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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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    As I understand it, quoted Uw values for windows don't have to take into account the presence of any trickle vents (do correct me if I'm wrong on that).

    It seems obvious that an open trickle vent is going to compromise the U-value, but is there a way of quantifying it, or is anyone aware of any standardised way of estimating it?

    Every time I see a nice new well insulated window with a trickle vent in it, I wonder just how much of an improvement it actually is on the slightly leaky single glazed window it replaced. Does the presence of the trickle vent compromise it to such an extent that it's hardly worth the cost of replacing the old window, unless you have a more thoughtful ventilation strategy?

    I know that in theory trickle vents can be adjusted, but I'm sure the reality is that most of them are either always open or always closed.

    Occasionally I come up against the argument that it's dangerous to change windows in older houses to double glazing because it will create condensation problems. My answer of course is that it won't if proper consideration is given to ventilation. And in cases where the budget is small, trickle vents might be the only realistic means of providing that.
    • CommentAuthorDarylP
    • CommentTimeJun 7th 2017
    Yes you are correct, Uw-values do not include trickle vents.
    Personally, I hate them.
    They always leak, either open, or open, and noisy.
    Munster IIRC do an acoustic-sealed trickle vent.....
    • CommentAuthorrevor
    • CommentTimeJun 7th 2017
    I do not like trickle vents either but accept in some situations they are necessary. I do not have any in my build even though I have not done a passive house per se I have adopted the general principles of such a construction so I have a MVHR. Interestingly when the BCO called for an inspection he remarked that my installation was the first he had come across. Next time he came he said when he left me the next job he came to had installed MVHR but was not going to work properly. The builder had installed windows with trickle vents!. We live in a very windy area and have heard people state that the wind whistles through the vents and house owners have been known to squirt expanding foam into them to silence them.
    • CommentAuthorGreenfish
    • CommentTimeJun 7th 2017
    Posted By: revor...have heard people state that the wind whistles through the vents and house owners have been known to squirt expanding foam into them to silence them.

    This is accurate. My parents council flat (in a very drafty Victorian villa) was compulsorily "improved" by fitting badly installed DG. So many drafts elsewhere including doors (they would only do windows), that ventillation was not a problem, but they of course fitted units with trickle vents. When the wind blew from the west the sound was unbelievable, even over the phone it was like "Scott of the antarctic" reporting. It howled, it sometimes sounded like a tuba played badly, it even drowned out the TV. So they called the council in to inspect, finally they came on a windy day and said "oh dear, no idea how to cure that".

    What I guess was happening is that the trickle vents, even when closed inside, still let the air into the hollow frame which them was behaving just like a musical instrument. So in despiar yes I got a foam gun and filled the vents. Volla, no more unbearable noise.

    Buildings need something to deal with human produced polutants and moisture, but in my experience they do not need the 0.3 m/s per 100sqm of the current building regs (to allow for VOCs). However trickle vents are a poor way to porovide this.
    At some point the building regs recognised that self-closing fire doors don't work in a domestic setting (people just wedge them open) and removed the requirement. Same needs to happen for trickle vents I think. It would be better to stipulate that all windows should have a night-latch type feature. Then it is clear to the occupants whether there's ventilation happening or not. Some people would still leave all their windows closed whilst cooking etc and have condensation problems...but they are probably the same people who would seal up trickle vents.
    • CommentTimeJun 7th 2017 edited
    Posted By: lineweightall windows should have a night-latch type feature
    To stickler-type BCOs, as it stands that's not acceptable because doesn't have documentation to prove airflow quantity! But so far I've got acceptance.

    But note that under present Part F these trickle vents are pretty much useless because don't give anything like the presently required open area.
    Are there any other jurisdictions which require trickle vents? I know they're not required in North America ...

    Paul in Montreal.
    • CommentTimeJun 13th 2017
    They came and now AFAIK they've gone, in UK - reqd open areas mostly now far exceed what they provide. Which ludicrousness seems to be intended to drive everyone to powered/controlled vent systems, without actually requiring it.
    • CommentAuthortony
    • CommentTimeJun 13th 2017
    My view is that there is virtually no influence on U value on a calm day, but as wind speed increases so do heat losses

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