Taping DPC / DPM or not to tape DPC / DPM

Discussion in 'Builders' Talk' started by chipperwolf, Jun 19, 2019.


Tape DPC joints under insulations or leave them be?

  1. Tape them

    2 vote(s)
  2. Leave them overlapped 600mm

    0 vote(s)
  1. chipperwolf

    chipperwolf New Member

    HI all,

    Trying to figure this one out and due to either inexperience on my part or a builder who seems to be less through than required:

    Builder has opted to go for a compacted hardcore (recycled with glass and metal debris in), sand blinding (after I mentioned it should be done), Visqueen DPM membrane, then 150mm polystyrene (cost saving), then another layer of DPM (not lapped up sides) and then 100mm of concrete.

    Rather than what the architect suggested: Concrete, membrane, kingspan, screed as it would be cheaper and quicker.

    My question is do the DPM overlaps (400mm in some places) need taping, or are they ok just overlapped? He's got the lower layer, under the dpm, and another DPM covering above the polystyrene, but the top/second covering does not lap up at the edges and just covers the insulation?

    He's also said that he doesn't normally install the insulation strips around the edge, but has done as i requested it.

    Am I in the minority here? I'm a listener so will take the advice of professionals.

    Potentially freaking out of nothing, but it's not the first mistake with my extension, Building Inspector noted the concrete slab depth wasn't going to be thick enough.

  2. stevie22

    stevie22 Screwfix Select

    He should do what your approved drawings show and BC should really kick up if he doesn't and certainly if what he's doing doesn't comply.. Thermally 150 polystyrene about equal to 75 Kingspan but not sure abut it's physical strength under load. I doubt if its cheaper by the time you've dug an extra 75mm and carted it away. I assume he is not intending to omit the screed: that would be a no no. Crushed concrete is often better than "proper" type 1
    chipperwolf likes this.
  3. chipperwolf

    chipperwolf New Member

    Thanks for your reply, There are so many typos in my first post sorry, typing fingers on fire as I didn't really want to have to join this forum and be in this situation.

    Basically, the thickness of the concrete slab is going to be 75-80mm which is under the specified 100mm. Building control already checked and said it wasn't right, builder spent a couple of hours screeeding off some of the blinding and corrected some but it's still 25mm out in places.

    Me and wife are at our witts end. He thinks we are being picky, but we just want the job done correctly for spending our well earned. Or am i being picky?

    My main question was about layer of dpm ontop the sand blinding and under the insulation, do builders tend not to tape the joints, because our builder thinks it's ok not to and overlap 600mm.

    Not sure what to do???
  4. gas monkey

    gas monkey Well-Known Member

    should be taped the base has been calculated for the load so thats how thick it should be get a new builder or put your foot down with b/c you have paid them to check so on them
    chipperwolf likes this.
  5. b4xtr

    b4xtr Active Member

    Not a Builder but, to me it seems obvious that either it's done as per Architects spec or take advice of Building control
    As for tape, for the cost of a roll of tape, i'd be taping all laps
    chipperwolf likes this.
  6. chipperwolf

    chipperwolf New Member

    Took some measurements again, and told the builder i'd had enough. Paying him up to today, we now have a building site and no floors poured. Looks like i'm going to be busy.

    Attached Files:

  7. b4xtr

    b4xtr Active Member

    At least you will get what you want
    chipperwolf likes this.
  8. gas monkey

    gas monkey Well-Known Member

    minus the cost to put it write

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