, a lower snow load might be acceptable because all of the structures depicted in the photos had substantial slope and, apparently, a very low coefficient of friction. It would need the approval of the authority having jurisdiction, but if the structure can be shown to shed the snow completely, I think approval from the authorities could be obtained quite easily.
That does not mean to say that snow load may be reduced on all fabric covered structures. It would depend on the type of fabric and the configuration of the roof. Perhaps some guidelines could be prepared but, at the moment, approval would seem to be required on an individual basis, that is, for each fabric covered structure.
BA
RE: Minimum Snow Load on Fabric Structures
RE: Minimum Snow Load on Fabric Structures
"3105.3 Design and construction. Awnings and canopies shall
be designed and constructed to withstand wind or other lateral
loads and live loads as required by Chapter 16 with due allowance
for shape, open construction and similar features that relieve
the pressures or loads..."
Not sure if there is anything similar in the NBC.
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.