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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    House is typical 1970s end terrace. We're adding a single storey extension on the back, including a downstairs toilet. Plan is here -> https://drive.google.com/file/d/1IDHe2EnyqoR_DdUsw06ncXnF3iINyswi/view?usp=sharing
    The party wall is on the left. Rear elevation faces east.
    Our bathroom is above the new toilet. Obviously, the new toilet has to be ventilated but I'd like to improve the ventilation to the bathroom as well. Currently, we have the window almost permanently open and even doing that we get some mould on the artex ceiling each winter. Bathroom window is new. Bathroom is small, without much external wall available, see photos ->https://drive.google.com/drive/folders/1GAp-K4Xne4EMYHQX0LMeMWi7KSlujqBG?usp=drive_link
    I have several thoughts and would appreciate any advice.
    1. Simplest option is basic extraction fans for both rooms, through the wall. I understand single room MVHR isn't very effective at HR, and can produce a cold draught, so have dismissed that. For extraction, I've seen iCON 15 recommended for the iris shutter design. Anything else to recommend?
    1a. Issue is finding enough wall to fit it in the bathroom. Any thoughts on how much wall is needed to put the hole through without tangling with the window frame? We've got 245 mm to the reveal edge on the right and 260 mm on the left next to the shower. Also, outside is currently tile hung on the right but we have planning permission to replace that with insulated weatherboard above the extension roof. Left side is brick cavity wall. Could possibly go through the ceiling and out the soffit. Very tight loft access, though.
    1b. I think the new toilet extraction will need to go through the current rear elevation into either the extension, or the cavity in the extension wall, turn 90 degrees left, and out the extension side elevation. Are tight bends in very short duct runs okay? This will be right on our neighbours fence - bit concerned about ponging them!
    2. Alternative is ducting both rooms out via a MVHR unit. The rooms are linked by the SVP. Issues are:
    Cost is £1000s rather than £100s. Will save a bit of heating but is it anywhere near worth it? House is not draughty, but won't be anywhere near airtight, and is not that well insulated.
    Are there MVHR units designed for this type of application. Would want extremely low background volume but decent boost triggered by bathroom humidity and toilet light switch.
    Does it need sophisticated calculations or can you just have two extraction points from wet rooms and 1/2 inlets in other upstairs rooms (ducted through the loft)?
    3. Are there other options. I've read about dMVHR with ducted extraction, like BluMartin, but I don't think our layout works well and, again, it's £££.
    Thanks for any thoughts.
    •  
      CommentAuthordjh
    • CommentTimeAug 5th 2024
     
    I can't help much, but welcome to the forum :bigsmile: And congratulations on posting images to google drive that actually work, unlike some people here :cool:

    One of the benefits of MVHR, even single room, is that it is continuous ventilation. It's not like an extract fan that turns on and off. So it helps a lot more. You say you still get mould with the window open though, so perhaps you need to raise the temperature in the room a bit more. A cheap T&H meter can quickly give you an idea of what conditions are like. I currently like the Govee bluetooth ones, but there are many alternatives. Other tricks like wiping the shower down with a squeegee every time may help if you don't already do that.

    I'm a bit confused by your descriptions of left and right. I don't understand where they are in relation to things like the party wall and the new extension's east facing wall and suchlike. As regards whether you've got enough space, you need enough for the duct and for the faceplate of the ventilation, of whatever type. Generally the fewer bends the better and the more relaxed they are the better, but read the product literature for exact instructions about particular things. I don't know much about single room MVHR or extract fans, although I believe there are systems that handle two rooms, so maybe you can put the through wall duct in the bathroom and an internal duct down to the toilet?
  2.  
    Many thanks.
    Beginners' luck - will probably forget the share settings next time!
    I think the bit of mould is just when it's manky wet winter outside so even with the window open after a shower it takes ages to dry because the cold air coming in lowers the temperature. Occurs to me the loft insulation might be bad over the ceiling by the window - it's right in the eaves and I haven't checked it's laid and vented neatly - so might be able to keep the ceiling a touch warmer. We could turn up the radiator but we'd probably have to turn the house thermostat up as well. Seems very wasteful.
    I've got a T&H meter. Never wrote down readings but in winter I'd say cool but not unpleasant, high humidity after a shower/bath then falling, but takes a while. Right now, it's 26 degrees / 70% :cool:
    The left and right refer to the small section of outside wall left and right of the window. This is in the upstairs bathroom. Sorry, not clear. There's room for a faceplate but I don't know how far the gubbins from the window frame extends into the wall. Just worried that cutting the hole will either chop into the framing, or hit whatever nails/screws are holding the window frame in position - have no idea what a uPVC window frame is attached to.
    MVHR seems complex and expensive with some expertise needed, I'm not convinced we need something running 24/7, and it needs filters changing and things. Suspect my wife would be sceptical about it as well. If it was cheap and largely foolproof that would be different, but I'm not convinced enough to take the risk, I think, atm. Open to persuasion, though.
    Yes, think I can do an inline fan extracting from both bathroom and toilet but I'm not immediately seeing ones that can be triggered by humidity in the bathroom and the light switch in the toilet. May just need to look harder, though.
    • CommentAuthortony
    • CommentTimeAug 6th 2024
     
    I like VentAxia Svara fans, app based, thinks for you, extremely clever triggered by movement, boosted when humidity rises, ramps down can be told not to go on at night

    Tragically like all extractor fans they throw heated air away, I have MVHR
  3.  
    Thanks, Tony. Will have a look.
    I reckon in my house, if I can extract just enough to keep the bathroom humidity down and the toilet from smelling, then the heated air thrown away won't be disastrous compared to running a MVHR. I may be wrong about that, though - more a guestimate than any kind of calculation.
  4.  
    Svara looks ike it is very adjustable (intermittent/continuous, turning triggers on/off/up/down, and lots of timed, timer and overrun options) with a hefty boost for that sort of fan. It just lacks a backdraft shutter but that could go in the duct. Choices, choices...
  5.  
    I put a SVARA in our new bathroom, along with a backdraft shutter in the duct. It annoys the hell out of me at night flapping in the wind. It currently has a pair of socks rammed in to stop it flapping in the wind and the fan is switched off.
    I'm going to swap the fan out for an ICON 15 (put one of these in the previous place and was very pleased with it) and do away with the backdraft shutter as it won't be needed because the ICON iris closes.
    Also the SVARA is quite a bulky object in the sloping roof where it is, the ICON has a much lower profile, gently curving dome.

    The SVARA can go in the downstairs bathroom which doesn't even have an extractor fan at the moment. Whether or not to install a backdraft shutter in there remains to be decided, edging towards not bothering with even though its away from any bedrooms.
  6.  
    I have a Svara (Pax) in a bathroom at the moment, it runs continuously on trickle so doesn't need a flappy shutter. It's very quiet and low power consumption. But I hate the phone app and I suspect it will become unsupported long before the fan wears out. The fan is very customise-able but loses its time setting whenever the power goes off.

    Elsewhere I have single-room mhrv units which are great if there is an external wall to mount them through. Not had problems with noise or cold draughts that others have mentioned.
  7.  
    Edit to add: the Svara comes with built in boost sensors for humidity, light on, and PIR movement detection which are all good, so I rarely need to use the phone app to boost it. Other fans seem to charge extra for these.
  8.  
    With ours being in the sloping roof of the upstairs bathroom, I thought without a backdraft flap it would just act as a permanently open chimney. AKA in-house winter cooling system. It will do a much better job in the downstairs bathroom wall.
  9.  
    That's all useful, thanks. I know what you mean about the app support being an issue. Backdraft flap probably bothers me more. I've seen a few iCON recommendations for exactly this reason. Seems nuts if no-one makes one with a little bit of rubber or something to stop it being noisy. There must be 100,000s of these out there annoying people. I was hoping the in-duct version wouldn't be flappy like the ones on external grilles.
    I've seen quite a lot of people mention cold draughts with single room MVHR in bathrooms, but also that under real world conditions they aren't very good at HR.
    Hmm...
    • CommentAuthortony
    • CommentTimeAug 7th 2024
     
    I think all extractor fans should have positive close/open shutters on them, otherwise they have to be draughty.
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