I have absolutely no water leaks but the basement is humid due to seepage through the walls.

Seepage can either be liquid or gaseous.

Assume it's water vapour. You have that as moisture-laden air moves from areas of high pressure to low pressure. Furthermore, basements are conducive to condensation, as the warmer air of the basement touches the cold usually concrete foundation walls and floors. If you condense that water behind an impermeable barrier, you will need drains to reduce mould growth.

Insulating the walls with spray foam or foam board will eliminate condensation. (But you will still get condensation and water vapour entry through the floors.) However, the problem with the foam is that Code requires it be covered with a fire protective barrier, typically drywall. Alternatively, you may be allowed to spray on an intumescent coating.

Depending on your climate and plans for the home, it can be cheaper to run the dehumidifier(s) than properly insulate the walls. Even with finished basements with three inches of closed cell spray foam on the walls, I have found it necessary to use mechanical dehumidification to keep the relative humidify under 50%.

This post was edited by worthy on Wed, Jul 9, 14 at 11:27