You may be wondering what shed companies have the most efficient designs, or perhaps you are on a tight timeframe to have your shed built and are wondering what design is the fastest to construct.
While there are a number of areas we could focus on, in this blog, we specifically look at the purlin-to-rafter connection and discuss the differences between three popular designs, pole sheds with timber beams, roll form steel sheds with rolled steel beams, and the Alpine design with the Alpine structural steel clearspan rafter.
What exactly is a purlin, joist hanger, and j-cleat?
A purlin is a horizontal structural member in the roof that is at right angles to a rafter or beam, this is located directly beneath the roof cladding and the cladding attaches to the purlin.
A joist hanger is a small steel bracket that is typically screwed onto the beam, this means the purlin sits in the steel bracket and creates the structural connection between the beam and the purlin.
A J-cleat is only found on Alpine structural steel rafters, as the name implies, it is shaped like a J and is welded onto the rafter. It performs the same job as a joist hanger and creates the structural connection between the rafter and the purlin.
Steps involved in each construction method
Connecting a joist hanger to a timber beam:
- Mark out the purlin centres as per the consented shed plans.
- Measure down the timber beam, the same measurement as the purlin depth. If the purlin is 200mm deep, measure 200mm down the beam to mark out exactly where the joist hanger will be located.
- Make sure the joist hanger is straight and tek screw it in place with 6-8 tek screws.
- Repeat steps 1-3 on the second timber beam.
- Place purlin into the joist hangers.
- Screw the purlin in place with another 6-8 tek screws in each of the two joist hangers.
Connecting a joist hanger to a roll form steel beam:
- Follow all steps as mentioned in the timber beam instructions above.
Connecting a purlin to an Alpine structural steel rafter:
- Place purlin in the pre-welded J-cleats.
- Drill two holes through each end of the timber purlin and secure in place using two M12mm bolts in each end of the purlin.
Why the Alpine system is both stronger and faster than other designs
As you can see, there are significantly fewer steps required when connecting the purlin to an Alpine structural steel rafter. No measurements will need to be taken to ensure the J-cleats are in the correct location as they are already welded on and only 4 bolts per purlin are required.
When using the joist hanger, there is a lot more time involved in making sure the joist hanger is in the correct location and then they require 12-36 tek screws per purlin.
The J-cleat is not only a faster method of construction when compared with a joist hanger, but it is also a lot stronger. A joist hanger is stamped out of a sheet of metal, around 1-2mm thick, and folded into shape. The J-cleat is made from 6mm structural steel, is welded onto the rafter, and is then hot dip galvanized, resulting in a more durable structural connection with superior rust protection.
Eliminate room for human error
Another key benefit of the pre-welded J-cleat is that it eliminates room for error. Since there are so many more steps involved with the joist hanger method, and the fact that every joist hanger needs to be individually measured and marked out, the risk of costly human error greatly increases.
These can lead, not only even longer build times, but a structurally deficient shed which could pose risk to both man and machinery. This is especially evident in areas with high snow loading.
As you can see, the Alpine rafter system can save a lot of time in this one area alone. Not only will your shed be built faster (saving money in hours of labour) and eliminate the risk of costly human error, but the structural connection will also be stronger resulting in a more durable shed.