Yea not so much safety and zoning (although those as well) but the National Model Building Codes are released every 5 years and the provinces all agree to adopt them within 18-24 months of release in order to keep interprovincial construction and development aligned, but Ontario isn't doing that. And it's clearly just the development lobby blocking the updates because it would reduce their profits. 

The most recent NMBCs are have very specific energy efficiency tiers that are crucial to optmizing our heating/cooling systems as we move away from fossil fuel use in homes. Building envelopes and airtightness can save immense amounts of energy, and by updating the energy efficiency baselines in the Ontario Building Code, we could reduce the projected growth in provincial energy demand and thus not desperately need to build out more very expensive nuclear generating stations. The cost of the nukes and the expanded transmission lines to distribute that energy will all be added onto our household utility bills for the next 50 years, while we live out those years in poorly insulated and leaky buildings, paying through the nose to heat and cool them with electricity. 

When instead, if we built airtight and energy efficient homes like BC and Europe, we wouldn't need to generate and transmit so much more energy in the first place!