Installing loft insulation

[Anthony]

Good Evening,

I've just bought my first house, and fine though it is, my first project is to make an effort to reduce my heating and electric bills. Loft insulation looks like the first place to start, given the current buy 1 get 1 free deals on offer at various places and I've got a couple of questions relating to its installation.

My house is an 18 year old three bedroom bungalow, with a total living space of around 120m2. The height of the ceiling joists is about 100mm while the insulation rises to 150mm in the loft. The central part of the loft is boarded up with tongue and groove boarding (chipboard/plywood I think). My plan is to add 170mm loft insulation to the existing insulation, bringing the insulation height to 320mm, and to replace the boarding with insulation board.

My living room includes recessed ceiling halogen downlights. In the loft there is no insulation around these downlights for 60cmx60cm around each light, which isn't very good for keeping the living room heat in. I understand that loft insulation needs to be separated from the downlights by about a 100mm radius from the luminaire. My thoughts in achieving this separation, and having loft insulation over the lights are simply to place a board across the joists above each lamp, and laying the insulation over this. Is this the best idea, or do better solutions exist for separating the insulation from the lamps?

The second detail is ventilation. The two gable ends in the loft each have a grilled 1ft square panel, and in addition there is soffit ventilation at eaves level. I understand that rafter trays are the solution for maintaining eaves level ventilation, but I can't find anywhere that stocks them (e.g. homebase or B&Q). Any idea where I can find such items, and how much would they cost.

Anthony

[Roger]

Yes, adding extra insulation is fairly straight forward - generally extra insulation is laid at right angles to lower layers. Using insulation board in place of the T&G is as good as it gets without removing the T&G and covering it with additional insulation.
You should fit downlighter fire hoods over the downlighters before you lay the insulation - I have heard some people use ceramic flower pots as an alternative. I think you need more of a box than just putting a piece of board on the joists - you could box between the joists but I think fire hoods are better/easier.
You're correct in saying you need eave ventilation - I've never seen rafter trays available for retro fit, only for when a roof is re-tiled (i.e. they fit from the outside). All you need do is ensure that you leave a gap between the insulation and the roofing felt - remember that this will be over the cavity wall rather than a room.