Looking to insulate attic of 1904 house in Manitoba, Canada where winter temps are -30 C and summers are +30 C. Currently, there is no insulation - just lots of wood. Under eves (crawl space) the floor joist are covered with double shiplap and roof rafters are covered with lath and plaster. Knee walls are lath and plaster with studs open on crawl space side. Ceiling above the rooms in attic is lath and plaster. No outside vents. Brickwork extends up to the roof decking.
Looking for suggestions on insulation type and vapour barrier. Thinking of skipping vapour barrier or applying poly over lath/plaster and re-drywalling, and using polystrene insulation boards on the hip (?) ceiling, instead of between roof rafters.