Mansard

Steep 21/12 faces on all four sides rising to a curb, then a shallow upper hip over the deck — framed as a portal bent with knee walls and a collar tie.

What it is

A hip/gambrel hybrid: steep lower faces from the wall line up to a break rectangle set in by a per-side offset (3-8ft, never past a quarter of the span), a curb trim around the full break perimeter, then a shallow upper hip. The bent is a portal frame — bottom chord, two knee-wall racks at the break line, a collar tie across them, and the shallow upper triangle hanging off the collar.

Also called: french roof · curb roof · steep lower slope · habitable attic

See it
Mansard
🔒ridgelinepostframe.com/project/mansar499
Equipment Storage
Framing · on schedule
Mansard corner: 21/12 steep face lapping the fascia, curb trim around the break, shallow deck above, hip cap running the full diagonal to the fascia-lap corner. Sample data — no customer information appears here.
How it works
  1. 1Everything riding a mansard face is placed by slope run and offset along the face NORMAL, never by a vertical lift.
  2. 2Steep rafters are seated so their TOP face lies ON the face plane, depth growing inward.
  3. 3Purlin rows sit on all four steep faces plus the four upper deck faces, each trapezoid-clipped by its face's plan inset so nothing overshoots into the corner hips.
  4. 4Lower and upper hip rafters run eave corner to break corner and break corner to deck ridge end, so every corner purlin bears on a member.
  5. 5The steep face runs a fascia-height BELOW the wall top so the panel laps over the eave trim, and the steel includes the fascia-lap corners so the hip cap does not die in a cut-out of exposed framing.
  6. 6Rails: upper deck clamps to 1-4/12 with the roofing system's own slope floor enforced against it; member sizes come from an IRC R802 span class; habitable-attic headroom follows IRC R305.1.
Why we built it

On a 60-degree lower face, lifting a member straight up buys almost none of the clearance it looks like it should and shoves it sideways out of its own plane — which is how the 2x10 steep rafters ended up driven through the steel and out past the wall at the eave. Members on the steep face are seated perpendicular to that face instead. Corner purlins used to die in mid-air where the two faces meet; hip rafters now carry them, so the corner is framed rather than implied.

The problem
  • Steep-face members placed by vertical offset poking through the steel.
  • Corner purlins with nothing to bear on.
  • A near-flat upper deck roofed with a product not rated for its slope.
Sound familiar?
What you get
Curb trim, hip caps and the two-tier panel package all land on the order.
The deck's drainage is enforced against the chosen roofing system.
The bent is framed with real member sizes rather than an idealised truss.

See it on your own jobs

Twenty minutes, your numbers, no slide deck. We’ll build one of your real buildings in front of you and send you the estimate link at the end — yours to keep either way.

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