Tony,

I suppose it depends on how much CO2 is released during the extraction of the raw materials and the manufacture of the product.

Jonti

Both! Question to ask is will it save more Co2 than it takes to make it. Will it do it quickly enough (and, before you ask, I've no idea how quickly that is).

Badly installed insulation cannot be justified.

I think that part of the reason that petro-chem insulation is made in conveniently sized sheets to to make the fitting easier. Then you get a knob-head on piecework fitting it.
I think that any insulation fitting is a specials job, not a hard job, just need training and understanding. Never having worked on housebuilding I suspect that fitting is left to 'the lad' or the labourer as it is itchy and not seen.
I think that most petro-chem insulation has pretty low embodied energy and CO2e, ICE is the place to look. There is the problem that the better the insulation the longer the payback period is as the house needs less energy. As Tony does not need hardly any heating his insulation embodied energy is possibly never going to get paid back, but compare it to an early 20th century house of similar size and it will in a couple of years.

Posted By: SteamyTeaThere is the problem that the better the insulation the longer the payback period is as the house needs less energy. As Tony does not need hardly any heating his insulation embodied energy is possibly never going to get paid back

Sorry ST but I dont understand this, surely the payback is related to the amount that would have been spent on energy if there was no or less insulation not what he is spending?. If tony spent £1.1k on insulation, his heating bill would have been £500 pa but with the insulation his heating bill is £100 then is not the payback period 2 years? Please correct me if I am wrong

Edit:-
AHHHHH, just spotted my error, we are talking embodied energy, but surely Tony and the planet are better off?

Posted By: SteamyTeaI think that any insulation fitting is a specials job, not a hard job, just need training and understanding. Never having worked on housebuilding I suspect that fitting is left to 'the lad' or the labourer as it is itchy and not seen.

This is why spray/pump insulation makes a lot of sense. (e.g. recycled paper or foam)

Yes , but preferable to use local products that can be grown, reused, recycled, composted, part of the organic nutrient cycle, leaving little long term impact post use.
What impact does phenolic, EPS, XPS or polyurethane foam have post use , ground up and buried in the ground or as dust floating about ??

Many petrochemical based insulation products perform better when water gets in than the natural alternatives (i.e. wood fibre versus polystyrene).

This will either mean the system life is on average longer for a given quality of installation or that the installation speed can be increased that effects the energy contribution of the installation element.

That said if space is no object foamglas and rockwool are great for both embodied energy and life.

Posted By: tonyPresumably when oil runs out we will develop ways of maling them from crops?

We already do, some PUs use 'natural' materials, mineral and glass wool come from minerals.
The energy needed to make them can come from any source.

Posted By: joe90I would balance that with also saying there are alternatives that use waste material such as straw and cellulose

AIUI petrochemical feedstock is from all the sludge at the bottom of the barrel. The main reason oil is refined is to get at the lighter, more lucrative top fractions. So in a way, petrochemical feedstock is a waste product. We'd be cracking off the lighter stuff for petrol anyway, so we might as well put the heavy stuff to some good use.

Posted By: tonyPresumably when oil runs out we will develop ways of maling them from crops?

Oil isn't likely to actually "run out" any time in the next few centuries, it'll just get increasingly expensive to obtain. It's likely there are alternative chemical pathways to all the compounds we want. I'm not a chemist, but I suspect coal and gas would be higher on the list of candidates than a biological source, judging by previous efforts such as those in WW2 or apartheid-era South Africa. That's proven technology for fuels anyway.

Posted By: SteamyTeaA very good point. There is this vision that anything grown is good while anything mined is bad, just not clear cut like that.

Oh I think we'd definitely be better off using a renewable source rather than a fossil one. I just think in reality it's likely that the well-understood, relatively cheap, reliable path would be the one that got used, even if it was much dirtier and not long-term sustainable. It's what we usually do!

Surprising. Perhaps the Green Building Advisor is thinking of a colder climate.

Suppose you're in a 3472.22… heating degree·day climate and you're deciding whether to insulate a wall to a U-value of 0.15 or 0.1 W/m²·K with PUR or PIR with mid-range figures from:

http://www.greenspec.co.uk/insulation-oil-derived.php#urethane

so conductivity 0.025 W/m·K, density 35 kg/m³ and embodied energy of 101 MJ/kg.

Heat loss is u × 3472.222 × 24 × 3600 = u × 300 MJ/m²·a

(megajoules per square metre for each year.)

For u = 0.15, loss = 0.15 × 300 = 45 MJ/m²·a
For u = 0.10, loss = 0.10 × 300 = 30 MJ/m²·a

Saving 15 MJ/m²·a (4.1666 kWh/m²·a)

Thickness of layer is conductivity divided by required U value.

For u = 0.15, thickness = 0.025 / 0.15 = 166 mm
For u = 0.10, thickness = 0.025 / 0.10 = 250 mm

Extra thickness = 84 mm.
Extra mass of insulation = 0.084 m × 35 kg/m³.
Extra embodied energy = 0.084 m × 35 kg/m³ × 101 MJ/kg = 296.95 MJ/m² ~= 300 MJ/m².

So energy payback on the incremental insulation would be 300 MJ/m² / 15 MJ/m²·a = 20 years.

Far from impossible but enough to make you think twice.

I think Ed was intending it more as illustrative of decisions taken at the design stage Tony. The point being the lower you push your target u-value the more the embodied energy will hurt you. Low carbon emissions from heating seem less impressive if the house has huge embodied energy in the first place.

What is the design lifetime of most of the boxes extruded by the big house-builders these days? If these houses are designed for comparatively short lifetimes is there a limit to how much they should be pressured to bring their u-values down?

Posted By: tonyI hope that they are designed to last more than 20 years, but it looks like the overall payback is much shorter which is why I dont much incremental analysis as it makes it look like it is not worth doing.

How does it look like the payback is much shorter?

I have a student who recently undertook a Dissertation looking at embodied energy v returns on incremental increases over a 50yr period - His conclusions were pretty much the same as all of the other studies - ie that there is a point at which the law of diminishing returns kicks in. We are way beyond that point with current u-values

Just to add to what Seret and Steamy said, any calculation of payback has to be done incrementally relative to some assumed level of insulation.

If you had literally zero insulation (house made of and filled with thermal superconductor surrounded by an infinite heat sink) then you'd need an infinite amount of power to keep it warm. Any insulation, however poor and however expensive in whatever measure you choose to use, would pay back immediately.

Even a post and beam house, if that's all you have, sitting in a field in a gale needs quite a lot of heating, what with the multiple air changes per second. You can't do sensible calculations on the payback of different sorts of insulation between the timber elements except by comparing different insulation methods against each other.

There does have to be a sensible calculation of how much insulation a house needs as clearly a point comes where more harm is done than good (well, more harm is done in insulation than is done in heating). The calculation I did above is very naive, though, in that it assumes all energy is interchangeable. For example, it equates petrochemical energy used in manufacturing PUR with sunlight coming through a window in the house. A joule of the first is much more costly to the environment than a joule of the second.

Still, exactly this sort of calculation is making me have a bit of rethink - probably changing from 240 mm of PUR to 250 mm of mineral wool with 90 or 100 mm PUR inside. Basically, I couldn't come up with a bullet-proof calculation that the last 40 mm of PUR were definitely a win.

Just for the insulation you get the least embodied energy using only mineral wool. However, the roof then becomes so thick that window reveals are a problem (particularly with relatively small windows), there's more general structure holding the whole lot up, and so on. OK, I'll have a lot of embodied energy in the PUR but I'd have had an OSB and airtightness layer at that point anyway which, while having a lot less, is not free of embodied energy.

Mike George's point that we're already way beyond the point of diminishing returns with U-values doesn't fit with my arithmetic. I think Passivhaus is hovering around that point (deliberately, I assume) whereas most building-regs-level houses fall well short.

Posted By: Ed DaviesBy calculations I did earlier this year PU foam has sufficient embodied energy and CO₂ emissions that you get to the point where payback starts to stretch out to many decades as you decrease the U value through about 0.15 W/m²·K so seriously considering switching from 240 mm of PU to 250 mm of mineral wool and 90 or 100 mm of PU.

What you're talking about here? - payback in money terms, or in carbon terms, comparative of PU vs min wool?