I understand there's an element of "How long is a piece of string" to this question, but how long does it take gutters to get dirty?
So, if a house was on a quiet road and had white gutters, would they get back to being filthy every year, two years, three years, etc.
The reason for the question? I'm think of offering a price for a first gutter clean for £x per metre, then suggesting that if they want it done annually it'll be £y per metre, and every other year for £z per metre. If they do get back to being filthy after a year, then there's no point offering this type of pricing, as I'd be shooting myself in the foot. Similarly, if after a year they'll look fine, then the customer's not going to want them doing.
So, you know the reason for the question and I know there's a lot of guesswork in the answer, but I'd appreciate your opinions.
Vin