Hi,
Does anyone have any experience of meeting Part L requirements and rammed earth structures? For instance does the high U-value mean they will always fail to pass? And how can they be treated in SAP 2005?

thanks
Justin

You could also highly insulate any stone plynth, which will further offset the insulation you would require elsewhere. This would be good practice anyway as it would be a significant thermal bridge compared to the earth above

I don't think R'd Earth alone as an external wall will comply with ADL2006 as although you could compensate with area weighted U-values and an individual building control office might be convinced (doubt it to be honest) the reg's state a 'limit on design flexibility' limiting the max U-value of any one element.

Bearing in mind this and the tendency of rammed earth to turn to mud/dust without protection form UK elements, perhaps the approach used at CAT in N Wales in their AtEIC building could be considered:

External insulated timber framed walls for insulation and weathering
Internal loadbearing R'd Earth walls for compressive strength and oodles of thermal mass

J

Posted By: James Nortontendency of rammed earth to turn to mud/dust without protection form UK elements

Does it truly? I used to hear that about cob, but not so, at least not to mud and dust, just very slow erosion over decades or centuries, provided the top's protected and water can't saturate it from above.

Posted By: James Nortonwithout protection / stabilisation additives rammed earth will eventually turn to dust and earth

For cob, I don't think it's correct to say that. Even naked without even limewash, cob only erodes almost negligibly. Is rammed earrth less durable?

Cob doesn't necessarily have straw or dung - it used to because they'd mix it by getting the cattle to trample it in their enclosure. Certainly can't repair by surface daub. sure needs needs 'a gud 'at 'n boots' but what doesn't? I still want to know if we're saying that rammed earth is more prone to erosion than trad cob.

One thing you left out - cob is more fun than anything!(though straw balers claim the same!)

Just to weigh in on the Rammed earth durability/strength and thermal properties.

I've almost finished at PhD looking at the structural behaviour of rammed earth, and looked at the durability of ancient rammed earth structures. Provided the mix design is correct, and you provide a reasonable protection, then unstabilised (no cement) rammed earth can be used.

The U value of rammed earth is fairly low, when compared to say concrete, so to achieve the required value to pass the building regulations you need a reasonably thick wall (probably about 400mm), because the building regualations don't allow for thermal mass. If you model the building as a whole then I think you can persuade inspectors of the thermal advantages of rammed earth, but I would agree with the previous comment, go for a timber frame with rammed earth internal walls to be on the safe side. Alternatively, add a little cement and you will massively increase the durability and strength

Paul
http://www.dur.ac.uk/p.a.jaquin

I'd be wary of adding cement, given what happens to clom and clunch when cement is added. As for thickness, 600mm is pretty standard for an earth wall, with no additives whatsoever save some chopped straw and maybe a little dung. They do like to have deep eaves, though, to keep the weather off.

Hi Joinerbird,

Rammed earth is just moist soil compacted between formwork. Take the formwork off, let the wall dry and you end up with something like a huge mud brick. It has been popular in many parts of the world, and more recently it has been picked up as a sustainable building material. There is a pretty good explanation on wikipedia I think.

I'm not an expert on this but I believe that currently the Building Regulations look only at the thermal conductivity (U value) of the material from which a wall is made. This value is just determined by putting something hot on one side of the material and something cold on the other, and seeing how long it takes heat to get through the material to heat up the cold stuff. So If you have something like polystyrene, with lots of air in, it takes a long time for the heat to travel though it. If you have a metal, the heat can travel much faster though, so so it isn't as insulating.

However, we haven't taken into account the temperature of the material (the wall)

Because temperatures fluctuate through the night and day (and through the year) in a house sometimes the heat is flowing from inside to outside, and sometimes from outside to inside. If you look at the walls their temperature is between that of the inside and the outside, sometimes they are 'giving' heat to the inside and taking it away from the outside, and sometimes the other way around. They basically act to dampen the temperature differences between outside and inside. If you have a wall with enough thermal mass, then it can warm up during the day (from the sun), and then pass that heat to the inside of the building during the night. Rammed earth is very good for this, but you can't prove it based on U values alone. The way to get round this is to do a more complex analysis of the whole building, which does take thermal mass into account, and can be allowed under the building regs.

Sorry for long and not very detailed explanation, there is a bit more to it than that, but I believe that is currently the situation.

Biffveron, Gervase,

I don't think 400mm is excessively thick, but currently rammed earth walls can be built as thin as 300mm according to the recommendations (Rammed Earth: Design and construction guidelines, Peter Walker et al), I would agree with Gervase and go for something more like 600mm. I feel lime is definitely the way forward, that is the historic method of strengthening rammed earth. However, it is much harder to 'prove' the strength when adding lime, and so the best way to get though the building regulations is to add cement instead. Cement stabilised rammed earth walls are popular in the US and Australia, but obviously aren't as good as a sustainable building material. A lime stabilised rammed earth wall would be best, but (to my knowledge) no-one has yet built one in the UK.

Paul

how can you test the whole house before it is built?

Ah yes 0.17 is the target for walls not overall. Still the figures do suggest some other form of insulation is required.

Ditto...

Does anybody have an idea of what insulation would be best?

Why is anybody on the greenbuilding forum considering meeting the building regs to be a constraint? Building Regs are there to 'persuade' the worst quartile of builders. Green builders should be aiming way above them, surely?