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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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    • CommentAuthorRex
    • CommentTimeMar 8th 2020
    What ho one and all,

    Because I built my own house, I get asked by neighbours for comments / thoughts.

    A neighbour built around the same time, 9 years ago. Modern design, some bad architectural detailing (acute angles!) flat areas with up-stands (poor drainage?), SIP construction with waterproof plasterboard (external render board) on battens and a thin render finish.

    In the heavy rain of a couple of weeks ago, they had water come though a speaker opening in the kitchen ceiling and it has been found to come from the sliding door on the balcony above. Fortunately for them, it found its way without dampening the insulation or bringing the ceiling down.

    They have started an NHBC claim which initially entails a damp investigation. They showed me the main body of the report, which is really badly written; one of the areas that the 'expert' had commented on mystifies me, and they don't know if he is right.

    I don't recall how the windows were installed, but once in the SIP openings, they were sealed with black expansion foam tape, I guess the render board was installed, then the render and completed with a substantial silicone bead, nicely finished at 45 degrees. It seals the render and frame.

    They have been told that silicone should not have been used as it does not have a suitable life expectancy and will break down, allowing water to ingress via capillary action. The implication is that all the windows are incorrectly installed and will have to be removed and done correctly.

    This seems to me, way over the top, but what do I know? However, I see this kind of silicone seal / detail being used on many buildings and cannot believe it is such an unsatisfactory material.

    What is the truth?

    Toodle pip and thanks

    • CommentAuthortony
    • CommentTimeMar 8th 2020
    I don’t like relying on silicone to seal things (upstands on shower trays are fail safe) I would investigate whether the water is coming in through the window head (no or inappropriate drip detail) the reveals or more likely the sill/under /through/ round the ends of the sill. Polythene taped over the elements should help and a hose
    • CommentAuthorgyrogear
    • CommentTimeMar 8th 2020 edited

    the ''black expansion foam tape" sounds like Compriband...


    • CommentAuthorrevor
    • CommentTimeMar 9th 2020
    Could be Iso Chemie iso bloco 600, could be unbranded there are some about I understand.
    • CommentAuthorRex
    • CommentTimeMar 9th 2020
    There is certainly no drip edge on the top of the reveal, but I have not seen any windows that have this detail.

    What the neighbour was told is that silicone should not be used as the primary weather seal. Of course, it all depends upon weather breaks / seals behind the external silicone.

    Their problem will be, if the insurance accept the case, they will attempt to apportion blame. As they employed a Project Manager, is the detailing his fault, or the people (experts) he engaged to do the specific tasks.
    • CommentTimeMar 9th 2020
    Posted By: RexWhat the neighbour was told is that silicone should not be used as the primary weather seal.

    I think that's true. Silicone is notorious for peeling away from surfaces that were not scrupulously clean.

    Their problem will be, if the insurance accept the case, they will attempt to apportion blame. As they employed a Project Manager, is the detailing his fault, or the people (experts) he engaged to do the specific tasks.

    Well (a) the insurance may not consider it's worth the bother and expense to determine cause exactly to recover their costs, and (b) your friends don't really care what the insurance company do after they've paid for the repairs do they?
    • CommentAuthorrevor
    • CommentTimeMar 9th 2020
    My BCO advised me when I started our build to wherever possible avoid the use of silicone particularly where it gets wet or not vey easy to replace. He advised the use of acrylic sealants. On my windows I have used silicone but only as a secondary or third barrier and not exposed to the weather. I had issues with the use of expanding foam tape in that in heavy weather (strong wind and rain) it would absorb the water and act like a sponge and channel the water downwards as if it was a pipe. This then came in at the bottom of the window. I had installed the windows exactly as per manufacturers drawings but I do not think they had factored in the severity of the weather we can get. I called in the technical rep of the expanding foam tape who said the install had been done properly and the water ingress was not down to the tape. I removed the tape and sealed with silicone onto backing rod and have had no problems since. In order to protect the silicon I then installed expanding foam tape of narrower depth to make a neater finished joint which the tape is good at.
    I must admit I am somewhat sceptical about silicon and water as I have seen many frameless glass fish tanks some very big held together just with a silicone bead.
    I used almost exclusively ARBO sealants of different grades and if you look at their data sheets they give recommendations as to their use and what primers to use. Their technical people are extremely helpful if you have a query.
    A thought about the balcony sliding doors were the drainage channels clear?
    • CommentAuthorRex
    • CommentTimeMar 10th 2020 edited
    Thanks for the thoughts. Did not think about silicone on fish tanks!

    I will admit to not being certain as to whether the frame / render sealant is silicone or some other material. it may be the correct sealant and I am using 'silicone' as a generic term.

    Just visited a coffee outlet on the A3 and noted that they have 'silicone' sealant on the frame / brickwork corners and on closer inspection, it looks just fine.

    What I don't understand, based on what the neighbour told me, which in turn is based upon what the 'expert' told them, the dodgy silicone is on the top edge of the window, which is under the reveal. Not a position that is likely to get wet?

    All I can say is that I am pleased that I have a 1m roof overhang (like a Huf Haus) and that certainly keeps the windows dry in all but strong winds.
    • CommentAuthorborpin
    • CommentTimeMar 17th 2020
    As an aside, for my render, I put a stop bead close to the window and then inserted expanding foam tape. Worked an absolute treat and no horrible sealant in sight!
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