bay roof insulation question

[richiereynolds]

Hi there, looking for some general info from the experts!

I have a double fronted 1870s terrace, bay windows on the ground floor only. The bay rooves are pitched, lead covered and have no insulation inside.
They join the house at the level of the downstairs ceiling and a bit higher than the first floor floorboards (bottom and top of the "thick end" of the pitch).
If I lift the boards on the first floor, I can see right out into the bay roof cavities. i.e. the iron beam supporting the first floor wall above the bays isn't as tall as the opening into the bay roof cavities.
So, downstairs, the only thing between me and the elements is the plasterboard ceiling, probably some plywood and the lead. And, the air in the bay cavity can freely circulate bewteen the downstairs celing and first floor floorboards i.e. under the bedroom floors.
So, mainly, my question is about airflow, can I block off the inside of the bay from the firstfloor underfloor cavity?
What are the requirements for airflow within the bay roof cavity itself? How much insulation can I put in there?

Thanks, Richard.

 

[pinenot]

I've sketched out this as a possible solution - View media item 59545 - this is dependent on access from the bedroom floor/wall into the top of the bay roof ceiling...pinenot