To replace the joist you need to measure the entire length.
Fixing flat roof joists to wall plate.
Fixing joists to wall plate with face fix joist hanger face fixed and face fixed wrap over hangers can also have the flanges through which the fixing holes are drilled either showing either side of the hanger or concealed where they are bent over to be only visible when there is no joist in the hanger.
Install steel joist hangers at each mark.
However replacing the entire joist gives the home much better structural integrity.
Clean the hole out thoroughly of all dust and debris either with a pump or hoover.
Mark the installation location for each joist along the wall plate.
Step 2 measure roof joist.
This article describes explains the directions of forces in roof structures illustrating downwards force horizontal thrust and the causes of rafter sags rafters that disconnect from the ridge or top plate and why a sagging roof pushes the building walls outwards at the wall top.
Mark off a joist every 16 inches along the length of the wall with the last joist lining up against the opposite verge wall.
We include photographs of collapsing wood framed roofs and photo sequences.
A cavity closer should be provided to the top of the walls to prevent fire spread and to stop damp air entering the roof space.
Fixing joists to an existing wall.
Fixings used to connect the roof structure to the wall plate should be specified according to the roof construction and exposure of the site.
Keep in mind that the joist extends through the wall.
Where a new flat roof abuts an existing external wall the joists can be hung on metal joist hangers which are fixed to a horizontal timber plate wall bolted to the wall.
To fix the joists and rafters down on to the wall plates they should be toe or skew nailed to the top plate like below.
Set out the ceiling joists onto the wall plates the ceiling joists are installed before the rafters as they will stop the roof spreading and also give something for you to lay planks across to stand on when building the roof.
Same size timber as your joists preferably i d look at fitting a 6x2 or whatever size joists are being used timber to the wall using m12 threaded bars around 200mm long drilled through the timber and wall using a 14mm drill bit at 600mm centers.
Start at one end of the wall so that the first joist is flush with the walls which run parallel to the joists.
