alternative roof vents
Which means if you install a vent pipe 10 feet or more away from the skylight then you can have a shorter vent pipe extension above roofline. I assume this is about a vent pipe from the kitchen outlet. As long as you do a proper and sound job that doesn't cause some silly damage, who's going to know if you only have a one foot vent pipe extension? I installed an additional downpipe in response to a poorly executed re-plumbing of my house (before i bought it.) I've joined the new downpipe to the only available connection the kitchen outlet, so now the rain downpipe acts as a vent pipe. I haven't had any problems.
If this is about vent pipe from water closet instead, then you probably want a long vent pipe extension to avoid the aromas.