I've just come across another U-value calculator - 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.

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.

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

A whole new world has opened up to me. Really good find, thanks for posting!

Thomas, the condensation calculation here is very simplified (following a simplified DIN standard method), because it assumes condensation will happen as soon as the dewpoint line is reached, somewhere deep inside the insulation layer, as stated on pg2 of djh's download. This is a common misconception, which messes up the 'drying time' calculations.

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.

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.

Posted By: djhwhereas I believe it would concentrate on and around the timber and the render

That'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.

Ubakus

+1 for this tool, have used extensively and would have been lost without it