The following example is for fiberglass asphalt shingles, add 20% to cost for cedar shakes. Given the cost vs. value of roof replacement should give any homeowner further reason to maintain their roof. More so for the cedar shakes/wood roof homeowners.
On average for less than 5% of the roof replacement cost the homeowner can have their cedar shakes/wood roof cleaned which will in return extend the normal life span of the roof anywhere from 5 to 20 years depending on present condition.
No roofing material is eternal, moreover, cedar shakes/wood roofs. Do not have to replace your roof in half-life or less for lack of not properly maintaining your roof.
As the saying goes: “An ounce of prevention is worth a pound of cure”.
Regional Data Comparison (West North Central)
Remove existing roofing to bare wood sheathing and dispose of properly. Install 30 squares of 235-pound fiberglass asphalt shingles (min. 25-year warranty) with new felt underlayment, galvanized drip edge, and mill-finish aluminum flashing. Assume a 5-square hip roof; custom flashing at two average-sized skylights; and custom cap treatment at vented ridge.
According to the Remodeling 2011-12 Cost vs. Value Report (www.costvsvalue.com)