Crazy Rafter Roll insulation cost

[MortarThePoint]

1 hour ago, ADLIan said:

The difference in density between all those mineral wool products will have no affect on the overall acoustic performance. Price of all insulation products has increased massively in the last 12 months - perhaps by 50-60%!!

 

Wish I had ordered last year when I started this thread, but space on site...

[sean1933]

Much appreciated all - in that case I think I'll be going with the cheapest option.

[MortarThePoint]

On 15/03/2022 at 16:15, sean1933 said:

I'm just going through this delightful decision at the moment. I have 220mm rafters and was aiming for a u value of 0.12 (rafters at avg.600 centres).

Having previously looked at pricing 2yrs ago I had planned to use 230mm Frametherm40 + 70mm PIR below.

 

Now I have come to ordering and I'm looking at pricing again. One thing for me is I hate noise so have started looking at density in comparison to stay Rockwool RTA45 (kg/m3). From what I have found the Frametherm 40 is only 13 kg/m3, 35 is 25kg/m3 and 32 is 32kg/m3. Does anyone have any experience of these densities in a pitched roof (I have 11mm OSB above rafters, planned for 38mm service battens and 15mm or double 12.5mm plasterboard below)? Should I just bite the bullet and go for the 35?

 

Nobody appears to mention the Frametherm40... which is substantially cheaper than 35 or 32. Is there a reason for this and has anyone used this?

Here is my quotes just to highlight the differences (over £3k between 40 and 35)!

			Unit price	M2 per unit	m2 price	TOTAL for 400m2
100mm PIR			£32.95	2.88	£11.44	£4,576.39
70mm "			£26.75	2.88	£9.29	£3,715.28
50mm "			£18.50	2.88	£6.42	£2,569.44
25mm "			£12.50	2.88	£4.34	£1,736.11
140mm Knauf FrameTherm Roll 40			£28.59	9.14	£3.13	£1,251.20
90mm Knauf FrameTherm Roll 40			£30.50	14.25	£2.14	£856.14
140mm Knauf FrameTherm Roll 35			£35.00	4.45	£7.87	£3,146.07
90mm Knauf FrameTherm Roll 35			£38.50	6.84	£5.63	£2,251.46
140mm Knauf FrameTherm Roll 32			£40.50	3.19	£12.70	£5,078.37
90mm Knauf FrameTherm Roll 32			£44.50	5.13	£8.67	£3,469.79

 

If I had my own way I'd go pumped cellulose but sadly on the south coast the only installer I have found wants horrendous money so a no go.

 

These are good prices for the current environment. What supplier(s) are they from?

[redtop]

We used to rockwool 45 in the timber partitions, floor between ground / 1st floor and IMHO there is far far less noise transfer between the rooms than other houses we have owned.

 

I wouldnt do it any different if doing it again tbh.

[MortarThePoint]

@sean1933 It might be worth taking a look at OmniFit Slab 35 as it may be slightly cheaper than the FrameTherm 35.

[Thorfun]

1 hour ago, MortarThePoint said:

@sean1933 It might be worth taking a look at OmniFit Slab 35 as it may be slightly cheaper than the FrameTherm 35.

and Isover Batts from Jewsons. I got a good price on my 32 batts when compared to Knauff stuff.

[SuperPav]

What am I missing here (something clearly)... For application in a pitched roof between rafters (200mm full fill)

 

Knauf loft roll (from Wickes) works out to £4/sqm at 200mm

Omnifit roll works out to someting like £11/sqm at 200mm

Recycled PET at £15/sqm

Sheeps wool at £35/sqm

 

Now, I understand why the recycled PET and sheeps wool would be a lot more, but what is the difference between the "loft roll" and the frame/omni roll products? The thermal performance doesn't look massively different to warrant going from £4/sqm to £11-12/sqm? Or is it that the loft roll stuff isn't suitable for use between pitched rafters for whatever reason?

[Thorfun]

2 minutes ago, SuperPav said:

What am I missing here (something clearly)... For application in a pitched roof between rafters (200mm full fill)

 

Knauf loft roll (from Wickes) works out to £4/sqm at 200mm

Omnifit roll works out to someting like £11/sqm at 200mm

Recycled PET at £15/sqm

Sheeps wool at £35/sqm

 

Now, I understand why the recycled PET and sheeps wool would be a lot more, but what is the difference between the "loft roll" and the frame/omni roll products? The thermal performance doesn't look massively different to warrant going from £4/sqm to £11-12/sqm? Or is it that the loft roll stuff isn't suitable for use between pitched rafters for whatever reason?

isn't loft roll for horizontal usage? might sag if installed vertically or diagonally between rafters?

 

also you have to compare the lamda values of each. they may be different and so will need different thicknesses of each to get the same U-value.

Edited March 29, 2022 by Thorfun
lamda value bit added

[MortarThePoint]

14 hours ago, SuperPav said:

Or is it that the loft roll stuff isn't suitable for use between pitched rafters for whatever reason?

 

Loft roll isn't self supporting so would just collapse down over time whereas the more expensive ones do self support.

 

That said I have often thought it would be easy to anchor Loft Roll in place and stop it sagging and so save a bunch. But as is often the case with such ideas, it's not going to be used as per the manufacturer's guidance and so BCO won't be happy nor the Warranty provider.

 

If filling rafters (ie no air gap) another approach that might work and be much cheaper than the correct product would be to squeeze something like 2no. 150mm into the 220mm rafter. The compression might be enough to hold it in place.

 

I spoke to a merchant years ago and he said some builders staple Loft Roll to rafters. They may have quoted competing against builders using the right stuff.

 

I would be interested if anyone has done something like this.

Edited March 30, 2022 by MortarThePoint

[PeterW]

The UValue is determined by the air ratio in the wool - compress it and you reduce the value. So 300mm in a 220mm gap will perform worse. 
 

 

[markc]

Just now, PeterW said:

The UValue is determined by the air ratio in the wool - compress it and you reduce the value. So 300mm in a 220mm gap will perform worse. 
 

 

Had a few “arguments” lately regarding this, far too many people have got it into their heads that cramming thick insulation into a small space must be better. Not sure if it’s some guidelines or Youtuber that’s giving out the wrong info.

[ADLIan]

And it is the compressed insulation thickness that is used in the U-value calculation.

[MortarThePoint]

I wasn't suggesting you'd get better than 220mm of equivalent thickness of something of order 0.040. The 'overfill' was to make it stay put, but to be clear I'm not suggesting anyone actual does it.