Inserting windows by WWR into a single LBT wall comprised of two different HB faces with different constructions

I have searched discourse and cannot find this particular question.

I wish to model a single wall made up of two distinctly different thermal paths: one part is insulated well, the other is more of a thermal bridge. I do not wish to smear the R-values and Heat Capacities of the single wall into an overall ‘average’ construction definition following something like the iso-thermal planes R-value calculation.

I want to create two LBT faces with different constructions linked to a percentage bar representing the proportion of each in the wall. Then I wish to have a second slider by which the WWR is assigned to the overall wall, not as happens where at the moment the WWR is applied separately to the two individual faces in the wall. Am i missing something in LBT 1.2?

Thanks in anticipation of your kind assistance.

Hi @MichaelDonn, I don’t think this will be possible with how the WWR component works. It is designed to work for one wall at a time. That being said if you can calculate the WWR for each segment of the wall based on their area ration then you can add them as two windows to these two walls based on a single value for the whole wall.

Thanks, @mostapha .

I thought as much. But wanted to check my still somewhat sketchy knowledge of GH.

I am building a sketch design script that looks to model the wall depth as well as shading by compass direction, and allows the ‘side’ walls to be a adiabatic as if in an apartment or ‘outside’ as in a single family home, and I want also to be able to explore modelling thermal bridges explicitly as feasible in E+, while still allowing in each wall windows to have a single shade system… The face to wall component made it very easy to create rooms where a slider determines what percentage of the wall is structure, and what is insulated construction.

I may separate the model making further so the thermal model is the only one that has this two faces per wall issue and the daylight model has only one…

Thanks for the quick response.


Really interesting experiment. Can you elaborate a bit more on this hybrid wall? Are these just two wall surfaces with different constructions, and the slider changes the construction % by changing the respective wall areas?

Is the assumption that the different constructions are isolated and don’t interact with eachother (i.e there’s no thermal bridging between them) or are you trying to account for edge effects in some fashion?


I am trying to explicitly account for standard through the wall thermal bridges in a one dimensional fashion (as per standard EnergyPlus). The normal recommendation is to calculate a hybrid Thermal Resistance based on the % of wall where conduction is through the structure and the % through the insulation between the structure. I am aware that this does not readily model the heat capacity of the structure vs the insulation and the 1 dimensional heat flow through the wall in the standard 1Dimensional model smears the R-values and the Heat Capacity of the structure and the insulation between the external skin and the internal lining. My goal is to set up a simple investigation which steps the % structure systematically by having each ‘wall’ in a room as a composite of two walls: one area of wall has the lining plus cladding separated by strcture, the other they are separated by insulation.

I hope this is clear?



Thank you for explaining. I think I understand: you’re trying to avoid the weighted average method of calculating an effective U-value in parallel (1D) heat flow scenarios, because it assumes the structure’s thermal mass has no impact on overall heat flow. And you can’t calculate effective specific heat capacities in the same way we calculate the effective U-values (i.e mass-weighted averages) due to the way discrete chunks of mass lags over time in relation to each other, so just modeling the different wall elements discretely makes sense.


Yes, exactly. A nice summary. It is also a legacy of my modelling with the SERI-RES/Suncode/SUNREL program in the past which adopted a two surface / 1 wall approach back in the 1980s. It allows for a quick and easy exploration of the effect of % of wall that is thermal bridges.