Insulation requirements in roof space (integral garageconv)

[kitessurfer]

Hi, would someone remind me please what thickness insulation I should be laying in the roof space of my intergal garage conversion,20cm? 27cm?
Should it be between joists or should I leave gap between joists then insulation on top. I gather there are different rules depending whether this is topping up existing insulation or new job. This is a new ceiling joist construction as part of garage conversion under building notice.
thanks
KS

 

[noseall]

if the whole of the converted garage is integral then the only insulation requirements are for sound reduction.

100mm of fiberglass or mineral wool should do.

if the joists are formed from a prefabricated matrix then you may not need acoustic protection at all.

 

[kitessurfer]

..must have been asleep,Imissed the vital info, its part integral as below in pic;


# View media item 1451

 

[noseall]

..must have been asleep,Imissed the vital info, its part integral as below in pic;


# View media item 1451

you will need minimum 270mm of insulation in the ceiling space.

we normally go with 150mm between joists and 150mm across. saves buying differing thicknesses.

use foil backed plasterboards on exposed joists.

 

[kitessurfer]

Thanks Noseall, I've aquired a lot of insulation over the last months from legitimate sources (builders skips next to relatives houses). Its amazing how much good new stuff is thrown away during building work. Obviously I won't be able to get 30cm towards the soffit end of the roof. I know you can purchase plastic trays to sit on the insulation to ensure the flow through of air to the soffit, any ideas on this? Are there any diy alternatives? I was thinking to cut back on the thickness in line with the roof line and leave as is. Thanks for any thoughts on this, if you read it ofcourse.
KS

 

[noseall]

the eaves area of the roof is the most vulnerable, as this is the area where your ceiling is closest to the roof tiles and the outside world. cold bridging can be at its worst at this junction.

do not skimp here.

if you have existing soffit or over-fascia vents then you can push fit eaves ventilators between the joists to assist airflow. then push the insulation in as normal.

if you don't have ventilation at the soffit detail at all, then you would be advised to fit some vent tiles and worry not about eaves ventilation and all that goes with it.

 

[kitessurfer]

Thanks again Noseall, I see what you mean as you state the ceiling is closet to the roof there, I think I'll purchase the eaves vintilator to assist. I do have new round suffit vents fitted but only at about 80cm gaps, (they should be 50cm intervals). I'll leave them as is for now. I think the two vent tiles nicely vent the roof space sufficiently...
View media item 4592photo shoing roof vents. The furthest on the right is for extraction fromwc/shower. There's no further vent on the right as this roof space above the door is bricked off.