GURPS Powers includes rules for using the Affliction Advantage on inanimate objects (see Afflictions and Inanimate Objects on p. P40).

When using that rule, if your Affliction bears the Area Effect Enhancement and the object is completely enclosed by the area of effect, then it does not gain a bonus to resist based on it's Size Modifier. If it's only partially covered by the area of effect, then for the sake of it's resistance roll, determine the Size Modifier of the portion outside the area.

Please keep in mind that all areas of effect are by default only 4 yards tall (see p. B239). Each level of Area Effect taken to increase the height doubles it.

For example, you're trying to affect a 30' ladder and you've only got a 2 yard radius Area Effect, so about 18 feet of ladder is still outside. This remaining portion has a Size Modifier of +3, so it gets that as a bonus to resist.

Special Enhancements

• Large Objects: Your ability works better than normal on large inanimate objects. This works just like Area Effect, but it's only useful for reducing the resistance of a single large object. This may be combined with Area Effect, in which case they work together for affecting a single large object or the Area Effect can work alone on multiple smaller targets. +30%/level.
• Negated Skill: The target loses up to the specified number of points in a particular Skill. If they don't know the Skill, this has no effect. +1%/Skill point lost.
• Skill: The target immediately gains knowledge of how to use a particular Skill. If they already know the Skill, then this only has an effect if the afflicted version is at a higher level. If combined with Cumulative, this adds to existing points in the Skill. +10%/Skill point.