I worked at a place that seemed to be this way, it wasn't a startup though but a fairly small company. The offices were in an older office park and kind of ding

I worked at a place that seemed to be this way, it wasn't a startup though but a fairly small company. The offices were in an older office park and kind of dingy and I think thats why. When you have certain types of insulation, etc and the building isn't well kept up I think it tends to harbor mold, etc, I know I would always smell something (like mold) when I walked in one of the doors. By contrast the building I work in now is actually quite old, but it has wooden ceilings, no layers of insulation, etc and is fairly open and airy. I think it really can be caused by the building and then of course the lack of space and number of people also contribute. I work in SF now too but the "sick office" place was in Phoenix, there they had to run the AC all day for 7-8 months out of the year, which I think is part of the problem, here the climate is milder and I would think you can figure out creative ways to use the ventilation system to get more fresh air into the building