[Wynott]

My exteriors are washing out when doing interior renders. Not debating whether this is physically correct or not... Is there anything I can do to control it? To get an exposure I'm happy with in the room the view out the windows doesn't look very good.

See attached.

[JDHill]

Generally in such situations, people either need to take multiple shots and composite them, or artificially boost the interior lighting (good tips can be found in the world of real world photography, just for example here; be sure to see the comments, photographers seem to like to talk about what they do). In rendering, of course you also have the luxury of arbitrarily reducing the intensity of the environment.

[kami]

what I do to avoid that is mostly render the image out much darker than I need it (around 2 f-stops darker). Or just as dark that there are no blown-out parts anymore. Then I brighten the image in Photoshop with the curves (sometimes brushing out the very bright parts in the mask for this correction). It is much easier to brighten up a too dark image than trying to get info out of a blown-out part.
Additionally, the Photoshop tool "Shadow/Highlight" works great too, but giving a more HDRI-Style feeling.

Directly in the maxwell engine, what you could also do is play with the Burn and Gamma values. Usually you're able to reduce the blown-out parts a lot, but the image may lose to much contrast and might not look good anymore.