First post here, so "Hi Everyone!"
I'm planning out the design for a veranda that needs to start under our first floor deck. The design is sort of tricky because there are some challenges with gum tree leaves and an old shed that get in the way - but suffice to say, a mate of mine that is an architect had some fantastic ideas - so I'm going to try them implement one step at a time.
First thing I need to do is span some new wooden rafters about 3.5 metres between existing extremely heavy gauge metal joists that are running the entire length of our house between the ground and first floor - the joists protrude from the back of the house and upon them is constructed the first floor balcony. Bottom line is that these metal joists are very solid.
From these new rafters, I'll string batons and then suspend the colourbond roofing - held from the top rather than the bottom. A slight slope on the colourbond will allow for the small amount of drainage necessary.
Although I'm pretty handy, I've never actually constructed anything original onto a house before - although I did replace a pergola once with an identical one.
I've been looking around for standard tables that tell me what cross section of wood by wood type I need in order to span 3.5 metres, and I'm a bit confused.
Can someone pls point me in the right direction to tackle the first challenge of fronting up to a timberyard and knowing what cross section and wood type I need to order so that it can securely span 3.5 metres and hold a roof up without sagging.
I figure that there will be 3 rafters running between each joist - i.e. each rafter will be less than 1 metre apart - like the little drawing below
...1m....1m
JJJJJJJJJJJJJ
R.....R.....R
R.....R.....R
R.....R.....R
R.....R.....R 3.5m
R.....R.....R
R.....R.....R
R.....R.....R
JJJJJJJJJJJJJ
R.....R.....R
R.....R.....R
R.....R.....R
R.....R.....R 3.5m
R.....R.....R
R.....R.....R
R.....R.....R
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