Various structural forms (SF) of canopies, typically constructed for use as carports, verandahs, pergolas and patios. {NB: Pergola and patio have otherwise been redefined by marketing: thus lost traditional meaning in terms of sales, but not in terms of regulations and codes.}
FREE STANDING ATTACHED
SF01F

SF01F

The maximum span of this type of canopy is controlled by the capabilities of the roof cladding. Published span tables for roof cladding are based on weather proofing requirements for habitable buildings like houses. Manufacturers don’t typically publish extended span tables for roof cladding when used for canopies. Extended spans are typically only quoted in carport and verandah span tables.

Using normal cladding tables maximum spans around 2400 mm, with extended span tables, spans around 3600 mm.

SF01A

SF01A

Similar to SF01F, but with supporting columns on one side replaced by support by another building. If the building already exists then the strengthening of the existing building to support the additional wind load can be problematic.

In particular it is difficult to access the wall frame of a house, especially the bottom plate to slab connections, and the wall stud to bottom plate connections.

Wind class N1 and N3 are likely most problematic as connections selected using AS1684.2 for the house, will have little to no reserve capacity for additional wind loading. Wind class N2 is most likely to have some reserve capacity in the connections.

The main problems with attached canopies is accessing the resistance of the house to additional wind loads, and then the practicality of strengthening. The larger the canopy the greater the problems.

It is generally better to opt for a freestanding canopy with columns and piers adjacent to the house.

To be clear many of the manufacturers and installers of carports and verandahs have fine print which indicate the house owner is responsible for ensuring the house is strong enough to attach the canopy to. Any strengthening they do install, is done so without assessing its adequacy for the specific project.

The primary purpose of hockey stick brackets, is to distribute bolt forces in the connection so that the forces do not split the timber. If the house construction was from steel sections with plates greater than 3mm thick, then 2 bolts is all that would typically be needed. The number of bolts in the hockey stick bracket is not due to the strength of the bolts but the weakness of the timber.

The hockey stick connection bracket may serve a secondary function of strengthening the rafter. It may not however provide adequate strength, and additional stiffeners may need to be used.

Strengthening the house can incur a significant cost, far greater than cost of opting for extra columns. Not so much because of the extra materials, but because of the additional labour, and the cumbersome nature of the work. {NB: Ignoring the strengthening is the short term cheap solution. The future damage will be to the house, and its contents, not just the verandah.}

SF02F

SF02F

Similar to SF01F, except the cladding is permitted to over hang the beams. It allows slightly larger spans.

SF02A

SF02A

Similar to SF02F, but with supporting columns on one side replaced by support by another building. If the building already exists then the strengthening of the existing building to support the additional wind load can be problematic.

SF03F

SF03F

Cladding rails (B2) span between fascia beams (FB1). The width is dependent on the structural capacity of the beams rather than the cladding. The spacing of the cladding rails is dependent on the span of the cladding. Stormwater drainage is along the length: this limits the maximum length of the canopy.

 

SF03A

SF03A

Similar to SF03F, but with supporting columns on one side replaced by support by another building. If the building already exists then the strengthening of the existing building to support the additional wind load can be problematic.

SF04F

SF04F

Cladding rails (B2) span between rafters  (B1). The rafters span between fascia beams (FB1). The width of the canopy is limit by the structural capacity of the rafters. The spacing of the cladding rails is limited by the span capabilities of the cladding.

The cladding rails, can be either placed between the rafters and set down flush with the top face, or they can span over the top of the rafters.

Cold-formed C-sections are available in lengths upto 12m. However large flat surfaces tend to highlight distortions, and lack of flatness. Monoslope spans typically require heavier structural sections than a gable roof. Monoslope spans also produce greater roof rise than a gable roof. Unless there is a necessary need for a monoslope roof, a gable roof is likely a better option.

SF04A

SF04A

Similar to SF04F, but with supporting columns on one side replaced by support by another building. If the building already exists then the strengthening of the existing building to support the additional wind load can be problematic.

 

 


Revisions:

  1. [05/12/2017] : Original