Condensation in loft space due to massively thick Rockwool insulation

Discussion in 'Eco Talk' started by diymostthings, Jun 11, 2021.

  1. diymostthings

    diymostthings Well-Known Member

    Son's "newbuild" (1919) has about 400mm of rockwool completely covering the loft space. Condensation is rife up there - the rafters are very damp and showing signs of mould already. I thought lofts had to be vented as well as insulated - although they are clearly conflicting requirements.

    Is this a common problem or is he just unlucky? Like many he has to dry washing indoors. Is there a cure?

    Thanks for any comments/practical advice.
  2. Hfs

    Hfs Screwfix Select

    Pull the insulation back making sure it’s not stuffed into the eaves and install felt lap vents.
  3. diymostthings

    diymostthings Well-Known Member

    Thanks HFS - I'll look that up on Google.
  4. Wayners

    Wayners Screwfix Select

    You need vents.
    Fit wedges in felt joins if any felt fitted.
    Fit air vent in wall in and out either end if you have one.
    Fit vents in soffits if you can.
    Get air blowing through.
    rogerk101 likes this.
  5. diymostthings

    diymostthings Well-Known Member

    Thanks Wayner - Looks like problem solved. Will do this over the summer (when washing is dried outside!)
    Thats great. kind regards
  6. Jimbo

    Jimbo Screwfix Select

    tile vents are an option too
  7. diymostthings

    diymostthings Well-Known Member

    Thanks Jimbo. Was awae of these from earlier in the thread but will try the easy option first!

    I presumbe you can't fit the tile vents from inside the loft space?
  8. koolpc

    koolpc Screwfix Select

    I agree with comments above. Defo need good ventilation. Tile vents are worth the cost too. A few either side. Good through air flow.
  9. fred812

    fred812 Active Member

    Ive fitted the felt vents after upgrading my loft insulation, can be fitted from inside.
  10. Alan Wright

    Alan Wright New Member

    I've been at new builds recently in various stages of completion and the main problem is joiners being contracted to do the loft insulation while they are doing the ceilings. I've seen strips of insulation pushed into the eaves before the plasterboard is put onto the ceilings so that they don't have to crawl into the eaves when they do the lofts; which of course is blocking all ventilation. I've also seen completed houses not reaching their thermal performance on EPC's and losing points where the loft insulation thickness is not as it should be because they are stuffing the insulation into the joists and not lofting the rolls (like shaking up your duvet) to the height it should be. This has cost customers who have fallen out of the points required for money back on a new home purchase for eco schemes.
    Shaquel likes this.

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