Blank cells are being summed as a value greater than five using a SUM(IF function

Hi! I have a large dataset of 7-day schedules that I am summing to calculate breaks.

The function is setup like this:

=SUM(IF(CELL1>5, 0.5, 0)), (IF(CELL2>5, 0.5, 0)) and so on until all seven days are tabulated.

Because a full time person would only work 5 days a week, at least 2 days are blank per row, but we're open all 7 days and I want to sum the entire spreadsheet, so I have to count all 7 days. A full time person should have 2.5 hours per week.

For some reason the function is mostly working, but about a third of the results are larger than they should be because it's counting some blank cells as greater than 5. For example, a part time person working only 3 days should have 1.5 break hours, but the function returns 3.5 because it is counting all the blank cells as containing a value > 5.

What's really strange is it is only doing this some of the time. Every row has at least two blank cells, but only about a third of the sums are wrong. I can't figure out why.

The columns are all formatted as a number. The value does update correctly if I manually enter a "0" in the blank cells, but this is a very large dataset and that would take forever.

Thoughts?