HUH - 35 C? It gets -35 F here and I asked the same question...I was told to keep a heat lamp on in the coop if the weather got to below freezing although some don't even do that and their birds are just fine. Our weather here has been down to 24 at night and it stayed above 40 in our insulated coop just with the hens heat alone...I didn't even turn on the heat lamp.
Make sure that your coop is draft free and you could add a heat emitter for warmth. It doesn't produce any light. The best price I found was from www.naturallighting.com $24.95 for a 250 watt emitter.
You could plug it into a thermostatically controlled outlet so that it turns on at 35 degrees F and off at 40. The best price for an inexpensive thermostat was at www.americanlivestocksupply.com about $12
Hope this info helps
i'm in southeastern ontario, near ottawa, it's been -14 so far, we aren't adding heat, just a 100w bulb for lighting and to keep the water from freezing. the chickens don't seem to care about the cold, they go outside, and don't hang around the light bulb.
i'd add shavings, and draft proof as best you can.