To which extent can outside walls make a room cold?
An association of insulation suppliers claims


More than 40% of all the heat lost in an average home is through the loft space and walls
Up to 45% of heat is lost through uninsulated solid walls
More heat is lost through walls than any other route – approximately 33% in an uninsulated home


Obviously, we need to take into account that they are not a disinterested party but this does support the idea that the more external walls a room has, the more heat it will lose to the outside in cold weather.



The solutions, unsurprisingly are


insulate the walls (and ceiling, and floors too)
install heating.


Insulation depends on the type of wall construction - which differs markedly between the USA and UK and other places. 



See http://www.engineeringtoolbox.com/heat-loss-transmission-d_748.html