Wasps prey primarily on other insects and are generally a beneficial insect. They should only be considered an annoyance or potential danger when they nest near or inside your home. In most cases, once wasps find their way inside your home to build nests it's wise to call a professional to exterminate them. Especially if they are inside of vents or walls, it's important not to try and eradicate them without the help of a professional. If a single nest is completely exposed, however, it is possible to carefully destroy and dispose of the nest with a little planning and effort.
Determine the exact location of the wasp nest. Follow the wasps, (in the morning is a good time to spot them coming and going from the nest) and be sure you can see the entire nest.
Prepare the loft for extermination. Get any children and animals out of the house. Seal the room where you'll be exterminating the nest by closing the door and covering any gaps where wasps could escape with tape. Cover anything in the room that you don't want damaged with plastic tarps, old towels or throws that can be washed off afterward.
Cover your entire body in several layers of shirts and trousers. Wear a bandanna around your neck and cover your face and head with a veil and hat. Seal off the veil to the clothing with duct tape and also duct tape the shirts to gloves, the trousers to boots, and the shirt to your jeans. Have a buddy assist you and check for any gaps in your outfit.
Prepare the chemical spray (Raid Wasp & Hornet Killer 33 is a good one and sprays up to 22 feet), and stand a safe distance from the nest (not underneath it) and fire directly at the nest. The spray will create a foam around the nest. Spray completely, and hit wasps directly with the spray as you see them exit. Leave the room once the nest is completely saturated and no movement is detected. Wait at least 24 hours in order to be sure all the wasps are dead before removing the nest. Be sure to cover yourself again before approaching the nest to throw it away. Carefully, throw it into a large thick plastic bag (garbage bag). Tie it off quickly and take it outdoors.
Observe your loft for several days after disposal to ensure that no other nests are present. If you detect any other visible nests follow the same procedures. If they are where you can't see them, hire a professional exterminator. With proper extermination and removal your home should remain wasp free.
Follow the directions on the back of the wasp spray and be sure to fully cover and protect not only yourself, but anything in your home you don't want damaged. Remove children and animals from the area completely until the nest is fully disposed.