The Order Goes In Thursday and the Break Is Still Freehand
The elevation arrives drawn the way barn elevations are always drawn: one bold pen line hinged somewhere around the middle of the slope, no dimension within a metre of the hinge, and a note reading barn form, to match existing. The yard wants a cut list on Thursday. Sitting between those two facts is a number nobody has yet decided — the height and the position at which the roof changes angle — and the length of every stick of timber on the job hangs off it.
Gambrel, mansard and king post are three answers to the same complaint about a plain gable. It either wastes the volume underneath it or it eats the room below with ties. Each of the three buys back what the gable wasted, and each pays for it by moving the load path somewhere less obvious than plate level. A gambrel hinges the slope so the loft walls stand up instead of leaning in. A mansard stands the lower slope nearly upright until the roof is a storey with windows in it. A king post frame stops tying every rafter pair at ceiling level and gathers the tying into one frame at bent spacing, which is what clears the floor below of anything propping the roof up.
What the three have in common matters more to whoever is ordering timber than what separates them. None of them is one length. Each is two or more members computed separately that then have to arrive at the same point in space — a break line, an apex, a bearing — and that meeting point is where a cut list goes wrong silently. Nothing in the numbers announces it. You find out when forty steep rafters are already cut and the loft floor lands sixty millimetres under the line the drawing showed.
The bent that gets repeated down the barn
- Ridge member — a spacer between two shallow rafters on most barns, but a sized beam with posts under it wherever the upper couple has no tie of its own Ridge Beam Tributary Load Calculator
- Upper rafter pair — an ordinary common rafter over a shortened run, which is why the shallow segment can be worked with a framing square while the steep one cannot Common Gable Rafter Length Calculator
- Break-line plate — the hinge made rigid: a purlin plate running the length of the building, carried down to the loft floor by a knee wall or by posts on every bent
- Lower rafter pair — the steep segment that gives the loft its headroom, and the one whose length moves furthest when the break ratio is nudged by a hand's width Gambrel Roof Rafter Geometry Calculator
- Loft floor framing — acts in tension from one knee wall to the other, which is why an open barn without a floor has to find that restraint somewhere else Ceiling Joist Spanning Lineal Lumber Aggregator
- Wall plate — the datum the whole bent is set out from, and the line that shows a spreading roof first by opening at the top of the wall Framing Stud Calculator
Setting the Break by Chord, Not by Eye
Barn framers had a drawing-board construction for this and it still works. Strike a semicircle on the span, divide the half circle into four equal arcs, and join the division points with straight chords; the lower two chords are the roof. It lands the steep segment at 67.5 degrees from horizontal and the shallow one at 22.5, with the break falling a little under three tenths of the half-span out from the wall — near enough 29 in 12 and 5 in 12 in framing-square language. That construction is why a nineteenth-century barn looks settled and a gambrel drawn freehand often does not. The eye is reading a circle it cannot see.
Nothing obliges you to use it. The break can be fixed from inside instead: draw the loft's headroom line, decide where the knee wall stands, and take the break from where those two meet. On a conversion that is usually the governing constraint anyway, because the adopted code's ceiling height provisions — in the building planning chapter of the International Residential Code, and in the equivalent chapter of whatever code is in force locally — discount floor area below a stated height and require a proportion of the room to reach the full one. What counts as habitable area, not what looks right, is what pushes a barn conversion's break outward and upward.
Either route ends at the same arithmetic: one half-span split into two runs, each with its own pitch, each producing a chord, summed for the material length. The break ratio is the fraction of that half-span the steep segment covers, and the two chords move against each other as it changes — steal run from the lower segment and its chord shortens by roughly two and a half times what the upper one gains, because the steep chord is climbing far faster per unit of run. Which is exactly why a break moved by eye on the drawing is not a small change to the timber schedule.
Before the ratio is frozen, lay it against the sheet sizes. Sheathing comes in fixed lengths and the covering comes in fixed course heights, and a steep chord finishing ninety millimetres past a full sheet buys a whole extra row of narrow rips down the length of the building. Nudging the break by half a hand on Thursday costs nothing. Discovering the same thing with the sheathing on the deck costs a day.
Two runs across one half-span, each with its own pitch: put the break ratio in and watch both chord lengths move against each other before that ratio ends up on a cut list.
The overall building width the gambrel roof spans.
The steeper lower roof segment's pitch, as rise per 12 units of run.
The shallower upper roof segment's pitch, as rise per 12 units of run.
The fraction of the half-building-width covered by the lower segment's run before transitioning to the upper segment.
Total gambrel rafter length
21.8 ft
- Lower segment length
- 14.53 ft
- Upper segment length
- 7.27 ft
They open the calculator with your figures already in it
Gambrel Roof Rafter Geometry Calculator: 21.8 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The figure covers one side of the roof only, from wall to ridge, and it is the sum of two separate members rather than one stick of timber. Order and set out from the two breakdown lengths, never from the total: one stick cut to the total length fits nothing on the roof. The layout is assumed symmetrical, with the ridge on the centreline and the same pair of pitches on both sides.
- Nothing is added or taken off for the cuts. The run is half the overall building width, so the length is measured to the theoretical apex on the centreline with no deduction for half the ridge board thickness, and no allowance for the birdsmouth or seat cut, the plumb cut at the ridge, the bevel where the two pitches meet, or the tail beyond the plate. If the wall plate sits inboard of the outer wall face, the true run is shorter than half the overall width by that offset.
- The break point is entered as a fraction of the half-span and is independent of the two pitches you type, so the default 0.5 is a free choice rather than the traditional barn setting-out. The classic method inscribes half an octagon in a semicircle drawn on the span, which puts the break at roughly 0.29 of the half-span with segment slopes near 29/12 and 5/12. Keeping 0.5 while entering those pitches describes a different roof profile and a different ridge height.
- This is geometry with no structural content. It does not size the rafters, set their spacing, check the span against a load table, or account for snow and wind, and it says nothing about the break line, which behaves as a hinge and normally needs a purlin plate, a collar or a gusseted truss joint to hold the two segments in line.
- Only length is returned, never rise or angles. The ridge height above the plate, which governs headroom in the storey below and any height limit imposed on the building, is not part of the calculation, and neither are the cut angles: a 24/12 lower segment sits at 63.4 degrees from the horizontal and the timber changes direction by about 37 degrees at the break with the default pitches. The input ranges stop the lower pitch being shallower than the upper one but not equal to it, so entering 12 for both returns a plain common rafter length for a 45-degree gable roof.
The Hinge Nobody Draws
A change of direction in a loaded member is a place where force has to go somewhere. The steep lower rafter pushes down and outward along its own line; the shallow rafter above it pushes down and outward along a different one. Their horizontal components do not match, and the difference is a real force acting at the break on every bent, all the way down the building. Something you built on purpose has to take it.
Traditionally the loft floor and the knee wall take it together. A purlin plate runs the length of the building at the break, a stud knee wall or a line of posts carries that plate down to the floor framing, and the floor joists work in tension from one side to the other. That is a complete path, and it is the reason old gambrels nearly always have a floor in them. Take the floor away — an open barn, a garage with a clear loft, a workshop somebody wants vaulted — and the restraint has to come from somewhere else: a collar at or near the break, a bent designed to work as a truss in its own right, or an engineered connection at the hinge itself. Deciding which is a design question, and it is the one that most often gets skipped because the drawing shows a clean line where the two slopes meet.
The failure is legible from the ground. The break line dips between bents, the eaves creep outward, and the big doors stop closing square. It is worth being straight with a client about where the guidance ends: rafter tables in the roof-ceiling chapter of the IRC, and the assemblies in the AWC Wood Frame Construction Manual, are written for single-slope rafters tied near plate level. A gambrel with its tie somewhere else is outside those tables. That does not make it wrong; it makes it a designed frame under the AWC National Design Specification, AS 1720.1 or Eurocode 5 depending on jurisdiction, and the fee for that belongs in the quote rather than in the argument afterwards.
Mansard: a Wall That Files as a Roof
A mansard's lower slope is not a pitch you can hold on a framing square. At seventy degrees from horizontal the rise per twelve of run is about thirty-three, and stepping that out with a square is an exercise in compounding error over a very short run. Mansards are angle work. The sloped length is the vertical height divided by the sine of the angle; the horizontal run it consumes is the height divided by the tangent. The square transfers that angle to the timber; it does not derive it.
One check comes before all the others: the two steep faces must still be apart when they reach the break. Take the height of the steep segment, divide by the tangent of its angle, double it, and set that against the building width. On a narrow building with a tall steep face the two runs eat the whole width and there is nothing left for an upper slope. The honest outcomes at that point are a lower break, a steeper face, or a flat deck at the top with no upper slope at all — which is a perfectly respectable mansard and means ordering a low-slope covering instead of a steep-slope one.
Assuming the run does leave something, the upper slope is ordinary work across the remaining half-width, and it is usually shallow because nobody was ever meant to see it. That is precisely where mansards leak. Its pitch has to sit inside what the covering manufacturer's published instructions permit, and asphalt shingles carry a documented minimum slope below which they are either not allowed or require a doubled underlayment; the adopted code's roof assemblies chapter and the manufacturer's literature both have to be satisfied, not one or the other.
Then the part that catches people out. Behind the steep face is a storey with rooms, windows and people in it, so the rules for habitable space apply to it — ceiling heights and the emergency escape and rescue opening provisions in the IRC's building planning chapter among them. Whether that face is judged an exterior wall or a roof for fire-resistance, covering and separation-distance purposes is settled by the adopted building code, where the IBC's Chapter 14 Exterior Walls and Chapter 15 Roof Assemblies and Rooftop Structures both have a claim on it. The answer changes the assembly rather than only the paperwork: a face read as a wall may need a rated build-up and a drainage plane behind whatever is hung on it.
So frame it as what it is. The steep segment is usually built as a raked stud wall — sole plate, studs at wall spacing, headers over every opening, a plate at the break — rather than as rafters that later get holes cut in them. Building it as rafters and then chopping window openings through the face afterwards is how a mansard ends up with no load path around its own windows, which is a defect nobody sees until a lintel is already carrying a wall.
Give the steep face its angle and its height rather than a pitch, and check the run it consumes against half the building width before there is nothing left for the upper slope to occupy.
How steep the mansard's lower (near-vertical) roof segment is, measured from horizontal.
The vertical rise of the steep lower segment, from the wall top to the break line.
The shallow upper roof segment's pitch, expressed as inches of rise per 12 inches of run.
The overall width of the building, wall to wall.
Total mansard rafter length
21.49 ft
- Lower segment length
- 6.92 ft
- Upper segment length
- 14.57 ft
They open the calculator with your figures already in it
Mansard Roof Rafter Geometry Calculator: 21.49 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The total is the sum of two segments that meet at the break line, not the length of one piece of timber. Cut from the two figures in the breakdown, not from the total: on the default 70 degree lower slope and 3-in-12 upper slope the two members meet at a change of direction of about 56 degrees, so a single rafter of the total length does not exist.
- The run is measured from the wall to the ridge centre line, so what you get is a theoretical line length. It excludes the eaves overhang, the half-thickness of the ridge board that has to come off each upper rafter, and the timber consumed by the birdsmouth seat cut and the plumb cuts at each end.
- This is the common rafter through one cross-section. A mansard is normally hipped on all four sides, and the hip rafters and the jack rafters running into them are longer and cut to compound angles that this page does not produce. No rafter spacing is asked for either, so there is no rafter count and no total timber quantity.
- Nothing here tests whether the roof stands up. The junction between a near-vertical lower slope and a shallow upper slope is a kink that pushes outwards under load and normally has to be restrained by a curb plate or purlin with a floor or collar behind it; the calculator returns no member depth, span limit or fixing detail for that transition.
- The upper pitch accepts 1 to 8 in (203 mm) 12, which is roughly 4.8 to 33.7 degrees, and the lower part of that range sits below the minimum pitch that slates and most interlocking tiles are rated for. Minimum pitch is set by the covering manufacturer and by local rules rather than by the geometry, so a shallow mansard top often has to become a membrane or standing-seam metal deck instead.
- The steep lower slope of a mansard is usually pierced by dormers, and the geometry here assumes it is unbroken. Each dormer opening cuts rafters that must be trimmed round with doubled trimmers and headers, none of which is reflected in the length or in the breakdown.
Punching the Storey Full of Holes
Every dormer in a mansard or a gambrel face is a trimmed opening in a structural plane. Whatever members it interrupts land on trimmers, the trimmers land on something below, and on a steep face a good share of that load is running down the slope rather than straight down. Doubled trimmers at the sides and a header at the head are the floor of what is acceptable; once the dormer is wide relative to the bent spacing, the header has stopped being a header and become a beam that somebody needs to size.
The dormer's own roof is a separate small roof at its own pitch, and it is nearly always steeper than the plane it sits in, because a short run sheds badly at a shallow angle and the cheeks want height for flashing. Work its rafters from the dormer's own width and pitch rather than from anything the main roof is doing, and settle the tail before the cheek walls are set out — the cheeks get positioned from the rafter, not the other way round.
Where a dormer roof meets a near-vertical mansard face, the junction behaves like a wall intersection and not like a valley. Step flashing and a proper head detail belong there. The other failure is dimensional rather than structural: a row of dormers set out from a string along the eave instead of from the building's own bay lines will arrive at the far gable out of step with the bents behind them, and the last one will have a trimmer sitting on nothing.
A dormer answers to its own width and its own pitch, and the tail belongs inside the length from the start rather than being added once the cheeks are already standing.
The full width of the dormer, measured across its own roof.
The dormer's own roof pitch, expressed as rise per 12 units of run.
The horizontal overhang beyond the dormer's side wall.
Total dormer rafter length
5.083 ft
- Rafter length to ridge
- 3.91 ft
- Overhang tail
- 1.18 ft
They open the calculator with your figures already in it
Dormer Rafter Length Calculator: 5.08 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The run is taken as half the entered width, so the figure only holds for a symmetrical gable dormer with its ridge on the centreline. A shed or mono-pitch dormer has a single slope whose run is its full depth, from the front wall back to the main roof, so entering that depth returns a rafter about half the length actually needed. For a shed dormer, enter twice the run you measured.
- Pitch is read as rise per 12 units of run, not as an angle in degrees, and the field accepts anything from 2 to 24, so a degree figure in that range passes with no warning. A 20 degree dormer entered as 20 is treated as 20 in 12, or 59 degrees, and the rafter comes out over 80 per cent too long. For reference, 8 in 12 is 33.7 degrees and 12 in 12 is 45 degrees.
- Overhang is treated as a horizontal projection beyond the dormer's side wall and is multiplied by the same slope factor as the run. A tail already measured along the slope, entered here, is inflated by that factor a second time, roughly 20 per cent at 8 in (203 mm) 12 and 30 per cent at 10 in (254 mm) 12. The tail also carries no allowance for the plumb or square fascia cut, nor any cutting waste for ordering.
- The length returned is a dormer common rafter only. Where the dormer roof meets the main roof plane the valley rafters are longer than this figure and are cut on a compound angle, the jack rafters running into them each differ in length, and a hipped dormer's hip rafters are longer again. None of those members are produced here.
- Nothing in this calculation tests whether the dormer is structurally adequate: rafter depth, section, spacing and permissible span all sit outside it. So does the trimmed opening in the main roof, where the main rafters cut away for the dormer are carried on trimmers and a header that normally have to be doubled. On a wide dormer that opening, not the dormer rafters, is usually the governing structural item, and both are sized from span tables or by an engineer rather than from a length.
The King Post Hangs, It Does Not Prop
The most durable misunderstanding on site is that a king post holds up the ridge. It does not. The two top chords lean against each other at the apex and push outward at their feet; the bottom chord stops them spreading and is therefore in tension along its whole length; and the post hangs from the apex to pick that bottom chord up at midspan, so the post is in tension too. A king post is a hanger, not a column.
That one fact decides all the joinery. In traditional work the post is strapped or bolted to the tie beam with an iron stirrup, or jointed so the connection can carry tension across itself — never simply seated on the beam in a housing, which resists nothing at all. A post cut to bear on the tie has been installed upside down in engineering terms. It will look correct for decades and do no work, and the sag it was meant to prevent will arrive on schedule.
The geometry is short. The rise at midspan is the half-span multiplied by the pitch expressed as rise over twelve, and that rise is the post's length exactly, because the post is plumb and centred. Each top chord is the half-span multiplied by the slope factor, so the chord is always longer than the post for any real pitch — it is carrying the run as well as the rise. The struts that run from the foot of the post out to the middle of each top chord are compression members, and their length depends on where the designer chose to land them, so they are not a consequence of span and pitch and should not be guessed off the same two numbers.
The bottom chord is the member to lose sleep over. It carries the whole horizontal thrust in direct tension, which means anything reducing its section reduces the frame: a notch for a service, a hole drilled for a cable, and above all a splice. Splicing a tie beam is a designed connection that has to carry tension across the joint, whether the answer is a bolted steel plate, a pegged scarf or a proprietary connector. A tie beam lapped the way a floor joist is lapped is not a tie beam; it is two beams that happen to touch.
The heel is the other place these frames fail. Where a top chord meets the tie at the bearing, the thrust has to transfer into the tie at a shallow angle, and shallow angles load timber parallel to the grain, which is the direction it is weakest in shear. Traditional framing answers with a housed joint and generous end distance beyond it; modern framing answers with a connector plate or a bolted shoe. In both cases the governing number is how much timber sits beyond the joint. Cutting the tie off flush with the bearing so it looks tidy is the quickest way to build a frame that splits along the grain at its own support.
Span and pitch give the post's length and each top chord's, which is enough to order the timber; the struts wait on the designer, because where they land along the chord is a decision rather than a result.
The overall truss span, bearing to bearing.
The roof's slope, expressed as inches of rise per 12 inches of horizontal run.
King post length
6.5 ft
- Top chord length (each side)
- 14.53 ft
They open the calculator with your figures already in it
King Post Truss Member Length Calculator: 6.5 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The geometry assumes the top chord and bottom chord lines meet at a point over the bearing, which is a zero heel height. A raised heel or a heel wedge lifts the apex by that same amount, so the king post grows one for one with the heel height, while the top chord length is unchanged because its horizontal run and its pitch have not moved.
- Both figures are line lengths between theoretical intersection points, not cut lengths. They exclude any eaves overhang past the bearing, the plumb cuts at the heel and at the apex, and the housings, tenons or gusset plates at the joints, and they do not say which face of the timber the setting out was taken from: an apex set out on the underside of the top chords sits a member depth, measured square to the slope, below one set out on the top face.
- The king post in a traditional truss hangs the tie beam at midspan and works in tension, not as a prop holding up the ridge. A foot joint that simply bears down on the tie beam carries nothing, and this page returns a dimension only, so it does not size the post, the strap or bolts at its foot, or the top chords, whose line length is the same whether they are 47 by 100 or 75 by 225.
- Both formulas assume a symmetrical truss, with equal pitch on each slope and the ridge exactly over midspan. Enter one pitch for an unequally pitched roof and the ridge sits off centre, so the plumb member at midspan is shorter than the rise shown and neither top chord matches the breakdown figure.
- Roof pitch is entered as rise per 12 units of run, not as degrees, and the field is unitless so it does not change when you switch between metric and imperial. Because it accepts anything from 2 to 16, a value typed as an angle passes silently: 15 meaning 15 degrees is modelled as 15 in (381 mm) 12, a roof of roughly 51 degrees.
The Frame You Cut Is Not the Truss You Buy
A metal-plate-connected truss delivered on a lorry is not a shape, it is a designed component. ANSI/TPI 1 National Design Standard for Metal Plate Connected Wood Truss Construction governs it, the truss design drawing carries a design professional's seal, and the plates were pressed in a factory to a depth the design assumes. None of that transfers to a frame with the same outline cut on sawhorses in the yard, however carefully it was cut.
The rules that follow are absolute rather than advisory. No web is cut, no chord is notched, no bottom chord is drilled to let a duct or a cable through, and no lifted plate is repaired with nails, without a written detail from the truss designer. A truss with a cut web is not a weakened truss — it is a different structure with no analysis behind it. Handling, restraint and bracing follow BCSI, the SBCA and TPI guide, which exists because more trusses are ruined lying flat on the ground and in the first hour after they are stood than are ever overloaded by weather in service.
A king post frame cut on site is legitimate, traditional and entirely buildable, and it is also an engineered design: member sizes and every connection come from a designer working to the NDS, Eurocode 5 or AS 1720.1, and a shape being two hundred years old does not put it in a prescriptive table. Where the frame is exposed and forms part of the architecture, agree the hardware before the timber is ordered. A designed steel shoe or a strap at the post head changes the length of the timber that has to sit inside it, and that discovery is expensive after the sections are cut to a drawing that assumed a housed joint.
Standing Something That Wants to Fold
A gambrel bent lying on the deck is a mechanism. It has hinges at both break lines and another at the apex, and until the break is tied and the plane is braced it will fold given the smallest excuse. Build the bents flat against fixed stops so every one comes out the same shape, and lift them as assemblies. Stick-framing a gambrel in the air turns each break into a separate improvisation at height, and the break line is the one line on the building where improvisation shows.
Bracing is most of the work on the day. The first bent gets plumbed and held with ground braces that nobody is allowed to borrow for anything else; the second is set at the correct bay and tied to the first at plate, break and ridge; from there the diagonal in the plane of the roof is what stops the row racking down the building like dominoes. A gambrel needs this more than a gable does, because it has two planes and no continuous straight rafter running through to stiffen them.
- Set one bent out full size on the deck and cut a pattern for each of the four members before any repetition starts.
- Assemble the bents flat against fixed stops, so the break line lands in the same place on every one.
- Mark bent positions on both wall plates from one continuous tape run, never bent to bent.
- Stand and plumb the first bent, ground brace it in two directions, and leave those braces untouched until the plane is sheathed.
- Tie each following bent at plate, break and ridge before the lifting gear is released.
- Run the diagonal in the plane of the roof, then string the break line the way you would string a ridge and shim before the first sheet goes down.
What the Extra Angle Costs the Rest of the Order
A gambrel covers a footprint with more roof than a gable of the same span and the same ridge height, and it is worth saying why out loud: the two-chord path from plate to ridge is longer than the straight line between those same two points, always, and it lengthens as the lower segment steepens. Everything that follows roof surface — sheathing, underlayment, covering, fasteners, labour — is therefore larger than the gable estimate the client is quietly comparing the price against.
The break itself introduces a joint into every layer that crosses it. Sheathing wants blocking or a plate at the change of plane. The covering restarts a course there and needs a transition detail its manufacturer actually publishes rather than one invented on the roof. A mansard adds a cornice, a gutter line or a projecting band at its break — a linear item with no equivalent on a gable at all — and its dormers add cheeks, flashings and small pieces of covering that get badly under-counted because they are estimated as area when they are really edges.
Length availability decides more than waste percentages do. A gambrel's two chords are each short, which is the shape's quiet advantage: a wide barn can be framed from stock a gable of the same span could not reach without splicing. A mansard's steep face is short in the same way. A king post frame is the opposite — long unspliced top chords and a long tie beam — and a tie that has to be ordered rather than picked off the rack is usually the item that sets the programme rather than the price.
Against a plain gable of the same span, the three shapes grow the order in different places, and they are not the places most estimates look.
| Shape | What it buys | Where the order grows |
|---|---|---|
| Gambrel | Loft volume with near-vertical knee walls, without raising the ridge | More roof surface than the gable it replaces; a purlin plate and knee wall on every bent; blocking and a covering transition along both break lines |
| Mansard | A full storey inside the roof, with windows in the steep face | Steep face framed and clad as a wall; dormer trimmers and headers; a cornice at the break; a separate low-slope covering on the upper deck |
| King post | Clear floor beneath, with the tying gathered into a frame at bent spacing | Designed connections at apex, post head, post foot and both heels; a tie beam whose splices carry tension; longer single lengths than a rafter of the same span |
Settling the break before the yard cuts anything
Four numbers decide a two-slope roof and three of them are pure geometry. Fix those first, then let the shape tell you which line items the gable estimate never had.
- Span, and the half-span each side works over — Taken to the outside of the plates; a barn measured off the drawing rather than off the standing frame is the usual reason a break line will not close.
- Break position as a fraction of the half-span — Set it from the loft headroom line or from the chord construction, then test it against sheet lengths and course heights before it is frozen.
- Both pitches, each in the notation it is honestly specified in — Rise per twelve for anything a framing square can hold; degrees for a mansard's steep face, where twelfths stop being usable.
- Whatever resists the force at the hinge — Purlin plate on a knee wall, a floor working in tension, or a designed connection — decided before the members are cut, not after they are standing.
- Connection hardware on a king post frame — Apex, post head, post foot, both heels and any tie splice; a designed shoe changes the length of the timber that sits inside it.
- The linear items the shape introduces — Blocking and covering transitions along each break, a mansard cornice, dormer cheeks and trimmers — none of which exist on the gable being compared against.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.