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:
• Why is my roof sheathing sagging between the trusses?
• Why is granule loss a problem for an asphalt shingle roof?
• What are the mistakes to avoid when doing attic improvements?
• What causes roof shingles to curl up at corners?
• What causes shingles to buckle along a line on the roof?
• What causes leaks at a fake roof dormer?
• What causes a sagging roof ridge line?
• What causes bubble-like blisters in a built-up and gravel roof?
• Why does it cost so much more to replace a steep roof than a low slope roof?
• What is "ponding" on a flat roof?
• Is an attic required to have a light by the building code?
• How can I inspect my roof for hurricane damage?
• Why is premature curl of roof shingles a problem?
• How can I tell if a roof has more than one layer of shingles?
• What are the common problems with attic insulation?
• What is the life expectancy of an asbestos cement shingle roof?
• What's the average lifespan of a roof?
• Why is it a mistake to replace a roof and not replace its flashings?
• Why is there no attic access hatch in the house?
• What is the building code requirement for an attic access hatch, scuttle, or door?
• Does a roof with multiple layers of shingles last longer?
• What can I do to prevent roof leaks?
• Are roof trusses better than roof rafters (stick framing)?
• Why is a popped nail in a shingle roof a problem? How do I fix it?
• What are the most common problems with wood roof trusses?
• What causes a lump or dip in the roof?
• If my roof is not leaking, why does it need to be replaced?
• How can I be sure my roofing contractor got a permit?
• How many layers of roofing are allowed on a home?
• What are the dark lines running parallel to shingles on my roof?
• Can metal roofing be used on a low slope/pitch roof?
• How can I make my roof last longer?
• What are the warning signs of a dangerous attic pull-down ladder?
• How can I find out the age of a roof?
• Should I buy a house that needs a new roof?
• Should I buy a house with an old roof?
• What are those metal boxes on the roof?
• What does "lack of tab adhesion" in an asphalt shingle roof mean?
• Why do roof edges start leaking?
• Why do my dormer windows leak?
• Do home inspectors go on the roof? Do they get in the attic?
• Should I put gutters on the house?
• How much of a roof truss can I cut out to make a storage platform in the attic?
• What's the difference between an "architectural" and a regular shingle roof?
• What does a home inspector look for when examining a roof?
• Do stains on the ceiling mean the roof is leaking?
• How can I tell if the house needs a new roof?
• Why does my homeowner's insurance want a roof inspection?
• What are the hazards to avoid when going into an attic?
Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.
Diagram - CodeCheck