Extension Ladder Guide: Sizing, Duty Ratings, and Safe Setup

Sizing and Working Height

An extension ladder's labeled length is not its working height. A 24-foot extension ladder has a maximum extended length of about 21 feet (the sections overlap by 3 feet for strength). Of that 21 feet, you lose 3 to 4 feet at the top because you should never stand on the top three rungs, and the ladder extends 3 feet above the roofline for safe mounting and dismounting.

To reach a standard 8-foot ceiling gutter (about 10 feet from ground level), you need a 16-foot extension ladder. To reach a two-story roofline (about 20 feet), you need a 28-foot ladder. To reach a two-story gutter comfortably, a 24-foot ladder works. Always round up — a ladder that is barely long enough forces you into unsafe positions.

Extension ladders set at the correct angle lose about 25% of their length to the base standoff. A 20-foot ladder set at the proper 75-degree angle only reaches about 19 feet vertically. Factor this into your height calculation. Standing a ladder too steep to gain height is the setup error that causes most base-kickout falls.

Consider storage and transport. A 28-foot extension ladder weighs 40 to 65 pounds depending on material, is 14 feet long when collapsed, and needs a vehicle with a roof rack or at least 14 feet of interior clearance. If you need a long ladder once a year, borrowing through FriendsWithTools beats storing one that takes up a full wall of your garage.

Duty Ratings

Ladder duty ratings indicate the maximum weight the ladder supports, including the person, tools, and materials. Type III (200 lbs) is for light household use. Type II (225 lbs) handles medium duty. Type I (250 lbs) is industrial. Type IA (300 lbs) is heavy-duty industrial. Type IAA (375 lbs) is extra-heavy-duty.

Your weight plus everything you carry must stay under the rating. A 200-pound person carrying a 30-pound tool bag exceeds a Type III ladder. A 180-pound person carrying a 50-pound bundle of shingles needs at least Type I. Be honest about the total load — exceeding the duty rating does not cause immediate failure but accelerates wear and increases flex that makes the ladder less stable.

Higher duty ratings also mean sturdier construction with wider side rails, thicker material, and more reinforcement at stress points. A Type IA ladder feels dramatically more stable than a Type III at the same height. For extension ladders specifically, the sturdier construction reduces flex and sway at full extension — which matters a lot when you are 20 feet up.

The duty rating applies to each section of the extension ladder, not the total ladder. Both the base section and the fly section must support the rated load independently since your weight transfers between them as you climb.

Fiberglass vs. Aluminum

Fiberglass extension ladders do not conduct electricity. If there is any possibility of contact with power lines, overhead wiring, or electrical equipment, fiberglass is the only safe choice. Aluminum conducts electricity and has caused electrocution deaths from contact with overhead power lines during ladder repositioning.

Aluminum is lighter — a 24-foot aluminum extension ladder weighs about 35 pounds, while the same size fiberglass ladder weighs about 55 pounds. That 20-pound difference matters when you are carrying it to the work site, raising it alone, and repositioning it between windows. For frequent use on non-electrical work, aluminum's weight advantage is significant.

Fiberglass resists weathering but can be damaged by UV exposure over years of outdoor storage. Store fiberglass ladders out of direct sunlight or apply a UV protectant. Aluminum does not degrade from sunlight but corrodes in salt environments. Both materials are durable when maintained properly.

Price difference is moderate — fiberglass costs 30 to 50% more than aluminum in the same size and duty rating. For a ladder you will own for decades, the safety advantage of fiberglass is worth the premium unless you are certain the ladder will never be near electrical hazards.

Safe Setup and Use

The 4-to-1 rule: for every 4 feet of height where the ladder contacts the wall, the base should be 1 foot out from the wall. A ladder touching the wall at 16 feet should have its base 4 feet from the wall. This produces the correct 75-degree angle. Too steep and the ladder kicks out at the base. Too shallow and it slides down the wall.

Set the base on firm, level ground. Soft ground, mud, gravel, and slopes cause base failure. Use a wide, flat base like a piece of plywood under the feet if the ground is soft. Level the ladder with leg levelers (most quality extension ladders have adjustable feet) rather than shimming with blocks that can shift.

Lock the rung locks (the hooks that hold the fly section at height) and verify they are engaged before climbing. Pull down on the fly section to confirm the locks are seated. Rung lock failure while you are on the ladder causes a sudden drop of 12 to 16 inches — enough to throw you off balance at height.

Extend the ladder at least 3 feet above the roofline when accessing a roof. This gives you a handhold for mounting and dismounting. Step off the ladder onto the roof — never step onto the roof from the ladder while holding the ladder. Tie off the top of the ladder to prevent it from sliding sideways while you are on the roof.

Frequently Asked Questions