UValue EPConstruction calculation

Dear Expert,

I created a set of custom materials for a E+ simulation that I then used to define a set of EPCostructions. Once added to the E+ library, I checked the UValue constructions (with HB call from EP library) in W/m2K which did not correspond to the values calculate by me using the standard equation U=1/R with R= Σ thickness/conductivity. I tried the calculation both with and without the external and internal resistivity (Rse, Rsi) but the results are in any case different.

The results are the same only if I set in each materials that compose the construction 0 for density and specific heat, that means a construction without mass.

Unfortunately, I did not find any literature about! Could you explain how HoneyBee (or perhaps E+) does the U-value calculation?

Thank you in advance.




It will be nice if you upload a file with your problem pointing out where the problem is. In this case also, what are the expected results and what are those that you get.

I don’t have access right now to GH but as I recall the results of the U don’t show the influence of the air layers but they are definitely taken into account during the simulation. There is a component, don’t remember which one, that you can ask for the U with those air layers.

Hope this is your “problem”, meaning there is no problem.



you said right, it was my “problem” or better my error. I made a mistake assigning the materials name. I have the same material in different construction, so that I gave the same name at this material for each construction even though the thickness was different and here my error. The same material with different thickness require a different name.

Thank you again.


Abraham is right [as usual]. check EPMaterialAux class to see how Honeybee calculates U-Values for materials and constructions:


Hi Mostapha,

thanks for the link, which confirms what said yesterday.