Earthwool wall insulation instead of Rockwool

[Jazz q]

I am having a single storey extension built and the builder has used 100mm Knuaf Earthwool insulation in an external cavity wall instead of 100mm Rockwool full-fill cavity insulation as specified in the drawings. I am annoyed at this because I understand rockwool is a better product and has better R value. Its too late to rectify as the wall has already been built. Approx 26 square meter has been used. How much should I be looking to deduct from the final account now that I have a deficient wall insulation that I will have to live with for the rest of my life. Any advice given would be much appreciated. I've attached pics of the one hes used

 

[23vc]

What’s the exact name of the rockwool product you think he should have used? Knauf earth wool sounds like dritherm which is the correct product. When you say 100mm rockwool it sounds like those acoustic slabs not suitable for cavity walls

 

[Jazz q]

I've attached a photo of the insulation that's been used by my builder. Remember it's for an external cavity wall.
In the spec it just says 100mm Rockwool full fill cavity insulation. I've also attached a screenshot of the one I think he should have used. Considering I have let the contract out for ££££s of pounds I would be suprised if he would stoop so low to save an extra few hundred pounds.

 

[^woody^]

They are basically the same material. Rockwool is just a brand name.

One is not a better product. Check the r-values for performance.

 

[Jazz q]

R value for rockwool is better than earthwool

 

[^woody^]

R value for rockwool is better than earthwool

What u-value has the designer specified for the wall?

I would suggest he has specified a value that does not actually congregate with the individual r- values of the components, and if that's the case it does not matter what product the builder uses as long af the relevant u- value is achieved.

 

[John D v2.0]

According to https://www.rockwool.co.uk/product-...b/?selectedCat=downloads#Specifications&Sizes
The conductivity for rockwool is 0.37 so you're actually getting a better product. Keep quiet and let the builder carry on using it!

 

[Jazz q]

John D so to confirm you think the earthwool product is better than rockwool? I always though rockwool was the better product as the earthwool only has an R rating of 2.25

 

[John D v2.0]

earthwool is a brand name, look at the packaging in your photos for the product information

 

[endecotp]

R value for rockwool is better than earthwool

Looking at the Insulation Superstore pages:
- The Rockwool is 0.035 W/mK which for 100mm is 0.35 W/m2K.
- The Knauf is 0.032 W/mK which for 100mm is 0.32 W/m2K.

So the Knauf is about 10% better.
But reading on, they also talk about it having a conductivity of 0.032 to 0.037 over its life.
Basically they are identical.

 

[JohnD]

How much should I be looking to deduct from the final account

If that's the way you look at it, you should obviously pay the builder extra because he provided a superior product.

£100 cash seems fair.

And a sincere "Thank you."

 

[^woody^]

Seems like a case of CFH.

As soon as they think "How much can I deduct here" you know it's not going to end well.