First Hip Rafters – green oak barn

Friday 5/2/21

I started the day ensuring that the sacrificial ridge was level and extended far enough to the right to take the king rafter (the central, and only common rafter in the hip of the roof). I ‘tacked’ the rafters in place with screws.

Top of king rafter

I secured the bottom of the rafters with these screws.

Timba screws

With the common rafters in place I started cutting the hip rafters.

King rafter in place

These are complicated! They have double bevels at the top end at an angle of 49.3 degrees and these need to be cut at an angle of 59.3 degrees. I have a digital, magnetic level which is excellent for setting the blade angle and I used a digital square to get the mitre angle right.

Checking the angle of the saw blade

Next I had to work out the position of the birdsmouth as I wasn’t sure how the roof calculator had calculated it. Had it assumed that the corners of the wall plate were angled like this or left square?

Diagonal cut for foot of second hip rafter

I worked out where the birdsmouth should be as follows. Using an off-cut of rafter as a locator, I placed a nail at the point where the top of the shoulder of the hip rafter would land.

Top of first hip rafter

I hooked a tape measure on to this nail and measured the distance to the edge of the wall plate where the inner corner of the birdsmouth will sit. With the tape really taught, the distance was 3750mm.

Measuring the hip rafter

I transferred this measurement to the hip rafter and as you can see, the birdsmouth moved up from that specified in the roof calculator. This indicates that the roof calculator assumed that the wall plate corners would be left square and not bevelled in the way that I have finished them.

Birdsmouth mark-up

This adjustment was successful. The hip rafter fitted well at the top…

Head of first hip rafter

… and at the bottom. [Addendum 5/4/21: Note that further adjustment of the birdsmouth was required – see Non-alignment of Rafters.]

Foot of first hip rafter - 2

This image shows how I fixed the feet of the rafters. This worked really well.

Foot of second hip rafter

This is how things looked at the end of the day. The common rafters on both sides of the roof were perfectly in line with the hip rafters. However, the common rafter on the hip is sitting slightly high. I’m not sure why this is – I’ll sleep on this and check things again in the morning.

Both hip rafters in place

This is how things stood at the end of the day.

End of the day 5/2/21




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