Wall Plate Flat Roof Joist Layout

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.

Wall plate flat roof joist layout.

The mark on the double top plate is where the joist will sit and the mark on the top plate is where the stud will fall. Wall sheathing as required use single i joist for loads up to 2000 plf double i joists for loads up to 4000 plf filler block not required. Start at one end of the wall so that the first joist is flush with the walls which run parallel to the joists. Begin wall assembly by planning the layout of the new wall.

Wall plates are to be fixed to masonery using hardened nails 4mm in diameter x 75mm long or 50mm long wood screws if fixed into timber. Mark both sides of the layout stick every 2 ft. We include photographs of collapsing wood framed roofs and photo sequences. Mark the installation location for each joist along the wall plate.

The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. All nails shown in the details above are assumed to be common nails unless otherwise noted. If the joists are parallel to the new wall adjust the layout so that the wall is directly under a joist. Their design span the exact length from face to face of the supports is 15 feet 1 inch see illustration figure 1 figure 1 when sizing joists use the clear span the length from support to support not the full length of the joist.

Attach i joist to top plate using 8d nails at 6 o c. Roof sag or roof collapse forces. Mark off a joist every 16 inches along the length of the wall with the last joist lining up against the opposite verge wall. 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.

Use a chalk line to mark where you want to place the new wall along the floor. Run a stud finder along the ceiling to locate the joists. 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. Using the layout stick place the edge half on the end of the wall plates.

Install steel joist hangers at each mark. By fixing the joists to the wall plates and securing the wall plate with vertical holding down straps at least 1m long and 30mm x 2 5mm in cross section at 2 0m centres. Lay out every stud in every wall but keep in mind that simplicity and clarity are the key.