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Help with Cross Ventilation - Flat Roof

Discussion in 'Roofing and Guttering' started by kookachoo, 18 Sep 2016.

  1. kookachoo

    kookachoo

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    As my builder buggered off without putting in the soffit vents I had BC out last week and lo and behold it's changed and we need cross ventilation on the flat roof of my extension and we're not able to just put in the soffit vents on the front overhang, but rather being asked to do it from side to side... so I found the over fascia vents, took off the board and it appears that I'm not going to get them up in there as the gap in the cross battens is lower than the felt - also I didn't think I'd get them behind the felt either. Any ideas short of cutting circles in the side and risking rain coming in, or even worse, putting trickle vent canopies on either side?
     
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  3. chappers

    chappers

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    It looks like you may be in luck, there appears to be cross battening across the rafters so you can vent at the soffit as you suggested and fit a few mushroom vents at the top end of the roof near to the abutment with the house. It will require some work doing to the felt roof though..
     
  4. vinn

    vinn

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    OP,
    are they "cross battens" - or are they tapered furring strips?
     
  5. kookachoo

    kookachoo

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    They're cross battens with the farings on top... ok mushrooms it is, but how do I work out how many? All BC can tell me is 'as long as it meets minimum requirements'. FFS. I know it's 25000 something, but I don't know what that relates to!
     
  6. noseall

    noseall

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    Do people still design/build cold flatties? This is the reason why warm roofs are 99% favoured.

    Use mushroom vents. Pig ugly, pain to fit but adequate. Fit four or summat, BC are unlikely to get their calculator out.
     
  7. chappers

    chappers

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    you should have the equivalent of 25mm along the whole length, how wide is the roof, but as nose says I would be inclined to just bung 4 in there take a photo send to building control and get them to sign it off also show them that the roof is cross ventilated with battens. Just make sure your mushrooms sit in the rafter gaps. and try and avoid the cross battens too.
     
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