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  1.  
    Very good, all the more reason to suspect that Greenfish's test result is perfectly acceptable and doesn't warrant spending a significant amount trying to improve it.

    Any idea at what level of airtightness it ceases to be a heat loss issue and turns into a comfort issue?
    • CommentAuthortony
    • CommentTimeSep 11th 2014
     
    Depends how windy it is!
    • CommentAuthorPeterStarck
    • CommentTimeSep 11th 2014 edited
     
    Apparently high levels of airtightness affect the level of moisture in the wall more than heat loss. I asked this question on the AECB Forum.

    http://www.aecb.net/forum/index.php/topic,3928.0.html
    • CommentAuthorGreenfish
    • CommentTimeSep 13th 2014
     
    Posted By: djhSadly perhaps, the reason quoted for such a tight airtightness level in PH isn't to do with the energy or cash saved directly. The point as I understand it is to avoid drafts and to maintain internal surface temperature everywhere. That in turn allows you to reduce the internal air temperature by a degree or two whilst maintaining the same level of comfort, and that is what saves the energy and cash.

    Have already noticed this effect. New build at 17C with the plaster still damp, felt more comfortable and warm than our old leaky house heated to 20C. Was flitting between them and old house just felt so chilly despite having heating going especially on windy days. Looking forward to living in new build this winter.
    •  
      CommentAuthordjh
    • CommentTimeSep 13th 2014 edited
     
    Posted By: GreenfishNew build at 17C with the plaster still damp

    Our new build is currently at 18.2°C and 101% humidity according to my cheap Chinese meter :bigsmile:

    Well, actually it's now at 100% humidity since I put a fan in there to stir the air around.

    edit: I should say that we've just applied some internal plaster, I suppose. Doh.
    • CommentAuthorGreenfish
    • CommentTimeSep 13th 2014
     
    I should have said that my comfort of air tightness experience was in Feb when we had just finished applying the internal plaster, gently raised the new build temp to 17C (while it was 9C outside and blowing a gale) and prefered staying there in middle of the mess to our furnished home at 20C in the sheltered city.

    djh - 100% humidity, open a window maybe?
    • CommentAuthorEd Davies
    • CommentTimeSep 13th 2014 edited
     
    RHs greater than 100% are quite possible. 101% would be typical of the air just below a cumulus cloud. If all the walls are saturated I wouldn't be terribly surprised if it could happen in a house. In extreme cases, under special laboratory conditions with very clean air, you can get up to 300%.
    •  
      CommentAuthordjh
    • CommentTimeSep 13th 2014
     
    Posted By: Greenfishdjh - 100% humidity, open a window maybe?

    Windows are sealed (a) for the duration to keep plaster particles and other dust out of the seals and mechanisms and (b) at the moment because the protective film stops them opening in any case.

    I'll see what happens over the next day or so and maybe use some forced ventilation to get it down. One of the wall terminals that will connect to the MVHR is open and so is the front door so I can probably jury rig a fan.
    • CommentAuthorborpin
    • CommentTimeSep 18th 2014
     
    I had massive problems with condensation on a very air tight build to the extent that one of the door locks rusted and failed completely! I thought I had a water leak round the velux windows - again condensation but somewhere inside that I could not see it actually forming. This with a dehumidifier running constantly! Of course, the condensation did not appear on any internal surface or the windows :)
    • CommentAuthortony
    • CommentTimeSep 18th 2014
     
    MHVR is a good idea in all airtight beildings
    • CommentAuthorGreenfish
    • CommentTimeSep 19th 2014
     
    Here's hoping Borpin is talking about the initial drying phase like djh. My build was dripping with condensation when first plastered and gently heated, and too wet outside to open the windows much. Dehumidifier eventually got on top of it, and getting the windows open once the rain stopped. Did not put the MVHR on, too much dust around would have damaged the filters etc.
    •  
      CommentAuthordjh
    • CommentTimeSep 19th 2014
     
    I haven't seen any sign of condensation so far. The humidity just sticks at between 97% and 100%, which I suppose is what I might expect whilst the plaster dries. And the smell is just wet plaster and fresh straw.

    We have cracked open one window to get a bit more air circulation; hopefully with the plasterer offsite at the moment we won't see too much dust. I've also got a couple of fans and a low-powered heater in there. The lime plaster does seem to be getting slowly stiffer.

    We haven't fitted any of the door hardware yet so it can't rust (well at least not from the plaster curing!) and tradesmen or visitors can't open windows! MVHR is indeed a good idea in all airtight buildings, but it's an extremely bad idea to use it in an unfinished building because of dust etc, especially one that isn't even at first fix stage so has no proper power or drainage.
    • CommentAuthortony
    • CommentTimeSep 19th 2014
     
    you can be pretty sure that mould will start growing there soon! open the windows 24/7 if possible if not all dat at lease, out door humidity is almost never as as it is in your building even when misty or raining.
    • CommentAuthorGreenfish
    • CommentTimeSep 20th 2014
     
    Oh yes had mould too. The MDF window ledges were like a magnet for it, bad choice in a wet finish build or should not have plastered them into the reveal in the traditional way. I could have wept at the worst point, but all is well now I am glad to say.
    •  
      CommentAuthordjh
    • CommentTimeSep 20th 2014
     
    Posted By: GreenfishOh yes had mould too. The MDF window ledges were like a magnet for it, bad choice in a wet finish build or should not have plastered them into the reveal in the traditional way.

    Thanks for that tip. I'll keep an eye on them.
    •  
      CommentAuthordjh
    • CommentTimeSep 21st 2014
     
    The RH has come down to 83% today and the plaster feels a bit harder. No sign of mould anywhere. I'm beginning to believe in all this lime and straw stuff :bigsmile:
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