Re-insulating loft: Lay new over old or get rid of old then lay?

pigpicker

We moved into a new house last winter and compared to our old house it is nad-numbingly cold! The central heating was on constantly from December until May and the gas bill was ... well enough to make me look up in the loft to check the state of the insulation and it can only be described as poor at best. I guess this is good as it means that I can get some good stuff in there and really make a difference to the heat retention of the house.

The current insulation is the powdered stuff that gets blown in through a pipe and was done in 1997 according to the piece of paper left in there by the contractor who did it.

In some places it's 150mm thick and in others it's 50mm thick.
Some of it sits on 1" thick layers of even older insulation but this is only in some places. No wonder the house was like a polar-bear's fridge last winter

My question is ... to get the best performance out of any new insulation that I put down, do I need to clear out the old stuff or can I just lay the new stuff over the existing powder?


cheers

evoke

I would have it cleared out. I had my entire loft cleared out of all the rubbish that was up there when I moved in. The job cost me £500 but that also included all the carpets and fitted wardrobes in the house too. So I guess a full loft clearance would be around £300.

It's well worth doing as you can see what pipes and cables are there and whether they need replacing.

You'll also know that state of the upstairs ceiling and be able to lay new insulation down properly and ensure that things like bathroom lights have cages fitted to them on the loft side for fire safety.

pigpicker

Thanks evoke.
To be honest the loft for this part of the house is quite small (3.8m x 4.1m) and the only things up there are:
- an aerial signal splitter
- a couple of old aerials
- lots (a spinkling!) of crap powdered insulation

I'm thinking that if I was to take a dozen bin bags, a dustpan & brush and a dustbuster then I can make a good job of it in one afternoon.

I guess it makes sense to have the new insulation in direct contact with the loft floor to maximise its effectiveness .... Doesn't it?

SailorSam

No it doesn't. Even old insulation is doing some good. I'd leave everything down and put the new stuff on top. That's what i did.

LeeSouthEast

Providing there aren't any gaps, I can't see how taking the old stuff up would provide a benefit. More is more, in terms of insulation!

pigpicker

Yes I see your point - I was just concerned about the potential for gaps between the 2 to occur and reduce the effectiveness of the new insulation.

I guess that if the new layer was as flush as possible to the old layer and was fitted correctly between the joists then it would be a good job.

mymedi

There is no issue of any gaps between different layers of insulation horizontally - it doesn't make any difference. As long as there are no gaps between pieces of insulation vertically - that would allow heat to escape.

cyclonebri1

SailorSam wrote: »

No it doesn't. Even old insulation is doing some good. I'd leave everything down and put the new stuff on top. That's what i did.

Totally agree. All insulation adds some value. Don't remove, add, but add big style.

From your post I suspect you think that a few centimetres of cover will be detectable?

Well, it won't.

Add 300mm or you will not feel the difference.

That is a qualified statement, with insulation you don't feel the difference if you heating system has the capacity to heat your home, the difference is about the reduced energy bills rather than any temp effect.

Alfrescodave

Don't give yourself work; the less time you spend up there the better. New goes on top of old, the more the better.