I'm going to replace the windows on my house, do I need a permit for that?

If you are simply taking out the olds windows and replacing them with windows of the same exact size and location, than no, a permit is not required. If you plan on taking out a 3 foot wide window and replacing that with a 6 foot wide double window, then yes a permit would be required because you are making structural changes. The new wider opening has to be properly framed out with the correct size header in order to support the loads of the larger opening. Please complete a Building Permit application describing in detail the work to be done, including window and header dimensions.