Siegfried is sent along less because the place will eventually house an eyrie and more because Riftwatch is short of hands. Even the non-engineering members of research are pressed into cleaning and heavy lifting, Siegfried included. He doesn't refuse or complain, but it's clear it's not something he's had a lot of experience with. He's not fast at it, for one thing. For another, Astrid is in clear ear shot the time he slams his thumb with a hammer and says sweet Andraste's tits rather louder than one might expect after dropping the tool to the floor.