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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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Essential for Newbies: Roof ventilation building regs

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  1.  
    • CommentAuthorWill Barn
    • CommentTimeJul 23rd 2008
     
    I recently bought a village
    school house which was converted some 28 years ago. Has a tower on the roof
    which I really like - problem is that is has open louvers on all four sides
    which provides ventilation - but not enough for the area of the loft space
    really - but also when the wind and rain combine in strength from a south
    westerly direction which is the prevailing direction we get the rain coming
    in and down the insider of the tower. The building walls are solid Dorset
    concrete from 1871 so no air vents. I want to close the louvers but make
    sure I have adequate ventilation but make sure I can also get maximum heat
    retention re loft insulation etc - trying to find out any applicable building
    regs or any views/options etc.
    • CommentAuthorCWatters
    • CommentTimeJul 23rd 2008
     
    Where is the insulation in the roof?

    If the insulation is at ceiling/joist level then the loft must be well ventilated.

    If the insulation is at rafter level then normally there is a 50mm void between the insulation and the sarking/roofing felt. This gap needs to be ventilated but the roof space/loft below doesn't need a huge amount of ventilation. Typically just that provided by trickle vents in windows of a habitable room or perhaps bit more.
    • CommentAuthorchuckey
    • CommentTimeJul 23rd 2008
     
    Will,, I am having trouble visualising your arrangement. Is the building a ridge type structure with a small sort of bell tower on the roof with a "tube" running down into the original hall like class room underneath? Or is it a building with an adjacent tower to it, like a church? Did the original building have a loft, i.e. the classrooms have a flat ceiling or did the classrooms have a skeiling, i.e. the ceiling plaster follows the pitch of the roof?
    As cwatters points out, what sort of covering (if any are directly under the tiles/slate covering of the roof). During the 50s, 60 s and 70s slaters felt was used. This is totally impervious to drafts so external ventilation is a must. If there is no material then the ventilation will probablely be adequate.
    In general If this tower is meant to ventilate the space and you have slaters felt, then a second air hole must be put in at a lower level, air can only get out if some can get in to replace it. A 4" hole bored through the gable ends with a nice grill would do.
    Just re-aligning the louvres, or putting some secondary one behind the existing should cure your wind driven rain problem. A built in drip channel and 3 metres of plastic tube to conduct the drips into gutter could be another way to go.
    Frank
    • CommentAuthorJune
    • CommentTimeAug 20th 2008
     
    I have similar queries over ventlation. We have a small roof over a living space which extends into the roof (i.e. the eaves are below ceiling level and not accessible from the roof. I want to increase the level of insulation (currentky none) but have been warned that I would need to increase ventilation first. [I also need to do something with the hot little spotlights for the room below which are shining light and heat ito the loft - but that's another issue!). The gable walls sem very thick (it's a 300-year stone cottage).

    How best to increase ventilation? I'm guessing trough the tiles/roofing felt but: is this best done near the apex or low down just above the level of the ceiling? And how best to do this without water ingress (this is the wettest year and the windiest house I have ever lived in and I fear it will get worse as climate change bites). I would like bats to colonise the loft but not birds or squirrels!
    June
  5.  
    You do not want bats in your loft get a bat box or get bat bricks cut in see ibstocks bat bricks.
    when you get a weather window take of ridge caps cut out felt replace with breathable paper membrane and fit vented ridge caps do the same at gutter level using several vented tiles and you will create a natural up draft
    if you have the height in the room put the insulation in side and plasterboard over it use celotex type mark out all joists screw on insulation plus 25x50 batton screw plaster board to battons bobs your dads brother good luck jgg
    • CommentAuthorJune
    • CommentTimeNov 16th 2009
     
    I do want bats in my loft - I'm an ecological consultant specialising in bats (for 15 years)! But thank you for the rest of your advice...

    One thing - where does the air flow from the gutter level tiles go (i.e. by what route)? From there, there is no access to the interior of the loft (they are well below ceiling level i.e. the floor of the loft).

    [There is absolutely no spare room height to insulate below the ceiling - these are VERY low ceilings - all the insulation needs to go above the celing (i.e. on the loft floor).]
    • CommentAuthorCWatters
    • CommentTimeNov 16th 2009 edited
     
    June see these diagrams..


    Conventional loft...
    http://www.iwight.com/living_here/planning/images/InsulatingPitchedRoof.jpg

    Room in the roof (vent at ridge not shown)
    http://www.dtag-building-technologies.com/images/cathedralroofventilation.jpg

    In the case of a conventional loft the air goes in one side of the house, across the loft and out the other side. In the case of a "room in the roof" design the air goes in at the eaves and out at the ridge.

    The same basic principle would apply to the ceiling you describe.

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