Knauf vs Rockwool Insulation

Mendonky

Hi All,

Looking at replacing the insulation in my loft which appears to be old, crumbly orange fibreglass.
I've been looking to invest in rockwool as everything seems to point to this being superior- however when looking at the products in my local shops I've also come across fibreglass insulation by Knauf. They both seem to have the same R value per 100mm insulation (2.25 m²K/W), but rockwool appears to be 3x the price (particularly with Wickes having Knauf on sale). My question is, I suppose, is there any benefit to going for rockwool over Knauf Fibreglass? Links below for reference- looking to go for a full 270-300mm total

https://www.wickes.co.uk/Knauf-Insulation-Super-Top-Up-200mm-Loft-Roll---5-61m%C2%B2/p/109451?fix&gclid=CjwKCAjw8ZKmBhArEiwAspcJ7i3SwwLudL6wLadBr-wrSZQ0bTylG1DT46EroSR7hpxROVywDmkd2xoCEasQAvD_BwE&gclsrc=aw.ds

https://www.wickes.co.uk/Rockwool-Thermal-Insulation-Roll---100-200mm/p/148843?fix&gclid=CjwKCAjw8ZKmBhArEiwAspcJ7jo33AI2kN68OzHjyXYefHVarvK1nneyIoDRpebkSIBjWI9JmXz8NBoC93wQAvD_BwE&gclsrc=aw.ds

-S

grumbler

I don't see any justification for paying higher price, but something doesn't add up in Product Details - for the same thickness 200mm, length and coverage are much higher for Knauf.
And you used 100mm figure only to compare R-value, don't you? 100mm is too little by modern standards.

Also, the width is slightly different. Make sure you buy the right one, although to fill the volume between the joists you'll need to cut the roll to slabs anyway.

daivid

No way would I pay 3x more for the rockwool, though I'd work out how much was needed the do a proper search to find the best price. Loft insulation seems to be a product that is always heavily discounted somewhere.

Chickereeeee

Yes Rockwool is, at the moment, much more expensive than Knauf fibreglass. I think it partly due to demand for wall insulation.

Having used both, I think Rockwool is probably superior for ventilated loft use as it seems denser, lays flatter, and is less susceptible to heat loss through wind-wash (imo)  It is also much easier to cut with the right tool (which is partly why Knauf comes pre-cut). 

But not 3x time better.

FreeBear

In terms of insulation value, there is little to chose from between Knauf & Rockwool. Same for installation - Both are easy to use. And if you do need to cut a roll to a nonstandard width, cut the roll (still wrapped in plastic) with a saw. Knauf has the advantage that they use a fair bit of recycled glass in their product (if you care about such things).

Aim for ~300mm of insulation, and the thermal performance of either product becomes academic, so base your choice on price.

sxd901

They are slightly different products.  Glass mineral wool is less dense hence the better R value.  Mineral wool is a denser product, is also moisture resistant and fire resistant.  Glass mineral wool is generally used for lofts in dwelling houses with mineral wool more common if fire resistance is required.

FreeBear

sxd901 said:

They are slightly different products.  Glass mineral wool is less dense hence the better R value.  Mineral wool is a denser product, is also moisture resistant and fire resistant.  Glass mineral wool is generally used for lofts in dwelling houses with mineral wool more common if fire resistance is required.

Wrong on all counts - Rockwool (when sold/used for insulating a loft) has the same thermal performance as fibreglass.

Fibreglass insulation is moisture resistant, it is also non-combustible and therefor fire resistant - I put this to the test recently when soldering some pipework with a large blowtorch. The fibreglass insulation discoloured a bit from the direct flame, but did not burn or break down in any noticeable way.

Yes, rockwool batts are denser, but they are generally used for insulating cavities or for noise reduction where the extra mass is required. For thermal insulation in a loft, it makes no difference which of the two products one uses (except price).

grumbler

'Moisture resistant' is a bit vague term in this context.  And so is 'non-combustible'.

The last rockwool I dealt with was marked 'water-repellent' - that, possibly, is important for a cavity wall, but not for a loft.

And there are different fire ratings for non-combustible materials, but the above products both have 'Euroclass A1' rating.

sxd901

Agree with FreeBear, look for 300mm ish of insulation.  Thought the fibreglass was better as more air entrained.
  
If fibreglass gets wet it will reduce performance.  Both are non combustible but rockwool is also fire resistant.  In UK, just to make things easy, fire resistant and non combustible are two different things, measured in different ways.  Does not make a difference in this case.

Is the rockwool better as you do not get so itchy installing it?