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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.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorgravelld
    • CommentTimeJul 9th 2019
    Rule of thumb is about £90/m2 for EWI but it can obviously vary a bit either way.

    My impression is most firms want to get a simple job done and this is what they often get away with on big council projects (see the Preston debacle). The key is in the preparation and the enabling works. Prioritise everything to make it fool proof, e.g. extend the roof to make sure you don't have caps on the EWI (a source of water ingress), make sure the window reveal detailing is done properly, move meter boxes, incoming power.

    TBH it gets on top of you, and I gave up simply because of the complexity (and not wanting to spend £ks on professionals on what is already a very costly improvement).
    A quick play with an on-line tool for U value calculator showed a 9" brick wall had a U value of 2.45 with a condensation risk on the internal face - Well it could be right there.

    Adding just 5mm of EPS to the outside removed the condensation risk and gave a U value of 1.87 It is always said that the first bit of insulation makes the most difference and from there it is diminishing returns.

    Adding 200mm of EPS gave a U value of 0.18

    For the purposes of speed with the game I ignored plaster and render.
    • CommentAuthorGreenPaddy
    • CommentTimeJul 12th 2019
    Hi Tania,
    Definitely don't be worried about what you're doing. You've got a lot of positives already....

    Simple 9"wall with planning for EWI.
    Part of the orig external wall will have a new build over it
    The damp in the walls is condensation rather than rising
    You can strip out a susp timber ground floor and replace with a slab, not an existing solid slab with no insulation.
    You've opted for MVHR, which along with warmer walls will almost certainly eliminate internal condensation

    That's about as straight forward as it gets.

    Main issue is that unfortunately your arch has been unwell, and so you're probably unaware of many of the details / facts. Also I suspect that the breathable insulation route may be a bit of a red herring?

    However, it's very easy to drop in lots of great ideas and criticisms, without spending a lot of time fully understanding all aspects. I hate it when I've spent a week or two designing for a client, and they speak with some clever dick who only half understands what he's talking about, but convinces my client of some much better way of doing everything. So I don't want to be guilty of that.

    So honestly, you need to get up to speed with all aspects of the work. What does the £17k include? If it's ashp, ufh, rads, hot cyl, all replumb, sanitary ware, it may not be such a bad price.
    Ask why the house requires breathable insul. I use pavatherm internally for tricky solid stone buildings, to stop external stone damage, but for your scenario, EPS EWI would be perfect. Get your arch to justify the extra cost he is setting you up for.

    P in Hungary is giving sound advice about the 200mm EPS and Uval around 0.18 W/m2K. I'm on holiday, so can't check accurately. You might get the same Uval with say 150mm XPS, if you need to reduce the EWI thickness. Do not skimp on the insulation. The cost of the installation and render is the big part.

    Once you are clear about the shell of the building, and therefore the heat loss, then you can start making informed decisions about the heating system.

    Your existing walls would lose around 10 times that of the EPS route, so you might only need 1 or 2 kW to keep the house warm. If the stove will be burned often, then you're on the page of most energy for hot water.

    Then you start considering what's the best way to supply that small amount of energy input. That could potentially be immersions? But you need hard facts to make those decisions.

    Now you are getting to the point of saying...do I want a RHI heating system, and therefore what is the best sequence for the work.

    Sorry for making this a long reply, and with no firm answers, but you need to do the hard work now, and crunch numbers and options. My experience of archs is they often can't or won't do that.

    With more facts, I 'm sure we (on GBF) can help steer you along the path, if that's helpful?
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