There's not much the builder can do but there are things you can do...
Condensation happens when warm wet air meets a cold surface - the air cools and is unable to hold as much water as it could when warm.
And you say "especially when we bring the cars in wet."
The moisture on the car evaporates in the heat being given off from the engine and exhaust and the resulting wet air meets the cold windows and you get condensation - a perfectly natural physical reaction and to be expected in the winter months given the circumstances.
How do you stop it?
Let the car cool down before putting it away. Don't put the car away wet. Leave the garage door open for a while to let any warm air out. Provide some ventilation if you can - do the windows open? Buy, borrow or rent a dehumidifier and get rid of any lingering moisture in the garage.
This is not a matter for the builder - just the modification of your current routine. It will not be much of an issue in the warmer months.
Good luck...
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There will be residual moisture that you can't see already lurking in the fabric of the garage. The moisture doesn't go away when you can't see any condensation - it's still there.
An inexpensive humidity meter from a garden centre will let you see the hidden depth of your problem.
Cut the builder some slack - he is NOT responsible for your condensation or the solution to it - but you are - you solve it by modifying your behaviour.
Condensation may also be forming unseen in the hidden nooks and crannies of the body of your motor car(s) which may lead to corrosion in the longer term.
Continuing good luck...
Peccavi, April 2013
