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Gas pipe in wall chase, in foam

Discussion in 'Plumbing and Central Heating' started by frank999, 7 Sep 2020.

  1. frank999

    frank999

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    A 130mm thick internal block wall,, in a kitchen has a shallow vertical chase - about 1.5mt, into which 22mm copper pipe has been placed. There are no joins in this length of pipe.

    This will sit behind a kitchen cabinet 715mm, and then beneath 500mm of tiling.

    The surface of the copper pipe is just below the face of the wall it sits in.
    It was advised to wrap the pipe in something protective by the gas engineer, prior to filling with a wall filler, 1000 gauge DPM has been used, and tape run along the joins, the DPM is like a sleeve, rather than tape applied direct to the pipe.

    The gas engineer has tested the pipe OK, and left, he will be back in a few weeks for another job at the site.

    Over the gas pipe I have asked the builder to place metal capping (cut down resilient bar has been used as traditional wiring capping is too thin, in my opinion).
    The builder though, rather than fill with filler, has used expanding foam, with the metal flush with the surface.

    I understand that sleeved gas pipes should be open one end, but feel the expanding foam will have expanded around the flexible DPM sleeve to remove any air gaps, which from my understanding will be a good thing. The end of the pipe before it goes into the chase has been left exposed, the space behind the cabinet will also be alllowed to vent.
    Guidance for pipes in walls - either recommends the pipe be encased in Dot and Dab filler, or encased in wood battens, where the wall is plasterboarded, but the wood battens would surely leave a small gap around the pipes, and then the gap sealed up.

    My understanding of Foam around copper is that it is not harmfull or corrosive in any way.

    If the builder had used filler, it would have been difficultto get it round the back on the pipe, and voids might have been created, albeit very very small ones, is it the large voids that the Regs are most concerned with ? and how is Expoandnig foam viewed if used in such a way.

    I will ask the gas engineer his opinion, of which he will no doubt have, but also good to aks others 'on the job' here.
     
  2. johnny2007

    johnny2007

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    Not a gas safe technician, but why would it be a problem to have a void around the pipe?
    There are gas pipes under the floorboards without any sleeve around them and I've seen them in very recent installations.
     
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  4. frank999

    frank999

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    My understanding is that any void containing a gas pipe needs to be ventilated, however small voids in ducts of less than 0.01m² and 0.01³ do not require ventilation.

    My use of the word sleeve might mislead, the DPM is wrapped around the pipe and was there to protect the copper from corrosion from the filler, but as the DPM was not tight fitting it could slide up and down the pipe in a sleeve like manner. The Filler however has not been used.
    The regs I believe require a sleeve around a gas pipe where it passes through a wall or foundation, but even that should remain open on one end.

    The pipe wrapped in Denso tape was an alternative, but that seemed a bit excessive as it wasn't going in a screed.
     
    Last edited: 7 Sep 2020
  5. Dangee

    Dangee

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    Johnny oh Johnny. Leaving restricted voids around gas pipes is exactly the the way an explosion happens in a house. If there is a free flow of air it is virtually impossible for a small gas leak to ignite.
    If it’s a dot & dab wall, it should be boarded up to the pipe & solid infilled around with drywall adhesive.
     
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  7. frank999

    frank999

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    Johnny oh Johnny. Leaving restricted voids around gas pipes is exactly the the way an explosion happens in a house

    The pipe sits in a chase little bigger than the 22mm copper pipe, with DPM wrapped around, originally the gap around the pipe was to be filled with Dot and Dab adhesive (the wall is solid plaster, not D&D), my concern is that the builder has filled this tiny void with expanding foam instead - could this be a restricted void ? Metal capping has been placed ontop flush with the plaster. Apart from the metal capping and foam the chase will be left open, and where it runs behind a wall cabinet ventilation holes will be created top and bottom at the rear of the cabinet.

    I understand where a wall is dry lined 'on battens', the pipe should be encased by tightly fitted parallel wooden battens, but no mention is made of using D&D adhesive around a pipe surrounded by battens - except where a wall is D&D dry lined - 'the pipe should be encased in continous adhesive dabs', in my mind unless the battening around the pipe is completely air tight, gas could escape to other voids behind the plaster board.

    The area around a pipe surrounded by battens would be very small, similar to the situation I have, the chase is only 1.5 mt long, but as long as the void behind the cabinet is well ventilated I can't see where else a Restricted void is creatred, my only concern is the foam, which fills a very small volume/area.

    small voids in ducts of less than 0.01m² and 0.01³ do not require ventilation.
    Is this restricted void volume/area then acceptable ?
     
    Last edited: 10 Sep 2020
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