I've been sealing many windows and doors since the Healthy Homes legislation has kicked off. Rental properties with gaps 3mm or larger around doors or windows need sorted out. There's some good stick-on draught strips available for wooden joinery made by Raven. Make sure to measure your gap from narrowest to widest to make sure the strip will cover it and clean the frame by rubbing a little meths onto the surface you're sticking onto. Aluminium joinery often needs the backseal replaced when it's shrunk or flattened out. If you need a hand or some advice, give me a call Jim 0210688932