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Energy Assessment: Cob Building - max efficiency with min loss of space

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1 to 14 of 14

  1.  
    • CommentAuthornjtkc
    • CommentTimeJun 22nd 2008 edited
     
    we have two relatively small old buildings to renovate and eventually live in.....
    but because of size and building regs we need to minimise the internal space lost for insulation any suggestions.
    • CommentAuthortony
    • CommentTimeJun 22nd 2008
     
    External insulation.
    • CommentAuthorgreenman
    • CommentTimeJun 23rd 2008
     
    As a matter of interest, are you just assuming you will need insulation in order to meet building regs, or have you been advised as to how much insulation will be required?
  4.  
    You might want to try a couple of inches of this stuff inside and out:-

    http://www.hempirebuilding.co.uk/ecoplaster.html

    I think they are getting the product tested for insulation value at the moment. Might be worth contacting them.
    • CommentAuthornjtkc
    • CommentTimeJul 16th 2008
     
    thanks

    can't cover up external stone but will look into ecoplaster, and yes we are assuming that we will need insulation cause our architect has told us, but will check it out.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 16th 2008
     
    'Ang on - external stone? I though it was cob.

    Massiveness can be a gd substitute for U-value - it's not so easy to calc though. Actual heat loss through a massive wall may be small, due to day/night heat flow reversal, the time lag caused by slow heat soak, etc. Cob buildings usually feel comfortable and fresh to live in, for these and other reasons, like humidity stabilisation. All this is lost by lightweight internal insulation. As far as possible, keep the interior in touch with the massiveness. If a bit more insulation really is necessary, try 3" to 6" of Hemcrete, which is medium-massive, medium-insulative, but has the advantage of bonding thermally to the stone/cob, so keeping the latter in touch with the interior.

    Rubble stone may not be as effectively massive as you think, because if its interior is full of air voids, the outside air will blow freely through the voids in a wind, bringing the cold outside very close to the inside face. However, cob not riddled with rat or bee holes should be solid and airtight.
    • CommentAuthorgreenman
    • CommentTimeJul 23rd 2008
     
    Tom

    I've had several attempts through this forum to try to establish a likely U value for cob, on the understanding that it was the U value that would be likely to matter if it ever came to selling the house. If as you say, the massiveness of cob can be a good substitute for a high U value (for the reasons you state), then is this likely to hold any sway, or will everyone insist on a blinkered 'U value centric' approach?
    • CommentAuthorEd Davies
    • CommentTimeJul 23rd 2008
     
    Posted By: fostertomMassiveness can be a gd substitute for U-value - it's not so easy to calc though. Actual heat loss through a massive wall may be small, due to day/night heat flow reversal, the time lag caused by slow heat soak, etc.


    I can see how this would be true in a climate with wide daily temperature swings but an average close to the indoor temperature you want. Could you explain how it would work, though, if the outdoor temperature is continuously chilly - like a lot of the year in Britain?

    Cob buildings usually feel comfortable and fresh to live in, for these and other reasons, like humidity stabilisation.


    I'll take your word for what you have said but you don't mention how much heating, if any, such buildings require.
    • CommentAuthorgreenman
    • CommentTimeJul 24th 2008
     
    I would suggest that there is an interesting strand that runs parallel to this and many other discussions on this forum, and yet neveer seems to be mentioned. There are numerous posts along the lines of how to insulate in order to maintain a given temperature with minimum possible (or zero) heating. When most ofnt eh older houses in this country were built there was no central heating, only stoves and open fires. Coal would probably have been a luxury for most, or non-existent. Cob houses were generally considered to be the poorest type of dwelling, and generally only built for the likes of farm labourers - a far cry from the desirable country cottages status of today.

    One of the problems with this part of today's housing stock is that they were built when the population who lived in them were much more hardy than most today. What temperature do you all have your thermostats set to? Yes, certainly we should insulate as well as can be managed, but that insulation would be even more effective if we acclimatised to having our houses a few degrees cooler.
  10.  
    ... and dressing according to the weather rather than short sleeves inside all year round.
    •  
      CommentAuthorfostertom
    • CommentTimeJul 24th 2008 edited
     
    Posted By: Ed DaviesCould you explain how it would work, though, if the outdoor temperature is continuously chilly - like a lot of the year in Britain?
    I don't know, Ed, but seems to be true. It's a mystery how many UK houses do stay cool in summer - except the ones that overheat like hell! A gap in my theoretical education that I'll try to fill when I have time or need arises. Anyone explain in simple terms?
    • CommentAuthorgreenman
    • CommentTimeJul 24th 2008
     
    I thought I understood this until joining this forum and having many of my preconceptions challenged!

    Our cob house is warm in the winter and cool in the summer. There are two separate issues - thermal mass, and the source of the heat. The house has solid floors with no insulation at all. the walls are similarly uninsulated. Any atmospheric heat (while the air inside/outside is warmer than the floors/walls) is absorbed by what are effectively heat sinks. If the air outside is cool, but that inside is warm (central heating, stoves etc) then although the walls may achieve some sort of thermal equilibrium (heated on the inside and cooled on the outside). The floor will absorb heat as long as it is cooler than the inside air, or release heat if it is warmer than the inside air.

    I suppose the floors and walls act to smooth out temperature fluctuations. Probably the most significant contribution comes from the floors as in not being insulated, the heat store is potentially huge.
    • CommentAuthorTerry
    • CommentTimeJul 27th 2008
     
    Greenman, if it comes to selling, I think most people will want to know what it costs to heat, rather than discussing U-values. Presumably this will be reflected in your bills, or can be calculated in some way depending on how you heat. Have you tried to acurately measure heating energy consumption in some way for your house?

    Good point regarding turning the temperature down (and Chris' regarding dressing appropriately)
    • CommentAuthorgreenman
    • CommentTimeJul 27th 2008
     
    Terry

    No, I've never tried to do a careful measurement. We are what might be called 'fresh air freaks' (not a term I'd choose, but couldn't think of another one at the moment), and tend to have the windows open, and not to have the heating on much anyway. When we do, the thermostat is seldom above 18C. My earlier question as to how others have theirs set was a serious enquirly as I'd be interested to know how this compares with other homes - if 18C is roughly 'normal' then our heating costs would presumably mean something to other people.

    I'm not up to date as to the introduction of HIPs, or their content - regardless of our heating costs, do these packs include a calculated or estimated U value?

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