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0431 Methods of Reducing Rafter Spans - Roof Framing - Collar Ties
0431 Methods of Reducing Rafter Spans - Roof Framing - Collar Ties -

Image Text: Cross section > Collar ties > span > span > if the collar tie is more than about 8 feet long, it requires lateral support in the form of a 1x4 nailed perpendicular to the collar ties (prevents buckling) > roof rafter > ceiling joist > collar ties can be used to reduce the span of a roof rafter when the roof slope is 4 in 12 or greater > collar ties are not effective when roof slope is less than 4 in 12 > wall > Purlins > span > span > purlins - typically 2x6 minimum running perpendicular to roof rafters > must be greater than 45 inches > supporting struts should be 2x4 minimum, typically every 4 feet > bearing wall > struts longer than 8 feet should be braced to prevent buckling > Knee wall > span > span > dwarf wall or strut > ceiling joists must be 1 inch deeper than normal (or even deeper if the roof slope is 3 in 12 or less) to carry the extra load > install solid blocking between joists when ceiling below is finished

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