Dave, simply you can’t double dip. If you PPOR is house a and you live in and also own house b, the time frame you selected for house a being you PPOR will be used to calculate the CG in house B when you sell it. In saying that if you own house B for 30 years and sold house A 24 years ago I highly doubt there are any tools sophisticated enough to calculate what capital gains tax you owe not to mention the tax man isn’t that well coordinated. Hope this helps.