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  • #31827

    We are looking at passivhaus windows and are having (seemingly) typical issues with lift/slide doors. We are looking at passivhaus certified windows, however the same supplier can not make the doors we require to meet the <0.80w/(m2k) Uw value.

    My question is as follows: is the <0.80w/(m2k) Uw value a minimum/mandatory requirement or can we install some doors with a value of ~1w/(m2k) - and make up for this elsewhere within the design?

    The criteria seems to be quire vague in what is mandatory and what are guidelines for meeting (the absolutely mandatory) <15 kWh/m2 SSHD.

    Also, the windows we have at the moment as noted are certified by the PHI – the certification data sheet for these comes with seemingly three approved installation details. I understand that if these are followed in the design then no additional calculations (Uw Install?) are required? IF this is so, how closely much the design match the detail on the data sheet – obviously no two wall build ups are the same and small differences are to be expected?

    Any help would be much appreciated.

    #39013
    Anonymous
    Inactive

    My question is as follows: is the <0.80w/(m2k) Uw value a minimum/mandatory requirement or can we install some doors with a value of ~1w/(m2k) – and make up for this elsewhere within the design?

    The criteria seems to be quire vague in what is mandatory and what are guidelines for meeting (the absolutely mandatory) <15 kWh/m2 SSHD.

    Even the 15 kWh/m² isn't mandatory! You can opt for the 10 W/m² instead. IMHO, it's generally a good idea to achieve both, though.

    Also, the windows we have at the moment as noted are certified by the PHI – the certification data sheet for these comes with seemingly three approved installation details. I understand that if these are followed in the design then no additional calculations (Uw Install?) are required? IF this is so, how closely much the design match the detail on the data sheet – obviously no two wall build ups are the same and small differences are to be expected?

    I'm no expert and hopefully a real one will come along and answer your question, but my understanding is that it's all a matter of negotiation with the certifier, and they in turn with the PHI if there's a doubt. If you can convince them that your build up will be at least equal, or slightly better, than the approved detail 'by inspection' then fine; otherwise you'll have to do some calculation to prove it.

    I believe it's the same issue with the windows. You need to convince the certifier that you will meet the minimum inside temperature criterion for the inside surface of the window (17°C is it?) as well as U-values. And remember you will have to derate the stated U-value if it's not PHI-certified.

    At least, that's how I understand the situation.

    #39014

    Thank you Dave,

    Is there somewhere where this process is documented?

    The process all seems a bit esoteric….

    #39015
    Mark Siddall
    Participant

    Hi John,

    Dave is correct. Speak to your certifer. The main thing with the windows is to avoid the risk of thermal discomfort from down draft and low radiant temperatures. For this reason the internal surfanpce temperature of the window should not fall below 16.4C on the design day (-10C). Whilst the 0.8 W/m2K is a good marker, and in the eyes of PHI applies to the UK, there are arguments for relaxation in the U-value if you are, broadly speaking, “south of Manchester”.

    With regard to install: The position of the window within the wall (between int. and ext. surfaces) and the overlap of the insulation across the frame (where utilised) are key elements, as are the used of equivalent insulation types (cellulose, mineral wool, EPS, XPS etc). Again, firm this up with your certifier before this is set in stone.

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