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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthoraviatrix
    • CommentTimeSep 10th 2008
     
    I am considering buying a solid block bungalow and, whilst bulldozing it and starting again seems attractive, that is a lot of embodied energy and expense. So I was wondering about the feasibility of renovating to passivhaus standard. Sitewise it is perfect - south facing to the garden with minimal overshading, and it is of compact rectangular form. The roof and the windows need replacing anyway so external insulation, installing MHRV and re-sizing of windows is not problematic . Any thoughts?
  1.  
    Sounds great , go for it
    I no little about passivehaus details , but the first problem areas that comes to mind
    floor insulation , would you have to break up the floor slab/screed then replace etc, this could be costly (at least £120m2 , did a easy one the other year , just happened be be looking at the costs a mniute ago)
    also theres the zero vat on new build , could you get the same for your renovation?
    • CommentAuthoraviatrix
    • CommentTimeSep 10th 2008
     
    VAT is not applicable where I live so not an issue. With the floor I was consideringthe possibility of simply raising it and adding another round of blocks before replacing the roof, as all windows and doors would have to be changed anyway.
    •  
      CommentAuthorrogerwhit
    • CommentTimeSep 11th 2008
     
    Posted By: aviatrixexternal insulation, installing MHRV and re-sizing of windows is not problematic


    Rather than insulating the external reveals to doors / windows, why can't the frames just be moved outwards to the plane of the insulation?
  2.  
    Historically because they would be subject to too much weathering, especially at the head. Not sure there is an effective way to eliminate the risk of water ingress
    •  
      CommentAuthorrogerwhit
    • CommentTimeSep 11th 2008
     
    Historically, Mike?
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      CommentAuthorOlly
    • CommentTimeSep 11th 2008
     
    I suspect that achieving the high levels of airtightness required will also be quite a challenge.
    • CommentAuthoraviatrix
    • CommentTimeSep 11th 2008
     
    Thanks for comments so far - with regard to the windows, what I meant was that I need to make the north facing ones smaller and the south facing ones larger anyway.

    Olly, why would airtightness be a challenge - can you be more specific?
    • CommentAuthorTheDoctor
    • CommentTimeSep 11th 2008
     
    if you are putting in a new slab/insulation, raising the wall height, replacing the roof, doors and windows, it sounds like a full passivhaus treatment will remain a compromise to what is left of the existing fabric, (which doesn't sound like much!)

    i think a full audit on the merits of retaining what is left is worthwhile. The extent to which you have to rebuild will be determined by how close you want to get to these standards
    •  
      CommentAuthorOlly
    • CommentTimeSep 11th 2008
     
    Posted By: aviatrix
    Olly, why would airtightness be a challenge - can you be more specific?

    Well it seems to be a problem for new houses in this country, you don't find many builders getting much below 5m3/m2/hr, if you were to ask an average builder to guarantee hitting 1m3/m2/hr (Passivhaus standard) I should imagine he'd probably run a mile, especially on a refurb where there are more unknowns.

    Much of this can be addressed at the design stage; so doing a refurb means you have fewer options. For example, there are all the joints between floors, walls and ceilings which need to be addressed. Of course many of the problems with airtightness are simply down to workmanship and service penetrations through the building fabric, these can be addressed during construction to a certain extent.

    How will the internal walls be finished?
    • CommentAuthorMike George
    • CommentTimeSep 11th 2008 edited
     
    Posted By: rogerwhitHistorically, Mike?


    I just meant that good design [in my eyes] has always meant windows being positioned well in from the external face. The Victorians for example placed them up against the inner face of external brickwork. Newer buildings often place them only 50mm in from the external face, though I prefer a deeper reveal.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 11th 2008
     
    Surround the whole thing with straw bales. Treat the uninsulated solid floor as a great asset!
  3.  
    Thermal bridges will be the greatest challenge, quickly followed by airtightness. If replacing the roof bridging can be addressed at eaves junctions, then it's the wall/floor junction (to achieve the standard thicker insulation will be required). Here the umbrella type detail works well (2m insulation running, say 450mm, below ground perpendicular to the wall.) Windows, move and mount on the external face of the building with cramps and then have the 250-300mm Neopor insulation overlap the frame to minimise themal bridge. This depth of insulation means that you are left with a 150-200mm deep reveal that protects the windows/wall junction from the weather (fairly standard detail in German PH refurb).

    Airtightness, good continuous plaster with no gaps with membranes to all junctions and interfaces with other materials.
    Careful planning is critical.

    Hope this helps.

    Mark
  4.  
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      CommentAuthorfostertom
    • CommentTimeSep 11th 2008 edited
     
    Posted By: Mark Siddall.
    Posted By: Mark Siddall.
    'Spot' on, Mark. Why shd there be any thermal bridging, with continuous external insulation? Gobsmacked to see you proposing umbrella insulation - since when have you been swinging that way? V gd. Is that coupled with still-uninsulated floor slaB?
    • CommentAuthoraviatrix
    • CommentTimeSep 11th 2008
     
    Have I missed something in the last 3 posts?

    I am fairly new to this and don't quite understand you description of what I should do with the floor - it is currently an uninsulated concrete slab. Are you suggesting that the main body of it is left uninsulated - I realise that the ground temperature below the floor will be higher than the outside temperature on cold days, but there will still surely be a thermal gradient of about 10C ??
    • CommentAuthorMike George
    • CommentTimeSep 11th 2008 edited
     
    Posted By: fostertom
    Posted By: Mark Siddall.
    Posted By: Mark Siddall.
    'Spot' on, Mark. Why shd there be any thermal bridging, with continuous external insulation? Gobsmacked to see you proposing umbrella insulation - since when have you been swinging that way? V gd. Is that coupled with still-uninsulated floor slaB?


    Careful Tom, one step at a time:bigsmile:
    • CommentAuthorTerry
    • CommentTimeSep 12th 2008
     
    large eaves will help to protect windows and doors (particularly in a bungalow) and also give summer shading
  6.  
    re the uninsulated floor, as I understand it, it is only the edge of the concrete slab that loses heat significantly. After researching this issue for my house I decided to cover the concrete floor with cork tiles rather than go to the effort and expense of either digging it out or raising it
    • CommentAuthortony
    • CommentTimeSep 17th 2008
     
    Thin cork will not do very much insulating but it will do something. Couldn't you dome perimeter insulation in the cavity?
  7.  
    Tom,
    The umbrella insulation is used in tandem with under floor insulation (say 250-300mm.) The umbrella helps to compensate for the thermal bridge by tweaking the isotherms. I don't mind the umbrella as a concept, just needs to be used in ways that I would deem appropiate i.e. on tricky refurb where TBs can't be addressed. (This detail has been proposed for PH refurb, see Abbildung 4: Umbrella-type insulation in the ground at http://www.hausderzukunft.at/results.html/id3955?active=)

    This doc sets out a draft standard on ground heave and shows some reasonable detailing concepts though not all address thermal bridging in a suitable manner.
    http://www.lcvarmegrund.se/pdf/lc_building_foundations_us.pdf
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