Go to Forum Home Building Refurbishment and Retrofit airtight timberframe porch & condensation

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    • #31599
      Anonymous

        Somebody on the forum helpfully pointed out that if I'm going to worry about gaps in insulation in my new porch, I should be thinking about airtightness as well…so I have. The builder (who seems more sensible than most and has just finished a very airtight project), says that I don't want to be too airtight because of condensation and is planning on using poly and not being too stringent. I had the same thought, as I'm not planning at any point to install ventilation in the porch (!). However, I'm also not planning to live in it or do any cooking, bathing or running of gas appliances therein either so I wonder exactly how much of a problem water vapour would be if I did try to get it fairly airtight – it is also going to be pretty throughly ventilated everytime I open the front door to go in or out.

        Any thoughts?

        Thanks,

        Tania

      • #38285
        Nick Grant
        Participant

          Hi Tania

          A few different issues here, moisture within the wall construction and moisture on surfaces within the porch.

          I have posted about our porch many times on the forum and we use it as an example of what not to do on the AECB Carbonlite course!

          The potential problem is where the porch is thermally halfway between inside and outside – often called a buffer zone in old school eco-building. In this case the surfaces will get cold and when you open the house door warm air at 50% RH, 20C will flood into it and if the windows are a bit cooler than 10C (ie most winter) condensation will form.

          If the porch is within the thermal envelope it will be warm and so not a problem and if it is truly outside and just keeping the rain and wind off as you get your keys out then that fine too.

          Nick

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