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There are three basic portable ladder types:
* Type I – Industrial Ladder: heavy-duty with a load capacity not more than 250 pounds.
* Type II – Commercial Ladder: medium-duty with a load capacity not more than 225 pounds. (Suited for painting and similar tasks.)
* Type III – Household Ladder : light-duty with a load capacity of 200 pounds. There are many types of ladders available on the market. If it is intended to be portable and used by a single person, it should fit into one of the three basic categories. It is rare that you just go up and down a ladder. You use it to do a job, so you could be carrying tools and materials up it. You could be on it and be sawing or drilling. You can apply many kilograms of thrust to the ladder, over and above your own weight when you are working on it, so you need a solid support.
As far as I know ladder rungs are set at 1 foot apart. So an 18 pin (rung) ladder is 18ft long, plus a bit. A double 18 pin extension will get you safely onto a 28 ft high roof. Say four rungs overlap at the join, three rungs over the top and a foot or so for the slope.
extension ladder safety
ladders - correct position.
On the right is a sketch of an extension ladder leaning on a roof edge.
The angle of the ladder to the vertical is important. Four to one is the recommended angle ratio.
Note! In nearly 50 years up and down ladders I have never done any sort of measurement for this. Always I've done it by eye and what feels right. Having said that, when I was taking the photo below, earlier today I decided to set the ladder at 4:1 ratio and straight away it felt too steep for me. I needed a bit more out from the wall to feel comfortable. Just my opinion, but you have to work with what feels right.
If you have it too steep, as you are climbing up it the top tends to skitter about or feel loose. There is not enough weight resting on the roof edge.
If you place it with too much angle, the bottom is liable to slide out, but more importantly you are making the ladder itself carry too much of your weight instead of the ground. Also you will be leaning at an unnatural angle as you climb. Inspect ladders regularly. household step ladders and extension ladders should be inspected for broken or frozen joints or latches. Aluminum ladders should be inspected for cracks and broken welds. Aluminum ladders should also be inspected for rough spots and burrs before first use.
Wood ladders should be inspected for cracked wood, splinters, and rot. Look for broken or loose hardware. Protect wood ladders with linseed oil or clear sealant. Never paint a wooden ladder - the paint may hide imperfections such as rot or cracks.
Fiberglass ladders are protected with a clear sealant. If the fiberglass is damaged through the sealant, sand lightly before applying another coat of lacquer. from:townhallladder
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