dormer insulation ventilation

woody1

this probably needs a sketch, ( il get to it later ) but for now il trust in your visualisation skills..
so i have a dormer roof, insulated with foil ( i know ! ) .. now something clicked in my head lately and made me check what was going on at the eaves / rafter wallplate area..
the foil carries down the underside of the rafter all the way to the wallplate, it doesnt follow down the stud wall that makes up the room wall .. but it isnt fixed to the wallplate ..or taped or sealed to anything in any way( except to itself at the overlaps ).. the eaves is ventilated as it should be but this cold air can blow straight into the void in my timber first floor.. instead of just ventilating the rafters
no there isnt any insulation on the attic section of the ceiling ...
solution.. lay fibreglass on the attic ceiling section ..forgot to check but im assuming its not foilback plasterboard..if not il have to get a vapour barrier of some kind..
anyway ..to make things clearer il scan in a sketch later ..
am i missing anything.. as long as the rafters are still ventilated then i shouldnt be causing any problems
if anyone ever thinks if a non invasive cheap and easy method to retrofit/improve on foil insulation can ye let me know:D

woody1

so drawing attached, ive drawn in insulation on the floor /ceiling and the stud where i think its needed..

Slig

If the foil is properly fixed and taped it is a pretty good solution, even though in this situation a cheaper product would have done the same job. It should however be fixed to the wall plate for maximum effect.

Ensuring air travel along the underside of the slates is essential however air travelling between the floor joists is very thermally inefficent. Any heat produced on the ground floor will obviously rise and without insulation between the floors should add to to the heating of the first floor. A ventilated air cavity between will stop heat from reaching the first floor and instead blow the warmed air out through the eaves on the other side.

woody1

mercifully the rooms its affecting are a hot press and wardobe , but it cant be good for overall heat loss from the house.. and the rooms below are colder than any other rooms in the house.. anyway i better get to it and we'll how much difference it makes