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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorPingy
    • CommentTimeApr 4th 2008
    I know there are differences in opinion on this forum about what level of floor insulation is necessary.

    Going down the path of more is better than less approach can anyone advise whether it would be possible to have a 100mm concrete slab on top of 300mm of flooring grade EPS?

    Is the concrete too thin?
    Does the concrete need steel reinforcement?
    Can underfloor heating pipes be cast into the concrete?
    • CommentAuthorMike George
    • CommentTimeApr 4th 2008 edited
    1. Probably okay but the concrete supplier will ask you what you are using it for and confirm a suitable mix. Also consider whether you need to put a screed over the top - concrete is not as easy to get level and smooth as screed is.
    2. Probably not but see 1.
    3. Sorry don't know

    I'm in the not necessary camp but it isn't always black and white. If you need to excavate 300mm then I would not do it. On the other hand, if you need to infil 300mm then I would.
    • CommentAuthorPingy
    • CommentTimeApr 4th 2008
    Thanks Mike.
    • CommentAuthorjoe.e
    • CommentTimeApr 4th 2008
    Underfloor heating pipes can be cast in, but check the joints really, really carefully before you lay the concrete! I saw this type of set-up being laid once and the plumber used a device to check the pipework that pressured up the water in the system; it was left overnight and the pressure checked in the morning before proceeding. There's an underfloor heating system in part of my house, which was there when I bought the place; I was told that it had never been used because the pipework was laid wrongly in some way, and the whole thing had to be disconnected and abandoned.
    • CommentAuthorBen
    • CommentTimeApr 4th 2008
    This just what i am trying to find out about. A underfloor heating company i spoke to said it is fine to lay it in the concrete mix. I plan to put 150mm celotex under it. That gets the mysterious U value down to about 0.13. They also said a mix much thicker than 100mm makes the heating very slow to respond
    Posted By: Benthe mysterious U value

    What's mysterious about it...?


    • CommentAuthortony
    • CommentTimeApr 4th 2008
    UFH is always slow to respond and the more mass inside the insulation the slower it will respond in either direction.
    Posted By: James Norton
    Posted By: Benthe mysterious U value

    What's mysterious about it...?

    :confused:" start="fileopen" height="15" alt=":confused:" ismap="false" hspace="0" loop="1" src="http://www.greenbuildingforum.co.uk/newforum/extensions/Vanillacons/smilies/standard/confused.gif" width="15" vspace="0" >


    Misused more like:bigsmile:
    • CommentAuthorTerry
    • CommentTimeApr 5th 2008
    Why not screed it rather than use concrete. This is quite standard with UFH, although as I understand it you have to inform the screed suppliers about the UFH.
    • CommentTimeApr 6th 2008
    how about using foamglas floorboard insulation with a lime mix screed.
    • CommentAuthortony
    • CommentTimeApr 6th 2008
    Pingy, why do you need heating?

    It is OK to concrete on top of the insulation that you suggest. It would be better in terms of maintenance/accessibility to have a screed too.

    Size of the slab will to some extent determines thickness.

    I would use an anticracking mesh (A142) as well it is nice to tie the pipes to apart from anything else.

    I once saw specifier ban the use of 100mm sheets and made them use 50mm sheets in that case x4 scared of air pockets and sagging!
    That's a good point about thick inulation. I have seen 100mm PUR sheets with quite a camber in them. I wonder if the weight of the screed is enough to flatten them and get rid of any trapped air underneath?

    Seems sensisble to use 2 x 50mm layers instead but even then is this a worry? Perhaps insulation under solid floors should only be allowed under the concrete? and not between the concrete and screed which is also allowed at present
    So We lay the insulation on top of the hardcore
    then DPM
    then slab with mesh and UFH as the finished floor
    got to be time/material saving

    whats the easiest way to get a decent finish
    never tried power floating or rolling ,
    how about getting it a good a possible then level tex

    Any good ideas for a simple builder who doesn't want to get a ( I presume) expensive specialist team in


    In my experience it is quicker, cheaper and aesthetically pleasing to use a steel trowel finish and then lay tiles on top. I tried power floating, grinding (exposes aggregate and anything else you through in) and sealing which looked amazing but was expensive (labour & skill intensive) in the end.
    I use compacted sand on top of the hardcore and get it nice and level to take the insulation. Then DPM

    I use a 'Part 1' concrete mix, which sets in a few hours. This allows you to tamp level when wet, Float up when tacky, and polish up to a final finish in a similar manner to finishing gypsum plaster.

    It is easier to do if you are very fussy with levelling the blockwork/ shuttering
    thanks 2 good tips

    Mike, your right I should of said blinded hardcore
    i'll look into that part 1 mix, I guess one of those long handled, wide broom like trowels would be used for finishing

    cheers Jim
    How about promoting Green Building? Just don't use concrete. At all.

    What your best solution to a heated ground bearing floor without concrete?
    Limecrete no doubt, even mixed with recycled glass or suchlike. Great if you can afford it and have got enough work to do elsewhere while you wait for it to go off
    That's one alternative, but let's think what folk did before OPC was invented :)
    I agree with your motives wholeheartedly, and I have considered what folk did before OPC. However, the reality is that people must make a living; and comply with building regulations, whether they like them or not.

    I have often broached the possibility of using more 'green' materials with clients. As soon as they find out the cost they lose interest very quickly.
    what did the romans do , they were pretty good builders, built things to last

    What are we after once we have a low energy consumption building

    The longer it lasts ( achieving its purpose, doing its job )the more sustainable it its
    or is it,
    The ease with which it can be created and returned to its original state without a negative impact on the enviroment

    Hay, I dont know the answer to that one

    any thoughts
    Posted By: jamesingramwhat did the romans do , they were pretty good builders, built things to last

    Didn't they invent concrete?
    • CommentAuthorstemack
    • CommentTimeApr 8th 2008
    In response to the title, good. This is what I did (albeit with 200mm polystyrene), and now the house is finished it's one of the high points of the build. See http://eastcambusmoon.blogspot.com for pics (around last October).
    Posted By: Mike George
    Posted By: jamesingramwhat did the romans do , they were pretty good builders, built things to last

    Didn't they invent concrete?

    Yes, but as you well know, they used a naturally hydraulic lime not Ordinary Portland Cement. They didn't burn very much of the world's fossil fuel resources or cause global warming, yet some of their buildings have lasted for two millenia and more would have survived if they had not cocked up their socio-political relationships.

    There are still too many people claiming to be hanging round the Green Building Movement who have not yet read Jim Hansen's paper, Target Atmospheric CO2: Where Should Humanity Aim?

    (Ok, so it was only published yesterday, but do try to catch up, this is urgent, we've a planet to save.)
    • CommentAuthorMike George
    • CommentTimeApr 9th 2008 edited
    Biff, Re "There are still too many people claiming to be hanging round the Green Building Movement"

    Would you care to name names?

    You're right about the Romans of course , but I think James knows that as well. I just looked at a site which discusses their use of pozzalans and came across a claim that the Egyptians may have use 'Burnt Gypsum' as a cementitious material at Giza. http://nabataea.net/cement.html

    But then if you've read Graham Hancock's books you may think that the Egyptians did not build the so called pyramid of Khufu, but that it supersedes the Egyptians by thousands of years. Now hasn't that lasted a long time.

    There's more to green building than cement v lime. It is not the be all and end all. It would be even better if those promoting and selling such materials would bring the prices within reach of the majority of the population.

    You will be pleased to hear that I am about to undertake a job using sheepswool -I finally found someone who is willing to pay 3 times the cost of the alternative glasswool.
    • CommentAuthorMike George
    • CommentTimeApr 10th 2008 edited
    Posted By: Mike GeorgeBiff, Re "There are still too many people claiming to be hanging round the Green Building Movement"

    Would you care to name names?

    That's a 'no comment' then?
    • CommentAuthorstephendv
    • CommentTimeApr 10th 2008
    stemack, nice site! I see you've used the Ubbink MVHR unit. I'd be interested in your experiences with it - how much noise does it make? Did you have to use any noise absorbing ducting? What are the real power consumption figures?
    • CommentTimeApr 10th 2008
    Stemack, the house looks great - very jealous, maybe one day I'll get my chance to do something similar
    • CommentAuthorbiffvernon
    • CommentTimeApr 10th 2008
    Posted By: Mike George
    Posted By: Mike GeorgeBiff, Re "There are still too many people claiming to be hanging round the Green Building Movement"

    Would you care to name names?

    That's a 'no comment' then?

    Not at all - I just don't read every thread every day on this forum (I have a life, I think).

    Of course it would be invidious to name names so let's just stick with anyone who has suggested using something made of petroleum derivatives or involves CO2 emission in its production and use. (That should include most of us.) We could then put folk into a rank order, with OPC enthusiast near the top of the list.
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