attic has no ventilation, identifying felt used...

timmer3

hi.
i found out at the weekend after removing old fibreglass insulation that there is not a single vent in the attic. it's a 1940s built mass concrete terraced house. i'm wondering if it's possible the felt used is a breathable vapour barrier type? i think it's highly unlikely as nothing in the house is new, almost everything is in its original condition. i've inspected the attic joists and rafters and there are no signs of damp or rot. but it's hard to see how the timber could survive so well for 65 years without any ventilation. it doesn't feel at all draughty up in the attic. i've attached a pic of the felt in case anyone might be able to identify it, i'd be very grateful.
i'm not sure what the technical term is but the attic floor is suspended from the rafters about 3 feet above the external walls. to put it another way, the upstairs rooms have the roof sloping in on them. i intend to fit 100mm of kingspan drylining/thermal boards to the inside of all external walls and i am assuming this should also be applied to the sloped ceiling upstairs. previously there was fibreglass stuffed all the way down the ceiling joists to the soffit, leaving zero air circulation which i am assuming was a bad idea. the plan is to install 300mm of sheepswool insulation, adding perpendicular joists on top of the existing ones, leaving all the rafters with an air-way to circulate from the soffit up to the ridge (and through to the other side), with several mesh vents installed along the soffit. is this a good way to do it? i.e. insulate the underside of the sloped ceiling rather than stuffing the space above with insulation?
thanks for any advice