I thought if the exterior structure was kept true then interior upgrades were okay?

Not sure about Canada of course.

The Gamma Phi house at U of Oregon appears to be on the list, too. I wonder if several are?

Nope, in Toronto (not sue about other parts of Canada) when a building is registered as a historic structure - the whole structure is "protected", so all interior and exterior work has to be in accordance with the various rules and regulations designed to keep it's "historic integrity" - it's a two-edged sword really... yes you get $$$ to support the upkeep of the building, but it may end up costing you more in the long run...

I know the chapter house at my chapter, which is a historical landmark, had to jump through hoops when they added on. The addition had to meet all of these architectural requirements to maintain the integrity of the structure. I remember hearing that it was a very expensive renovation because of the historic landmark issue.

That strikes me as a little funny since the AOIIs have recently had to move out and recruit at another location because the roof is caving in at the Rhodes lodge. :)

I know the Chi Omega roof is slate -- not sure if they all are? Very expensive to replace, but I guess it lasts forever.

my new chapter's house is a texas historical landmark. it's a pretty cool old victorian that was built the same year the organization that became our chapter was founded, in 1902. (if that made sense...)

I'm pretty sure you do get money from it. I could certainly be wrong, but I believe Little Rock Central High School gets money for being on the register.

Also, the Chi-O theatre as mentioned earlier on in the thread, is amazing. Just a great place to have pep rallys and so on.

Oh, is it ever! Talk about a place where you can build suspense! When I cheered there, the cheerleaders and the band would be behind the hedges before the pep rally and the band would be doing drum cadences. Then they'd start the one that signaled that the band was coming and the crowd would go wild! Then the drummers would march down to the grass in front and keep that cadence up while the band ran in. Finally, we'd come racing down to the grass and the band would break into the fight song. by then the crowd was screaming...I hope they still have that ritual!

I went back as an alum cheerleader a few years ago and it was done that way then. It was great because Greeks all over the theater were yelling the names of their brothers and sisters on stage, including ours!

Oh yeah, that's stilll how it is...
All during the pep rally, chants start breaking out (Pi Phi Pike, so on. z-e-t-a-t-a-u-a-l-p-h-a, zeta tau alpha... ) where the people on stage can't speak. So much fun.

Psi Alpha Historic Building
 

I am actually an alum of the Psi Alpha Chapter of Chi Omega at Oregon. The house underwent an interior remodel before getting listed on the history registry. I believe a lot of thought was put into the remodel in order to bring the interior spaces back to their original state and to ensure that the remodel would not jeopardize the listing of the house on the historic registry. As such, I think the listing does impact a house's ability to remodel. I am not sure that there is any money to be received, other than a break on property taxes which, as someone pointed out, is generally not a big issue for non-profits.

Here is a link to pictures of the sorority houses at Oregon. I believe several other houses, including Alpha Phi and Gamma Phi Beta, are also on the registry. http://darkwing.uoregon.edu/~greek/sororities.shtml. Most are beautiful buildings.