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Housing - New Build: Trickle vents - an alternative approach

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    I hate trickle vents: those plastic strips covering holes that are cut into very expensive highly insulated windows. Why cut a hole in a beautiful new aluminium frame and stick in a white plastic strip, covering the hole with a thin bit of plastic that must nullify the effect of the thermally broken frame? All that high value insulation gone to waste for a cold spot.
    Instead, I want to put in a through wall vent, using something like a marine 'mushroom' vent, operating on a screw that turns a stainless or plastic dome. That is what I want, that is what I am sure will work, but difficult to pursuade the Building Inspector or to get an official free air area. I have emailed several vent suppliers but am now getting back statements saying that they cannot give that info. One sent pictures of them measuring the size of the object, but couldn't measure how high it was shut, and how high open.
    This is going through a timber frame, so a tube through the frame - 100mm should do it - then the mushroom vent, either inside or outside. Inside, you twist the dome, if outside you operate via a screw thread. With the dome inside I would put a grill with fly mesh outside. This still leaves a 100mm dia. cold bridge: not good news.

    Having trouble sourcing a good external grill that offers adequate 5000 sq.mm. of open area, and also satisfying myself that the mushroom vent itself would give this amount. I think that a circle of 100 dia. would give 314mm circumferance, which means it has to open only 16mm to provide 5000 sq.mm.
    Am I right?

    Any comments, suggestions as to sources or ideal options?
    • CommentAuthorCWatters
    • CommentTimeOct 5th 2016
     
    Just for info..The area of a doughnut shape is the area of the outside circle minus the area of the inner circle.
    • CommentAuthortony
    • CommentTimeOct 5th 2016
     
    Double position window handles that allow the window to be open a crack but secure.
    • CommentAuthorgravelld
    • CommentTimeOct 5th 2016
     
    Whenever I have asked BC how they will accept no trickle vents, the only answer is mechanical ventilation to provide a known, controlled level of ventilation.

    Of course, its daft to say passive ventilation via TVs-good, passive ventilation via other vents-bad. But there you have it.

    Personally I think it's passive ventilation-bad full stop.
    • CommentAuthordelprado
    • CommentTimeOct 6th 2016
     
  6.  
    Posted By: gravelldWhenever I have asked BC how they will accept no trickle vents, the only answer is mechanical ventilation to provide a known, controlled level of ventilation.

    Some have combined the idea of trickle vents with the idea of filling DG window frames with foam (after sign off)...
    • CommentAuthorgravelld
    • CommentTimeOct 6th 2016
     
    I don't understand, how is the conductivity related to ventilation?

    Oh you mean fill the trickle vents after sign off?
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      CommentAuthorjoe90
    • CommentTimeOct 8th 2016
     
    I got a building inspector to accept double position window handles ( like Tony says above) instead of trickle vents but he was a decent chap ( not like other building inspectors I have met 😱)
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      CommentAuthornumenius
    • CommentTimeOct 9th 2016
     
    Every window I've looked at so far in our price range has trickle vents so I've just figured I'll block them off (we are having MVHR). Whether it's before or after BC will depend on his view. Since the very first sentence of the first letter they sent to me after engaging the BC firm was "do not do anything until we say so" (!) which betrays a mindset that they see their job primarily as stopping us, rather than working with us, I have a feeling we are not in for a very helpful ride from them.
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      CommentAuthordjh
    • CommentTimeOct 9th 2016
     
    Posted By: numeniusWhether it's before or after BC will depend on his view. Since the very first sentence of the first letter they sent to me after engaging the BC firm was "do not do anything until we say so" (!) which betrays a mindset that they see their job primarily as stopping us, rather than working with us, I have a feeling we are not in for a very helpful ride from them.

    Tell them thanks, but no thanks, and find a more helpful firm.
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      CommentAuthordjh
    • CommentTimeOct 9th 2016
     
    Posted By: archess200All that high value insulation gone to waste for a cold spot.
    Instead, I want to put in a through wall vent, using something like a marine 'mushroom' vent, operating on a screw that turns a stainless or plastic dome. That is what I want, that is what I am sure will work, but difficult to pursuade the Building Inspector or to get an official free air area.

    I have a friend whose flat has these in the walls in place of trickle vents. It was built by a housing association so I guess it is kosher.

    I guess you need something like a statement in a BBA cert or similar.
    • CommentAuthorsnyggapa
    • CommentTimeOct 10th 2016
     
    my question would be how the large cold spot of a mushroom ventilator would be more thermally efficient than a number of smaller cold spots on the window frame - assuming the air space for ventilation is equal?

    We got windows (wood, not uPVC) without trickle vents. In fact , the chap who made them (biff vernon, used to hang around here) said "I am not drilling holes in my windows. drill a hole in the wall"

    We used MHRV so I guess ended up with a couple of big holes in the wall - but pleased with the result. I had it turned off for 24 hours on Sat/Sunday as I cleaned the heat recovery chamber for , erm, the first time in a long while. Apart from being surprised quite how many files managed to bypass the filters and wedge inside the chamber, the air quality of a sealed house was noticeably poorer after just a few hours

    -Steve
    • CommentAuthorEd Davies
    • CommentTimeOct 10th 2016
     
    Posted By: snyggapamy question would be how the large cold spot of a mushroom ventilator would be more thermally efficient than a number of smaller cold spots on the window frame - assuming the air space for ventilation is equal?
    Just guessing but I'd think there are two reasons:

    1) A single large cold spot has a shorter overall perimeter so there's less of a cold bridge round the sides.

    2) The ventilator goes through a thick wall so the cold bridge has a longer path length and so less heat loss.
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      CommentAuthordjh
    • CommentTimeOct 10th 2016
     
    Posted By: Ed Davies
    Posted By: snyggapamy question would be how the large cold spot of a mushroom ventilator would be more thermally efficient than a number of smaller cold spots on the window frame - assuming the air space for ventilation is equal?
    Just guessing but I'd think there are two reasons:

    1) A single large cold spot has a shorter overall perimeter so there's less of a cold bridge round the sides.

    2) The ventilator goes through a thick wall so the cold bridge has a longer path length and so less heat loss.

    3) It's easier to block a six inch circular hole through the wall than a narrow trickle vent, especially with something that can be removed again if desired.
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      CommentAuthorfostertom
    • CommentTimeOct 11th 2016 edited
     
    See http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13981 Jan 27 on.

    It's not a straight choice, nowadays, between window and wall trickle vents - window vents are out (surprised they're still sold), as Part F now requires 'insane' mm2 figures, which only massive through-wall holes can provide.

    Part F's intention seems to be to drive us towards 24/7 mechanical ventilation or MHRV, without actually making it mandatory.
    • CommentAuthorgravelld
    • CommentTimeOct 11th 2016
     
    MVHR on gale force setting more like.
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      CommentAuthordjh
    • CommentTimeOct 11th 2016
     
    Posted By: gravelldMVHR on gale force setting more like.

    MVHR capable of gale force setting, perhaps. There's no requirement to operate it that way.
    • CommentAuthorwookey
    • CommentTimeOct 12th 2016
     
    Trickle vents are indeed evil. The easiest way to avoid them is MVHR. My BC fellow was very uninterested in ventilation. I was expecting an argument about lack of TV - not even mentioned. Just pointed at vent for MVHR up wall and that was that. No flow-rate questions, no checking it actually worked, no questions about model of machine.

    Part F does indeed specify a massively-excessive ventilation level. We find that 8hrs a day of 'min' is plenty. Which is something like 5% of the PartF mandated levels.

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