Most people blame the windows. Windows are usually not the main problem.
A draught is air moving, and air moves because of a pressure difference. Understanding where that pressure comes from tells you where to spend money - and it is rarely where the cold feels worst.
The stack effect
A heated house behaves like a chimney.
Warm air is lighter than cold air, so it rises and pushes out through any opening near the top of the building - attic hatch, light fixtures, plumbing stacks, gaps at the top of interior walls. As it leaves, it creates a slight negative pressure lower down, and the house pulls replacement air in through the lowest openings it can find.
That is the crucial part. Air leaving the top is what forces air in at the bottom. They are one system, not two problems.
So the cold draught you feel at ankle level in the living room was very often caused by warm air escaping through your attic. Sealing only the draught you can feel, at the bottom, does not remove the force pulling it in.
In winter this runs harder, because the bigger the temperature difference the stronger the pressure. Alberta gives it plenty to work with.
Wind makes it worse
On top of the stack effect, wind pressurises the windward side of the house and depressurises the leeward side, pushing air straight through. In exposed or windy parts of the province that can dominate on a bad day.
This is why draughts come and go with the weather rather than tracking the thermometer.
Where the air actually gets in and out
In a typical older Alberta house, ranked roughly by how much they matter:
- The attic hatch and ceiling penetrations - the top of the stack. Small openings, constant flow.
- The rim joist - the band on top of the foundation, running the whole perimeter. Usually filled with a batt that filters air rather than stopping it. This is where a large share of replacement air enters.
- Where additions meet the original house - junctions built at different times by different trades.
- Service penetrations - anywhere a pipe, wire, vent or gas line passes through the envelope.
- Around window and door frames - the gap behind the trim, not the window itself.
- The windows themselves - genuinely last on this list for most houses.
The order to fix it in
Seal the top first. Attic penetrations and the hatch. This reduces the pressure driving the whole system.
Then seal the bottom. The rim joist and any foundation penetrations. Now you are closing the intake.
Then insulate. Depth is worth adding once the air is controlled. Adding it first means you are insulating around a moving air stream.
Windows last, if at all. Replacing windows is the most expensive item on the list and usually fixes the smallest share of the problem. If the budget is limited, sealing will give you far more comfort per dollar.
Why sealing beats adding insulation
Insulation is rated in still air. It slows heat conducting through a material. It does nothing about air moving around it.
You can add depth indefinitely and not fix a draught, because the air is not going through the insulation - it is going past it. Spray foam is used in these situations specifically because it seals and insulates in the same pass, filling irregular gaps that a batt cannot be cut to match.
Want someone to find where yours is actually leaking? Get a quote.
Related: cold floors - high heating bills - rim joist insulation - attic spray foam