Sun, 19 Apr 2026 12:35:09 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62388#Comment_62388 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62388#Comment_62388 Mon, 21 Sep 2009 13:06:36 +0100 bjd
Just had a thermal study done to try and highlight the areas that need attention - the report has used a U value for these windows of 2! Older 4/12/4 dg windows have been rated at 2.8, so I find it hard to believe that 2 is achievable with the secondary glazing (gap is around 100mm).

Has anyone got any experience of the typical U values when such glazing is used? It rather drastically affects the numbers in this study. I did a heating demand calc on the house (such as you would do to size a boiler) and used 3, but don't really have a clue.

Creative DIY should allow me to renovate the windows at a low cost to around 1.5, but if we are already getting around 2 then it would be a waste of time - apart from sorting out the masses of condensation we get on the outer panes all winter.

Thanks for your help.....]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62415#Comment_62415 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62415#Comment_62415 Mon, 21 Sep 2009 15:31:47 +0100 Ev
Windows: http://www.historic-scotland.gov.uk/thermal-windows.pdf]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62421#Comment_62421 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62421#Comment_62421 Mon, 21 Sep 2009 15:49:56 +0100 James Norton
J]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62425#Comment_62425 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62425#Comment_62425 Mon, 21 Sep 2009 16:30:16 +0100 Nick Parsons https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62439#Comment_62439 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62439#Comment_62439 Mon, 21 Sep 2009 19:05:59 +0100 bjd
Sounds like the existing 2dry glazing is doing a reasonable job, and would do a lot better if we draftproofed the sashes properly.

Condensation is a problem on the inside of the outer panes, which is one reason for wanting to improve things - I can't work out if this is likely to be moisture from outside coming into the gap and warming/ cooling to a condensate, or moisture from inside (i.e. if the 2dry isn't doing a brilliant job at draftproofing). I suppose if failed dg units mist up - you have no hope with a secondary system.....]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62457#Comment_62457 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62457#Comment_62457 Mon, 21 Sep 2009 22:49:35 +0100 rogerwhit
With ref to draughtstripping, you DO want to vent the original outer window to the outside air to prevent condensation being trapped in the void, and seal the inner (secondary) window to prevent room air entering that same void. A certain amount of draughtproofing to the outer may be permissible but don't seal it right up! However from its nature a double hung sash window is hard to seal perfectly (and still work).]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62728#Comment_62728 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62728#Comment_62728 Thu, 24 Sep 2009 16:50:19 +0100 bjd
Some of the windows have been seriously painted over and are immovable currently (I have freed up a few) - I am wondering if these are actually the ones that mist up the most (can't remember from last winter just now).]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62801#Comment_62801 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4572&Focus=62801#Comment_62801 Fri, 25 Sep 2009 12:56:31 +0100 djh