Thoughts on removing tar paper in loft?

Discussion in 'Builders' Talk' started by rogerk101, Feb 20, 2018.

  1. rogerk101

    rogerk101 Screwfix Select

    My question is whether to remove the tar paper in the loft or not, but there is a lot of context here, so please bear with me ...

    Original house
    The house was built in the 1960s, and tar paper was used between the rafters and the tile battens. The entire roof is covered like this. There was NO ventilation and NO insulation at the time. In the early pre-central-heating days the house must have been freezing! Later, when central heating was installed, their heating bills must have been awful. I don't know anything about condensation back then.

    First step
    Ten years ago, the new owners insulated the loft extremely well. The heating bills dropped, but they noticed a lot of condensation forming on the underside of the tar paper.

    Second step
    I installed several tiled-roof vents in the loft space to create some air flow, and this improved things a little, but not by much.

    Third step
    I then core-cut 8 venting holes through the gable ends of the house to create even more air flow, and again, this improved things, but didn't fix it completely. On cold nights, condensation literally drips off the tar paper, making the loft unusable for any storage requiring dry conditions.

    Next step
    My next suggestion is to cut out the tar paper from the inside of the loft, which would expose the undersides of the tiles, and allow the roof to breath. My thinking is this ... I have worked on numerous houses from before the tar paper times, and their lofts might be a bit dusty, but they are never dripping with condensation.

    I know that the correct thing to do would be to rip off the entire roof and replace the tar paper with breathable membrane, but that is far too expensive at this stage.

    Can any of you experts think of any negatives about my "Next step" suggestion?

    Thanks in advance
  2. KIAB

    KIAB Super Member

    Eaves ventilation, soffit vents, make sure insulation isn't rammed tight into the eaves.

  3. rogerk101

    rogerk101 Screwfix Select

    Thanks for sharing that well known diagram, KIAB.

    Unfortunately that depicts the perfect world, i.e. how you would do things if starting from scratch with a new-build.
    However, this is a house that was built over 60 years ago, so far from the perfect world.
    There are no soffit vents.
    The tar paper covers the entire roof (between the rafters and the tile battens) and is a continuous non-breathing membrane. This means it also covers the ridge.
    The ridge tiles are set in place with mortar and the joints between them grouted to be waterproof.
    Seriously, I wasn't kidding when I said above that this loft had absolutely NO ventilation and NO insulation 10 years ago.
    It has now got heaps of insulation, and I've provided some breathing (as described above), but it's clearly not enough.
    Can you foresee any problems with my idea of cutting out the tar paper from inside the loft to expose the underside of the tiles and enable to roof to breath via the small but numerous air gaps that there are between the roof tiles?
  4. Paul mullen

    Paul mullen New Member

  5. Paul mullen

    Paul mullen New Member

    Hi Roger,

    I can see that you have fitted a fakro loft windoe in the past.
    I am fitting a 78x98 I have cut the struss.

    Can you tell me what the gap should be around the new window frame. Is there a gap all the way around or just top and bottom and the sides of the new window from are tight to the roof studdes.


  6. rogerk101

    rogerk101 Screwfix Select

    Hi Paul
    Take a look at page 2 of the fitting instructions in the link here (
    They suggest 3cm to 5cm for the width and 3cm to 4cm for the height as clearance. (This actually means 1.5cm to 2.5cm on each side for the width and 1.5cm to 2cm for the height.
    I've fitted several different models of Fakro and they all have the same clearance requirements.
    The metal angle brackets that you mount on the top and bottom (or the sides, depending on your situation and preference) more than adequately span the clearance gaps.
    All that said, I usually only leave 1cm all round and have never encountered a problem. I fitted two more this summer in my garage to granny flat conversion, and actually only had clearances of about 0.5cm on each side.
    Good luck! You'll love 'em!
    Paul mullen likes this.
  7. Paul mullen

    Paul mullen New Member

    Thank you so much.
    Would you mind if I ask any more questions.
  8. Severntrent

    Severntrent Screwfix Select

    Depends whether you are confident with your tiles being totally weatherproof. When you say tar paper I assume you mean bitumised roofing felt that was used back in the day as secondary protection from rsin snow dust being blown under the tiles My childhood home had tiles with no roofing felt with the tile joints mortared up from underneath.Can't recall any condensation problems but it was a dust bowl up there.
  9. masterdiy

    masterdiy Screwfix Select

    Roger, I have exact same roof as you describe.
    I drilled round holes in soffit, & fitted the round vented plastic covers 4 each side. Really need 6 per side.

    I then fitted the roof/tar felt vents. This helped amazingly.
    I have only 6 in the loft, so maybe another 6 would make all the difference.
    Along with that, extra insulation would be a bonus.

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