In theory it appears like you lose value but in actuality you gain value. Say you purchase a flat for 1 BTC @ 300k. Now say 1 BTC is worth 200k a little while later. Your house value is not dependent in the BTC but rather what the free market says in the real estate market. Lets say your house didn't lose that much value in one year and was worth 280k now. In this example scenario you would have gained 80k equity despite the fact that it looks like you are losing 100k equity.