The refinance share of mortgage activity increased to 80.5 percent of total applications, up from 80 percent the previous week.
In January, the investor share of applications for home purchase fell to 6.4 percent from 6.9 percent in December, led by a decline in the West and East North Central regions.
In addition, the share of purchase mortgages for second homes increased to 5.9 percent in January from 5.4 percent in December.
Loan rates continued their downward trend across the mortgage spectrum, with nearly all types hitting record lows.
The average contract interest rate for 30-year fixed-rate mortgages with conforming loan balances ($417,500 or less) decreased to 4.05 percent from 4.09 percent, the lowest rate in the history of the survey.
Rates on 30-year mortgages with balances greater than $417,500 dropped to a record-low 4.29 percent from 4.33 percent.
For 30-year fixed mortgages backed by the Federal Housing Administration, rates were down to 3.89 percent from 3.96 percent, another record low.
Meanwhile, 15-year FHA mortgages also hit survey lows, falling to 3.33 percent from 3.36 percent.