There are four classifications of extension ladders, and they’re based on fully loaded weight. That means your weight plus the weight of the materials you’re carrying. The biggest mistake DIYers make is buying a Type III ladder to save money. An extension ladder is a long-term investment, so think about how much your weight may change over the years—and don’t be delusional about it. The average American male weighs 189 lbs. Add a gallon of paint and a few tools and you’ve already exceeded the weight limit of a Type III ladder. Carry a heavy power tool and a few hand tools and you’ll blow past a Type II. And if you ever have to lug up a bundle of shingles (70 lbs.), you’ll need at least a Type IA ladder. Heavy-duty Type I and Type IA ladders weigh more and cost more, but you’ll get a stiffer ladder with better construction.
The decision is based on how much weight the ladder will have to support