It is an interesting and mathematicaly complicated document that whilste studing variablilty of the blowing agent on life time performance also juggles other factors, such as the diminishing return when increasing insualtion depth.

The report has a methodology for aging blown insulations but does not age open cell/ fibre insulations. As anybody who has inspected old insulation in a loft they will know that there is a huge amount of evidence to show that aging is a significant problem with mineral fibre. This also does not include the potential for reduced performance due to moisture (etc), something not covered in the report.

The report starts of by looking at EPS and XPS then seems to loose EPS. It is very important to distinguish between the two. XPS (extruded) is a bit of an anomoly - it does not have the performance levels of Urethane based insulation, but seems to 0ff-gas at a significantly higher rate and may be more harmful.

I am not completely convinced by the calculation method and a simple summary report, as presented, does not include all of the mathematics. (table 2 uses an RSI of 1, same as a U value of 1, a completely unrealistig figure). It would have been better to fix the study on a set U value, say Canadian building regulations or Passiv Haus levels as the primary analysis.

Al lot to absorb - maybe we should send copies to Kingspan et al.
--------------------------------------------------
"....all this kind of suggest that SIP Systems have a major hurdle to cross...."
This is a bit of a leap! (although I agree with most of what you say)

Firstly not all SIPs are the same.
- I will be building using Expanded Polystrene (EPS) where the blowing agent is recovered at the factory + EPS is low density!
- So my comment, on this thread, relate to EPS


To consider building methods correctly a holistic approach has to be taken, the RSI is only part of the story.

SIPS do lead to very air tight buildings (the report ackowleges that air exchange can contribute up to 40% of heat loss - actualy this is the average for total ventilation)
- SIPS effectively provide three air barriers - the inner and outer pannels are sealed and the insulation layer is sealed (details may vary)

SIPS have vastly reduced thermal bridging (which is typiically 20% of heat loss).

EPS SIPs - there is no evidence of reduced performance as EPS starts off containing air and continues to do so (the report does not cover the two part blowing and mold forming process for EPS fully).

EPS is not know to deteriate in the way mineral wool has been proven to do (it can even be used under a damp proof membrane)


Embodied and finite building resources:
When using SIPS's there is significantly reduced timber use compared to a timber frame.

Compared to masonry constructions an entire layer of block work is removed which represents a huge amount of embodied energy.

This last fact high-lights the dangers of extrapolating too much, however valuable from such reports. This report, and others, is very valuable in identifying specific issues; however it is important that we consider the whole building.

That is why, when I wrote about SIPs specifically, I asked that all of the benefit of using an integrated system was not lost by simply cladding the home with massively high embodied energy brick and block work.

So.... how does using Celotex/Kingspan between and over rafters compare? May take a few years for carbon payback, but overall is environmentally sound...?

Ok, to be clear, will Celotex/Kingspan insulation have a short enough carbon payback to warrant it's use? Do we actually have enough information on the embedded energy of these products? (Hoping I'm not wasting my money on the new roof for very little environmental benefit....)

[quote]Mark Siddall
The payback is linked to the thermal performance of the insulation and the GWP, as explained in the paper. Personally I am skeptical about the use of foam insulations. Maybe in a few years when the GWP is <1 I'll start to believe in their merits again. I suggest using them as a last resort when nothing else will do (i.e. under floor slabs etc.) [/quote]

There are other options for under slab insulation, e.g. LWA. What I'm not sure with the extruded clay/glass insulation is how big the embodied energy is. Does anyone know? But al least it doubles up as hard core and is recyclable.

I've now read the report, and it appears that PU/PIR produced with pentane as the blowing agent should have a payback of only a few years when moving from "poor" to "good" insulation (my inverted commas). The problem comes when increasing insulation from a good level to a better level - the decreasing returns in terms of thermal resistance means that the payback becomes much loonger.

So, for my circumstances - going from a roof with at most 50mm glassfibre (over 35 years old) to a between & over rafter insulation set up using PU/PIR (giving a u value of 0.18) - the payback should be just a few years.