you dont as it will sweat and create condensation and give you more trouble you use 1f slating felt or roofing paper which stops condensation build up if you are competant person and good with your hands remove tiles and measure each lathe before removing replace felt making sure to go under the old felt at least 100 mm on the upward slop if you are not competant get a roofing contractor in making sure to price around
craig, April 2011
