It's 3.5m closed they mean mate. On most I do, 1 3.5m section gets you up there enough to clean them. But, I tend to go up 1 stile with my second 3.5m section to get just under the cill. However, I find that a double 3.5m ladder is a pain to carry around however, especially over the fences at the back. It's quite heavy. So, I tend to split em apart & use just the 1 3.5m section for most houses.
Don't get a triple 2m though. A double 3m or pref 3.5m is the best option. You'll always find a double is alot better to work with than 3.