Do the floor joists between ground and 1st floor need ventilated?

[iwilson16]

i have an old Victorian double upper flat in Edinburgh. The joists run front to back, and the back of the property has a north facing coom ceiling joining up to a flat roof. There is no roofing felt. Tiles are nailed to wooden boards laid horizontally.

So a lot of cold air comes through the pitched roof section, and blows directly under the floor and over the ceiling. I plan to fit 100mm PIR boards above the ceiling, leaving a 50mm gap under the roof deck. But does the underfloor need ventilated? There is only about 50mm under the floorboards, since there is the old "deafening" ballast above the ceiling of the room below.

I'm thinking of sealing between the joists at the coom ceiling and, and/or adding some insulation below the floor. Thoughts?

Thanks,
Ian

 

[KenGMac]

Ian.

Perfect timing to sort out your insulation, what with the room being stripped out.

By all means fit PIR Insulation under the flat roof section and down the slopes of the Coom ceiling, I would pack in as much as you can afford while still leaving a 50.mm. air gap, I would also use Foil backed Plasterboard to face off the walls, this would act as a VB and reflect radiant energy both ways, those top floors get quite warm in Summer the extreme reverse in Winter.

As for blocking off at floor level? yes I would simply to stop the free movement of air getting into the floor spaces, even stuffing Glass Wool in to the gap below the roof line, there to allow maximum air flow in the Coom but stops the air flow within the floor.

Ken.