Roof Framing: collar ties, rafter ties, tension beams & structural ridge beams: many of these can offer the roof and stop ridge sagging and wall spreading.
Roof framework definitions & help alternatives for sloped roofs, cantilevered roofs & cathedral ceiling roofs.
This informative article series describes and illustrates different types of support that prevents roof sagging and wall bulging at buildings, including definitions of collar ties, rafter ties, and ridge that is structural.
Minus the proper support of rafter ties or a structural ridge, a typical gable or sloped roof will droop downwards while pushing the building walls outwards towards a disaster such as for instance that shown inside our web page top photo of a barn in Amenia, NY: the failure of rafter ties in this building combined with snowfall loading in Amenia, nyc, pushed the ridge down and the walls outwards as the building slowly settles right down to our planet.
Right Here we include sketches of collar ties, rafter ties, and ridge that is structural also illustrations of collapsing and collapsed structures where these roof rafter ties were lost or omitted.
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Roof Framing Definitions
Below we supply the places and functions of various roof framing people, rafter kinds, collar ties, rafter ties, ceiling joists, and ridge that is structural.
Which are the Names for the several types of Rafters?
And where are they present in which roof shapes or sections?
[Click to enlarge any image]
Drawing adapted from Swanson’s Book of Rafter Lengths and construction that is roof was at change copied in Empire degree Co.’s Rafter Square guide both of that are cited below.
Definition of typical Rafter: shown in red within our design, a rafter that is common runs right perspectives to (90В°) towards the building front and straight back walls, as seen when looking down from above. A typical rafter operates through the roof ridge to the top of the front or wall that is rear, and extend beyond the wall surface to supply an overhang or eaves or soffit.
In our type that is rafter drawing common rafters are used red .
Cripple Jack Rafter
Concept of Cripple Jack Rafter or Valley Jack Rafter: a rafter running at right perspectives (90В°) from the ridge of a roof right down to the valley below. Cripple jack rafters or valley jack rafters never make it up to a wall top dish – instead they intersect a valley created by another roof.
In our type that is rafter drawing the cripple jack rafters are drawn in purple additionally the valley location or valley rafter is drawn in yellow
The valley itself is formed where in fact the hip roof abuts a lower or adjoining roof surface.
Definition of Dormer Rafter: a rafter whose upper end rests atop a preexisting roof without cutting into it, supplying a roof and ceiling for a dormer or building space with greater head-room than underneath the roof that is main.
A roof dormer may be gabled like in our design above or it could be a low-slope, or flat roof.
Definition of Hip Rafter: a rafter that runs diagonally between your roof ridge while the the surface of the wall surface dish, forming a roof that is hipped.
In our rafter kind sketch over the hip rafters are used blue . Notice that the hip rafter forms what amounts to a descending ridge – a solitary line that starts the roof and descends to the wall top plate at a wall surface corner.
Below: a hip rafter and jack rafters seen from below. This is a palm that is woven roof located in La Manzanilla, Mexico.
The hip rafters increase through the ridge down seriously to the most notable plate and tend to be marked within our picture by yellow arrows. This may be a roof that is pyramid there is absolutely no ridge board. Most of the hip rafters meat at the ridge peak.
Hip Jack Rafter
Definition of Hip Jack Rafter: a rafter stretching at right angles (90В°) from the wall surface plate or over to abut into a existing hip rafter.
Over the hip-jack rafters are indicated by the arrows that are white in the photo.
Within our roof framing drawing over the hip jack-rafters are drawn in green .
Concept of Valley Rafter or cripple jack rafter: a rafter extending through the roof ridge down to the most effective bowl of a wall at the intersection of the gable expansion roof that itself abuts or intersects with the roof that is main.
In the sketch over the valley rafter is drawn in yellow .
Definitions of Rafter Span & Run, Roof Span & Slope, Collar Ties
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Definition of rafter span: the un-supported amount of the rafter along its slope – the diagonal or hypotenuse of the triangle that is right. In our sketch the «rafter span» is called the RAFTER LINE LENGTH.
Definition of rafter run: the horizontal or level distance covered by the rafter – the underside chord or base of the right triangle. Within our sketch above the rafter run is shown as RUN under the left half of the roof.
Definition of roof span: generally a roof period matches the building width involving the exterior edges associated with the wall surface plates that are top.
Definition of roof slope: roof slope is the level of change in height being a ration of horizontal distance traveled, usually expressed as inches of increase per foot of horizontal run, or cm of rise per m of horizontal run.
According to its location over the roof rafter span or run, a tie that is horizontal reinforcement may enjoy various names and suffers different forces. We detail these below:
- Concept of Collar ties: High ties that are horizontal the top of third of this roof – under compression
- Definition of Mid-Span rafter ties: situated horizontally the rafter’s run or horizontal period – neutral & varying
- Concept of Low rafter ties: found in the bottom 3rd or in the bottom associated with the rafter’s run or horizontal span – under tension