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hondapro

Central Pa

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Posted: 09/01/19 04:54am Link  |  Quote  |  Print  |  Notify Moderator

Chum lee wrote:

"He suggested going 14 foot side wall and using a scissor truss, for more room in the center.

My building can only be 14 feet wide due to space limits."

IMO, the scissor truss is a good idea. Light frame (2" x 4") trusses should be fine.

As long as you have no height limits, you could go as steep as a 12:12 roof pitch (custom truss) which would put your top of roof (exterior) at about 14 + 7 = 21 feet. With a 14 foot span, the scissor depth would only need to be about 18 inches which would give you about 18'-6" inside clearance at the center of the span. Less at the sides. (tapering down to about 14' at the plate line)



Chum lee






If I could ask what is the formula to figure inside clearance with the scissor truss with different roof pitches.
Thanks


Steve
2016 F-350 6.7 Diesel
2015 Springdale 311RE

sayoung

Tx

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Posted: 09/01/19 11:49am Link  |  Quote  |  Print  |  Notify Moderator

hondapro wrote:

Chum lee wrote:

"He suggested going 14 foot side wall and using a scissor truss, for more room in the center.

My building can only be 14 feet wide due to space limits."

IMO, the scissor truss is a good idea. Light frame (2" x 4") trusses should be fine.

As long as you have no height limits, you could go as steep as a 12:12 roof pitch (custom truss) which would put your top of roof (exterior) at about 14 + 7 = 21 feet. With a 14 foot span, the scissor depth would only need to be about 18 inches which would give you about 18'-6" inside clearance at the center of the span. Less at the sides. (tapering down to about 14' at the plate line)



Chum lee






If I could ask what is the formula to figure inside clearance with the scissor truss with different roof pitches.
Thanks

H = run x rise . Building is 14 ft so run = 1/2 width so using a 12/12 pitch is 7 ft x 12 in = 84 in tall at center

Chum lee

Albuquerque, NM

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Posted: 09/01/19 02:50pm Link  |  Quote  |  Print  |  Notify Moderator

hondapro wrote:

Chum lee wrote:

"He suggested going 14 foot side wall and using a scissor truss, for more room in the center.

My building can only be 14 feet wide due to space limits."

IMO, the scissor truss is a good idea. Light frame (2" x 4") trusses should be fine.

As long as you have no height limits, you could go as steep as a 12:12 roof pitch (custom truss) which would put your top of roof (exterior) at about 14 + 7 = 21 feet. With a 14 foot span, the scissor depth would only need to be about 18 inches which would give you about 18'-6" inside clearance at the center of the span. Less at the sides. (tapering down to about 14' at the plate line)



Chum lee






If I could ask what is the formula to figure inside clearance with the scissor truss with different roof pitches.
Thanks


Unfortunately, there is no general formula, just some general calculations. For your application, in general, (this is NOT a specific design) the rule of thumb (that I use for preliminary sizing calculations) is that you need about 1 foot (12 inches nominal) of structure depth for every 10 feet of span. So in your application with 14 feet of span you will need 1.4 feet of structure depth, rounded to 1.5 feet or 18" of beam (maximum truss depth in your case) depth. The fact that the roof slopes and the truss tapers doesn't matter that much for now. It might later.

So with a 12:12 pitch roof, you have half the span, or 7 feet in rise above the plate line minus the structure depth. Don't worry about the exact dimensions for now because you can change the truss cord dimensions from 2" x 4" to 2" x 6" if you need to, or you can space the trusses closer together (24 inch on center nominal) if you need to compensate for heavy roofing materials (concrete tile) or for snow/wind loads, if required. There are 1,000's of different ways to do this, but the above is what GENERALLY gives the most economical roof structure over all.

Chum lee

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