Building permits are required for most significant construction or renovation projects around the home. They are not required for things that would be considered ordinary repairs or maintenance. For example, replacing the roof on the house would require a building permit, while replacing a small area of damaged or defective shingles may not. Having proper permits in place and inspections of the work performed provides assurance in the future that work was done in a safe and legal manner. This also provides a valuable record of the building's history for future owners.
If you have questions regarding a specific project you may be planning contact the Building Department early in the planning process to find out if you need a permit.