Note this post has been updated following the loss of photos on RMWeb
Converting a loft for a model rail layout
The only internal timbers in my loft are three ties at roughly chest height you can just see all three in this shot of the loft as it was insulated:
It seemed logical to use this to support my layout. Timber in 1946 was clearly of better quality as these are just 50x100mm in section and yet they stop the roof sagging by being connected to purlins around the edge