Installing Celotex around central heating pipes

Discussion in 'Eco Talk' started by Wolfmeister, Jul 22, 2020.

  1. Wolfmeister

    Wolfmeister New Member

    Yesterday I pulled up the laminate flooring in my son's playroom on the ground floor to lay new carpet, only to discover that the chipboard flooring below was saturated with black mould. Having consulted with a local damp proofing company, their opinion is that this has been caused by condensation rather than damp. There's no sign of damp under the floor and the joists appear to be in good shape. The advise I was given was to install Celotex insulation in between the joists and re-board. I just have a couple of questions.

    Firstly, when I started pulling the old boarding out I discovered central heating pipes running close to the top of the joists, right where the Celotex needs to go. Is there any way to insulate around these pipes, if it's safe to do so, or will the pipes need to be moved?

    Secondly, what thickness of Celotex should I be using? Is that just a case of preference? I was thinking of going with 100mm.

    Thanks
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  2. Hans_25

    Hans_25 Screwfix Select

    50mm would be more than adequate I'd have thought, its what I used in the man cave. Lay it between the joists and you can cut it into bits to fit it under/around those pipes.

    Put a vapour control layer (polythene sheet) on top of the Celotex before laying floor boards.

    I am rather surprised at this though, is there adequate ventilation under the floor? Normally this isn't a problem so would look at why the condensation formed in the first place before trying to fix it.
     
  3. rogerk101

    rogerk101 Screwfix Select

    I would address the lack of ventilation problem first. Insulation and vapour barrier are secondary nice-to-haves, but you absolutely need some air flow down there or the joists will rot, which will be a major ache in the scrotum. Some of the joists look pretty moldy already, and should ideally be treated before closing them back up again.
     
    Hans_25, Wolfmeister and Abrickie like this.
  4. Jimbo

    Jimbo Screwfix Select

    The problem with rigid board insulation in this scenario is that it needs to be completely air-tight to have any effect. I have to wonder if rockwool would be a better solution.
     
  5. Wolfmeister

    Wolfmeister New Member

    Thanks guys for the responses, much appreciated. There are two air bricks, I will check to see if they are blocked. I also noticed that one of the air bricks is very near to ground level, I'm wondering if there's any water getting in to the sub floor, I will check this out.
     
  6. Wolfmeister

    Wolfmeister New Member

    Thanks rogerk101, in terms of treating the joists, what would you recommend?
     
  7. rogerk101

    rogerk101 Screwfix Select

    Our hosts sell quite a few.
    This is the one I use as it "Protects against wet rot, dry rot and fungi. Also treats wood-boring insects in timber and joinery. For interior and exterior use.".
    For some reason (covid-19?) the price has skyrocketed since I bought it, when it was only about £20 (around last Oct), so you may want to shop around. Toolstation also has a few.
     
    Wolfmeister likes this.
  8. Wolfmeister

    Wolfmeister New Member

    So I discovered that one of the two air bricks was 100% blocked, which I've now cleared. I'm also wondering if that air brick is sufficient to ventilate the entire sub-floor, given that the path is partly blocked by a joist?

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  9. rogerk101

    rogerk101 Screwfix Select

    Where is your DPC with respect to the concrete base? Some of the blocks look to be damp, and if that's the case, maybe you've got bridging for moisture across the DPC, allowing damp to rise above DPC and causing a lot of the issues you're seeing. If the DPC is in good nick and not bridged by a build up of silt from previous flooding or something else, then the air vents should be enough to keep the space aired. It doesn't need a howling gale down there ... just a slow movement of air ... and usually one side of the house will be at a higher air pressure (windward) than the other side (leeward) and that's enough to cause the change of air that you need.
     
  10. Abrickie

    Abrickie Screwfix Select

    Minimum of 150mm for air flow under joists, best thing for that is concrete floor slab
     
  11. Wolfmeister

    Wolfmeister New Member

    To be honest I'm a little bit out of my depth when it comes to DPC... I think I will get someone in to check this out in more detail. Thanks for all of the advice so far, much appreciated.
     

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