In addition to standard insulation where insulating materials are put in the walls or ceiling, there are other things you can do to reduce the loss of heat or cool air (depending on the season). These are mostly temporary, inexpensive adjustments you can make that limit the air exchange around doors and windows.
There is often a gap around a door that allows air drafts to transfer heat in or out of a house. Weather stripping can be added to reduce the drafts. You can also put a towel or other easily moved object at the foot of the closed external doors.
Stores sell plastic sheeting that can be used to add an extra layer of insulation to windows or sliding glass doors.
Electrical sockets on external walls can also provide a way for air to flow. Using child socket protectors or special insulation cut-outs that fit behind the socket plates and around the sockets can help.
In the winter, try walking around the house, near the walls to find "cold spots" that could benefit from additional insulation.
Another quick and easy way to improve insulation during the hot months is to close the blinds, curtains or other window coverings during the day, especially during the hottest parts of the day and in rooms that aren't in use.
Caulking around windows and doors can help around those trouble spots.
Regular insulation can also shift and become thin in spots.
- EnergyPRZ on Attic & Spot Insulation
- How to Fix Thin Spots in Loose-Fill Attic Insulation on Dummies.com