Injected dpc needed for timber frame lean-to on masonry?

Discussion in 'Builders' Talk' started by JonEC, Jan 8, 2020.

  1. JonEC

    JonEC New Member

    Hi guys

    I'm planning to put a side porch onto an 1890s semi, architect has specified on the drawing that there is a need to inject a dpc along the existing external (soon-to-become-internal) masonry wall along the new roof line to stop moisture coming down within the masonry wall into the house. Does this sound reasonable? I'm no expert but own research online suggests that injected dpcs are of limited effectiveness in general and I've not seen any mention of them being used in this way in the context of timber-on-masonry extensions, and would be happy to avoid any needless cost...

    Grateful for any thoughts..
  2. KIAB

    KIAB Super Member

    Expect it will cause more problems than it solves.
    Joe the Plumber and rogerk101 like this.
  3. Bob Rathbone

    Bob Rathbone Screwfix Select

    One of the big problems with injected DPC is that it prevents the masonry from breathing, so any moisture that gets into the brick etc, cannot get out and freezes in the winter causing surface damage. I would not use it.
    KIAB likes this.
  4. Abrickie

    Abrickie Screwfix Select

    Never heard of that been spec’ed, by the same principle every conservatory should be done too, does your architect have a relation with a damp proofing company ;)
  5. Joe the Plumber

    Joe the Plumber Screwfix Select

    I didn't know John Wayne was an architect. But apparently he must be, because ANYONE recommending an injected DPC is nothing but a cowboy.
    KIAB likes this.
  6. JonEC

    JonEC New Member

    Many thanks for all your replies, confirmed my suspicions! I will decline this recommendation and instead ensure that there is good ventilation around the masonry wall section that's becoming internal. It's a bit frustrating to be the one pushing back on the spec as I'm paying the architect good money for it, but they've been pretty good otherwise.


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