The preferred method is to take each wall as a separate section. Say your first wall is 4.8m, you will need 1x 2m rail and 1x 3m rail leaving .2m of offcut.

When measuring the next wall and it's, say 5.2m, you can either use the same configuration as before using the .2m offcut or to minimize the number of joins in the rail, use 2x 3m and leave yourself with an offcut measuring .8m to use up elsewhere. As you measure each wall, keep a note of the offcut size so you can use it where appropriate. With shorter rails you will obviously need at least two fixings available per rail. We offer this service for free so if you provide your measurements then we can work out the best way to do it for you, measurements can be emailed to; info@picturehangingsystems.com.au or you can of course call us on 1300 88 36 45.