( cellotex or rockwool in a cavity wall? )

[geraint]

In my opinion Dritherm cavity batts (100mm full fill) is the simplest method by far.

They do not wick water.

...and you can set the brickwork (external leaf) out first.

I personally thing partial fill rigid foam is pants!

that was the problem... so thank you..

 

[geraint]

In my opinion Dritherm cavity batts (100mm full fill) is the simplest method by far.

They do not wick water.

...and you can set the brickwork (external leaf) out first.

I personally thing partial fill rigid foam is pants!

to change the post... i have never come across any design with a full fill... they all seem to specify celotex maybe its going back to the days when they made the roofs sweat.... but who can answer that.... and who can prove that it does not work.... yet....

 

[PrenticeBoyofDerry]

an ignorant member... did you post a valid reply... no...

could you.... no...

and i thank the persons that have..

My reply was in regards of not only your confusing question and off hand reply to someone who clearly was trying to help you, with the addition that your original post and subject title was as clear as mud.
Plus I also agreed with what freddymercurystwin had to say. regarding your replys.
If I had understood your question and seen a more politer response to those who did try to help, like Deluks.
I would have only been too pleased to offer you advice, but as you did not. I thought it not worth my while to someone so arrogantly rude!
But I am pleased that you have now found the answer you were looking for and thanked the member that helped.
Just out curiosity, have you thought about using sheep's wool as an insulator!

 

[ajrobb]

In my opinion Dritherm cavity batts (100mm full fill) is the simplest method by far.

I like this as phenolic foam loses its insulating gas over years and ends up little better than mineral wool of the same thickness. So 100mm mineral wool will probably be much better than 50mm of Celotex after 10 years.

DON'T use untreated mineral wool though, as that can wick water. DriTherm is designed for the job.

 

[JohnD]

phenolic foam loses its insulating gas over years and ends up little better than mineral wool of the same thickness.

that's a surprise to me

do the Building Regs people know?

can you point us to the evidence?

 

[mointainwalker]

John

if you do a search for it, you will find confirmation.

This is the reason that there is a (small) movement to rate insulation materials after 7 years. No doubt kingspan et al will react even more furiously than they have to multi-foils.

 

[JohnD]

I assert that the moon is made of green cheese. I don't provide any evidence to back up my claim, if you want it you can find it yourself.

Am I being reasonable?

 

[ajrobb]

I assert that the moon is made of green cheese. I don't provide any evidence to back up my claim, if you want it you can find it yourself.

Am I being reasonable?

http://www.faqs.org/patents/app/20100010111

Or this one from Knauf themselves:

http://www.knaufinsulation.co.uk/solutions/hvac.aspx
"Phenolic foam ages over time due to the release of the insulating gases"

The impervious foil facings on Celotex and Knauf slow down the degradation in the middle but cannot stop it. The problem is worse in applications where the sheet is cut into strips or punctured by retaining clips - the average diffusion gradient is higher so diffusion is faster.

The trouble with the moon being made of green cheese is not so much a matter of quantity but more a matter of quality and distribution costs.

 

[jeds]

In my opinion Dritherm cavity batts (100mm full fill) is the simplest method by far.

They do not wick water.

...and you can set the brickwork (external leaf) out first.

I personally thing partial fill rigid foam is pants!

I agree with this. I've been specifying full fill for a few years now and in my opinion it does a better job. It gives a better U-value, is much easier to fit (you don't get the gaps and misplaced boards that is common with semi rigid foam boards) and it gives more flexibility in the build.

Of course it must be the right stuff. No good using ordinary mineral wool off the roll.

 

[JohnD]

Or this one from Knauf themselves:
"Phenolic foam ages over time due to the release of the insulating gases"

Thanks, I have had a look at the Knauf link you provided. It appears to be a page selling wooly insulation, that does not make Celotex or similar, so I would not expect it to tell us how wonderful the foam is.

But where is the evidence that "phenolic foam...ends up little better than mineral wool of the same thickness"

How little is little?

Are there some figures available?

 

[jeds]

John,

There's no doubt that 100mm full fill cavity slab is a better thermally than 50mm foam with a 50 cavity. The foam comes out about 0.33 (U) in a brick/medium block construction and the full fill is 0.30.

 

[mointainwalker]

http://en.wikipedia.org/wiki/R-value_(insulation)

Insulation aging
R-values of products may deteriorate over time. Some types of foam insulation, such as polyurethane and polyisocyanurate are blown with heavy gases such as chlorofluorocarbons (CFC) or hydrochlorofluorocarbons (HFCs). However, over time a small amount of these gases diffuse out of the foam and are replaced by air, thus reducing the effective R-value of the product. There are other foams which do not change significantly with aging because they are blown with water or are open-cell and contain no trapped CFCs or HFCs (e.g. half-pound low density foams). On certain brands, twenty-year tests have shown no shrinkage or reduction in insulating value.

This has led to controversy as how to rate the insulation of these products. Many manufacturers will rate the R-value at the time of manufacture;[citation needed] critics argue that a more fair assessment would be its settled value.[citation needed] The foam industry in year? adopted the LTTR (Long-Term Thermal Resistance) method,[9] which rates the R-value based on a 15 year weighted average. However, the LTTR effectively provides only an eight-year aged R-value, short in the scale of a building that may have a lifespan of 50 to 100 years.

Open-cell foams ( expanded polystyrene) do not change.

I have read somewhere ( don't remember where) that PIR drops to about the same level as fibre insualtion, so since 200 mm of PIR has an R value of 8 and 200 mm fibre is 5, then the PIR loses approx 40% of its insulating ability ( if my memory is correct).

I would also be grateful if anyone knew more exact figures for this.