Loft insulation: things to avoid?

[Mike Barnes]

I had a CERT (Carbon Emission Reduction Target scheme) assessment the other day.

There are three lofts that need extra insulation. One is fully boarded. One has a few boards lying around on top of the joists to make it easier to walk around. One is almost (but not quite) impossible to access, being under a shallow roof over a single-storey extension.

The agent pointedly asked me if it was OK to roll out insulation over the boards, and to blow insulation into the tight space. When I asked why I wouldn't want that, he replied vaguely that some people wouldn't be happy with it, but wouldn't explain why not.

Is there any reason why I shouldn't have roll insulation over the boards, and blown insulation where roll insulation would be impossible to put in place?

[Tim S]

Mike Barnes wibbled:

Partly it's your choice - I rather be less efficient than have a loft I couldn't store stuff in because the boards were buried under fluffy.

But - big but - the important question to ask is: will your electrical cables stand being buried under >=200mm insulation?

Under the worst case, if the cable is buried in the middle of too much insulation, 2.5mm2 cable derates to rather less than the 20A it is required to be capable of carrying in order to form part of a British 32A ring final circuit. Electric shower cables and other high power circuits may be at risk too.

Personally, I think loft insulator contractors should be Part P registered[1].

Cheers

Tim

[1] If we must have Part P...

[Jules]

How do they normally handle that in order to blow insulation in? Cut a hole in the ceiling, up through the soffits, down through the roof, or through a hole in an adjacent wall?

We've got a small section of the house with no access panel, and judging by the way it's lost snow before anything else, there can't be much in the way of insulation in there...

cheers

Jules

[Mike Barnes]

We've had a larger garage built (not DIY :), so we don't need the space in the loft any more.

That would be the case whether or not the loft was boarded. As it happens, there's only lighting up there - no problem.

[Mike Barnes]

In this case there is small hatch in one corner and I can squeeze in and crawl halfway along, at the high side next to the first floor wall. The other half has a slightly higher ceiling and no adult could get in there. As soon as you move away from the wall... well, you can't, it's too low, and there are trusses in the way. To make matters worse the space is obstructed by three... I don't know what to call them, there's a Velux window in the roof and four little walls going down from it to the ceiling (times three). All in all you can get pretty close to everywhere but there's no room to manoeuvre.

I'm assuming they'll go up with a tube, crawl in as far as they can, spray as far as they can, then gradually retreat spraying as they go. Even if they stood up in the hatch opening they could do a pretty good job, depending on the strength of the spray of course.

We've got one of those as well but it's in an area we don't heat.

[Peter]

'Blow what'? Lofts around here (houses built 40 years ago) were insulated with that polystyrene stuff that looks like popcorn. Now known to chemically disagree with electric cable sheathing. It attaches and slowly dissolves the cable sheath finally blowing the fuse. Worth seeing too, one length of lighting cable I lifted must have had 200-300 bits of the crap firmly embedded in the cable.

Peter

Peter

[Andrew Gabriel]

Expanded polystyrene leaches the plasticiser out of PVC, which will make the cable less flexible. It won't blow any fuses, unless you go up there and start vigourously bending cables back and forth - if you are losing fuses, that's a different problem.

[RobertL]

We had a similar problem with our victorian house there was a 100mm gap between slates and lath+plaster ceiling. Blowing in fibres leaves no air gap surely, also, fibre is not as good an insulator as Kinspan/ Celotex and if the space is limited it might be better to use one of those.

First we decided to 'post' 50mm kingspan slabs in there leaving a 50mm gap above them. then we decided to pull down the ceiling and lower it creating bigger space for Kingspan. Havign sone that and examined the roof thus exposed we decided to have it reslated as well.

Robert

[george (dicegeorge)]

......>>> then we decided to pull down the ceiling and lower it

I'm thinking of leaving a ceiling as it is then sticking kingspan underneath it (with the vapour barrier downwards) then a layer of plasterboard under that..

much less messy than removing an exisitng ceiling can't see why not?

[g]

[RobertL]

Sounds OK to me, we had originally planned to do that. Part fo the reasoning was to conserve the old ceiling for posterity. However...

our decision to pull it down for us was based on a mixture of reasons. First, it would reduce the height of the ceiling a little more if we left the old ceiling up (by 50mm) and it was low already. Second, we needed the void to be debris-free so rentokil could spray it for woodworm, third: part of it was going to be damaged anyway when a chimney breast was removed. Finally: When I made an inspection hole I found it was full of debris in the void ; it seems that when the slates has been replaced in the 1960s the builders had simply dumpoed the old slates and bits of cement onto the top of the ceiling! So for us, we just thought, oh what the hell, let's just pull it down. It took me about 2 hours to pull down (onto plastic sheets) and my wife about 2 hours to bag it up and take to the dump.

What an amazing amount of dust!!!!

Robert