External wall = 13 mm gypsum, 215 mm existing brick wall, 170 mm insulation + 8 mm render max.

What's the most cost-effective insulation if I need to reach 0.15 u-value?

Thanks James. 0.15 is my target for passivhaus retrofit.

I think we'll need to go with 125 mm phenolic.

Shevek, Graphite EPS at 170mm (TC 0.031W/mK) will give you a U value 0.17W/m2K; 170mm phenolic (say 0.022W/mK) will give a U value 0.12W/m2K; 170mm PUR (0.025W/mK) a U value of 0.14 and 170mm PIR (0.023W/mK) a U value 0.13 and non CO2 blown XPS a U value of 0.16

Thanks Tom but then also not forgetting 170mm aerogel would of course give a U value of 0.07W/m2K. You'd need to sell your belongings to pay for it

BTW, the rendering company which I'm using was warning me off Phenolic due to the realively high failure rates which they'd been hearing about from their EWI supplier's rep. It has a considerably higher GWP too, and when you're talking about thicknesses of 170mm, that may never pay back (in terms of CO2 emmisions alone) compared to graphite-enhanced EPS, or the lower embodied energy EWI systems.

I've come to the conclusion that whilst a passive house retrofit is a good thing to aim at, getting the final 20% of the way to meeting that spec could easily cost 50% of the total project cost in many instances. Getting 80% of the way to the passive house retrofit spec will still give you an excellent home which is better than >99% of UK homes of the same age. By all means use the PH methodology (I have, it's a good one), but don't go mental trying to reach it. Your house will still qualify for SuperHomes, and have an outstanding carbon intensity (and comfort level) for a building of its age...

New build is a different matter, and PH makes much more sense for that IMO!

So with all that in mind, given your situation, I think I'd go for Platinum EPS.

Posted By: TimSmallGetting 80% of the way to the passive house retrofit spec

See AECB Silver standard - or the new PH standard for retrofit.

Don't know cost - they had an intro day recently, at that time nothing online. Take a look now - I will asap.

Posted By: TimSmall
So with all that in mind, given your situation, I think I'd go for Platinum EPS.

that's a sensible practicial conclusion
Interesting what you say re. Phenolic and EWI rep . discussing shrinkage here
http://www.aecb.net/forum/index.php/topic,3612.0.html

Re. Cork , quick google seems swistherm come up a lot
0.038
http://www.alumascfacades.co.uk/cork-insulation/
http://www.ribaproductselector.com/swistherm-with-cork-external-wall-insulation-system/249/col3700249/download.aspx

I recon it'll be pricey

Thanks all. Yes the 0.15 u-value is just a general minimum target I've seen for Passivhaus, so we could well have to aim lower once our PHPP calcs are done, good point.

I like the Passivhaus standard because it's not an arbitrary target. Rather it's the optimum standard for human comfort without waste. Isn't the EnerPHit standard just a way of saying its too hard so we'll arbitrarily lower the requirements and call it something else?

By the way, we're a mid-terrace house and we'll need 50 square metres of EWI.

My understanding of Passivhaus is that it aims to achieve a comfortable healthy human environment by ensuring all objects within the house are between 17-25 degrees and the air is clean. And that it does this in an efficient manner by using optimum amounts of insulation + passive solar design + heat recovery ventilation.

This is what I mean when I say it's not arbitrary. By using a lesser standard you may be creating an efficient building but not an optimal one, and therefore a lesser standard is kind of arbitrary.

Posted By: TimSmallGiven a budget of £80000, you could either:

That is an interesting way to put a market price on CO2. How much are you willing to pay not to produce CO2.

Say the house will last 60 years and there is no change in the fuel CO2 intensity.

Scenario 1 would price CO2 at £150/tonne.

Scenario 2 at £85/tonne.

I think the Government is thinking of putting a floor price of £30/tonne (though that may be Euro).

The numbers can be varied, as most things get cheaper over time.
It is interesting though that people are willing to pay to directly save something but are unwilling to pay to indirectly save something. The numbers gets even worse when you look at the shorter time scales of say 5 to 10 years.
Food for thought.

Posted By: fostertom

Posted By: Shevekpassive solar design

PH is not serious about that. Much more solar gain cd be gathered and usefully deployed in winter, without risk of summer overheating (which is the limiting consideration in PH), if only alternative ways of doing so were considered within PH. Dr Feist apparently researched that 25yrs ago and concluded that it was impractical or ineffective, so put PH's major focus on insulation and airtightness. But new thinking has happened since - which PH hasn't incorporated. If more winter solar gain were allowed, then the rest of the PH standard could be relaxed.

Tom, do you have a link to a description of what passive measures to capture more winter solar gain you are thinking of?

Posted By: djhdo you have a link to a description of what passive measures to capture more winter solar gain you are thinking of?

Just about any way other than radiation coming thro the window glass and falling on internal elements, has better potential. That's the only way that PH recognises AFAIK. I've been describing, on and off on GBF, the 'other' way (two ways actually) that we've evolved.