[fsckboy]

>sauna is often built first because it serves as a place to live while you're building the house

wouldn't a kitchen accomplish that goal better?

[wolfpack_mick]

Due to lack of running water in those times (and still in many cottages) cooking is done above a fire, water is brought from the lake. A kitchen won't serve you well if you're just trying to get through a long winter of -30c.

[oldestofsports]

The sauna provides heating.

[vixen99]

Average yearly temperature in Finland is reported as 6.5 Celsius