Here's a simple explanation of how low rates create an overheated housing market.

Buyers' annual income $150,000. Downpayment 20%.
A- Mortagage rate in early 1990's, 8,5%. Maximum affordability $692,315
B- Mortagage rate today, 2017, 2.47%. Maximum affordability $1,224,281

The lower rate of 2.47% allows the same buyer to purchase a home $531,966 above the average rate in the early 1990's. Any questions?