Loft insulation advice

[gjb1970]

The house originally had a flat roof when built in the late 60s, but due to conti nuous problems a tiled and felted pitched roof was added a few years later. The floor in the loft is the old flat chipboard covered in tar roof with no form of insulation. When i enquired about adding some form of insulation I was told that overlaying would leave the air pocket between the bedroom ceilings and the old flat roof leaving a air pocket prone to condensation. Does anybody have advice on insulating this area? I was thinking of insulating between the rafters but this would just leave a warm loft area, so air would need to be pushed back down with some form of heat recovery unit.
Any advice please?

Gary

 

[freddiemercurystwin]

You can insulate immediately above the old flat roof provided there is adequate ventilation to the space above. Has it no ventilation at the moment then?

 

[gjb1970]

The soffits are well vented, so the loft space is vented. I was told the problem was the air space between the flat roof and the ceiling.

Gary

 

[RoyMacDonald]

Air immediately under a ceiling is relatively hot so I doubt that you would get condensation forming in the void as that would only happen when the warm air meets cold and starts to cool down. Most likely to happen in the roof space proper hence the need for ventilation which you have.

I take it the flat roof doesn't have cross ventilation?

 

[gjb1970]

No it doesn't have cross ventilation.
This is confirming what I thought.
For some reason when we had a survey done we were told we couldn't insulate this way because of condensation.

Gary

 

[RoyMacDonald]

Maybe the concern is the vapour barrier in the form of a bitumen roof between the room and the insulation, in which case you could paint on a vapour barrier on the underside of the ceiling as a precaution.

Personally I'd take up the chipboard covering and insulate between the joists add some packing to get 270 mm depth to the joists and then put back some plain chipboard for storage or a useful space.

 

[gjb1970]

I guess another easier option would be to drill through the old flat roof and pump in loose insulation to fill the whole cavity.

Gary

 

[freddiemercurystwin]

Personally I'd take up the chipboard covering and insulate between the joists add some packing to get 270 mm depth to the joists and then put back some plain chipboard for storage or a useful space.

Yep, bout time it was said, anything else is just a bodge job really.