You might want to do the math with an actual amortization chart. Even with 100% appreciation, you will only have paid something less than 10% of the principal after 10 years on a 50 year loan. So you are still looking at 90% of the principal to be borrowed at the shorter term.
Even if my estimates are wrong by a factor of 2, you are looking at 80% of the principal after 10 years.
I'm pretty sure the numbers don't work.
It might make sense if you plan to keep the house for 20 years and downsize when the kids leave home.
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