# how to measure for building trusses



## mudhen490 (Jan 28, 2010)

I am starting to build trusses for a covered bridge.  If the bridge is 22" wide and the center of the truss has a 6" rise how wide will each side of the roof be?  My bridge will be 16 ' long and I am trying to decide how many trusses to build.  I am thinking of building each truss from 1/4 inch plywood.  Should I use exterior or interior plywood and treat the wood?  What should I treat it with?  Any help or suggestions would greatly appreciated as this is my first scratch building project. Thank You


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## Michael Glavin (Jan 2, 2009)

Checkout this calculator:


http://www.csgnetwork.com/righttricalc.html
Looks like 12.53".

Marine plywood wood be best in my opinion... What are you thinking for truss design, layout or shape? And why plywood?

I can draw it up ACAD with a little more info with scale size and dimensions.

Michael


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## R.W. Marty (Jan 2, 2008)

That calculator is slick and gives you some numbers to work with but is not much for visulizing the roof lines.

Try this.
On a piece of plywood, cardboard, or even the bench top; lay out a horizontal line about 30 inches long, at the center of this line scribe a vertical line up about a foot. Make sure that the vertical line is 90 degrees to the horizontal one. Mark the point of intersection "A" go up the vertical line from point "A" 6 inches and mark point "B". Now go out the horizontal line on either side or both sides of point "A" 11 inches and mark point "C". Now draw a line from point "B" to point "C" and you have your roof line silouette, just measure it for the dimension you seek. 

This method allows a person to change dimension "A" to "B" and draw new angles to point "C" to get roof angles that may look better on the model. the run to rise that you are asking about will give a roof pitch of about 20-21 degrees. That pitch may be unnecessarily steep in rain country but not steep enough in heavy snow areas, depends on what/where your modeling. By actually laying the run/rise out on cardboard you can cut templetes and try them to the building to see which pitch gives the best look to the structure before cutting any wood. 
Just an opinion.
Rick Marty


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## mudhen490 (Jan 28, 2010)

Thank you both for the information. i will try and lay the truss out and then i will have more info to send along. I was going to use 1/4 or 3/8 plywood to make triangles and outline them with 1/2 by 1/2 pieces around the outside for strength. These are only my first thoughts on this and will take any and all help given. Thanks,Rick


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## R.W. Marty (Jan 2, 2008)

What you discribe sounds like you could park your car on it when it was finished, pretty strong in other words. 

How you build depends on your goal. wheather it is for looks or hidden. 
If hidden, 2 or 3 trusses of 1/4 inch ply will hold a roof sheet of 1/4 inch ply pretty stable.

If your building for looks, exposed to view, then I would consider another approch, using cut lumber and building up 
trusses just like the real deal.

Mostly it depends on your weather exposure need as to how you build.

Attached are a couple of shots of a truss roof on a locomotive shed I built a few years ago, of course this building
is not exposed to the weather but is on the indoor section of the railroad.





















Have fun with your project.
Rick Marty


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## Torby (Jan 2, 2008)

Measure? 

Don't believe in it.


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## mudhen490 (Jan 28, 2010)

My goal is to build for strength and make a section of the bridge roof removable to have access to the track. The bridge will be 16' long,so strength is of great importance.I plan on leaving the bridge out for the winters. The outside will be built for looks in 1/2" scale. My largest train is a 1:20.3 K-37. I don't think 2 of these will be able to pass on the RR. My other concern is the length of the bridge at 16'. Iwill need to carrie it from the workshop to set it in place. I was thinking of building it in 4' sections and nailing it together at the site. I have not  decided how or what to do. Any suggestions or ideas. Thanks for the help so far, this gives me more to think of while on vacation. Rick


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## denray (Jan 5, 2008)




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## denray (Jan 5, 2008)

is this what you are looking for?
Dennis


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## mudhen490 (Jan 28, 2010)

YES, Dennis. Thats what I needed. Thank you very much. I will hit the work shop on Thursday and get started. Mudhen490


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