A-Frame, Mansard, Gambrel and Hip Roof Pitch Explained

Each roof type has its own characteristic pitch, and the Roof Pitch Calculator lets you turn any of them into a ratio, an angle, and rafter lengths, whether you are checking an A-frame’s steep slope or matching a hip to an existing roof. It is the quickest way to compare and work with the pitches of different roof shapes.

What pitch an A-frame roof is

An A-frame roof is one of the steepest roof forms, typically pitched around 45 to 60 degrees or more, which is roughly 12/12 to 20/12 or steeper as a ratio. The A-frame is defined by its steep sides that reach almost or all the way to the ground, forming the letter A, so the pitch is very steep by design, far steeper than a normal house roof. Some A-frames are even steeper, approaching 60 degrees or beyond, for the dramatic, tall triangular shape they are known for.

So the pitch of an A-frame roof is steep, usually a 45 to 60 degree angle, which sheds snow and rain superbly and gives the distinctive tall triangle. This is much steeper than the 4/12 to 8/12 of a typical house roof, reflecting that the A-frame roof is essentially the whole structure, walls and roof in one. If you are checking or designing an A-frame, the pitch in degrees guide and the calculator convert between the steep angle and the x/12 ratio.

Why A-frames are so steep

A-frames are so steep because the roof is the structure: the steep sides come right down to or near the ground and act as both walls and roof, so the pitch has to be steep enough to enclose a usable space beneath the triangle. The steep pitch also sheds snow and rain superbly, which is why A-frames are popular for cabins in snowy, mountainous areas, where the snow slides straight off the steep sides rather than loading the roof.

The steep A-frame pitch gives a tall, dramatic interior with high ceilings and a lofted upper level, and a striking exterior, at the cost of floor area lost to the sloping walls. So the steepness is both structural and functional: it makes the roof-walls enclose space, sheds snow, and creates the A-frame’s character. The best roof pitch for snow guide covers why steep roofs shed snow so well, which is a large part of the A-frame’s appeal in mountain and cabin settings.

Building an A-frame roof

An A-frame roof is built as a series of steep rafter pairs (or A-frames) that rise from a low base, often near ground level, to a ridge at the top, forming the triangular cross-section. The rafters are long and steeply pitched, meeting at the ridge, with the floor and any loft hung within the triangle. Because the pitch is so steep, the rafters are long and the structure tall, and the build is more like framing a series of large triangles than a conventional roof.

The steep pitch means the rafter lengths are long for the span, and the calculator gives the rafter length from the span and the steep pitch, along with the angle for the cuts. Working on an A-frame is steep-roof work, so it needs the fall protection covered in the steep roof guide. The A-frame is a specialised form, but the pitch drives it as with any roof: set the steep pitch, and the rafter lengths, angles, and height follow from it.

Hip roof pitch

A hip roof slopes down on all four sides to the walls, with no gable ends, and its pitch is usually a conventional 4/12 to 8/12, similar to a gable roof. The hip pitch is the slope of the main roof faces, and it can be any normal roof pitch, chosen for drainage, looks, and the covering, just like a gable. So a hip roof is not defined by a special pitch but by its four-sided shape, and it typically uses the same moderate pitches as other house roofs.

The hips themselves, the sloping ridges where two roof faces meet at the corners, run at an angle related to the roof pitch, and the hip rafters are longer than the common rafters. A hip roof is more complex to frame than a gable because of these hip rafters and the way the faces meet, but its main pitch is a normal one. The standard roof pitch guide covers the usual house pitches that a hip roof shares. So expect a hip roof to sit in the 4/12 to 8/12 range like most house roofs.

Can a hip roof have different pitches

Yes, a hip roof can have different pitches on different faces, though it takes careful framing. Normally a hip roof has the same pitch on all four faces, which makes the hips run neatly at the corners, but it is possible to build a hip roof where, for example, the end faces are steeper than the side faces. This changes the geometry of the hip rafters and the way the faces meet, so it must be set out carefully, but it is done for design reasons or to fit an irregular plan.

Framing a hip roof with different pitches is more complex because the hip line is no longer a simple diagonal, and the rafter lengths and angles differ between the faces. It is a job for careful setting out or a designed roof, using the pitch of each face to work out its rafters. The calculator gives the rafter lengths and angles for each pitch, which helps when the faces differ. So while a uniform pitch is normal and simplest, a hip roof can have different pitches with the right framing.

Mansard roof pitch

A mansard roof has two different pitches on each side: a very steep lower slope and a much shallower upper slope, so it has a dual pitch by design. The steep lower slope is often around 70 degrees, nearly vertical, to create full-height rooms in the roof space, while the shallow upper slope, sometimes almost flat, caps the roof out of sight from the ground. So a mansard’s defining feature is exactly this pair of pitches, steep below and shallow above, on all sides.

This dual-pitch shape maximises the usable space within the roof, which is why the mansard is used to gain rooms in the roof, historically to add a floor within the roof line. The steep lower slope is the visible, characterful part, often with dormer windows, and the shallow upper slope is hidden. So when asked what pitch a mansard roof is, the answer is two pitches: a steep lower one (around 70 degrees) and a shallow upper one. The steep roof pitch guide covers the steep lower slope.

Gambrel roof pitch

A gambrel roof, the classic barn roof, also has two pitches on each of its two sides: a steep lower slope and a shallower upper slope, meeting at a mid-slope break. Like the mansard, this dual pitch maximises the space in the roof, giving the tall, roomy loft of a barn or a gambrel-roofed house. The lower slope is steep, often around 60 to 70 degrees, and the upper slope shallower, around 30 degrees, though the exact pitches vary with the design.

The difference from a mansard is that a gambrel has gable ends (it slopes on two sides, like a gable), while a mansard slopes on all four sides. But both share the steep-lower, shallow-upper dual pitch that opens up the roof space. So a gambrel roof, like a mansard, is defined by its two pitches per side, chosen to give headroom in the loft. The gambrel is common on barns, and gambrel-roofed houses borrow the roomy loft. Each slope’s pitch can be worked out and cut using the calculator.

What a dual-pitch roof is

A dual-pitch roof is any roof with two different pitches, and it covers several forms. The simplest sense is a roof with two slopes at different angles, such as a mansard or gambrel that changes pitch partway up each side. It can also mean a roof where different parts have different pitches, or a building where two roofs of different pitches meet. So dual-pitch (or dual-pitched) is a general term for a roof that is not a single uniform slope but has two pitches, whether on one side or across the building.

The mansard and gambrel are the classic dual-pitch roofs, each with a steep lower and shallow upper slope. But the term also covers a house where, say, a lower extension roof has a different pitch from the main roof. The common thread is two pitches rather than one. Understanding a roof as dual-pitch helps when working out the rafters, since each pitch is calculated separately, using the calculator for each slope. So a dual-pitch roof is simply one with two distinct pitches, in one of these forms.

Double-pitched roofs

A double-pitched roof usually means the same as a dual-pitched roof: a roof with two pitches. The most common double-pitched forms are the mansard and gambrel, with their steep-lower, shallow-upper slopes, but a simple gable roof is also sometimes loosely called double-pitched because it has two slopes (though both at the same pitch). So the term can mean either two different pitches (mansard, gambrel) or simply two slopes (a gable), depending on how it is used.

To build a double-pitched roof in the mansard or gambrel sense, you frame each pitch separately: the steep lower rafters and the shallow upper rafters, meeting at the mid-slope break, with the pitches chosen to give the headroom and shape wanted. Each slope’s rafters are worked out from its own pitch, using the calculator. So a double-pitched roof, in the sense of two different pitches, is framed as two sets of rafters at the two pitches, joined at the break, giving the roomy roof space these shapes are known for.

Can you mix roof pitches

Yes, you can mix roof pitches on a building, and it is often done, but it needs thought to look right and drain properly. A building can have a main roof at one pitch and an extension or wing at another, or a porch or dormer at a different pitch. Mixing pitches is common where additions are built over time, and it can be deliberate for design effect. The key is that the different pitches meet cleanly, with proper flashing and drainage where they join.

That said, matching pitches usually looks more harmonious, so mixing is best done deliberately rather than by accident. Where a lower-pitched extension meets a steeper main roof, or vice versa, the junction must be detailed to shed water and look intentional. So you can mix roof pitches, and it is often necessary or desirable, but plan the junctions and consider the look. The next sections cover whether pitches have to match and how to join roofs of different pitches, which is the practical side of mixing them.

Do roof pitches have to match

Roof pitches do not have to match, but matching them often looks better and simplifies the junctions. On a single roof, the faces usually share one pitch for a clean look and neat hips or ridges, and an extension that matches the main roof pitch looks like part of the original building. But there is no rule that pitches must match, and mixing them is common and can be deliberate, as with a lower porch or a modern contrasting wing.

The reasons to match are appearance (a consistent pitch looks unified) and simplicity (matching pitches meet cleanly at ridges and hips). The reasons to differ are design effect, fitting an addition under a height limit, or practical constraints. So pitches do not have to match, but consider whether matching or contrasting suits the building, and detail any junction between different pitches well. Where you want an extension to blend in, matching the pitch is the way; where you want it to stand apart or fit a constraint, a different pitch is fine.

Joining two roofs of different pitches

Joining two roofs of different pitches, such as where an extension meets the main house, is done at a junction that must shed water and look right. Where the two roofs meet, the junction is often a valley (where two slopes meet in an internal angle) or a point where one roof abuts the other’s wall or slope. The different pitches mean the valley or junction line runs at an angle set by both pitches, so it must be set out carefully and flashed to keep water out.

Where a lower-pitched roof meets a steeper one, the junction is flashed and often formed as a valley or an abutment with a flashing into the higher roof or wall. The rafter lengths and the valley line come from the two pitches, which the calculator helps work out for each slope. So joining roofs of different pitches is a matter of setting out the junction from both pitches and detailing it to drain, which is skilled work best done carefully or by a roofer. Done well, roofs of different pitches join cleanly and stay watertight.

Framing a hip with different pitches

Framing a hip roof with different pitches on different faces, as noted earlier, changes the hip geometry and needs careful setting out. Normally the hip rafter runs at 45 degrees in plan because all faces share a pitch, but if the faces have different pitches, the hip line shifts off the 45 and the hip rafter’s length and angles change. Each face’s common rafters are set by its own pitch, and the hip rafter is worked out to suit both faces meeting at the corner.

This is advanced roof framing, usually set out with care or designed, using the pitch of each face to find the rafters and the hip line. The calculator gives the common rafter lengths and angles for each pitch, which is the starting point, and the hip rafter is derived from the geometry of the two faces. So a hip with different pitches is buildable but is a specialist job, needing the pitches of the faces and careful setting out of the hips. For most hip roofs, a uniform pitch keeps the framing simpler.

Gable, hip and pitch

Gable and hip roofs typically share the same range of pitches, a conventional 4/12 to 8/12, since both are common house roofs. The difference is the shape: a gable has two slopes and vertical gable ends, while a hip slopes on all four sides. The pitch of either is chosen for drainage, looks, and covering, not fixed by the shape, so a gable and a hip on similar houses often have similar pitches. The shape affects the framing and the look, but the pitch range is shared.

So whether a roof is a gable or a hip, its pitch is likely a normal house pitch, and the choice between gable and hip is about shape, cost, and appearance rather than pitch. A hip is more complex and uses more material for the same pitch, while a gable is simpler. The what is a pitched roof guide covers these roof shapes, and the standard pitch guide the usual pitches both use. So gable and hip differ in shape, not in the pitches they typically carry.

Roof types and pitch compared

Bringing the roof types together, the table shows the typical pitch of each.

So the pitch of a roof depends heavily on its type: the A-frame is very steep, gable and hip are moderate, and mansard and gambrel are dual-pitched with steep lower slopes. This is why knowing the roof type tells you roughly what pitch to expect, and why the calculator is handy for converting the various pitches to angles and rafter lengths. Each type’s pitch suits its purpose, from the A-frame’s snow-shedding steepness to the mansard’s space-making dual pitch.

Choosing a roof type and pitch

Choosing a roof type and its pitch depends on the space, look, climate, and cost you want. For a striking, snow-shedding cabin, an A-frame with its steep pitch suits. For a normal house, a gable or hip at 4/12 to 8/12 is standard. For maximum rooms in the roof, a mansard or gambrel with its dual pitch gives the space. For a snowy area, steeper pitches shed snow; for a mild area, shallower is fine. So the roof type and pitch go together, chosen for the building’s needs.

Once you have chosen, the pitch drives the build, giving the rafter lengths and angles from the calculator. Whether it is a steep A-frame, a moderate hip, or a dual-pitch gambrel, the pitch of each slope is what you calculate and cut to. The what roof pitch do I need guide helps choose the pitch, and the snow guide the climate side. So pick the roof type for the space and look, the pitch for drainage and climate, and build to the pitches the type calls for.

A-frame headroom and floor space

The steep A-frame pitch is a trade-off between dramatic height and usable floor area. Because the walls and roof are one steeply sloping surface, the full-height space is only in the centre of the building, and the floor area near the sloping walls has little headroom, so it is used for low storage, seating, or built-in furniture rather than standing space. The steeper the pitch, the taller the central ridge and the more the usable floor narrows toward the walls.

This is why A-frames often have a lofted upper level tucked into the upper triangle, making use of the height that the steep pitch creates. The ground floor keeps the tall central volume for living space, while the loft sits above the lower rooms. So the A-frame pitch shapes the whole interior: it gives soaring central ceilings and a loft, at the cost of floor area lost to the steep walls. Anyone planning an A-frame should picture the usable floor within the triangle, since the steep pitch that makes the shape also limits where you can stand.

Dormers and pitch

Dormers, the windowed projections that stick out of a roof slope, interact with the roof pitch in a way worth understanding. A dormer is set into the main slope and has its own small roof, which can be a flat, shed (mono-pitch), or gable roof of its own pitch. The steeper the main roof, the more room there is for a dormer and the more headroom it gains inside, which is why dormers are common on steep roofs and on the steep lower slopes of mansards.

The dormer’s own roof pitch is usually shallower than the main roof, especially a shed dormer that runs back at a low pitch to gain headroom, so a dormer is a small example of mixing pitches on one roof. Where the dormer meets the main slope, the junction is flashed and often forms small valleys, set out from both pitches. So dormers add usable, lit space within a pitched roof, with their own pitch chosen for headroom and drainage, and their junctions detailed like any meeting of two pitches. The steeper the main roof, the more a dormer can offer.

Valleys and pitch

Wherever two roof slopes meet in an internal angle, they form a valley, and the valley’s angle depends on the pitches of the two slopes. On a roof where both slopes share a pitch, the valley runs as a neat diagonal; where the two slopes differ in pitch, as when an extension of one pitch meets a main roof of another, the valley line skews and must be set out from both pitches. The valley carries the combined runoff of both slopes, so it is a concentrated drainage path that must be watertight.

Because a valley collects water from two slopes, it is a common leak point if the pitch is too shallow or the valley is poorly detailed, so valleys are lined with metal or a membrane and given enough fall to clear the flow. On lower-pitched roofs the valley works harder, since water moves more slowly, so the detailing matters more. So valleys are where pitch, geometry, and drainage come together: their line comes from the slopes’ pitches, and their lining and fall must handle the water those slopes shed into them. The calculator gives each slope’s pitch to set the valley out.

Mistakes to avoid

The common mistakes with roof types and pitches are these.

Avoiding these means treating each slope’s pitch separately, matching or mixing pitches deliberately, detailing junctions between different pitches, and respecting the steep pitch of an A-frame. Do that and roofs of any type and pitch combination work and look right.

Working out the pitches

Whatever the roof type, the roof pitch calculator works out each slope’s pitch, angle, and rafter lengths, whether it is a steep A-frame face, a moderate hip, or one slope of a dual-pitch mansard or gambrel. Enter the rise and run, or the pitch, and it gives the angle and rafter length, which you calculate separately for each pitch on a dual-pitch or mixed-pitch roof. This is exactly what you need when a roof has more than one pitch or you are matching a new roof to an existing one.

The connected guides cover the roof types and their pitches: what is a pitched roof for the shapes, standard roof pitch for gable and hip pitches, steep roof pitch for A-frames and mansards, and pitch in degrees for converting the steep angles. The roof pitch tool sits with the other estimators in the construction calculators category, near site tools like the dirt calculator, and the full roofing library is in the roof pitch blog off the homepage. Work out each pitch, and any roof type follows.

A frame roof pitch: frequently asked questions