Laying insulation - what not to do

[davebrien]

Hi,

I have reviewed the post regarding insulation but I want to double check. I intend to lay 400 mil - cross laying the 200 mil roles on top of the existing layer which must be 10 years + and I estimate is only 50 mil.

Can I lay it right out to the felt at the roof?

I understand I should move the cables etc so they are laying on top of the insulation?

I shouldn't lay any under the water tank?

For areas around fittings should I leave a gap - I have no spotlights just standard cables?

Are there any other gaps I should leave.

Thanks,

Dave

 

[Towger]

Can I lay it right out to the felt at the roof?

No you must leave a air gap, you can get plastic trays to keep this gap, but most dont bother.

For areas around fittings should I leave a gap - I have no spotlights just standard cables?

No need to leave a gap unless if gets hot or high powered, eg a spotlight, electric shower cable.

 

[brogan]

I've just upgraded the insulation in the attic and I'm not sure I've done it right. I've cross laid the second layer, it is okay that it's covering the wires? Some of the wires were already under the old fleece layer so I assumed it would be fine.

In one of the rooms is small downlights do they need a gap?

 

[kbie]

I am not an expert but I heard or saw somewhere that the spotlights, low wattage type, need to be kept clear of insulation. However, if the clay type flower-pots are fitted over them the insulation can cover these. The wiring can be disconnected from the bulb and fed througt the drainage hole. Anyone any views on this?

 

[BRICKTOP]

These are the jobbies.......

[broken link removed]

 

[Leo]

I am not an expert but I heard or saw somewhere that the spotlights, low wattage type, need to be kept clear of insulation.

I'm guessing you mean low voltage here...if they were 'low wattage', there would be low power use and low heat emissions along with it.

 

[kbie]

I'm guessing you mean low voltage here...if they were 'low wattage', there would be low power use and low heat emissions along with it.

No I do mean the 50w halagon flush ceiling lamps. The covers on Bricktop's post seem to be the job.

 

[buyingabroad]

Someone else might clarify this - there may be a limit to the thickness of the insulation layers that you can put on top of each other as it may compress the insulation and reduce its effectiveness. Eg. 100mm + 200mm + 200mm - the last 200mm may compress the insulation beneath with resultant drop in u-value..........

 

[sydthebeat]

Someone else might clarify this - there may be a limit to the thickness of the insulation layers that you can put on top of each other as it may compress the insulation and reduce its effectiveness. Eg. 100mm + 200mm + 200mm - the last 200mm may compress the insulation beneath with resultant drop in u-value..........

sort of correct....

insulation suffers diminishing returns. eg you get significantly more energy conservation when going from 0 insulation to 100mm than 100mm to 200mm and than 200 mm to 300mm and so on. Yes there may be slight compression but a further 200mm on top of 300mm is not going to compress back down to 300mm.

what more important is that, the better your u value, the more significant thermal bridges become. Kind of like water in a dam... if the dam is leaky the water will trickle out all over the place, but if its strong and robust the any gaps will have water flying out at high pressure... its the same with heat and insulation. The better the insulation the faster heat escapes through thermal bridges.