What was your OG and your FG? How long did you wait before drinking?
It's an ale yeast, which means that fermentation temperature should be more between 16° C and 24° C. It also says 'California Ale' yeast, which should give it a better resistance against relatively high temperatures, because fermenting in California will most of the time be at higher temperatures.
If your basement is really a constant 13° C, then you better start using lager yeast.
My process for simple beers up to 6.6% ABV: 2 weeks fermentation, two weeks conditioning after bottling (for CO2), two weeks lagering. Your basement should be fine for lagering. Conditioning after bottling should be done in a relatively warm chamber. I normally go for 18° C, as that seems to be the base temperature in my home on the floor and outside heated areas.
If you want to brew an imperial stout: 2 weeks fermentation, rack it into another vessel with as small as possible headspace (I always add a couple of grams of sugar so that the fermentation pushes out as much oxygen as possible), let it rest four weeks, bottle, two weeks conditioning, then lager. After that you could taste one bottle. However, with big beers you can be be sure they get better after a couple of months and longer, so don't drink it all at once.
After fermenting your imperial stout, brew again a lighter beer, to fill the time waiting for the imperial stout ;-)