As per the Sept FAQ (found in the webstore cost of free)
If you target a unit in a building or an empty building with a multiple launcher, how do you work out how many templates hit the building?
When firing a multiple launcher against a unit in a building (or an empty building), measure the 6″ for additional targets from the building itself. Note that only one of the rockets can hit each building, even if it includes multiple enemy units on different floors. Then resolve a normal indirect fire heavy mortar shot on each target. You cannot fire if any potential target building includes any friendly units.
When I fire a multiple launcher, do I have to hit the target unit in order to then measure range to other targets?
When firing a multiple launcher at a unit, you put the template on the unit as usual and then measure 6″ from the edge of it for any other units. You don’t have to hit the first unit to be able to target the others, you get to roll a die for each target.
HE weapons can target empty buildings (to demolish them). However, with multiple launchers, because they also can hit anything within 6″ of their primary target, they can target an empty building and then be able to hit anything within 6″ of that building. Is that correct?
Yes, you can target an empty building with a multiple rocket launcher, just as you would target a unit inside the building. Measure the range to other potential targets from any point of the floor in the target building where the rocket explodes (see rules for indirect fire against buildings). This might indeed make multiple launchers slightly more effective when fired this way.
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