There was a project of a ship made from ice&papper. This is quite workable solution. You may want to use hay, wool or some synthetic threads instead of papper for even better results. So yes ice provide more than enough bouyancy to keep small house afloat.
Solid ice block would have only 1/10 above the water, but you don't need to make it solid. Metal wich is most current ships are made from is six times havier than water and it is absolutely not a problem. Since ice is lighter than water you may have quite a thiсk walls for your waterhome.
The only thing you should think about - is a form. Sphere is not approprite. From stability point of view form of the ship is not defined by the material it is made from. So keep to traditional "reverse trapeze" or "half-elipse" hull shapes.
Ice is also a good boatbildiong material since it can "heal" itself: sea water in cracks quickly loose salts consentration and resulting freshwater frezes in a crack and closes it.
The only disadvantige is melting. And even on high lattitudes melting is a problem, since ice is floating in antifreeze. So you would need some active cooling system inside ice hull, to keep temperature of the ice bellow -4 C all the time. Luckely ice has quite a low termal conductivty, but much higher than water and high termal capacity. So it's not that hard to do it, but you will need quite a tight grid of coolant tubes inside ice hull.
You will need to remove about (it greatly depends on hull shape) several watts (5-20) of heat per cubiс meter. Since "carring capacity" of solid ice is about 50kg per cubiс meter (100kg is too much) for, say, "standart cottage" (up to 20t) this means 400 cubic meters of ice (20x20x1 meters ice plate) and 2 kWt of cooling power - about 3-4 kWt of energy consumption. But if we shape that ice in a boat-like hull it would be able carry up to 100t.
For 100 000 t aircarrier-like home (about thousands of people) you will need about 4MWt power to cool it reliably. It's not that much. Boeing 878 produces 1MWt of power for all it's electrical needs during flight. This aircarrier-like home would consume for cooling 10 000 L of disel fuel (less than a tank car) per day, few litters per person . Less than 300$ per person per month.