Hold up to the rafter a scrap piece of 2 by 4 lumber a few inches longer than the planned knee wall height with its base on the floor.
Roof support knee wall.
This article describes and illustrates the different types of support that prevents roof sagging and wall bulging at buildings including definitions of collar ties rafter ties and structural ridge beams.
Purlins as shown in sample photos below are installed for rafter support.
You can see the image below for an example of a knee wall.
Some of these can support the roof and prevent ridge sagging and wall spreading.
Check that the 2 by 4 is plumb with a spirit level.
In most instances they are no taller than 3 feet but some builders may custom fit them according to the roof s shape and size.
Unlike other kinds of knee walls this kind of wall extends all the way to the rafters but because of the slope of the roof it is shorter than a full height wall.
Ching defines a knee wall as a short wall supporting rafters at some intermediate position along their length the knee wall provides support to rafters which therefore need not be large enough.
A knee wall is a short wall typically under three feet one metre in height used to support the rafters in timber roof construction.
Knee walls are short usually wooden walls installed around the sides of an attic where the rafters meet the floor.
An important notation is that the purlin bracing should be off of walls or beams as needed.
Homeowners cannot take chances with the structural integrity of their roofs.
In his book a visual dictionary of architecture francis d.
How to brace rafters in an attic.
The knee wall forms the wall of the attic room and it also creates an enclosed space under the eaves behind the wall.
Add craftsman brackets to your home even it s not craftsman style if it has overhanging exposed eaves.
The braces struts or kickers should be within every 4 and should not be at a greater than a 45 degree angle towards the roof slope lower side.