Draughtproofing loft

[StuBeeDoo]

Our loft serves a dual-purpose. As well as for storage, I use it as a big-boy's playroom. The floor area is boarded, with insulation beneath.
We are in an exposed location, and south-west facing, so anything more than a gentle breeze can seem like a gale. I would like to, somehow, stop the draughts that come in through the eaves.
I'm not particularly bothered about heating the space for the amount of time I spend in there, so I feel that 100+mm of PIR is going to be overkill. Will a 25mm thickness of PIR overlaid on the rafters, taped at the joints, and expanding foam where the PIR meets the walls and floor (it's a mid-terrace house), be sufficient to cut the draughts to a minimum?
All comments/suggestions welcome.
TIA
Stuart

 

[oldbutnotdead]

You need to keep the rafters ventilated but it sounds as if you've thought of that. Yes your plan will make the space more usable, you'll still need some sort of heat up there to make it anywhere near comfortable (oil rad or fan heater would be my choice).
EDIT Best way to avoid blocking the airflow through the eaves will be to finish the pir with a vertical section a couple of feet in from the eaves- it'll be easier to seal as well.

 

[StuBeeDoo]

Best way to avoid blocking the airflow through the eaves will be to finish the pir with a vertical section a couple of feet in from the eaves- it'll be easier to seal as well.

That ^^^ is the plan.