Recently moved to Cape town SA from the ME and one of my biggest challenges is the temperature in our house. Unlike the Uk or americas the houses here are not heated so we have a fairly cold room most days. I'd say between 10*C to 14*C.
It is impossible for butter to get soft so I cut it into little bits and place in a zip lock bag under a hot water bottle (luke warm water filled in). This works ok for the baking bit. Where I am constantly struggling is with the buttercream. The butter tends to chill up while i am beating it and adding sugar making it fairly stiff to deal with. Again i have tried to over come this by placing my KA bowl in a bath of tepid water to maintain a spreadable consistency.
But when I start to spread the buttercream the thin layers are impossible to keep from hardening and smoothing the cake is near impossible.
Any of you have had a similar experience or have an idea that might help????

Maybe put a heater in the room that you are working in?

I used to work in a bakery that in Winter time it was so cold that everyone working there will work in their coats, scarfs and hats. (And it was still freezing).

When I was icing the cakes I would put the buttercream in the mixer to whip up and after it would start to harden because of the temperature. I then started putting the bowl in front of the heater and would turn it occasionally and that helped alot. But it was a pain to have to take it away from the heater and to rotate the bowl when it got too hot.

Humm... well you could always try a blow torch! And no I'm not kidding. If you have a metal bowl that your whipping your butter cream in then you can do this. I once forgot that I needed butter at room temp and added it to my eggs. yikes I was so happy to have a blow torch to save the day! if you dont like that idea then maybe try this link for buttercream comes out great for me!

http://www.youtube.com/watch?v=GfRXxORYXsY&feature=related

(She says Swiss but for some reason I'm stuck on the thought that it is Italian, oh well still turns out great!) Hope that this will help!

Can you let it sit out overnight. While it won't get totally soft where you are, it could be soft enough and not cold enough to work.

And I have read where some people use a blow torch to heat up the bowl. I would think that it would heat unevenly.

And I have had success warming it up in the microwave in 3-4 second spurts. I use a digital thermometer to make sure I don't go over the heat I want. In a pinch it works, but there is a very fine line between just right and too much. So let it sit for about 30 seconds in between the 3-4 second spurts or you will get it too warm.

BTW, room temp is considered any where between 68-70F, but I have had success with it as low as 65 F. HTH