I'd be v. grateful for advice on re-insulating my (1970s build) loft which has 100mm joists, 70mm rafters/trusses and quite a lot of downlighters scattered over approx 70m2 of ceiling area below. I recognise that the current patchy 100mm of fibreglass is inadequate and plan to install 100mm or even 140mm Celotex / Kingspan boards with appropriate cutaways for the downlighters. I understand from previous posts on this forum that this will be a fiddly job (especially with a fair bit of wiring) and that there are cheaper and / or greener options. Having been initially seduced by the concept of multifoils, previous threads have served as a welome cold shower and I have been put off this approach. However, as a newbie I should be grateful for any advice as to whether I am barking up the wrong tree here and, if not, whether it is worthwhile going for the extra effort of 140mm vs 100mm boards. Thanks.
Tony
posted on 16-10-06
Expensive idea and a possible fire hazardous project too. Missing out the insulation arround the downlighters will cost disproportionately to the areas missed out and cause awfull airleakage problems even if you solve the fire hazard ones.
It isn't easy to sort but how about thinking in terms of quilt? And sourting the air leakage would be more cost effective and energy efficient and therefore a greener thing to do first. Then add insulation if you have any get up an go left!
Tim John
posted on 17-10-06
Thanks Tony.
I was thinking of isolating the downlighters within fire resistant metal casings which I saw in B+Q last week but your point re. air leaks is also taken. Do you really think I should discard and block up as many of the downlighter holes as poss. and revert to traditional ceiling roses? Will that much warm air escape upwards thru the downlighters to negate the investment in all that loft insulation?
Your advice is appreciated as I am prepared to do the neccessary - I just want to get the decisions correct and do it once only!
Tim John
posted on 26-10-06
Oh well...
On the other hand I have found a potential solution to my ceiling downlighter problem of insulation short cuts vs fire hazard without blocking up all those holes. I don't know whether this will be regarded sufficiently green for this site but it may be of interest to somebody who, like myself, wishes to become more energy efficient by re-insulating the loft.
To achieve a fire, acoustic + air leak barrier in the midst of a sea of loft insulation, I plan to upgrade the old lights to "Click" Flameguard low voltage downlighters and I got them from http://www.thelightingsite.com/flameguard.htmip65 who were quite helpful. They comprise a rigid steel body, various seals and use a special aluminium reflector lamp which chucks the heat and light mainly downwards away from the ceiling cavity (c.f. conventional low-voltage halogen MR16 dichromic bulbs which get extremely hot). They are said to satisfy Parts B, C, E, L and P of the building regs. The main catch is that, compared with bog standard ceiling spots, they are "reassuringly expensive"! Like 4-5 times as much - as are replacement bulbs. The info sheet says you still need 5cm lateral and 2cm vertical clearance rather than simply bury them in insulation - the insulation support boxes they sell look the dog's b******* but cost a fortune and I shall probably source some flowerpots instead!
Does anyone know whether it is OK to use foil-backed rigid foam polyurethane insulation boards in this environment and in contact with mains electric wiring in the attic? I have a central chipboarded walkway and requested 100mm polyisocyanurate to go under. However, these PUR boards turned up on the lorry instead and I am now concerned that they may not be as fire resistant as the PIR boards I thought I was gettin? Any thoughts?
mark brinkley
posted on 27-10-06
Tim,
I think you are on the right track to pay attention to the downlighters first. In fact, I wouldn't think about the thickness of insulation in the loft until you have sorted the downlighters. The best method is to install sealed, fire rated downlighters. Have a look at Snaplite, they have an excellent reputation.
www.snaplite.co.uk
Even if you go to this expense, you still need to place a box over each downlighter to maintain an air gap of 100mm around and 75mm above. Then you can lay insulation above and eliminate the cold bridge.
If you don't replace the downlighters, you should attempt to use boxing to make an effective seal. First use place something like Envirografs fire hood above each light:
www.envirograf.co.uk/products/product032.html
then build a small box which you need to make airtight - you want to stop both heat and water vapour - by sealing around the box with mastic. Then you should be able to lay insulation over the top.
David
posted on 29-10-06
If anyone can be bothered, I'd appreciate some more background on this issue, having found myself with downlighters in a new property. I was going to put low energy bulbs in but was also planning on increasing loft insulation. At the moment there seem to be gaps in the insulation around the lights but it doesn't look like its been done too carefully. Is boxing around them absolutely necessary, even with the more fire-minded fittings.
There's a fitting here
http://www.commerciallamps.co.uk/acatalog/copy_of_Emergency_Batteries.html designed to accomodate the larger CFL low-energy downlighter bulb.
