£1 per roll Loft Insulation

andrew-b

paddy's mum, i think the part about lifting cables above the insulation is acting a bit overcautious much of the time ..not always but often. Note the wording in the npower/rockwool guide says "where possible"...not "it's essential".

The problem relates to overheating of cables and is in relation to the maximum electrical load a cable can take without overheating/melting ..and that relates to the ambient temperature, the power of what is connected to that cable, plus the cable length as well as the diamater of the conductors inside the cable itself.

That is why for a cooker or electric shower circuit which are high powered (above 10kW for more powerful electric shower) larger diameters of cable are used to take the bigger power load without melting..smaller diameter cabling would overheat and possibly even catch fire.

For longer cable runs thicker cable may be required due to a voltage drop across the length of the cable. A voltage drop means a higher current required to power the same device. The higher the current the more heat is generated and therefore the thicker the cable required to avoid overloading it and melting it.

The higher the temperature the cable is likely to get the larger the diamater of cable will be required. Obviously by surrounding a cable with loft insulation any heat generated in the cable will take far longer to dissipate to the surrounding loft space - so the ambient temperature of the cable is raised slightly. The insulation won't stop heat to dissipate completely..it will just slow it down. Ideally you don't want to hold the heat generated by the cables in with insulation - however in many cases the cable will be sufficiently over-rated (i.e sufficiently thick enough) to deal with the insulation without a problem.

There is an excellent calculator to use a guide here .. play around with that and see how the different variable influence the size of the cable required.

With most houses (i live in a bungalow with concrete floors so nearly all the wiring is via the loft!) it's likely that the majority of the cabling is for lighting circuits. With the predominance of energy saving bulbs now alot of lighting won't get anywhere near overloading the cable ..the bulbs draw the same voltage but being lower powered draw a smaller current.

Note that low-voltage (as opposed to low energy!) lighting a higher current is drawn for the same power compared to mains-voltage and so thicker cables may actually be needed compared to mains-voltage lighting so may be an issue. Any transformers lift them clear of the insulation (i'd lay them a piece of wood or something to lift them clear).

With recessed lighting insulation should not be placed around the light fitting protruding into the loft space..either leave a gap or fit a fire hood (available from any decent electrical wholesaler such as TLC-direct website in my link amongst others) - don't use an upturned plant pot it's not the same!

If your not sure get someone in to check!

TBH if you got someone to come install the insulation they will likely just roll the insulation out over the top of everything anyway! A neighbour of mine had insulation installed and i believe they just chucked it down..complete with cables and junk underneath!!

andrew-b

Deluks wrote: »

There is an irony with rockwool insulation, it needs lots of heat in it's manufacture (it's basically molten rocks!) and therefore has an large carbon footprint of it's own.

It has a carbon footprint but the energy saving properties of the installed insulation outweigh it.

See http://rockwool.co.uk/sustainability/the+road+to+zero+carbon and nearby webpages. Actually the 170mm Knauf insulation i have sat in my loft waiting to fit that i got from Homebase earlier in the year is called "carbon zero insulation" - how it compares to Rockwool i'm not sure exactly!

Deluks wrote: »

If they are fixed to a joist it will either be plastic clips or staples, both of which can be easily removed with a large bladed flat screwdriver.

Could be more hassle than it's worth and cable could easily be damaged..making the cable more dangerous than being under the insulation in the first place. Cables do get brittle with age..messing with them may cause internal breaks..more hassle!

Deluks wrote: »

Round downlights you can place terracotta flower pots, these will keep insulation from flopping onto them and have a little 'chimney' in the top for heat to escape.

As in my previous post don't use terracotta plant pots ..use proper fire hoods such as these:
http://www.tlc-direct.co.uk/Main_Index/Lighting_Menu_Index/Fire_Cover_Downlight/index.html

"In a fire situation the cover expands internally to fill all the available space with a highly insulating fire resistant char. Thus, the fire is unable to penetrate the hole and the cover is able to give additional insulation protection to the ceiling void to reduce the chance of heat build up and ignition of flammable materials such as accumulated dust and insulation."

Deluks wrote: »

Handy tip: If you have any intention of boarding your loft for light storage, you will get away with using the 170mm stuff, but you will need to screw 2x2 timber crossways to the top of your joists to make sure that the insulation isn't too compressed, before laying the boards. Do NOT nail, as this could crack your ceiling plaster in the rooms below.

Don't understand what you mean here...170mm insulation above ceiling joist = 6 3/4 inches... how is a 2"x2" timber going to help? Or do you mean 6"x2" which is commonly available in DIY stores. 7"x 2" is actually also available from timber merchants. Good point about not nailing though.

moneyhoney1

volcano99 wrote: »

:money:This is a cracking deal! Not the ceiling I hope.
I have tried the website this morning and at lunch time, only manage to get to the calculator page and no further.

Then I read this forum again and followed andrew-b's advice/link (post #18) to find out the phone number for my local build centre. They picked up the phone within minutes and then I went through the order with them. Then they told me that they can deliver as early as next Wed. Fantastic! :beer:

Phone your local Build Centre or any Build Centre near your area - fast and hassle-free. No need to wait as long as you know approximately how big is your loft in m2 and the thickness of insulation that you want (100mm or 170mm or both?). Then work out how many rolls you need from the table on the nPower webpage. However officially there is a limit of 100m2 per household. Perhaps you can sweet talk you local branch for more and I think some fellow/lady has been very successful (post # 11, #19, #21?, #34). Especially for post #34, how did you manage to order so many - 49 rolls? :huh:

I was the #19 post. I have 42 square meters of loft to insulate. Thank you for bringing it to my attention that I have possibly got too much. It seems like the calculator on the website has doubled my order! Or was it me? Anyway, I used the formula posted by THe Grim Reaper (post#63) and I should have 8 x 100mm and 14 x 1700mm rolls and not the following as my order suggests:-

DIY100 DIY ROCKROLL 4.8MX1200X100MM
16.00 @ £0.87
Line Total: £13.92

DIY170 DIY ROCKWOOL ROLL 2.8MTR X 1200MM X170MM
26.00 @ £0.87
Line Total: £22.62

Carriage and Packing: £0

Total value, including carriage and packing, excluding VAT : £36.54
VAT : £5.48
Total value including carriage and packing and VAT : £42.02

Not really sure what to do, but before I ring them could someone else do the math to make sure I have the right quantity please? Maths was never my strong point!

Canucklehead

paddy's_mum wrote: »

I'm aware that you must not cover recessed lights, which need extra protection - but what do you do about not covering electric cables if they are already loosely tacked to the joists and there isn't enough slack to lift them above the insulation you propose to lay?

My total re-wire is only recently installed (and certified as per the building regulations) but I can't find any recommendations online as to how you handle the matter if you're stuck with non-moveable cables.

Any ideas, anyone?

Good afternoon: take advice from your electrician as he/she is responsible for the electrical installation and would be best placed to comment on whether the wiring in your loft would cope with additional insulation.

HTH

Canucklehead

andrew-b

Hi MoneyHoney,

You've ordered too much i'm afraid..

For 42 square metres with no insulation...you would need 8 rolls of 100mm and 13 rolls of 170mm.
So yes you need to call them up and change your order ..or fob them off on friends/family! Thought 42 rolls looked alot!

See http://shop.build-center.co.uk/build/DIYcalculator/diy_loft_calc_new_v2.htm for the calculator (link from many offer isn't taking me there now but that's where it was going before!)

white_witch

Just ordered my rolls on the 0845 number.:j Thanks muchly just missed out last time.

paddy's_mum

I suspect that maths isn't a strong point for many of us? I just ordered the maximum allowed, knowing that any left over can be used to top up my Mum's loft space.

How long before some bright spark has their excess rolls on ebay at triple the original purchase price?

Don't suppose it matters much so long as the buyer makes some degree of saving and another home is effectively insulated.

moneyhoney1

andrew-b wrote: »

Hi MoneyHoney,

You've ordered too much i'm afraid..

For 42 square metres with no insulation...you would need 8 rolls of 100mm and 13 rolls of 170mm.
So yes you need to call them up and change your order ..or fob them off on friends/family! Thought 42 rolls looked alot!

See http the calculator (link from many offer isn't taking me there now but that's where it was going before!)

Yes you're right, I've worked it out to the same amount! I don't know how that could have happened. As I live on my own in my house I was going to employ someone to help me fit it for a small fee. I could try offering the spare insulation as payment instead!! I have no idea when it will be delivered and I have nowhere to store the excess. Hmmm , I'll have a think, I don't really want to deprive someone by not changing my order.

andrew-b

Give them a call..seriously that number of rolls of insulation is going to be a big problem to store anywhere.

I've got about 11 huge 8 square metre rolls of 170mm insulation in my loft awaiting fitting ..since realised i bought 2 too many (i remember now i deliberately bought too much!) but can no longer take back to homebase where i bought as had them too long now - probably give to my parents.

Ebay is no good unless buyer collects..they aren't particularly light and quite bulky!

Steffan

Whilst ordering I was told there's a max amount of how much you can order, 100sqm apparently. So only got 34 of the 36 170mm rolls I needed