Thread: Insulation question

Hi Sandra,

I put insulation in the roof over our previous external patio which is now our internal office a few weeks back and the instructions specifically said that electrical wiring should rest on top of the insulation, and if this wasn't possible, the insulation should be raised slightly to make a small air pocket for the wiring. I'm not sure how critical it is, but I prefer not to argue too much with safety instructions like these.

Regards
Des

If your wires are getting hot, you have MAJOR PROBLEMS NOW
Why wait until the place burns down??

Al

Hi Sandra,

Most of your electrical wiring shouldn't be lying on the plaster sheet anyway and should follow timber battens and joists safely fixed out of the way. I put in insulation 25 years ago and the only thing I left clearance on was fan outlets and the transformers for 12V lights and the lights themselves both of which we put in much later.

House has shown no sign of burning down and our current loads should not be sufficient to heat up the wiring, if it does I suspect you can expect to burn the house down either with or without insulation over the wiring. I don't remember anything in the instructions back then about wiring at all.



Regards, John

Wouldn't wiring get hot from uninsulated roof spaces anyway?

In my house there is a section that has very small roof space with a tin roof, I reckon the heat buildup would be phenominal therefor insulating ontop of wiring would make the air around the wiring cooler?

I'm not giving advice here, so please don't take it as advice. (to be on the safe side)

Also if you flick thru the yellow pages some pink batts garauntee that their batts are vermon resistant among other things.

Insulation is not magic.
All it does (and in a limited way) is to slow down the transmission of heat from the source, Sun-tiles-trapped air inside the roof-gyprook-air inside the house. Or reverse if it is winter.

For the fearful, the cables under the insulation would recieve more heat from the outside in winter and less in summer. If left above the insulation will receive more heat in summer and less in winter.

How much more? 5 C if you are lucky and only during a small period of the day. If heat from outside is a problem with wiring, then wiring shouldn't be in the roof cavity in the first place, that with fancy black tiles can reach temperatures of 60C or more.
Why don't we have a tradition of white tiles in Australia is beyond me. Why doesn't the building code determine big wide opening to ventilate roof cavities is a mystery.

On the other side a cable that overheats is a symptom of a serious problem that has absolutely nothing to do with insulation. Will insulation aggravate the overheating problem? In a minor way.

I have a few suggestions. If your wiring is overheating you can install a fan next to the offending cable to cool it down ... or, you can rewire the place with proper size wiring that can take a variation in outside temperature of +5 / -5 C and so you can place the insulation battens over them, under or anyway you like.

I would be much more concerned with the health risk involved in having a ton of Fiberglas over your head dropping invisible health hazard fibres through every crack night and day..

I agree with Mark re: the fibreglass health hazard, with lv downlights and the wind blowing you can see tiny fibres blowing out of the lights. I would at least use poly batts no fibreglass or irritation.
Keep the insulation away from transformer and the lv lights (the lights turn off when the transformer get over heated)
Cheers
John

The main concern with home insulation is when you have two or more circuits running together where they will tend to heat each other up when a load is applied and from memory the SAA Wiring Rules state that they should be separated by at least 150mm when running in insulation.

As some of the others have said if the correct wiring is used there should be enough safety factor in the cable.

More important is the correct fuses or circuit breakers are used for the size of the cable.

When metric cable was introduced the allowable circuit breakers for 2.5mm² was a 30 amp breaker. In the 1983 SAA Wiring Rules it was reduced to a 20amp breaker. And this was done similarly for all the different cable sizes because they found that the breaker resistance was to high.

Sorry to reawaken this thread at this late stage BUT I can't see where anyone said their wiring was getting hot and if it ever does you should get it checked out IMMEDIATELY :eek: As far as the original question goes you should never cover your wiring with anything as it de-rates the current carrying capacity of it and may lead to overheating. As Bazz pointed out the Circuit breakers are only there to protect the cable and it is most important to ensure that they are not oversized.. If in doubt get it checked out by a Leco.

Cheers Mark

Just to add a different slant to this after insulating quite a few ceilings for clients, the big issue is the cost and swearing the electrician will do when he has to lift and (hopefully !!!!) relay the insulation batts to carry our repairs to the wiring.

My suggestion is to follow the instructions and put the Batts under the wiring.
Always recheck the batts after any tradey has been in the roof as my experience is that very few of them re lay the batts properly.

Best of Luck