Pricing a roof from the ground
The calculator above prices square feet of roof surface, and that is the number people most often get wrong before they have entered anything. What you can measure from the ground is the footprint — the outline of the roof seen from above, eaves included. The surface you actually clean is larger, because every foot of horizontal run becomes a longer sloped rafter. The steeper the pitch, the bigger the gap, and quoting from the footprint quietly discounts every steep roof you sell.
The correction is a single multiplier: the slope length per foot of run, which is the square root of rise squared plus twelve squared, divided by twelve. A 4/12 roof is about 5% larger than its footprint, a 6/12 about 12%, and a 10/12 about 30%. The roof area from pitch tool does the arithmetic and drops the result straight into the calculator. Read the pitch with a level and tape on a gable end or from a ladder at the eave, or take it from the plans if you have them.
Same footprint, three pitches
A 1,300 sq ft footprint in moderate condition, priced at $35 per crew-hour of labor cost, $60 of chemical, $20 of travel and a 55% target margin:
Priced off the footprint alone, all three would have gone out at $780. On the 10/12 roof that is $235 of work you would have done for free — before you account for the fact that steep work is also slower and riskier per square foot.
Steep roofs cost more than their area
The pitch factor corrects the area. It does not correct the pace. The calculator's hours scale with square footage and condition only, so it has no way to know that a steep roof means harnesses, anchors and a crew that moves carefully rather than quickly. OSHA draws the line at 4 in 12: anything steeper is a steep roof under 29 CFR 1926.500(b), and the fall protection that comes with it is time and equipment that belongs in the price. Put it there deliberately — by stepping the condition up, by raising your labor cost for that job, or as a separate access line on the quote — so it does not come out of your margin by default.
Soft wash, not pressure
That is the reason roof work is priced as chemical-and-dwell rather than pressure-and-passes. Chemical is a real per-job cost here — log it in the chemical field for each roof rather than absorbing it into overhead — and ARMA's own warning about protecting the building and surrounding landscape is the landscaping pre-wet and post-rinse time that belongs in your hours. The same bulletin is also the sentence to put in front of a homeowner who asks why you will not just blast the roof clean.