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Why is there diagonal bracing at the roof rafters in the attic?
Wednesday, November 27, 2019
We often see this detail in older homes built before manufactured roof trusses became the standard for residential construction. It was a way to provide additional rafter support, and also some resistance to lateral movement, for longer-span roof rafter framing. The beam running perpendicular to the rafters at approximately the midpoint between the top plate of the wall and the ridge board is called a “purlin," and the diagonal braces are “kickers.” The bottom of the kicker bears on an interior wall or beam below.
Because this is an old-fashioned construction style, sometimes homebuyers that see purlins in the attic think that the bracing has been added as a repair because the rafters were sagging or due to some other structural problem. But, if the purlins appear to be the same age as the rafters and professionally installed, it’s just because that was the way things were done back then.
The only issue to consider when there are purlins in the attic is that there are interior walls directly below the base of the kickers that provide structural support through the kicker/purlin configuration to the rafters. If you remove any of those walls, the roof won't fail, but will likely sag over time. Some ceiling joists may also bear on those walls. So proceed carefully, and with the advice of a contractor or engineer, if you plan on removing any interior walls to “open up” the floor plan.
This purlin is only one of several types of structural members that are perpendicular to the roof rafters and also called purlins. See our blog post What are roofing purlins and battens? for more on this.
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To learn more about roofs and attics, see these other blog posts:
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