Replacing Your Roof Before Solar Panels Go On

The rule of thumb

The Department of Energy's consumer guide to home solar, prepared by the National Renewable Energy Laboratory, puts it plainly:

If your roof is more than 15 years old, you may want to consider replacing it when you purchase your solar electric system. Most solar vendors recommend using roofing material that will last as long as the system, which is about 25 to 30 years.

— DOE / NREL, A Consumer Guide to Solar Electricity for the Home

The same guide gives the weight of a system at an estimated 3 to 5 pounds per square foot and says to make sure the roof can hold it.

Roof life against panel life

HUD's useful-life table for capital needs assessments plans asphalt shingles at 20 years, metal at 50, slate at 75 and clay or concrete tile at 60. A shingle roof that is already 15 years old will, by that measure, need replacing well before 25- to 30-year panels are done. Replacing it first means the panels come off once, not twice.

That is also why some homeowners choose metal before solar: at 50 years by HUD's figure, it outlasts the panels. Metal roofing.

If the panels are already up

Replacing a roof under existing panels means taking the panels off, setting them aside, and putting them back. That is electrical work as well as roofing, and the panels' owner has a say:

• If you lease the panels or buy the power under an agreement, read what the agreement says about removing them, and call the company before you schedule the roof.
• If you own them, ask who will take them down and put them back, whether that is in the roofing quote, and whether the town needs its own permit for it.

Tell the person on the line that there are panels on the roof.

What to ask

• How old the roof is, and how many layers it has (a tear-off is required over two layers, IRC R908.3.1.1).
• Which material will outlast the panels.
• Who handles the panels, and whether their removal and reinstallation is a line on the quote.