Code Experts....

Table 802.5.1 specifies a Rafter Span Adjustment Factor in Note a.

Hc

---

Hr Factor

1/3 0.67

1/4 0.76

1/5 0.83

1/6 0.90

The upper limit shown is 1/3 the way up, above the wall plate. There are no restrictions that say you cannot place the rafter tie above 1/3. But could you? The 0.17 to 0.33 range is a Fibonacci Sequence (3,5,8....) that can be extended to:

802 802

Frac Decimal Fib Factor Fac Incr

1/2 0.46 13 0.60 0.07

1/3 0.33 8 0.67 0.07

1/4 0.25 5 0.76 0.07

1/5 0.20 3 0.83 0.07

1/6 0.17 2 0.9

We know that using the span adjustment factor reduces the allowable span because you are multiplying the table spans by the decimal factor.

If I wanted to place the rafter tie 1/3rd the way up, I would have to find a appropriate span, species, spacing, thickness. etc. using the factor.

But, If I wanted to go above 1/3rd, could I use Fibonacci calculations to further reduce the span and be in compliance with the code?

I would not be interested in 1/2, but I might be in the area between 1/3 and 1/2.

Thanks, Dave