The short answer
There is no single number of years. How often a house needs repainting depends on the siding, the paint that's on it, how much sun and weather the walls get, and how well the last job was prepped. The better question is whether your paint is still protecting the siding. If it is cracking, peeling or chalking, or the wood underneath is showing, it's time. Waiting until the paint fails means paying to repair the siding as well as paint it.
Signs it's time to repaint
- Peeling or flaking. The paint has lost its grip on the surface.
- Cracking or blistering. Often a sign of moisture or old, brittle paint.
- Chalking. Rub a hand on the wall. If a powdery residue comes off, the paint is breaking down.
- Fading. Mostly cosmetic, but it shows the paint is aging.
- Bare or gray wood. Nothing is protecting it from water now.
- Mildew or mold growth. Wash it and see whether it keeps coming back.
- Cracked or missing caulk around windows, doors and trim, where water gets in.
What makes paint last longer or shorter
- Sun and weather. The sides of a house that get the most sun, rain or snow usually wear out first. Don't assume every wall needs it at the same time.
- Prep. Scraping, washing, sanding the rough spots, caulking and priming bare wood decide how long a job lasts more than the paint brand does.
- The paint. A good exterior paint costs more per gallon and usually saves the work of doing it again sooner.
- The siding. Wood, fiber cement, vinyl and stucco each need different prep and paint.
- Moisture. Leaking gutters, sprinklers hitting the wall and plants against the siding all shorten the life of the paint.
Can you paint over what's there?
If the old paint is sound, yes, after a good wash and a light sanding. If it's peeling, it has to be scraped back to a firm edge first, or the new coat will peel with it. Bare spots need primer before paint.
A warning about older houses
If your house was built before 1978, the old paint may contain lead. Scraping and sanding it makes dust. Have it tested before you start and follow lead-safe practices, or have someone qualified do the prep.
Painting it yourself or hiring it out
A single-story house with sound paint is a reasonable weekend-after-weekend project. Ladders, two-story walls, lots of scraping or lead paint are where it's worth hiring someone. Whoever does it, ask what the prep includes, because that is where jobs succeed or fail.
DRAFT NOTE for the owner: if you do exterior painting in Idaho and Washington, say so here and describe how you prep. I did not state that you offer it.
What to do next
If you want someone to look at your siding and tell you whether it needs paint now or can wait, request a consultation.