Replacing Loft Insulation

[S2D2]

Here's one that might cause a healthy debate, but I'm having trouble deciding so thought I'd offer it up to the experts. I'm about to board out our loft for light storage on XL Loft legs which leave a 300mm gap above the ceiling joists. The house was built in 1992, so the ceiling joists are only 70mm deep, giving a 370mm void for loft insulation. Currently we have two forms of loft insulation: the original loose fill fibreglass "filling" the 70mm joist depth and approx 170mm of newer (approx 8 years old) fibreglass insulation rolls installed before we moved in under one of the previous energy company schemes. The newer roll is generally in good condition, heavily compressed by the previous owner's loft boards in some places yet should be reusable.

 

The debate I'm having is on whether to replace the loose fill fibreglass insulation which is now 30 years old with new fibreglass rolls. It is heavily compacted across the loft and probably has an average thickness now of ~30-40mm instead of the 70mm it should be filling which will obviously be impacting the R-value and allowing air currents between the two layers of insulation. My options as I see it are as follows:

 

1) Fluff it up as best as possible, get on with boarding the loft. Save a lot of faff and swearing in a low head height loft space.

2) Redistribute and fluff into half the area, fill the other half with new insulation. Old stuff presumably twice as dense after this, R-value reduced to..?

3) Get rid of all the loose fill and replace with new loft roll (100mm squashed slightly into 70mm, R-value reduced to..?). Sending it to landfill doesn't sit well with me but maybe freecycle could avoid that issue?

 

After relaying the 170mm I'll add new 100mm roll which should give me 340mm insulation and a 30mm air gap below the chipboard, which I've heard some people recommend to avoid condensation issues under the chipboard. Our loft has had severe condensation issues in previous years but that appears to have been fixed by the addition of felt lap vents which have left it dry for a whole year now.

 

To allay any concerns, I'm using a proper fitted/filtered mask, goggles and long clothing. Loose fill fibreglass is the devil when disturbed.

[joe90]

Taking the old insulation out is a filthy job, I would be tempted to leave it there and put you’re new insulation on top, to make it more efficient you need to put wax paper between layers and in the insulation in opposite directions.

[Radian]

35 minutes ago, joe90 said:

to make it more efficient you need to put wax paper between layers

Tell me more, google won't...

[Mr Punter]

Leave the old stuff it makes me itch just thinking about it.

 

The newer Knauff insulation seems far nicer to work with.

[Onoff]

1 hour ago, joe90 said:

Taking the old insulation out is a filthy job, I would be tempted to leave it there and put you’re new insulation on top, to make it more efficient you need to put wax paper between layers and in the insulation in opposite directions.

 

Never heard of using wax paper.

 

Why?

[S2D2]

Thanks all, leaning towards option 1 or 2 to avoid having to remove any. Here's a picture for reference showing the state of the old stuff, the visible side of the joist should of course be hidden by nice fluffy insulation. Not sure on the insulative properties of kitchen roll, have the previous owner to thank for that. New stuff laid in the same direction in the middle section for ease by the energy company's fitters, I'll correct this to make it perpendicular.

 

I'm also curious on the waxed paper!

Edited February 17, 2022 by S2D2

[joe90]

36 minutes ago, Onoff said:

 

Never heard of using wax paper.

 

Why?

Ha, can’t find it now ? but I read somewhere with a cold loft (draughty) the laying of paper between layers of insulation cuts down the “washing” effect robbing heat. Perhaps I was dreaming (I am old?). 

[vala]

@S2D2

as another option if you're thinking of replacing you could use a product like Supersoft insulation.

It's made from recycled plastic.

I replaced all my loft insulation with this stuff and it was a joy to install, no itchiness and easy to cut.

[Radian]

1 hour ago, joe90 said:

Ha, can’t find it now ? but I read somewhere with a cold loft (draughty) the laying of paper between layers of insulation cuts down the “washing” effect robbing heat. Perhaps I was dreaming (I am old?). 

 

That makes a certain amount of sense. The more stationary the encapsulated air, the better the R-value. I have a very draughty loft (not a euphemism) so I'm considering a top layer of breathable thermal quilt to do a similar job. This is also reflective so may reduce overheating in the rooms below during the summer.

[S2D2]

2 hours ago, vala said:

@S2D2

as another option if you're thinking of replacing you could use a product like Supersoft insulation.

It's made from recycled plastic.

I replaced all my loft insulation with this stuff and it was a joy to install, no itchiness and easy to cut.

Thanks @vala, I noticed B&Q do a similar product now too. I can definitely see the advantage but unless I'm mistaken it's still about twice the price of fibreglass? If I was starting from scratch I'd be tempted but I'm at least keeping the 170mm top up so unfortunately the loft will remain an itchy torture chamber regardless.

[Marvin]

 

2 hours ago, S2D2 said:

Thanks @vala, I noticed B&Q do a similar product now too. I can definitely see the advantage but unless I'm mistaken it's still about twice the price of fibreglass? If I was starting from scratch I'd be tempted but I'm at least keeping the 170mm top up so unfortunately the loft will remain an itchy torture chamber regardless.

We recently removed all the insulation in the loft and replaced it with supersoft, which is a better product to use from an itchy point of view. It is also alot more expensive, but so much easier to use.

 

Good, if like us we need to move it to gain access to heating/cooling systems.

 

As @Mr Punter says the knauf seems to be the best alternative.

Edited February 17, 2022 by Marvin
Add info

[Mr Punter]

12 hours ago, Marvin said:

 

We recently removed all the insulation in the loft and replaced it with supersoft, which is a better product to use from an itchy point of view. It is also alot more expensive, but so much easier to use.

 

Good, if like us we need to move it to gain access to heating/cooling systems.

 

As @Mr Punter says the knauf seems to be the best alternative.

 

Can you test it with a lighter or blow torch to see if it catches fire?  Maybe try outside!

[Marvin]

45 minutes ago, Mr Punter said:

 

Can you test it with a lighter or blow torch to see if it catches fire?  Maybe try outside!

Already done with blow torch. No it would not sustain fire on its own in my tests.

[JohnMo]

The other alternative is to use sound acoustic insulation, it tends to hang together a bit better, but has the same thermal resistance.  I found it a little less itchy.

[hb1982]

On 17/02/2022 at 17:53, joe90 said:

Ha, can’t find it now ? but I read somewhere with a cold loft (draughty) the laying of paper between layers of insulation cuts down the “washing” effect robbing heat. Perhaps I was dreaming (I am old?). 

 

probably same principle of using breathable membrane in suspended floor insulation application (rather than just chicken wire), to avoid wind washing.

[S2D2]

As a follow up, I went with option 2, redistributing 50% of the flattened insulation into the other half of the loft and topping up the resultant gaps with new. Nothing to the tip or through the house which was a big win. Average insulation depth now 400mm and loads of storage up on the loft legs, which worked really well with P5 T&G chipboard sheets 2.4x0.6m. In case anyone else is doing something similar, I used a dustpan to scoop the old loose fill insulation and an old bread knife to cut the new rolled insulation, worked a treat. Fitted a couple of 1.5m batten LED lights before doing the job which made everything a lot easier, highly recommended.

Edited March 17, 2022 by S2D2

[Radian]

Thanks for the update @S2D2 You've just reminded me to fix up the batten LED I bought for my loft. Had it plugged in under the sofa for 'ground lighting' effect. Nobody else liked it so I unplugged it and forgot about it.