Bird houses should face away from the prevailing winds to prevent rain from blowing in. You might want your wren house to point east, since most bad weather in your area comes from the west. Wrens seem to prefer houses hanging from a tree limb. They will be safer from predators than if you mount it in a fixed position. Courtship and nest building begins around April 10th and may continue into early July.
Wrens often have two broods per season.
House Wrens are more likely to nest in your birdhouse than Carolina Wrens since you are at the northern edge of the Carolina Wren's range. Place the house 6 to 10 feet above ground. Both Wrens prefer dense shrubs, vines and woodland edges. If you have a well-manicured lawn with no place to hide, you will not have much success in attracting Wrens. Wrens nest in tree holes, so leave dead trees standing to attract Wrens and other cavity nesting species.