# LBT 1 Window Construction U-Factor or U-Value?

**URL:** <https://discourse.ladybug.tools/t/lbt-1-window-construction-u-factor-or-u-value/11790>\
**Category:** uncategorized\
**Tags:** honeybee, u-value, window\
**Created:** [November 4, 2020, 8:46pm UTC](https://discourse.ladybug.tools/t/lbt-1-window-construction-u-factor-or-u-value/11790 "2020-11-04T20:46:43Z")\
**Posts on this page:** 1\
**Showing post:** 11

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**Author:** ![chris](https://discourse.ladybug.tools/user_avatar/discourse.ladybug.tools/chris/32/10179_2.png) [@chris](https://discourse.ladybug.tools/u/chris)\
**Post date:** [September 22, 2021, 1:34am UTC](https://discourse.ladybug.tools/t/lbt-1-window-construction-u-factor-or-u-value/11790/11 "2021-09-22T01:34:28Z")

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> [@MaxMarschall](#):
>
> Do you know whether, in general, manufacturers specify their glazing performances in U-values or U-factors?

Yes, I know that the values that you get from glazing manufacturers are almost always U-factors and NOT U-values. U-Values and R-Values are typically only used to describe opaque constructions.

Also, the recommended way to use the SimpleGlazing material is to plug the “Whole System” U-Factor rather than the “Center of Glass” U-Factor. While it’s true that different window geometries have different amounts of frame and therefore should technically have different constructions, this tends to be at a level of detail that’s beyond what is needed to get decent estimates of energy use. That is, unless you have very different types of framing materials across your windows or you have very different types of window frame geometries.

In the future, we will add detailed frame objects to honeybee-energy WindowConstructions, which will make it easier to just specify the frame material and EnergyPlus will take care of computing the effect of the frame for the different window geometries:

> <https://github.com/ladybug-tools/honeybee-energy/issues/209>
>
> This is a feature that most users probably don't need but it will be really help…ful for THERM integration and for the users who care deeply about modeling window U-values as accurately as possible.
> 
> I just wanted to record how I think this should be implemented. Specifically, I think it should be a property of the WindowConstruction and not a property of a fenestration surface (as it is in E+). This is because the frame performance is often tied to the type of window construction and not to a specific property of a specific window. So, on the GUI end, the user would have something like this:
> !\[image\](https://user-images.githubusercontent.com/5567574/83357373-f198ae80-a339-11ea-83fc-4cb33d3fa388.png)
> 
> And the honeybee-openstudio-gem would take care of assigning the frame object to all Apertures that have the WindowConstruction with the frame.

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