Sat, 16 May 2026 16:35:34 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229513#Comment_229513 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229513#Comment_229513 Thu, 10 Sep 2015 01:56:11 +0100 Paul in Montreal Posted By: ActivePassiveAs a would-be PH chaser, it *does* seem quite odd to have to adhere to a German baseline, whereas one's local climate might be far different...

The whole point of HDDs is that, but using the same baseline, you're comparing like with like. Over here, the baseline temperature for both HDDs and CDDs is 18C. If you have data for another location that's referenced to the same baseline temperature, you can see if your climate is warmer (fewer HDDs) or colder (more HDDs).

For example, last winter we had 4383 HDDs (baseline 18C) and this summer we've had 346 CDDs (baseline 18C), whereas winter 2009/2010 had only 3684 HDDs and summer 2011 had 388 CDDs.

Paul in Montreal]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229520#Comment_229520 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229520#Comment_229520 Thu, 10 Sep 2015 09:56:33 +0100 gravelld Posted By: ActivePassiveYou are right some of the Passivhaus requirements are very much focused around colder German winters and may be a little OTT for the UK. For example window U values of 0.8 are required to avoid convection currents setup because the inside surface temperature of the glass drops below 16C - but this is only when the temperature is -10C outside (or -5C????). If you look at temperatures in southern England I think you could get away with 1.1 U value double glazing 99% of the year without getting draughts because of internal surface temperatures dropping too low.

This is quite interesting. Begs the question why the numbers aren't adjusted a bit? It might make a difference for take-up if people could "get away" with buying slightly cheaper components.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229523#Comment_229523 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229523#Comment_229523 Thu, 10 Sep 2015 11:19:21 +0100 djh Posted By: gravelldBegs the question why the numbers aren't adjusted a bit?
Because it takes time and money and people to do the research to form the basis of any such decision.

At the moment you can't even use PHPP to demonstrate Part L compliance so until such time as the people of this country and their elected representatives and their civil servants, show some sign that there might be some official blessing and support I wouldn't hold out much hope of any UK specific changes, let alone southern England-specific changes.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229530#Comment_229530 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229530#Comment_229530 Thu, 10 Sep 2015 12:00:00 +0100 gravelld https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229541#Comment_229541 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13647&Focus=229541#Comment_229541 Thu, 10 Sep 2015 13:39:00 +0100 ActivePassive
If you are using Degree Days for comparing different climatic areas for Passivhaus you should use a much lower 'balance point' or 'base temperature' and even then you need to be careful. For 'normal' poorly insulated homes in not too dissimilar regions then comparing Degree Days for example with a 15.5C base is a good approximation; it can also be used for estimating the impact of small changes in U values and air permeability.]]>