When the temp goes up, it also goes up for the columns and roof members.
Essentially, everything elongates. I guess one or two items may have some
load added/reduced, but it seems to work fine from projects I have seen.
I still prefer simple rod bracing to portals and windposts provided that
access is not any issue. Portals and windposts laterally deflect far more
than rod bracing for the same loading.