Loft Insulation: how much insulation, baarding, electrics

[MAJ786]

I was going to insulate my loft under the Government’s CERTS-backed scheme using Mark Group (Yea haa?) - but was hesitant as they refused to deal with boarding and electricals properly: That scheme has now expired.

According to Mark Group's survey I have 70 sq meters of loft with 25mm of existing insulation (I reckon it is more like 10mm insulation at best).

I seem to have normal (400mm wide) joists, that are about 10cm deep.

The recommendation generally is to U Value of 0.16 = 6.25 Thermal resistance [R] (m2K)/W.

I reckon I can best this by:

1. Using 100mm Loft Roll Insulation from Wikes in between the existing joists (2.25 Thermal Resistance)
2. Cross / counter batten with 170mm timbers, allowing
3. 170mm Loft Roll Insulation to be installed in the new raised gaps at 90 degrees to the 100mm, then
4. baardin over that marking with position of electricals for future easy location

I assume I should use Terracotta pots around down lights that do not have a fire-rated housing, and leave 2"-3" of clear space (no insulation or boarding) around the lights?

By my reckoning 70 sq meters of insulation = £400 at today’s prices.

Thanks

M'

 

[PrenticeBoyofDerry]

It is generally accepted that 270mm of insulation(rock/mineral wool type) is required.
With respect to the electrics downlights require ventilation as do any transformers attached. The cables to the fittings can also become hot and melt, so they need to positioned so heat from lamps is not causing the cables to burn. Also downlights in kitchen and bathrooms should be moisture resistance, under part c of building regulations, so preventing moisture in to the loft space and causing condensation.
Also the cables of circuits require heat to dissipate, by introducing thermal insulations to them by surrounding or covering. This will reduce the cables' maximum current carrying capacity(CCC). Normally in lighting circuits rated at 5A or 6A this not an issue, as the standard 1.00mm T&E can be derated without becoming unsafe. But power circuits, such as sockets, showers, cookers, heating. Will have the cable rated by design, much closer to the CCC, so issue can arise. In most cases it would be wise to have cables run above the insulation.
Also any junction boxes must be left easily accessible.

Link to: downlight hoods and loft braces
Link to: downlight safety
Link to: derating factors of cables
Link to: Junction boxes

 

[kbdiy]

Shop around for the 170mm insulation - prices can vary a lot. When I did mine a couple of years ago Homebase were doing Carbon Zero 170mm insulation for £5 a roll AND on a BOGOF! £25 for 10 rolls - what a bargain! It's a lot dearer now but still worth keeping an eye out for deals. Am sure you will cover 70sq m for a lot less than £400.

 

[Ecohouseconvertor]

I can endorse the above posts - they are all correct.

Additional things to consider:

1. Leave a gap between the insulation and the bottom of the boards. You need decent air flow under the boards, otherwise there is a risk of condensation forming on the underside, and dripping down on to the insulation.
2. Cables should always be put on top of the insulation, not underneath it, as they may overheat. This is true for all cables, but particularly for any high current cables (eg power showers, cookers).
3. You can cross-batten with timber (the tried-and-trusted old fashioned way!) but there are new products on the market now which are faster and easier to install, and which don't weigh nearly as much. Google for Loft Legs or Loft Stilts (both plastic vertical supports) or for StoreFloor by LoftZone, which is what I used.

 

[deniance]

all of the above advice is spot on, all i can add is before you put anything down in the loft seal up every hole you can find, eg light cables hole, switch cable hole, pipe holes

, once you cover your ceiling with insulation your attic becomes just as cold as outside, but the underneath of ceiling keeps warm, so any moisture laden air from the rooms below will rise up and float about on the nice new warm ceiling until it finds a hole to escape up into the attic, and if it does your attics form of ventilation should dry it ou

but if there is more moisture than the ventilation can dry out droplets can form, espeacially if you have the old style felt under your tiles, these droplets then drip and run to various places in the attic, they can end up wetting your insulation which will make it not insulate as well and then drip off that to your newly painted ceiling leaving a nice brown stain, it will also soak into your roof timbers causing further problems, it can condense on the cold chimney breast in the attic then run down behind the plaster of the room below building up and up until you see a big damp patch which mold will then grow on!!

i guess it depends on how well ventilated your attic is, turn all your lights on below the attic, climb up and close the hatch, if you can see any light shining through seal it up with caulk or expanding foam, well even if you cannot see any light seal them up, it only takes half an hour to run around and seal them, in my opinion its better to stop the cause of moisture getting into the attic rather than depending on the ventilation to stop it

oh and if you have an extractor fan that goes into the attic it is essential that the venthose or pipe is airtight, ive visited a lot of houses that just have the pipe attached using the supplied zip ties, it needs to be airtight, to aid best performance and stop moisture escaping, oh and because your attic will be very cold the fan ducting has to be insulated or the steam in the pipe will condense and fill the pipe and eventually get so full it drips back out of the fan,

and another vital point, if your means of ventilation is at the eaves of the roof when you tuck the insulation into the eaves part of the roof, put a black bag over the ends of each roll of insulation, just like a sock!!!!, other wise the air blowing through the eaves will wick away at the ends of the insulation giving you a cold perimeter in the rooms below, which if you have some extra humidity below will condense on and become damp and mouldy,

if the attic insulation you choose is the standard bare stuff, cover it over when you finish with builders paper so the ventilating air flowing through your attic doesnt wick away the heat the insulation is trying to store

dont forget to check the seal on the attic hatch, this needs to seal really well also, and be insulated as well

downlighters are the worst culprits for letting heat and moisture up into the attic, you can get sealed ones witch cans on the back, but a lot of the ones i tend to see are the cheap 5 for twenty quid b and q jobbies, which are nothing more than 63mm holes in your ceiling with a lamp in the middle,

the source of my attic condensation was my stupidly high humidity in the rooms below floating up the stairs and flowing freely through the 63mm x 3 spotlights on my landing, my attic was soaking wet, all the timbers were wet all the felt was covered in droplets, mould growing on felt, stains on the ceiling, wet insulation, and you can see the outside world through my roof eaves, obviously too much moisture for the ventilation to deal with,

i swapped all my downlights for led lamps, stuck a tin over them and sealed them, and after various risky experiments of covering them with insulation, they do not even get warm, so i covered them over for maximum heat loss, probably kill the lamps a bit quicker but been 6 mths now, attic dry and no fires!!!!!!! phew, id hate for you to experience all the stuff i did, i wish i was told before i insulated my attic, but anyways if your reading this post now and have already insulated your attic, just stick your head up there with a torch and have a look just in case, check roof felt for condensation, chimney breast and top of insulation!!!!!