nzer57

That cuts down its effectiveness considerably. The whole idea of insulation is to create an air trap within the material. If you crush it any way it's almost useless as an insulator. The other issue is that it must be up against the surface to the other side. If there's a gap between then heat still transfers into the gap before encountering the insulation.

Dollar for dollar I don't see this stuff as anywhere near as good as blown in or mat type insulation products. Even as an odd-on you could get a better bang for buck using other options and strategies.

lardyl

that's useful info - I had a fire recently where this matting was stapled into and over first-fix wiring, the metalised film acted as a conductor, the wiring passed the second fix "mega" tests but caught fire a few days later! Should have used slab between the rafters - I'm sure that the spec sheets for the rolled stuff suggested nail/staple onto rafters....but I bet you are right on that one as it will seriously reduce the trapped air at that point and bridge over the thermal barrier!

nzer57

I'm not a sparky but when I was building I ran the wire myself to cut costs. Wiring through floors and raftered ceilings had to go through the middle of the rafter and insulation had to be positioned under the wiring IE wiring on top not underneath the insulation.

nzer57

Another one you have to watch is down lights. Because they're in a very small shroud for asthetics most vent the bulb heat into the cavity behind.

2 Problems here.

1. They act as thermal air pumps drawing hot air out of the living space and in to the cavity which works against you, and

2. When installing insulation you have to ensure they are not in inadvertently covered up as they can catch fire if they don't have ventilation.

lardyl

yep, plus the transformers for the LV ones can also get mighty hot - there are some fire rated covers for the downlighters themselves that double up as shades preventing people dumping their stuff on top when using the loft as a store!!

lardyl

the IEE wiring Regs refer to "birdsmouthing" the rafters to take cables........that's the only time I have ever heard of that........it means cutting a notch that shape at the base of the rafter to take the cable.
You are only allowed to drill a certain &age of the rafter out in order to preserve structural integrity - but then using "notched cableways" or birdmouths can be dangerous too.....
One piece of advice is to be careful that you may de-rate your cable (overheat it) if you put too much insulation over the top and then you could end up with a fault/fire.......

nzer57

Correct me if I'm wrong but you can now get 12v LED down lights. Misers on power and don't suffer the heat problems of halogen down lights.

nzer57

Not done in NZ to my knowledge. If you're fixing to truss frame rafters which are usually 100 x 50 you simply clip to the rafter and the gib baton (40mm) provides the spacing for the cable. That's generally considered cheating though. Cable is supposed to go on top of the rafter and some inspectors will make you clip it as well.

In 2 story places the ground level ceiling/1st floor rafters are going to be a minimum of 150 x 50. You can go up to about a 50mm hole center or slightly above of the rafter without compromising its strength.

lardyl

seen em in a catalogue somewhere but never "in the field" - OK I suppose unless you are in the habit of looking directly into them..............

lardyl

more ueful info for when I come to investigate fires with this type of wiring - just got a timber frame construction book from one of the surveyors at work and there are lots of terms to bone up on!!
Back in UK a 50mm separation in floors/ceilings is OK so if you clip on the side of the rafter then that is OK as you usually have 50mm to play with....in the case I mentioned they were clipping on the base of the ridge joist and did not have any space alongside as the rafters all tied into the ridge along the full height - oopps - should have taken the cable down the side of the relevant rafter and birdsmouthed it at the wall plate/bearer......

nzer57

Haven't built in NZ for nearly 10 years now so don't take anything I say as gospel as far as specs go. Things are changing all the time and the different local authority building inspectors aren't always working outa the same book or on the same page. Used to drive us builders nuts. Getting a pass often depended on what inspector you got and how pushed for time they were

lardyl

yeah the loss adjusters I work with will do almost anything to avoid having to "get approval" - same the "developed" world over I'd imagine

Burt Badger

Why would you need loft insulation in a country that enjoys a perfect climate, where the winters are as warm as UK summers and it only rains for 20 days of the year. Christ! you don't even need heating on the North Island, just ask any real estate agent!

My advice - Just leave it as it is "She'll be right mate!"

Burt

karonious

Do you think I should install a sunroof mate?

Burt Badger

My advice would be to remove the whole roof and replace it with a big sheet of plastic. Don't worry it never gets windy either in Kywy land!

Burt