Starting on the Roof – green oak barn

Tuesday 2/2/21

Today was very varied. I started by doing a final bit of fettling of the final truss joints and then turned my attention to how this was going to interface with the softwood elements of the roof.

I made a template to slot into the cog joint on the tie beam and this gave me the reference points I needed for the wall plate that this tie beam will lay on top of.

Wall plate template

I then needed to cut the first softwood common rafter. To do this I was going to need some sort of support. The temptation was to buy a couple of these.

Roller stand

But I know that these are great in theory but fall over too easily in practice. So I decided to modify one of the trestles to do the same job in a more stable fashion. I started by filling the central part of the I-beam of one of the trestles.

Trestle modification - 1

I then used some 4 x 2 and OSB board – plywood would have been better but I didn’t have any – to extend the height of the trestle. This extended the trestle height to 2-3mm below the height of the saw bed.

Trestle modification - 2

I then slotted in some wedges to allow for the fine adjustment of the height.

Trestle modification - 3

And hey presto!

Trestle modification - 4

You’ll notice that I did need to use a spacer but the wedges were still good to tweak the height so that the wood sat perfectly flat on the saw bed.

Trestle modification - 5

The time spent working on the roof geometry (here and here) really paid off. The common rafter fitted pretty much perfectly, leaving a 45mm gap between the underside of the common rafter and the top face of the green oak principal rafter.

Common rafter - 1

And the overhang was spot on although I need to try harder with the horizontal cut of the birdsmouth!

Overhang check

The icing on the cake was that the same common rafter fitted on the other side of the roof as well. Result.

Common rafter - 2

Most of the gap between the green oak principal rafter and the softwood common rafter will be filled with insulation and plaster board – see below.

Roof detail 175 overhang

Onwards and upwards.




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