Cómo calcular los cortes en ángulo para vigas del techo cubiertas

7/28/2019 Cmo calcular los cortes en ngulo para vigas del techo cubiertas

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Cmo calcular los cortes en ngulo paravigas del techo cubiertas

Un techo hace que una cubierta sea ms til, proporcionandoproteccin contra el sol y la lluvia. Los techos de cubiertas a dos aguas pueden ser un estilo quecombine con el techo de la casa o un estilo simple de cobertizo con una pendiente nica. El estiloinclinado es eficaz y fcil de construir. Normalmente tiene un marco exterior con un lado junto a lacasa y con vigas o viguetas de apoyo dentro del techado.

PendienteLa pendiente o grado de inclinacin, es el elemento ms importante en el clculo de las vigas, lascuales a menudo se llaman vigas en techos planos o de baja pendiente. las viguetas de cubierta dela azotea realizan la misma funcin que las vigas o cerchas principales acordes a un tejado de dosaguas (son el marco para sujetar la plataforma del techo y las tejas u otro recubrimiento comopaneles de metal o vinilo).

LongitudLa longitud de cada viga es el segundo elemento clave. Esta es la distancia que cada viga debesoportar del techo de un extremo de la cubierta al otro. En un techo cubierto, es la longitud entre laconexin de la pared de la casa y la banda exterior de la estructura del techo. Las vigas del techopueden unirse a la banda exterior de dos maneras, con colgadores de vigas de metal o conmuescas triangulares en las vigas para que encajen encima de este apoyo.

EscuadraUsa una escuadra para calcular los ngulos de un techo especfico. Coloca la punta o taln de laescuadra, en la parte inferior de un extremo de una viga, normalmente una tabla de 2 por 4pulgadas (5 x 10 cm). Coloca la marca de pulgada sobre la lengua delgada de la escuadra en lainclinacin, 2 pulgadas (5 cm) para un techo que desciende 2 pulgadas por pie (30 cm) por ejemplo.Coloca la marca de 12 pulgadas (30 cm) de la hoja ancha en la parte superior para crear un nguloen el extremo de la tabla de la parte superior o corte vertical de la viga para conectarla a la partesuperior del techo.

Determinar el largoCalcula la longitud de la viga con una tabla sobre la hoja llamada "longitud de viga comn". Mostrar

bajo la marca de inclinacin el diferencia o espacio adicional que una viga inclinada debe cubrir enla distancia. En un techo de 2 pendientes, es decir, 12,16, cada viga tiene que seraproximadamente de 12 1/4 pulgadas (30,6 cm) por cada pie (30 cm) de largo. Esto colocara unaviga de un techo de 10 pies (3 m) de ancho alrededor a 10 pies y 2 pulgadas (3 m y 5 cm) entre lossoportes finales de los extremos.

Clculo de los extremosUna viga inclinada tiene que tener cortes en ngulo a cada extremo, a menos que se coloque en laparte superior del soporte de la cubierta exterior. Calcula el extremo contrario del corte superior con


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la escuadra en la parte superior en lugar de la parte inferior de una vigueta. Para una viga que secolocar en la parte superior de una tapa de pared, utiliza la longitud de viga para determinar elpunto de apoyo donde la viga se encontrar el final y haz un tringulo para que se adapteexactamente sobre esa tabla, una horizontal de 2 por 4 (5 x 10) o una vertical de 2 por 6 (5 x 15).Realiza ese tringulo marcando el punto exterior del rodamiento, en donde la vigueta se encuentracon el borde exterior del soporte. Mide 3 1/2 pulgadas (9 cm) hacia atrs para una muesca de 2 por

4 (5 x 10) por una muesca de 1 1/2 pulgadas (3,8 cm) o una de 2 por 6 (5 x 15 cm), la madera de 2pulgadas (5 cm) es de hecho 1/2 pulgada (12 mm) menor a eso.

Special Roof Techniques

Although pre-fabricated trusses are used to frame the vast majorityofnew roofs, there's almost always a need for hand-framing to somedegree to finish the roof framing. And there are some roofs that justcan't be trussed.

We've collected helpful information on a few of those hand-framingsituations here on this page.

For definitions throughout this project, seeFraming Glossary.

Tying a New Roof Into an Existing Roof

How a new roof ties into an old roof will obviously depend on the existingstructure and the planned addition. In fact, "tying in" is often not even coveredon an addition plan, being left to the framers' discretion. But the process usuallyfollows these steps:

Establishing ridge point on old roof: Run a string along the peaks of the new

trusses, establishing aridge line, and extend the string to the old roof alongthat line to determine where the ridge would hit.

Establishing valley lines: Snap chalklines from the ridge point to the points where the new wallsintersect the old roof.

Cutting and securing valley boards: Measure the valley lines, cut twoboards to that length with 45 degree angles on each end, nail those in alongthe valley lines.

Cutting and securing ridge board: Measure between the ridge point and thepeak of the last new truss, cut a board to that length with an angle on one endto match the slope of the old roof, nail that board to the last truss and to the

old roof at the ridge point.

Cutting and securing valley jacks:Mark 24" on center along new ridge board,use framing square and straight-edge to mark points on valley boards 90 degreesfrom each mark on ridge board, cut boards to fit with compound miter cuts forvalley jacks at theroof pitchneeded (angles given on framing squares) and naileach in place.
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Hand-Framing a Small Hip Roof

Framing a full hip roof is beyond the scope of this page, but we cangive you the basic steps for framing a small hip roof like the one we didin one of our projects.

The first step was to secure a 4-foot ledger board to the house wallcentered between the addition side walls to anchor a series of commonrafters, which will run down over the outside wall at a 2/12 roof pitch.

We also nailed up angled boards running from each end of the ledgerboard down along the house wall to the tops of the addition side walls (as nailers for

theroof sheathing).

We decided to have the common rafters cross right over the studs inthe outside wall, so we just measured out the same 16" on centerlayout from the side of the addition to determine the matching positionsfor the ends of the rafters on the ridge/ledger board. Then we measureddown from the top of the ledger board at each mark to the outside ofthe wall plate at each corresponding mark and transferred thosemeasurements to the 2x8 boards we were using for rafters.

NOTE: To transfer that measurement EXACTLY you must account for theheight of therafterwhere it crosses the wall on the board you're measuring. We

first cut out a template of the plumb cut and seat cut we wanted on each rafterwhere it rested on the wall plate (known as the birds mouth cut), lined that upalong the bottom of the rafter so that the top corner of the template wasexactly the same length from the end of the rafter (measured from the top) asthe length we measured on the wall. Then we traced the pattern on the rafter

and cut each birds mouth.

The angles for the plumb cut (which you also need at the end of the rafter) and the seat cut aredetermined by your roof pitch, and they're listed in roof framing tables. Any overhang you want

should be measured out past the plumb side of the birds mouth.

After cutting and securing the common rafters, we next measured and cutthe hip ridges. For those, we measured from the ends of theledger boardto

the outside corners, added extra for the overhang (which we would cut toproper length later) and cut 2 boards to those lengths with the appropriatebirdsmouth cuts (plumb cuts set for a 2/12 pitch but the seat cuts for a2/17 pitch, following the "rule of 17" for hips and valleys to account for theshallower pitches of those members).

We secured the hip ridges at the ends of the ridge/ledger board and ran those over the 2 outsidecorners of the addition.

We needed hip rafters running from the hip ridges out over the wall plate inthe same layout as the common rafters. To mark the rafter positions on theridges, we lined up aframingsquare with one leg resting on the wall plateand used a straight edge along the other leg to mark perpendicular points onthe ridges corresponding to the rafter positions on the wall plates. Then wemeasured between the marks, transferred the lengths to 2x8's as describedabove and cut the rafters with the same birds mouth cuts as the commonrafters.


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NOTE: The end of a hip rafter requires a compound miter cut to rest solidlyagainst the hip ridge, which runs at a 45 degree angle to the wall plates. Youmark for the plumb cut angle for your roof pitch as on all the other rafters, butset your saw blade for 45 degrees and make your cut.

After installing the hip rafters, we then plumb cut the rafter tails to the

overhang length we wanted and sheathed the roof.

Framing a GableDormerGable dormers are smaller pitched roof and walls units framed on top of themain roof. Shed dormers are built about the same but have a low-pitched roof.Gables add character and space to the roof level.

A gable dormer is framed by marking existing rafters and cutting out the areathe dormer will occupy. The remaining outside rafters are doubled with same

size lumber.

A doubled rafter header caps the cut rafters at the bottom. The front dormerwall sets on top of this header. The two side walls set on the doubled roof rafters. Top plates cap allthree dormer walls.

A down-sizedgable(end) truss sets flush on the top of the front wall. A dormer ridge board runs level

from the gable peak back to the old roof surface -- or make a top rafter header if you have exposedrafters there.

Once that dormer ridge board is nailed in, each valley rafter can be cut. Thevalley rafters form the slope (valley) where the dormer roof meets the mainroof.

Valley rafters go on each side of the dormer; between the point where theridge board meets the old roof or top rafter header and the point where the

side walltopplatesstop.

After nailing the valley rafters to the roof/top header and through the sidewall top plates, dormer rafters are bevel cut on the bottom, mitre cut on top,spaced on 16" centers and nailed to the ridge board and side walls.

If you have enough trusses exposed, additional jack rafters may be nailed16" on center (o.c) to the back side of the valley rafters up to the roof's

ridge board.

Some dormers may have added rakes and eaves to protect and decorate thedormers. A rake is built by nailing short perpendicular lookouts (16" o.c.) to thegable truss rafters. The lookouts are capped with fly rafters that run at the sameangle as the truss rafters. Asoffitboard can be nailed on the bottom of thelookouts to finish off the rake.


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Eaves are created by extending the dormer rafters past the side walls. Lookouts are nailed betweenthe rafters and the side walls, and a soffit board nailed to the lookout bottoms completes theoverhang.

Cómo calcular los cortes en ángulo para vigas del techo cubiertas

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