Framing & StructuralQuestion 321 of 700
Why does a structural RIDGE BEAM allow a roof to be built without rafter ties, whereas a simple ridge BOARD does not?
a.The ridge beam is lighter
b.The ridge board is stronger than a beam
c.Ridge boards are only used on flat roofs
d.A ridge beam carries the rafter loads to posts/bearing points, so rafters do not push the walls outward
Explanation
A structural ridge beam supports the upper ends of the rafters and carries that load down to posts or bearing walls, so the rafters act as supported members and generate no outward thrust, eliminating the need for rafter ties. A ridge board only aligns rafters and offers no vertical support, so ties are required to resist thrust.
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Related questions on this topic
- In conventional roof framing, where should rafter ties (which resist the outward thrust of rafters) generally be located?
- What is the practical difference between a collar tie and a rafter tie in a gable roof?
- When rafters frame to a non-structural ridge board (not a ridge beam), what is the minimum requirement for that ridge board's depth?
- Collar ties used to resist wind uplift should be spaced no farther apart than what, measured along the ridge?
- CALCULATION: A common rafter runs horizontally 12 feet from the wall to the ridge and rises 9 feet. Ignoring overhang and cuts, what is the approximate rafter line length?
- CALCULATION: A gable roof has a 5:12 slope. If the horizontal run from the wall to the ridge is 24 feet, what is the rafter line length (rounded to the nearest foot, ignoring overhang)?
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