Rafter Length - Estimating 

Hi Mate, it depends on the MGP rating but 2100 is a general rule.

@@Buildsum thank you! I appreciate it I just completed my first ever granny flat

Hi Mate, try it on a Calculator or do 3.464 / 30 cos if you are using your phone as the order of operation works differently on phone based calculators. You answer has to be larger than the half span of the building so 0.115 can not be the correct answer. Hope this helps.

Hi Krisneel, as the purlin in usually positioned half way up the roof the length of the purlin is the Average of the Length of the wall plate and the length of the ridge. Add the length of the Wall Plate and the Ridge together and then divide by 2.

Hi Hass, all my videos are done to comply with Australian standards, however, there is no standard on how to work out the length of materials. The standards will give you the required size of the material based on the span required and the strength of the material however how you calculate the length is not specified. Hope this helps.

@@Buildsum yes helped a lot thanks

Hi Mate, to work out the rise of the roof you multipy the pitch of the roof by TAN and then multiply that by the 1/2 span of the roof.

HI Steve, COS is short for Cosine, "the trigonometric function that is equal to the ratio of the side adjacent to an acute angle (in a right-angled triangle) to the hypotenuse". Hope this helps

Thank you, much appreciated 👍

Thanks, Sir, hope you are getting something out of these videos.

Hi Alex, that's not a bad idea however it tends to depend on the calculator or phone app that you are using and the steps shown in the video are pretty much the way it is entered. There is also a link in the description that will take you to a spreadsheet that will do it for you. As for the ridge because this video is only looking at estimating the length for ordering purposes half the ridge thickness is not going to change anything. There are more details about working out the Cutting length in the video link in the top right-hand corner of the video near the end. Thanks for your comments

thanks for your reply. Much appreciated. I'm on my way to becoming a better chippy thanks to your vids :)

Normally run divide by cos, then an open bracket should appear, enter the pitch and close bracket and then equals. If you use a bit of common sense to establish if the answer is correct as some calculators do vary with brackets etc.

Sorry Mate i only work in metric, there are lots of videos out there using imperial measurment.

Watch all the USA videos on rafters. They tell you how to do it and personally after watching heaps of them, I can do it in inches easier than metric which is still confusing me.