Ceiling joists & penetrations

[Crofter]

I'm building a warm roof timber frame house with the airtightness layer at the VCL.

In one part of the building the ceiling will be vaulted, and there will be three beams at c.3m above FFL, acting as structural ties between the rafters as well as serving as somewhere to position the lighting. That's six penetrations.

In the rest of the house, the ceiling will be normal height so I will need joists to carry it. The easy and obvious way is to fly these across between the rafters at eaves level, adding a fair bit of strength to the building. However that would be an additional 16 penetrations in the airtightness layer, which is more than I would like.

 

Any suggestions for a better way of doing this?

[Crofter]

Still trying to work out the best way of doing this. I can think of three options:

 

1- A ceiling joist at each rafter pair, spanning the building. Nice and easy, simple, and supported by a partition wall part way. But lots of penetrations (16).

2- Run two joists as above, and then run the remaining ceiling joists at 90 degrees to these, i.e. lengthways along the building. Cuts number of penetrations to four. Loses benefit of support from the partition wall so probably need heftier timbers.

3- Fix a high level batten and put the ceiling joists on hangers fixed to that. No penetrations other than the screws, but now the joists are adding little or no strength to the building.