Squaring and plumbing is a very important step. So make sure your YZY granny flat is square and plumb before putting your rafters and ceiling boards.
Take a long quality Spirit Level and check if all walls and the corners are plumb. Determine which walls need to be pushed and which way to make them plumb.
If you need to push some walls, use a pushing rod. Take a piece of 90 x 45 mm pine board, use another block of timber in between the walls and the pushing rod. Counter the corner that needs to be pushed and push down on it whichever way it has to go plumb. Check and recheck all walls until they all plumb and square.
If you miss this step, you might have trouble when you comes time to put rafters and ceiling boards on. So, it is very important to make sure your walls are all square and plumb.
Experts Tip: “If you have any trouble with pushing or banging corners with a rubber mallet, get your self a hardwood block and bang the end grains. And just work away around the building, get all corners nice and square to start with.”
Now as your building is square and plumb, you can put your rafters in. Roof rafters will lock the building into place and the whole building will become structurally sound and solid. All granny flat building steps can be found on Builders Guide page.