As surprising as it may sound, it is "normal" to observe ants of different species inside the house in the spring and at the beginning of the summer. They are looking for food sources with the least amount of effort, and a house they can enter (through cracks, holes in screens, etc.) is the ideal place. As the weather grows warmer and more food sources appear outside, they are less frequently seen inside.
The best thing to do (and this is easier said than done) is to fill the spaces through which they enter (cracks in the foundation, holes in screens, gaps in door and window frames, etc.)
You can tell whether ants are living in your house by their presence (activity) in wintertime and by the presence of winged ants (the ants that reproduce).
That being said, you should make sure the ants in your house are indeed carpenter ants. There are more than 100 species of ants in Québec, only five of which are carpenter ants. Carpenter ants cannot live in healthy, undamaged wood – wood that is free of humidity. Despite their reputation, ants of this genus (Camponotus) are often the symptoms of a humidity problem rather than the problem itself.
No matter the species you’re dealing with, to fix the problem, you must destroy the queen. Finally, if you decide to call an exterminator, be sure the exterminator is a member of the Association Québécoise de la Gestion parasitaire (AQGP).
To learn more about ants, consult the fact sheets on ants in the Insects and other arthropods section.