Green Building Forum - Another U-value calculator Fri, 07 Aug 2026 20:10:11 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273601#Comment_273601 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273601#Comment_273601 Sat, 04 May 2019 12:58:45 +0100 djh https://www.ubakus.de/u-wert-rechner/?

It looks professional and works out condensation and decrement delay and suchlike to EU standards.

It has an English language option, but only some of the content is in English. The rest remains in German. So if anybody with better German with me wants to have a go and see how useful it is, that would be helpful.

PS It might be better to use it before brexit, from some of the statements on the site about access within the EU.]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273603#Comment_273603 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273603#Comment_273603 Sat, 04 May 2019 14:24:47 +0100 djh Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273608#Comment_273608 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273608#Comment_273608 Sun, 05 May 2019 08:08:15 +0100 PeterStarck Posted By: djhI've just come across another U-value calculator -https://www.ubakus.de/u-wert-rechner/?" rel="nofollow" >https://www.ubakus.de/u-wert-rechner/?

It looks professional and works out condensation and decrement delay and suchlike to EU standards.

I had a look at that a couple of months ago to calculate decrement delay but I couldn't find the calculator, maybe you have to register.]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273609#Comment_273609 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273609#Comment_273609 Sun, 05 May 2019 11:30:29 +0100 djh Posted By: PeterStarckI had a look at that a couple of months ago to calculate decrement delay but I couldn't find the calculator,
The U-value calculator just calculates and displays it?]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273615#Comment_273615 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273615#Comment_273615 Mon, 06 May 2019 07:54:22 +0100 PeterStarck Posted By: djh
Posted By: PeterStarckI had a look at that a couple of months ago to calculate decrement delay but I couldn't find the calculator,

The U-value calculator just calculates and displays it?
Thanks]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273639#Comment_273639 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273639#Comment_273639 Tue, 07 May 2019 13:19:00 +0100 Doubting_Thomas Posted By: djhI've just come across another U-value calculator -https://www.ubakus.de/u-wert-rechner/?" rel="nofollow" >https://www.ubakus.de/u-wert-rechner/?

+1 for u-bakus. Previously called U-wert.

I've been using it for a few months and it remains my go-to calculation software for testing theoretical wall build-ups.

djh, curious to know what you think about the 'drying time' calculation it performs, given what you mention about the condensation predictions vs. where it would actually occur. Is this also a slightly flawed (i.e. simplified) approach?]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273640#Comment_273640 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273640#Comment_273640 Tue, 07 May 2019 13:35:17 +0100 bhommels Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273642#Comment_273642 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273642#Comment_273642 Tue, 07 May 2019 14:14:43 +0100 gravelld Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273644#Comment_273644 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273644#Comment_273644 Tue, 07 May 2019 14:52:23 +0100 WillInAberdeen
In reality the vapour molecules have a 'choice' whether to condense or to carry on diffusing until they reach an even colder place, such as the cladding, they will always 'choose' to condense at the coldest (lowest energy) point they can easily reach, always at the outside edge of an insulating layer or the inside edge of a low permeability layer.There's some nice photos explaining this at https://www.buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion

Once condensation does occur, it will wick and drip away through the material, not sit still in a discrete blue layer until next summer.

I would use this website as it is intended, a nice and handy u-value calculator, for constructions where condensation will never occur, but if condensation amount and drying time are important to you, then use a more appropriate tool such as WUFI.]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273646#Comment_273646 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273646#Comment_273646 Tue, 07 May 2019 17:47:26 +0100 fostertom Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273647#Comment_273647 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273647#Comment_273647 Tue, 07 May 2019 17:47:48 +0100 djh Posted By: WillInAberdeensomewhere deep inside the insulation layer, as stated on pg2 of djh's download
Actually, it's showing condensation within the render, not the straw, I think, since that's where the dewpoint line crosses the temperature line. So it's not too far from the truth in this particular case.

In another model I did (attached), that had some timber immediately behind the external render, it did predict a thick blue layer throughout that layer of insulation, whereas I believe it would concentrate on and around the timber and the render.

Once condensation does occur, it will wick and drip away through the material, not sit still in a discrete blue layer until next summer.

It will certainly spread by capillary action to some degree in both the straw and lime (they are intimately coupled so both materials will be involved regardless of where the condensation first occurs. But I wouldn't expect much in the way of free water that could drip. Indeed I have a theory that some of the condensate may be carried all the way back into the interior of the building.

I think the assumptions it makes are generally conservative (i.e. pessimistic) so if it says something is safe, I would generally trust it. But as you say, a more accurate tool, especially one that uses 2D or 3D flow would be better.]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273648#Comment_273648 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273648#Comment_273648 Tue, 07 May 2019 19:48:40 +0100 WillInAberdeen
Quote:

"The dew-point indicates the temperature, at which water vapour condensates. As long as the temperature of the component is everywhere above the dewpoint, no condensation occurs. If the curves have contact, condensation occurs at the corresponding position." End quote

To be fair they do include this disclaimer:
Quote:"Convection and the capillarity of the building materials
were not considered. The drying time may take longer under unfavorable conditions (shading, damp / cool
summers) than calculated here" end quote

Just to be clear, I think this is a really neat u-value calculator, and for checking that condensation will never occur, but I wouldn't use a u-value calculator for drying calculations.]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273650#Comment_273650 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273650#Comment_273650 Tue, 07 May 2019 22:03:24 +0100 fostertom Posted By: djhwhereas I believe it would concentrate on and around the timber and the renderThat's talking about two different kinds of 'simplification' -
the first being what Will was talking about
Posted By: WillInAberdeenwhether to condense or to carry on diffusing until they reach an even colder place
where it 'carries on' along the in-out axis to the render;
the second being that it will concentrate somewhere laterally, around the timber rather than in the insulation between - simply a limitation of a 1D model, where only that in-out axis exists. A 2D modeller such as super-WUFI or whatever it's called would handle that side-to-side axis.]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273706#Comment_273706 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273706#Comment_273706 Fri, 10 May 2019 16:31:01 +0100 PeterStarck Posted By: djhI've just come across another U-value calculator -https://www.ubakus.de/u-wert-rechner/?" rel="nofollow" >https://www.ubakus.de/u-wert-rechner/?

It looks professional and works out condensation and decrement delay and suchlike to EU standards.

I ran ubakus and also the Dynamic Thermal Properties Calculator written by Arup for the Concrete Centre and using the same data got very different results for decrement delay. I wonder if the decrement delay models are modelling the effect very accurately. Results following.]]> Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273707#Comment_273707 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273707#Comment_273707 Fri, 10 May 2019 16:33:31 +0100 PeterStarck Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273708#Comment_273708 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273708#Comment_273708 Fri, 10 May 2019 16:34:14 +0100 PeterStarck Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273721#Comment_273721 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=273721#Comment_273721 Sun, 12 May 2019 10:39:21 +0100 Silky Another U-value calculator https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=299897#Comment_299897 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112&Focus=299897#Comment_299897 Thu, 26 Jan 2023 11:19:22 +0000 Shevek