Loft insulation

[BDJ]

Hi All
I’ve found this article that suggests loft insulation should include a vapour control layer underneath and and an air tightness layer on top. The theory makes sense to a beginner like me, but is it really necessary? Thoughts welcome.
https://www.eco-home-essentials.co.uk/how-to-install-insulation.html

 

[MatthewC]

I used Thermafleece (mostly sheep's wool) in my loft and didn't add anything like that - IMHO, it is just not necessary if your roof doesn't leak (and if it does, fix that first!). That was done over 11 years ago and it's been great. Expensive perhaps but so much nicer to lay that that horrid Rockwool stuff

 

[malcolm]

The modern way of doing things is to make ceilings waterproof so there is no need to vent the roof space. That plan is not all that fail safe.

The old way of doing things is to accept ceilings are not waterproof and use that to let water out of the house that you can easily ventilate away in the ventilated roof space.

Water is a problem in buildings. The roof is an easy way to get rid of some and it doesn't cause any issues with insulation. Bung 300mm rockwool up there being careful to not block the eaves vents and you'll be good. The sheep wool is good too. Just don't add breathable waterproofing liners underneath.

 

[Lacan07]

Old, solid brick wall houses were designed to allow moisture to pass through the fabric of the building, if you seal your loft like that you're just removing a large area for the moisture to escape.

 

[Lacan07]

I used Thermafleece (mostly sheep's wool) in my loft and didn't add anything like that - IMHO, it is just not necessary if your roof doesn't leak (and if it does, fix that first!). That was done over 11 years ago and it's been great. Expensive perhaps but so much nicer to lay that that horrid Rockwool stuff

I was reading a discussion about Rockwool on another forum last week. The OP was asking why, as a breathable insulation, it was frowned upon in old houses, apart from the fact its not so nice to handle.

Bearing in mind the expense of Sheeps wool its a common question on forums, whats your take Malcolm?

Thermofloc is another option of course but loose fill.

 

[MatthewC]

Thermafleece has a small amount of plastic in it which gives it body, so that if it gets wet it doesn't collapse like Rockwool but it will retain its body and dry out. I think damp Rockwool is NOT breathable!

 

[steveb]

Curios why sheep wool is so expensive, as I believe at the "farm" , the going rate for a sheep pelt is less than the cost of shearing it - some lowball number like 10p or 50p

Where does the cost come from - is it such a low volume/niche product at the moment that it's the fixed costs that dominate the product cost. Or does demand outstrip supply so much that suppliers can "name their price". Or something else?

 

[Lacan07]

Thermafleece has a small amount of plastic in it which gives it body, so that if it gets wet it doesn't collapse like Rockwool but it will retain its body and dry out. I think damp Rockwool is NOT breathable!

Yes, well this was my reasoning, fine when dry but what happens when it gets damp from moist air, which it likely will

 

[Lacan07]

Curios why sheep wool is so expensive, as I believe at the "farm" , the going rate for a sheep pelt is less than the cost of shearing it - some lowball number like 10p or 50p

Where does the cost come from - is it such a low volume/niche product at the moment that it's the fixed costs that dominate the product cost. Or does demand outstrip supply so much that suppliers can "name their price". Or something else?

I've wondered this too, it's quite frustrating when you got farmers desperate to give it away. It needs cleaning / treating of course. You'd think with the government so keen on green issues, carbon footprints and insulation, etc, they'd come up with a scheme to utilise a product that's literally being thrown away in many cases.

 

[LadyArowana]

I've wondered this too, it's quite frustrating when you got farmers desperate to give it away. It needs cleaning / treating of course. You'd think with the government so keen on green issues, carbon footprints and insulation, etc, they'd come up with a scheme to utilise a product that's literally being thrown away in many cases.

Unless it’s a pet sheep which has been pampered and brushed and groomed like a pedigree dog then the fleece will come off fairly nasty. They can’t not shear them because it’s an animal welfare issue, but it is strange how much more £ the stuff processed to insulation is.

 

[a twig]

It has to be treated ( long and multistage process) and there’s only one company that owns the IP around the technology to do it the final stage.

Ionic treatment I think it’s called

 

[TudorCottage]

What’s the view on putting Thermafleeze between floors to add a bit of sound and heat insulation.

Or is the potential to trap moisture too risky?

 

[paulc]

What’s the view on putting Thermafleeze between floors to add a bit of sound and heat insulation.

Or is the potential to trap moisture too risky?

I've been putting fibreglass in between the floorboards & joists. Can't say I've noticed any difference in noise, maybe heavier sound blocking batts would be more suitable. The main reason I'm doing it is to try and kill any draughts. In terms of thermal insulation, it isn't going to do much as the rooms above & below are of a similar temperature, so heat loss is not going to be very large.

 

[Lacan07]

What’s the view on putting Thermafleeze between floors to add a bit of sound and heat insulation.

Or is the potential to trap moisture too risky?

I would say it's not at all risky as such but people tend not to bother as they prefer to allow the heat to rise and warm the bed / rooms above with the main insulation in the loft.

 

[Lacan07]

I've been putting fibreglass in between the floorboards & joists. Can't say I've noticed any difference in noise, maybe heavier sound blocking batts would be more suitable. The main reason I'm doing it is to try and kill any draughts. In terms of thermal insulation, it isn't going to do much as the rooms above & below are of a similar temperature, so heat loss is not going to be very large.

Yes I would say it's worth putting some insulation against the external walls to prevent drafts under the floor. My house was previously a farm and when they converted it they hacked huge holes out the walls to fit joists.

 

[TudorCottage]

I would say it's not at all risky as such but people tend not to bother as they prefer to allow the heat to rise and warm the bed / rooms above with the main insulation in the loft.

Our cottage has radiators upstairs which are so efficient keeping warm upstairs is never going to be an issue, the added bonus being that our gas usage seems to be low.

Downstairs on the other had is a bit harder keeping warm. It has electric underfloor heating that gets nice and warm, but unfortunately comes at a price on the electricity bill. There seems to be quite a draft that comes through from the floorboards from upstairs so I thought some insulation between floors might lesson the draft and keep some of the heat generated downstairs.

I was concerned that all that wool might trap moisture causing issues, but I guess it would have to be a water leak rather than atmospheric to really cause a problem.

 

[Jahouli]

TudorCottage - exactly what I did - 90mm Thermafleece Ultrawool under all the upstairs floors whilst I was lifting the floorboards to spray woodworm treatment. A gap was left above to aid airflow and for cables and pipework to run above. Filled the full depth around external walls to reduce drafts. I mainly did it to keep the warmth downstairs as upstairs heats up quite nicely after insulating with cork boards and lime hemp plaster. I'll get round to insulating the downstairs at some point....when I can face the disruption again!

Overall it's worked well and I've seen an improvement in heat retention downstairs, but Thermafleece is pricey. Sound deadening is an added bonus. Hopefully no damp issues, but I'm not lifting the carpets to find out!

 

[Lacan07]

Our cottage has radiators upstairs which are so efficient keeping warm upstairs is never going to be an issue, the added bonus being that our gas usage seems to be low.

Downstairs on the other had is a bit harder keeping warm. It has electric underfloor heating that gets nice and warm, but unfortunately comes at a price on the electricity bill. There seems to be quite a draft that comes through from the floorboards from upstairs so I thought some insulation between floors might lesson the draft and keep some of the heat generated downstairs.

I was concerned that all that wool might trap moisture causing issues, but I guess it would have to be a water leak rather than atmospheric to really cause a problem.

I doubt you'll get moisture issues as long as the temp between lower and upper floors is similar.

 

[BDJ]

The modern way of doing things is to make ceilings waterproof so there is no need to vent the roof space. That plan is not all that fail safe.

The old way of doing things is to accept ceilings are not waterproof and use that to let water out of the house that you can easily ventilate away in the ventilated roof space.

Water is a problem in buildings. The roof is an easy way to get rid of some and it doesn't cause any issues with insulation. Bung 300mm rockwool up there being careful to not block the eaves vents and you'll be good. The sheep wool is good too. Just don't add breathable waterproofing liners underneath.

Very useful, thank you