Why this isn't a single, nationwide answer
Permitting for exterior work is set locally, not by the state licensing agencies that issue a contractor's license, so the same siding job can need a permit in one city and not in the next one over.
What the three states covered by this directory do control is who's allowed to do the work, and in some cases, when a permit has to be requested relative to the contract.
Florida ties permit timing to the deposit
Florida puts a hard number on it once a contractor has banked upfront money past the 10%-of-price mark: 30 days to submit the permit paperwork, then 90 more to actually get a crew on-site once that permit clears, barring just cause or your own written OK for extra time.[1]
That rule doesn't mean every siding job needs a permit. It only sets a clock once a permit is required and a deposit over that threshold has changed hands.
California ties licensing to permits, value and labor
California requires a CSLB license for anyone contracting on a project that needs a building permit, uses employees, or is valued at $1,000 or more in combined labor and materials, which covers most full-house siding jobs before you even get to your city's own permit rule.[2]
In practice, a small patch job might trigger neither a permit nor a license requirement, while a full re-side almost always triggers both.
Washington keeps registration and permits separate
Washington's L&I registration governs who's allowed to advertise and bid as a contractor at all, requiring a bond and liability insurance, and that's a separate question from whether your city or county requires a building permit for the siding work itself.[3]
L&I's own disclosure-statement rule kicks in on home improvement work priced at $1,000 or more, on any property with four units or fewer, whether or not a permit ends up being pulled for it.[4]
What to check before work starts
Ask your contractor directly whether the job needs a permit, then ask for the permit number once it's issued rather than taking their word that one was filed.
A contractor who suggests skipping a required permit to save time is offering to cut a corner that protects you, not them, since unpermitted work can complicate a home sale or an insurance claim later.
What happens if the work was never permitted
An unpermitted siding job rarely causes trouble on day one. The problem tends to show up much later: a home sale where the closing company or a buyer's inspection turns up permit records that were never filed, or a storm claim where an adjuster finds work no inspector ever signed off on.
Some jurisdictions let an owner apply for a permit after the fact, sometimes for an added fee, which is a slower and pricier path than simply confirming the permit before the crew shows up.
A permit typically triggers an inspection once the water-resistive barrier and flashing are on but before the siding covers them up, which is the jurisdiction's way of confirming those hidden layers were actually installed, not just billed for.