Insulating attic, how to compare rockwool versus earthwool?

[johnnyg]

Hi,

I’m looking at insulating my mother’s house myself and trying to work out the best option of attic roll insulation:

I’m looking at Rockwool (200mm thick and 1200 wide. 3.3 sq metre per roll. U value 0.44) and earthwool (200mm, 1200 mm wide, 5.97 U value?) as products to use but i’m confused as how to compare these products e.g.

Is 200mm of rockwool equivalent to 200mm of earthwool?

What’s the best approach to work out what product is best and what thickness i require of each.

Existing insulation has been removed.

Thanks,
Johnny

 

[onq]

I suggest you read other threads on insulating attic spaces on AAM before you decide on insulating with rolls in an attic.
The strategy you suggest can lead to freezing conditions above the insulation, with consequences for service pipes and water tanks.


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matter at hand.

 

[johnnyg]

Thanks onq, i have read previous treads and in particulars your treads, the attic is not used for storage and does not have any pipes/water tanks or services, its an old house attic with resticted access.

What i'm trying to do is strip away the jargon and find a simple way to compare products.

Also can anyone explain how it is so expensive to buy insulation here compared to the north or in the uk?

 

[onq]

Your very welcome johnnyq.
I hope these comments are not perceived as "jargon"
I intend them only to help divert people from making errors which may have been made last year by others.

If this is an old house with lime mortar and friable timbers these can suffer enormously from the reduced heat coming from the rest of the building.
If a vapour check is not installed on the warm side of the insulation, water vapour in the air can migrate through the insulation into the attic.

Once in the attic space an depending on the ventilation/still air conditions the water vapour will condense on any cold surface.
We have had several instance of the attic microclimate in houses experiencing internal condensation last January.
This can lead to a build up of moisture in the roof timbers and the masonry which can lead to other problems.

If you are proceeding with "natural" materials you have to read up on them to see how they perform in attics.
Materials what can offer good results in walling may not work a well in attics for the reasons stated above.

A Grade 1-3 Conservation-accredited or architect with experience in this field can advise.


ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matter at hand.

 

[johnnyg]

thanks onq, the jargon is working out the calculations, u values, k values etc nothing wrong with your advive which is sound and makes logical sense.

As you rightly pointed out, i have been considering your points already on condensation and thats what i can't seem to find out as how the materials react. earthwool does not rot etc

two thirds of the house was re-roofed recently, but there is still a section that has the lime mortor as insulation and this is what i'm concerned with.

you do assume if they are selling this for attics that it should be suitable?

 

[lowCO2design]

thanks onq, the jargon is working out the calculations, u values, k values etc nothing wrong with your advive which is sound and makes logical sense.

As you rightly pointed out, i have been considering your points already on condensation and thats what i can't seem to find out as how the materials react. earthwool does not rot etc

rockwool (mineral wool) and the cleverly named earthwool (glass/mineral wool - although some of their literature states recycled bottles...)
they are both about the same U-value (circa 0.040W/mK) and fire resistance (A1 to relevant BS EN) for your purposes there are both the same although the knauf stuff is easier to install as it's less itchy and you can tare it (you don't need a knife)

none of these products should be placed in a damp space, in fact your attic should not be damp.

two thirds of the house was re-roofed recently, but there is still a section that has the lime mortar as insulation and this is what I'm concerned with.

you do assume if they are selling this for attics that it should be suitable?

now, here's where you loose me and alarm bells start ringing that you need professional advice

there is little or no insulation properties in lime mortar. it has better hygroscopic properties than say ordinary plaster and is good for old buildings, as it allows the wall to 'breath' (as in it absorbs and releases moisture) but insulation? someone's telling you fibs!

do you want to explain a bit more about your project and what has been installed.. do you mean hemp-lime for instance? (this has insulating properties and is great for old buildings?)

 

[lowCO2design]

Also can anyone explain how it is so expensive to buy insulation here compared to the north or in the uk?

The uk is offering ridiculous subsidies direct to the product at point of sale.. this enables more people like you to go do it themselves... (this was evident recently where B&Q were selling your earthwool (imported from the Uk) for less than 10€ a roll)

In Ireland we have a grant aided system that means we must go through a contractor to claim a discount on energy saving measures such as attic insulation..

nothing wrong with either system in theory (they both have the pros & cons) but the latter allows for some unscrupulous individuals to take the preverbal.. but this problem is not the contractors, its the legislation and governing body the SEAI (governing my backside)... imho (biased opinion as an arch tech) there should be some sort of sign-off/supervision process either by an independent professional or the LA's building control, to ensure the likes of you put in the product in right situation and its done correctly..

excuse my little rant, i hope that answers your question