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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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    • CommentAuthoraclarky
    • CommentTimeFeb 7th 2019

    bit of advice if anyone can help.. We have moved into a 1900 house, 600mm stone walls, sash windows, very cold and just electric heaters - not even storage!

    1 - can you inject foam into the void behind the old plasterer - sounds hollow ? lath and plaster. I don't really want to pop it out..

    2 - any advice on Ultrotherm/spacetherm wall liner. Scarily expensive but it would do the job. I calculated 10mm spacetherm = 1.5w/m2K and Ultrotherm 3.3w/m2/K [wouldnt put money on my calls however]

    3 - the windows are single glazed, we may add secondary glazing. Can you inject foam in to the window surrounds [not near the weights obviously]. The wood is so so cold!


    ''1 - can you inject foam into the void behind the old plasterer ''

    I feel sorry for the old plasterer!
    Is your stay long term? do you own the house or rent it? Any issues with conservation areas or listing that my 'influence' what you can do?

    1 plaster may sound hollow because it is not (properly) attached to the wall (blown) I don't see how/why you would have any intentional void behind plaster on an external wall.

    2 I have no experience of Ultrotherm/spacetherm wall liner however I have put external wall insulation on stone walls with good results. Internal wall insulation is never as good as external, but there are occasions when that is the only choice.

    3 Foam around the window frames will only help if there is a draft coming through. Sash window are notoriously difficult to thermally improve. Secondary glazing is often a good choice - short of changing the windows.
    Are you talking about the 10mm Spacetherm with 3mm MgO board bonded to it? I think that would drop the U value down to about 0.83. Here's how I think that:

    Estimated worst U value of 600 rubble wall approx 1.8W/m2K. 1/1.8 = R1 = 0.55

    Spacetherm lambda value 0.015W/mK, so at 10mm, R2 value = 0.66

    R1 + R2 = 1.21.

    1/1.21= U = 0.826W/m2K.

    ...and you can pop sash boxes apart with foam. I know....!
    • CommentTimeFeb 7th 2019 edited
    Posted By: Peter_in_Hungarydon't see how/why you would have any intentional void behind plaster on an external wall
    Very common, Victorian/Edwardian, for lath and plaster to be on battens, lining a stone wall. I often thought to filling the void with insulation but never did. Any plaster cornices? They're usually hard to the stonework, no void behind.

    Strangely, often quite tall floor joists, significant wall area can be generously insulated within the floor voids, with airtightness benefits too.

    Digging a french drain trench around the perimeter, down to base of founds but no further, fixing EPS insulation boards against the outer face of the foundation wall before backfilling, will significantly reduce heat loss from the lowest floor, whether solid or suspended, without any internal disturbance. As well as ending any rising damp.

    Injecting here and there is prob fraught with unintentional consequences.

    Give us more info about the house - freestanding/terrace, Listed or not, or appearance inside and/or out otherwise fiercely protected? Some pics? Each such house is a special case, no standard solutions.
    The gap between the stone and the lath& plaster is vital for outside air to circulate and dry out dampness, from condensation on the cold stone, or penetrating rain. It was partly filled with insulation by a previous owner of our house but we found that insulation was wet a few years later.

    We found the biggest immediate gains were from filling the very many draughts these houses come with, not 'airtight', but just stopping the howling gales through fireplaces and floorboards and round pipes and doors. Then insulate above the ceiling, then under the floor.

    More expensive and disruptive measures are to replace the windows and the heating.

    Last priority is to insulate the walls, either remove the lath+plaster and replace with insulation board, or cover the outside with insulation and render, whichever you find least damaging/disruptive (we did the inside).
    • CommentAuthoraclarky
    • CommentTimeFeb 8th 2019
    Thanks guys,

    More house details - 2 1/2 story detached house 1900 ish, in Glasgow and sandstone and exterior insulation is a no go for various reasons although it is not listed. We plan to stay long term - the last people were in for 65 years! There is coving everywhere and hence the attraction of putting on a thin internal insulation board.

    OK so foam / insulation behind lath & plaster is off the agenda. Thanks for saving me the pain of doing that!

    Thanks Nick for working that out - I used to be good at maths but k r u etc values confuse me!

    Draught proofing is happening room by room.

    There is just elec in the house - gas on the street but not connected .. yet.. Plans to get GSHP over the summer if they can get in to do the boreholes.

    I was wondering today - about using a thinner PIR board+plasterboard ? <40mm on the walls to save money.. And edging it with a wooden detail to be sympathetic with the internal architecture of the place.. Any experience with this?

    I will do the loft and eves soon - hate using glass wool - any suggestions considering cost / green / ease of use?

    • CommentAuthoraclarky
    • CommentTimeFeb 8th 2019
    for example I could use this: https://www.insulationsuperstore.co.uk/product/celotex-pl4015-24m-x-12m-x-275mm.html

    same U as spacetherm wallboard - and for 25% the cost. All for20mm!

    Celotex wouldn't be breathable right - but if there is the lath and plaster cavity could I just dot and dab it on? Please say yes!

    Wouldn't it be cheaper, for both installation and on-going fuel costs, to connect to the gas supply rather than digging boreholes and installing a GSHP?

    We have used aerogel for our window reveals. It worked but it was super expensive. I guess if you're wedded to retaining the coving then perhaps it'd worthwhile to fit earogel everywhere. I'd imagine it'd be cheaper though to fit a less expensive insulation product and get a specialist company in to reproduce the coving.
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