ᐅ Double Carport – Experiences and Tips on Ridge Beams and Purlins
Created on: 7 Aug 2018 10:48
I
Illo77Hello,
I would like to hear your opinions and advice.
First, here are the two data points: snow load zone 2, wind zone 3.
I want to build a detached double carport and I am uncertain about the purlins or collar beams or whatever you might call them (I believe in some regions they are referred to as wall plates?). I have seen many different versions used in carport construction.
My original plan was to notch a 12x12 cm (5x5 inch) structural timber post by 6 cm (2.5 inches) and place a 6x24 cm (2.5x9.5 inch) collar beam on top, which I would then bolt to the post using 12x140 mm (0.47x5.5 inch) carriage bolts. This is how I’ve seen many carports built, both in kit versions and some constructed by craftsmen. However, I have often read that removing 50% of the post material at the top weakens the structure. Could it fail there, or is this approach safe? Would it be more secure to use glulam posts or larger 14x14 cm (5.5x5.5 inch) posts for more material?
Alternatively, I could use a collar beam that is also 12 cm (5 inch) thick, but how do I attach it to the post without requiring advanced carpentry skills? At my parents’ house, they used a 12x20 cm (5x8 inch) collar beam and fastened it from above with one large or long washer-head screw through the collar beam into the post head. Is that sufficient? I’m a bit skeptical about driving a large screw into the end grain.
Using angle brackets mounted from below looks awkward, and nailing perforated metal plates from the inside doesn’t look very clean either.
There will be 5 posts per side spaced 138 cm (54 inches) apart, with three sections per side featuring wall cladding about 100–120 cm (39–47 inches) high. The rearmost section and the back side will be closed up to the top edge (the back side will also have posts spaced similarly).
Oh, and regarding diagonal bracing—should it be included if there is wall cladding?
I would like to hear your opinions and advice.
First, here are the two data points: snow load zone 2, wind zone 3.
I want to build a detached double carport and I am uncertain about the purlins or collar beams or whatever you might call them (I believe in some regions they are referred to as wall plates?). I have seen many different versions used in carport construction.
My original plan was to notch a 12x12 cm (5x5 inch) structural timber post by 6 cm (2.5 inches) and place a 6x24 cm (2.5x9.5 inch) collar beam on top, which I would then bolt to the post using 12x140 mm (0.47x5.5 inch) carriage bolts. This is how I’ve seen many carports built, both in kit versions and some constructed by craftsmen. However, I have often read that removing 50% of the post material at the top weakens the structure. Could it fail there, or is this approach safe? Would it be more secure to use glulam posts or larger 14x14 cm (5.5x5.5 inch) posts for more material?
Alternatively, I could use a collar beam that is also 12 cm (5 inch) thick, but how do I attach it to the post without requiring advanced carpentry skills? At my parents’ house, they used a 12x20 cm (5x8 inch) collar beam and fastened it from above with one large or long washer-head screw through the collar beam into the post head. Is that sufficient? I’m a bit skeptical about driving a large screw into the end grain.
Using angle brackets mounted from below looks awkward, and nailing perforated metal plates from the inside doesn’t look very clean either.
There will be 5 posts per side spaced 138 cm (54 inches) apart, with three sections per side featuring wall cladding about 100–120 cm (39–47 inches) high. The rearmost section and the back side will be closed up to the top edge (the back side will also have posts spaced similarly).
Oh, and regarding diagonal bracing—should it be included if there is wall cladding?