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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.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorPugliese
    • CommentTimeFeb 28th 2013
     
    Should I leave gaps under my internal doors (bedrooms mainly that get closed) to aid the MVHR circulation and if so what sort of gap? Of course the trade off will be noise transmission, but like with so many building matters there has to be a bit of compromise (haven't gone OTT with soundproofing between rooms - double soundblock/100mm rockwool/soundblock)

    The subject was touched on in this thread http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9298 but was mainly concerned about the effectiveness of fire doors. BTW, why doesn't Building Regs specify smoke alarms in bedrooms. With most teenage bedrooms full of electronic equipment and doors shut, having 'smokes' on landings are pretty much useless if a fire breaks out in a bedroom. Needless to say we have installed alarms in every bedroom
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 28th 2013
     
    I have a door that 'whistles' when the wind comes in from the East, does not happen often but is quite loud.
    • CommentAuthortony
    • CommentTimeFeb 28th 2013
     
    8mm clear of floor finish when closed
    •  
      CommentAuthorjoe90
    • CommentTimeFeb 28th 2013
     
    Posted By: SteamyTeaI have a door that 'whistles' when the wind comes in from the East, does not happen often but is quite loud.


    Methinks your house is quite leaky.
    • CommentAuthorbarney
    • CommentTimeFeb 28th 2013
     
    Regarding fire detection, it's probably worth noting that BS 5839 - 6 (and building regs which quote it) doesn't require or set out to achieve protection fo the person in the room of fire origin - the intention is to provide early warning that the means of escape is becoming compromised.

    Regards

    Barney
  1.  
    Regarding MHRV and fire alarms I have specified alarms that will shut down the power to the MHRV unit if the alarms are triggered.

    I know that you can also install dampers with fusible links on all the inlets and outlets but I figure any fire will need to be pretty well advanced before they are triggered whereas it is likely that smoke alarms will (should) be triggered well before that stage.

    Right or wrong?
    • CommentAuthornigelm
    • CommentTimeFeb 28th 2013
     
    Regarding soundproofing, I believe the key is to have an uninterrupted barrier to the sound. One article that I have read suggested that a well engineered sound proof wall could have its effectiveness reduced to zero by drilling a single 25mm hole through it.

    This would imply that a gap under a door would in effect completely negate the soundproofing you have carried out. Have you though about using acoustic vents and fitting door seals. (assuming you have an acoustic door, fire doors make a reasonably effective low alternative).
    • CommentAuthorbarney
    • CommentTimeFeb 28th 2013
     
    Chris, there is no specific requirement to shut down MVHR in a domestic setting in the event of fire - in the same way we don't shut off the bathroom extractor or cooker hood - there air volumes involved are so small as not to be an issue.

    If you do shut it down, there is potentially more risk of cold smoke traversing the ductwork.

    as for fire dampers - well the whole house is usually a single compartment so again no requrement to segregate - if you use dampers then you'll need (at least in part) fire rated ductwork.

    So no reason not to do it, but again no reason in practice to do it

    Regards

    Barney
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 28th 2013
     
    Posted By: joe90Methinks your house is quite leaky.

    Pretty airtight, why I have to keep the back windows open a crack, the back is North East facing.
    Was only after improving the airtightness that this one door gap started making a noise, before that it was leaking air almost every where.
  2.  
    Cheers Barney but what is this cold smoke you speak of? I'm from Barcalona!
    • CommentAuthorbarney
    • CommentTimeFeb 28th 2013
     
    Well, the products of combustion cool (and potentially stratify) as they leave the plume from the fire source.

    They cool, and can travel significant distances without ever operating thermal link dampers - not hot enough essentially

    With MVHR turned off, you run a risk of cool smoke using the dusts to penetrate areas that they would get to by stack effect - if the MVHR was running you'd be evacuating them

    Regards

    Barney
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 28th 2013
     
    Pugliese, there is no one dimension that is correct for allowing air to move from a "supplied" room to an "extract" room. It's based on the volume of air you need to move, and at what velocity. You have to allow the air to move, or the whole system won't function as intended. Your design will tell you how many litres of air per minute will be entering the room (various quantities depending on low, medium, high fan speeds). That same volume needs to leave the room somehow, and get to the "extract" room. Do some maths and determine the area you require, to keep the air velocity low (so no drafts).

    You may want to keep the gaps all the same, once you've calc'd the worst case. Or you could maybe fit a grille at the foot of the door, rather than a gap? Won't help with sound travel, and will cost.
    • CommentAuthorGaryB
    • CommentTimeMar 3rd 2013 edited
     
    You would be surprised at just how much ventilation can pass via the tolerance gaps around a door.

    Operating theatre ventilation design uses this to create a physical barrier against bugs / dust particles and to control flow between the rooms.

    A standard single leaf door with 2mm gaps at top and sides and 4mm at the bottom will pass 70 litres/sec at 25 Pa pressure difference across a door. These differentials will not be present in a house with MVHR but neither will the flowrates. We never ask for increased gaps or door undercuts, except for public WCs with larger ventilation requirements.
    • CommentAuthorJecop
    • CommentTimeMar 22nd 2013
     
    The building regulations approved document part F (ventilation) covers this - check here: http://www.planningportal.gov.uk/buildingregulations/approveddocuments/partf/
    Section 5. Covers undercuts for doors with all types of ventilation
    • CommentAuthorborpin
    • CommentTimeMar 24th 2013
     
    Posted By: JecopThe building regulations approved document part F (ventilation) covers this
    Not Scotland of course.
  3.  
    Once you're in, you can always trim a few mm off the doors if theyre not leaky enough. Harder to add it back on.
    • CommentAuthorShevek
    • CommentTimeMar 24th 2013 edited
     
    Posted By: JecopThe building regulations approved document part F (ventilation) covers this - check here:http://www.planningportal.gov.uk/buildingregulations/approveddocuments/partf/" rel="nofollow" >http://www.planningportal.gov.uk/buildingregulations/approveddocuments/partf/
    Section 5. Covers undercuts for doors with all types of ventilation

    I was wondering about this today.

    For all four ventilation systems described in the regs the minimum area should be 7600 mm2, so a 10 mm gap above floor finishes for a 760 mm door. Which sucks for sound proofing.

    Then I was wondering what applies if you're installing Ventive ventilation, which is a separate supply and extract to every room except the hallway. Why would you need gaps under the doors with this system? To move some air through the hallway? You'd do that just by the process of opening doors now and then wouldn't you?
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