I have a late 1980's brick veneer home with a concrete tiled roof, no sarking under the tiles, but batt insulation on the ceiling.
I'm about to replace the 12v halogen downlights with 240v compact fluorescents, and hope to seal over the top of the light fitting to prevent warm air leakage up through the fitting. This made me think about the insulation in the roof - I'll be able to put the batts back around the light fittings (the previous owner installed the lights and made a joke of the insulation, gaps everywhere - I'm assuming the fluoro's won't heat up like halogens so I can fill the gaps in?).
I'm wondering what effect laying a sealed blanket of sisalation over the batts would have? I'm thinking it will fully seal the ceiling and so reduce heat loss into the roof space, but would the gain be worth it? It wouldn't be hard to do and should be relatively cheap...
Am I missing something, cos I've never seen this done but it seems like it should help?