The message .com
from sm_jamieson contains these words:

On Jul 2, 4:04 pm, "Roger Mills" wrote:
In an earlier contribution to this discussion,

snip

What size is the roof, and what size rafters are you intending to use? Are
you sure that you need *six* purlins? With suitably sized rafters might it
not be possible to use just *one* RSJ to support them in the middle? With
regards to supporting them off the original house wall, bolting a
horizontal
wooden beam to the wall, and cutting them into that is likely to be easier
than using masonry hangers.

Yep, all designed and signed off by struct eng.
Design (by me with help from this group) minimized roof thickness.
Roof about 4m in purlin direction,
5m in rafter direciton. Metal avoided for various reasons, including
BCO familiarity. (!)
Its just the purlin support that was in question. Beam on wall and
cutting in I agree should be OK.

Seems a bit like overkill to me too even if purlins one and six are
there as an alternative to supporting the rafter ends on walls.

FWIW my house is about 11 feet horizontally from ridge pole to wall
plate with only 2 purlins between them and the widest span is about 14
feet. OK so the purlins are substantial tree trunks but they need to be
as the roof is rough stone slates with an average thickness of over 3"
(That's the average thickness of the slatebed, not the individual
slates, most of which aren't much above 1" thick).

--
Roger Chapman