We spend a lot of time here worrying about embodied energy/CO2e, which is a good thing.

Someone somewhere, posted a link to this analysis a while back:
http://www.censa.org.uk/docs/ISA-UK_Report_07-04_OSM_House.pdf
which I've just got round to reading.

It has some interesting figures in it, like an average UK house (85.5m2 floor space) has 117 tonnes of material in it (or 1.8 tonnes/m2) and accounts for CO2e of nearly 56 tonnes or 0.66 t/m2

It goes on to compare this with a factory-built house to show that that has much better numbers, not too surprisingly (although the one studied is only 10m2 so I'm not sure how valid that comparison really is).

They also find that transport is not a large component of house-building energy costs (generally about 5%-7%, even if you made houses in china and shipped them over it would only be 17%).

Over an assumed 70 year lifetime of a building the CO2e from building is 0.83t/yr. Which means that occupant energy use still dominates, at 4.5t/yr in a 2006building-regs house, or 20% less in a code4 house.

All interesting stuff, but not actually the point I wanted to highlight.

Pages 11 and 13 have graphs of the GHG Emissions for the various components of the building which has some pretty odd-looking numbers.

For the conventional-build house:
window/doors timber: 1t
steel:1.3t
concrete: 1.3t
mortar: 1.5t
polyurethane: 2.8t
aluminium: 3.3t
bricks: 3.4t
other timber: 6t
uPVC windows: 6.1t
membranes: 6.2t

Is it really true that 1.2t of membranes generates 5 times as much GHG as 28t of concrete?

We all go crazy about membranes here and many have a big downer on concrete. Perhaps that's not as clever as we thought. (Or this report is complete nonsense).

So, discuss.

ji: but that might be saying that 1kg of feathers is a lot more than 1kg of lead... A lot more what? Volume or embedded energy?

Rgds

Damon

so if you look at it as per dwelling it may get back to the presumed figures (league table of nasties) we may (wrongly) have in our heads

Yes those figures are per-dwelling. So saying "a few tonne of it will do lots of roofs where as a few tonne of concrete might only do one wall footing." isn't really relevant. This one house has 28 tonnes of concrete in it, accounting for 1 tonne of CO2e emissions and 1.2 tonnes of membranes, accounting for 6 tonnes of CO2e emissions.

I'll add the masses of materials used as well as the CO2e numbers to make it a bit clearer, and then the Kg CO2e per Kg material that must have been used (they are not in the report).

timber doors: 0.5t, 1t CO2e 2
steel: 0.6t, 1.3t CO2e 2.2
concrete: 28t, 1.3t CO2e 0.05
mortar: 9t, 1.5t CO2e 0.17
polyurethane: 0.5t, 2.8t CO2e 6.0
aluminium: 0.25t, 3.3t CO2e 13.2
bricks: 15.8t, 3.4t CO2e 0.21
other timber: 2.9t, 6t CO2e 2.1
uPVC windows: 1.5t, 6.1t CO2e 4.1
membranes: 1.2t, 6.2t CO2e 5.2

So timber is half as bad as uPVC per Kg, and ten times as bad as bricks. Really? I'd always assumed timber was much lower embodied energy than bricks, and might even mostly offset itself due to sequestration.

Apparently these numbers come from another of their projects: http://www.resource-accounting.org.uk/
If they are right then I think this is rather interesting.

BTW those material-masses-per-house number don't correspond to any particular design but to the 'average british house', so you'd have to work out the material masses in SIP, timber frame, brick+block in order to compare those.

Has anyone tried this excercise for their own house/design?

Posted By: wookeyIs it really true that 1.2t of membranes generates 5 times as much GHG as 28t of concrete?

So the ratio is 117 times?

As ST says, ICE is a good cross-check. The relevant kgCO2/kg figures are

concrete, say .13
DPM 4.2
plastics, say 2-6

so ratio DPM/concrete = 32.3
and plastics spread around that number

So it looks on the face of it like the numbers in that paper need further investigation.

The ICE numbers for concrete always make me suspicious but I suspect they are heavily researched albeit with a lot of input from vested interests. It may be that the numbers for other materials have not had quite as much examination. But ICE is generally held out as the closest thing to a gold standard.

Another question that might be worth asking is how much CO2 do the materials save throughout the life of the building in return for their embodied CO2? Does the membrane save 117 times as much, weight for weight? (or even 32 times as much?)

And here's a zen question - does the third EPDM draught strip on a triple-glazed window save enough CO2 to justify its own existence? How about saving enough energy?

Rendered straw bales don't have membranes, though they usually have lime. And floors usually have membranes, roofs sometimes. But there are a significant group of people that try to design them out.

Oh BTW, thanks for the link to the paper. I don't remember seeing that before.

Up to a point, I agree with you but if that 56t of carbon for building the house is right, then that's 0.83t/yr footprint over 70 years. For a couple that's nearly half of the target annual CO2e levels we need to aim for. i.e 40% of your total allowance has been used up by the house. Getting down to 1t was always going to be awfully difficult, so this really isn't going to help. Now I'm not sure how much that reduces if the energy supply is decarbonised (CCS, nuclear, renewables etc). 'some',

But I bet you can easily halve that by using suitable materials. So the art is making something passive, but also low CO2e.

Ed, I don't think its the usual way to do it but if you're doing cradle-to-grave you have to explicitly account for what happens at end-of-life, so I guess you might need to keep track of it somehow.

Wookey, Yes, I agree that it is an issue that needs to be considered seriously. But I suspect that heavyweight houses last longer than 70 years. I guess the average is brought down by things like the post-war concrete and other system-built pre-fabs (i.e. the previous generations of what this paper is pushing now).

I've now read the paper and was disappointed by it. It says it is contrasting traditional and off-site manufactured houses but in reality does nothing of the sort. What they do do is a comparison of heavyweight construction versus lightweight construction, and a not very good comparison at that.

My first issue is section 5.1. They say that the average weight of a new home was 117 tonnes and then they add on 10% each for contingency, over-ordering and waste. My problems with this (apart from the arbitrary nature of the 10% estimates) are:
* the contingency is built in to the house so presumably already included in the weight, so shouldn't be counted again.
* the over-ordering is presumably not scrapped but is eventually reused as part of some other house, so again, it shouldn't be counted.

I'd like to explore the materials breakdown (table 1) further but the reference isn't at the URL they say it is and google didn't find it for me. In particular, while the weights were given for building an average new house, they say that table 1 contains the materials in an average house (i.e. not necessarily new) although the weight does roughly match, so its not clear what's going on. For example, if it is a new house then any polyurethane insulation will NOT contain HCFCs! But if it's an average old house I wouldn't expect it to contain much polyurethane insulation at all. And is the glass additional to the glass in windows? (If so, what is it? And if not, why is there so little of it?)

I also tried to find the embodied carbon data that is the basis for figure 4 at the www.sei.se/reap link they gave but haven't managed to find it. Did anybody succeed?

Looking at section 6.1, I got very confused. They're looking at a lightweight module instead of a proper house and table 2 leads to a number of questions. Is there any insulation included and if so where? Are there any external walls included (facings) and if so where? What are the floor and roof made from and what vapour barriers are included? Again, it would be nice to have a reference to the design and construction details.

They talk about the need for durability and then discuss using materials such as vacuum insulation!

So they've compared a heavyweight house against a lightweight module. When they come to compare the emissions, they give no consideration to the very different thermal behaviours of these types of construction but appear instead to use off-the-shelf numbers for the operational energy used. So the graph is pretty meaningless. IMHO.