Trying to understand how reflections work in Exterior Windows

If you don't want to see inside the glass, don't make the glass transparent. Personally I just colour it black and re-name the colour to "House Glass". The other way I do it (if I have a window/door component) is not to model the interior room space at all: the space just behind the window is black.

You may want to increase the Specular value of the glass. This works slightly like the coating of sunglasses. This tends to look more natural than tinting the glass, but you can do both. (Note: the interior is a mint green with little light.)

I would advice against your setup with a wall with a sky texture. Use a panorama instead. First of all, the brightness intensity of the wallpaper will not resemble the rest of the sky and second, the texture of the sky might only be visible in reflections on Ultra settings due to optimizations.

I encountered the same issue, where the reflection of a treeline image did not show up in the glass. I ended up dropping in a row of tree proxies so there was some geometry to reflect, but I think the solution you're saying Thomas Willberger is to use an environment map in the sky settings?

Quote from andybot

I encountered the same issue, where the reflection of a treeline image did not show up in the glass. I ended up dropping in a row of tree proxies so there was some geometry to reflect, but I think the solution you're saying Thomas Willberger is to use an environment map in the sky settings?

Exactly, ideally an HDRI image from a page like https://hdrihaven.com/

Remember that glass ior is typically 1.54 - 1.6. By default, Enscape glass material doesn't have that as default. It's set to 1.0 I think. It makes a big difference since I know that skp user typically don't add thickness to glass faces.

I had the same problem and as Sean recommended adjust the two sliders for Specular and the one above it for Roughness. Roughness has to be right down.