We're carrying out a retrofit and targeting EnerPhit, and therefore we need to target at least 0.15 u-value to walls. We're restricted to 150 mm insulation because of our existing eaves detail. So the cost to insulate our 35 m2 existing solid brick walls is as follows:

150 mm Grey EPS = 0.18 u-value = Ă‚ÂŁ400
150 mm PIR = 0.15 = Ă‚ÂŁ600

Financially the PIR is a no brainer. So it comes down to:
1. CO2 emissions savings of 0.18 vs 0.15
2. Environmental impact of EPS vs PIR
3. Stability of EPS vs PIR
4. Longevity of EPS vs PIR
5. Risk of rising damp at ground level where we potentially create a problem due to lack of breathability.

So let the games begin... how do they compare?

Not much in it.

Happy to have been of assistance.

I would say that the breathability of eps would swing it,

Keeping the house dry and happy with continuous drying of the structure, with impermeable insulation this it not necessarily true.

So probably about what a hedgehog would fart in that same year.

Fantastic abstract realism

How big a hedgehog? EU standard size?

vapour resistance values (r) for : ( from NBT paper )
PUR (without foil ) 300 (10,000 with foil, though EWI boards for rendering will be foil less )
EPS 150
Woodfibre 25
Mineral wall 6

from bs12524 water vapour resistance factor
PUR 60 (presume PIR polyisocyanurate is same ?)
EPS 60
wood particle board 5-10
mineral wool 1
phenolic 50

to convert between r and vapour resistance factor see.
"excellent illustration here http://builddesk.co.uk/wp-content/uploads/2013/01/vapourResistances.pdf "

Ah right, thanks James. No I hadn't thought about that or a supplier yet.

Am I right in saying there's little difference in breathability from the figures you posted above though? (putting aside glueing sheets)

Shevek , Seems that way , though SW3000 is PIR rather than PUR which NBT paper list only with foil at r=43,000.
(i'm presuming similar value of 300 without foil ?)
though as discussed in Mike George's render breathablilty thread, figures dont tally with BS12524 and sources unclear .
The whole area of breathability of products seems quite muddy to me.

Posted By: ShevekWe're carrying out a retrofit and targeting EnerPhit, and therefore we need to target at least 0.15 u-value to walls. We're restricted to 150 mm insulation because of our existing eaves detail. So the cost to insulate our 35 m2 existing solid brick walls is as follows:

150 mm Grey EPS = 0.18 u-value = Ă‚ÂŁ400
150 mm PIR = 0.15 = Ă‚ÂŁ600

Financially the PIR is a no brainer. So it comes down to:
1. CO2 emissions savings of 0.18 vs 0.15
2. Environmental impact of EPS vs PIR
3. Stability of EPS vs PIR
4. Longevity of EPS vs PIR
5. Risk of rising damp at ground level where we potentially create a problem due to lack of breathability.

So let the games begin... how do they compare?

1.some , but little, by Seret figure 600kg CO2e over 60 years (life time of refurb (will EWI last that long)?)
2.EPS wins
3.EPS wins
4.EPS wins
5.EPS wins

http://www.natural-building.co.uk/images/downloads/Breathability_in_buildings.pdf actually gives ranges of resistivity values - so EPS not just 150, but 100-750, XPS 600-1500, and PU foam not just 300, but 115-1000. So it's wide open.

Can't really see how EPS can be considered breathable or should I say more correctly vapour permeable when in the BBA certificate 90/2558 for Springvale's EPS Wallshield partial cavity fill boards it says:

11 Water vapour penetration

11.1 The product has a minimum water vapour
resistivity values in the range of 145 MNsg–1m–1
for SD grade to 719 MNsg–1m–1 for EHD grade
and will therefore provide significant resistance to
water vapour transmission. Joints between boards
will facilitate the passage of water vapour under
normal conditions of temperature and humidity.
11.2 If the product is to be used in the external
walls of rooms expected to have high humidities,
care must be taken to provide adequate permanent
ventilation to avoid possible problems from the
formation of interstitial condensation in the internal
wall leaf.

Its not a special grade of EPS, its just made in smaller board sizes to fit in a cavity.

Thermal condiuctivites are given as:

12 Thermal insulation

12.1 For the purpose of U value calculations to
determine if the requirements of the Building (or
other statutory) Regulations are met, the thermal
conductivity (
value) of the insulation board may
be taken as shown in Table 3.

Table 3 Thermal conductivity values
Product Grade Thermal conductivity
(W/mK)
WallShield SD 0.037
WallShield SD lo
0.035
WallShield HD 0.035
WallShield EHD 0.033
MicrofoamX32 — 0.032
WallShield Platinum Neopor NEO 0.031

Depends where the dewpoint occurs and if the moisture vapour gets through to that point

Yes, when they say things like 11.2 above, which appears to follow from 'significant resistance to water vapour transmission' in 11.1, in fact 11.1 doesn't lead to 11.2, so they're just throwing in vague stuff to cover arse. Short of full VCL resistance as innermost layer, any construction needs to be checked for intersitial condensation.

'Significant resistance to water vapour transmission' doesn't mean it's unsuitable for use in 'breathable' construction. It's not all that 'significant' - just 'not near-transparent' as dedicated breather products are. It's still way down the at the low-resistance end of the scale, amongst building materials. As long as the 5x (some say 3x) rule of thumb is applied, so something 5x (or 3x) as resistant is provided inboard, then it should be a safe 'breathable' construction, albeit at a modest rate of 'breathing', but preferrable IMHO to an industry-standard non-'breathing' construction with inboard full VCL.

Having said that, are we sure about

Posted By: SaintIts not a special grade of EPS, its just made in smaller board sizes to fit in a cavity.

My prev researches held up Springvale's Neopor EPS as having particularly low resistance, 50 I think, not 145, i.e. even lower (because Neopor) than the 100-750 range given in http://www.natural-building.co.uk/images/downloads/Breathability_in_buildings.pdf .

Posted By: ShevekSo it seems to me there's no winner on item 5 (vapour permeability). Both PIR and EPS are increasing the risk of interstitial condensation by similar degrees.

If you want vapour permeable you'll need to look at mineral fibre, Rockwool etc.
No plastic foam is particularly vapour permeable. Kingspan who bought Springvale as part of the CRH acquisition insulation and then let them Springvale go (they didn't want EPS) get very shirty about the whole idea of breathability...well they would do...http://www.kingspaninsulation.co.uk/Knowledge-Base/Breathability-1.aspx