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Garden room / outhouse damp advice

Discussion in 'Building' started by ThomasHD, 13 Aug 2021.

  1. ThomasHD

    ThomasHD

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    Hello,

    We have recently been having an outhouse / gym built at the end of our garden. Unfortunately, things did not work out with our original builders and we have had to start looking else where to get the work completed (so far the shell has been completed). On getting new quotes from other companies, we have been told that no DPM was put in place when laying the original foundations and the incorrect blocks were used for the first run around the building (breeze blocks have been used from bottom to top). All in all meaning that damp would rise, and it would probably be best in the long run to knock the building down and redo it properly.

    I've read up online about dpm and how it should be done, and can only see a thin sheet of it placed between the first and second block, but nothing else. The original company have mentioned black jacking it, but is this a viable solution?

    I've attached some images. Any help or advice on the situation would be really greatly appreciated. I don't want to have to knock the building down, but in the same way I would rather make sure it is done correctly rather than have a temporary solution.

    Thank you!

    4.jpg 3.jpg 2.jpg 1.jpg
     
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  3. sxturbo

    sxturbo

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    The insulation is bridging the damp course so you will get issues.

    You could DPM the floor now on the internals of the building and insulate it then screed, but this will bring your flooring up 75+mm

    You can also black jack the first course of breeze block upto the DPM to stop internal penetration.

    The insulation below the DPM already in place will cause issues.

    I would probably have expected engineering brick or normal brick to have been used on the first 2 courses. Breeze blocks are quite soft and . especially so when damp

    I'm no expert mind and I'm sure there are others who will come along and tell me I'm wrong very shortly.

    I would say that the other companies you've had in are likely correct in knocking down and starting again

    @^woody^ would be a good one to advise.
     
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  4. ^woody^

    ^woody^

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    A photo or diagram of the wider area would be helpful, including details of the floor slab and foundations arrangement.

    Those blocks are frost rated, so suitable at ground level and there does appear to be a DPC so that's a start.
     
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  5. ThomasHD

    ThomasHD

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    Hi @sxturbo and @^woody^ - thanks so much for your replies.

    I've attached some photos of its current state (It's been this way for about 10 weeks now), as well as some pictures we were taking at the end of each days work during the initial start of the project. Hopefully they can help?

    There was a concrete base to the right which was already in place, so the builders only worked up to the edge of that. I can remember a mesh and some stones going in with the concrete, but can't remember if there was any dpm style material that went in underneath it all. From what I have seen online, I would have thought if there was this in there it would come up through the concrete? I don't really know much about the process though, so its hard for me to comment.

    @sxturbo - where you mentioned blackjacking the first course, would this need to have been done when the bricks were first laid 10 weeks ago? Would this also be a valid option, or would it be more of a temporary fix for a few years?

    Thank you both again for your replies.

    8.jpg 7.jpg 6.jpg 5.jpg
     
  6. sxturbo

    sxturbo

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    As woody states the blocks are suitable then I would just insulate the floor and black jack the first course.

    But this is just what I would do.

    You will need to do something about the insulation bridging the DPM.

    I'm sure woody will advise further
     
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  7. ^woody^

    ^woody^

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    You could potentially treat this as a garage conversion and lay a polythene membrane on the slab and up the walls. See many of the garage conversion threads for the detailing. Or a suitably liquid DPM. Either of which will require a proper timber floor or screed above it

    The external DPC projection should be cut off is possible to prevent it holding water.

    As for the insulation being below the DPC, that's common detailing in new build, but the issue here is whether the concrete slab will have enough moisture to cause it to wick up the insulation. Probably not, but there will be an inherent risk albeit slight, and whether any risk is worth living with or spending the time and expense of removing the lower insulation I don't know - it could be done by cutting out every third block below the DPC.

    You could just leave it, DPM the slab, turn that up the wall and then dry-line the wall.
     
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  8. ThomasHD

    ThomasHD

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    Hi both,

    Good to know there are some options with what we can do. Where we have paid a fair bit to the builders already, we would probably look to remove the insulation as you mentioned. I would rather have to pay more to get the job done properly / lower the risk of anything go wrong with it.

    Thank you for the replies and the knowledgeable advice, hopefully some of the project can be salvageable.

    Cheers
     
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