Verandah rafters

**madmuso** · 18th January 2016, 03:44 PM

Hi guys,

I have a question regarding rafter lengths, plumb and birds mouth cuts.

A mate of mine asked if I could help him knock up a small verandah at his place, its approx 3 meters wide by 2 meters. We are going to base it off the verandah at my place (already done when we got the house), which isnt too complicated, except for a few important points.

I understand that obtaining the rafter lengths and plumb cut angles is based upon a2 + b2 = c2 (get square root of a2+b2). But im not sure where to actually take my dimensions from in order to do the math correctly.

I have attached a picture to help describe our scenario.
On the house end, the rafters will be fixed to the house fascia via joist hangers, the rafter will have a birds mouth cut so it sits inside the seat portion of the hanger. On the opposite end, the rafters will be plumb cut and nailed to the verandahs fascia. (posts will be notched out to accommodate the fascia).

I have checked out vids on youtube and other sites but I am confused about where I actually take my measurements to obtain the run and rise in order to do the math to obtain my plumb cut angle/degrees. The part thats confusing me is the bird mouth cut at the house fascia end.

We will be working with a datum line to ensure all heights line up true to each other, so we only need to do the math once which is nice!

If anyone can give me some tips it would be greatly appreciated.

Thanks,

**david.elliott** · 18th January 2016, 05:10 PM

This site is your friend...

Calculators + Templates - Builders, Carpenters, Woodworkers + DIY

**rustynail** · 18th January 2016, 05:37 PM

Your true length of rafter will be from top inside edge of beam to top point of rafter where it hits the fascia. The plumb cut on the top and tail of rafter will be the same angle if both fascia and beam faces are plumb. A string line run from beam top inside edge to a nail in the fascia where top edge of rafter will strike will show the angle between line and face of fascia and beam. A sliding bevel can be set to this angle.
If the beam is plumb and the fascia is plumb then the angle can be taken from a scale drawing.

**madmuso** · 18th January 2016, 05:55 PM

Originally Posted by david.elliott

This site is your friend...

Calculators + Templates - Builders, Carpenters, Woodworkers + DIY

Thanks David. Found the appropriate calculator to get my angle using the run and rise measurements but I'm stuck on the rise dimension. To get my run I'm gonna hang a plumb bob from the house fascia and measure from the string to the inside of the verandah fascia, done. But I'm not sure about where I should be getting my rise dimension from.

Do I shoot a level line from the TOP of verandah fascia and measure from that point to where the top side of the rafter will meet the house fascia?

thanks,

**madmuso** · 18th January 2016, 06:10 PM

Originally Posted by rustynail

Your true length of rafter will be from top inside edge of beam to top point of rafter where it hits the fascia. The plumb cut on the top and tail of rafter will be the same angle if both fascia and beam faces are plumb. A string line run from beam top inside edge to a nail in the fascia where top edge of rafter will strike will show the angle between line and face of fascia and beam. A sliding bevel can be set to this angle.
If the beam is plumb and the fascia is plumb then the angle can be taken from a scale drawing.

Excellent, thanks. So I wasn't too far off! Your string method is great, so I can basically rest one side of the bevel on the house fascia and then move the bevels adjustable leg to the string line giving me the angle which I can use for my plumb cuts. Correct?

**rustynail** · 19th January 2016, 12:53 PM

You've got it .

**madmuso** · 24th January 2016, 05:50 PM

Hey guys,

Thanks for the help so far. Making a start tomorrow on this so hopefully it doesnt give us too much trouble. I did however have another question, maybe someone has a trick of the trade they can share.

I was wondering the best way to make sure the verandah stays square to the house wall we are coming off.
The only thing I can think of is to use a decent size square and make sure the leg against the brickwork is in line with the bricks, then scribe a pencil line on the concrete against the other leg of the square. Then to get that line to the post destination (approx 2.5 away from house) use a straight edge/spirit level to continue scribing the line. As well as use the spirit level to "climb" the line up the brick wall to the rafter location on the house fascia. Once I have the sides and front of the verandah marked on the concrete I was going to run a tape diagnally (corner to corner) to check its ok. Will this work ok? Or is there another more trustworthy way?

Thanks!

**david.elliott** · 24th January 2016, 08:53 PM

Use the 3/4/5 triangle.
If you (say) measure 3000 out from the wall at a "right" angle on your first rafter, and 4000 across the front of the house wall, if the corner is square then the distance between those two points will be 5000.

https://www.youtube.com/watch?v=69cslx6ER7k

You can multiply those out to get as close as you can to your finished dimensions.

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