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Thread: Calculating roof geometry?

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    Default Calculating roof geometry?

    I'm working on a building that has two differently oriented roofs (one north/south, one east/west) -



    At this point I need to build the two angled roof sections on the left that abut the roof on the right. And not being a mathematical genius, I was wondering if there was some way to determine the required angles ahead of time (rather than resorting to simple trial and error)?

    Thanks!
    -Mark

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    A construction crew would first build the north/south roof on the right. Then the larger roof on the left. As for math, not my strong suit.
    Cheers!
    Gordon
    Rheinland Bayern Bahn
    http://www.nscale.net/forums/showthr...4-x-9-5-layout

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    I don't bother with calculations; rather I lay things out based on the things I can measure directly. As Gordon mentioned above, begin with one simple gable then build the over-framed gable that meets it. Each of those trapezoidal panels are actually just a rectangle with one angle at the valley. You can measure the lengths of each of the three orthogonal sides, leaving the angle to just be struck as needed to connect the ends.

    What I do to take my measurements on the fly, though, is to cut out a strip that is the width of the sloped edge, and just make sure it is at least as long as the ridge. Then, put this strip in place with its bottom edge touching the bottom of the mating roof. This leaves a triangular gap at the valley; just measure the width of this gap at the top. Then mark that measurement on the bottom of the strip and cut off the angle that joins the top corner to the marked bottom corner. I do this kind of "fit and scribe" technique all the time, building without a lot of prior measuring.

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    ...My 2 cents... FWIW... and if it makes any sense...

    Having spent quite a few years building architectural models, I have found that the best calculations still won't account for the tiny discrepancies in measuring and cutting of the angles of scale roofs, leaving you to finesse (trial and error) anyway. i have found that mocking up in paper/cardstock can help and then use as templates.
    Take the dimensions you do know, length, width, peak height, mock that roof. (I'd start on the right side myself) Then you can see and layout/draw and measure the valleys of the two roof intersection for the adjoining roof.

    If cutting styrene/wood/cardboard for the actual model, you can cut a steep bevel into the valley cut to meet the adjoining roof for a better glue surface.

    Many roofs tend to have the same pitches. We kept a series of angled templates to duplicate roof angles. I took it a step further and made some pitched "jigs" that held the roof at proper pitch and adjusted a disc sander at an angle to create (almost) perfect valley joints. Helps when you are doing a model with dozens of buildings with multiple roof lines...

    Edit
    Quote Originally Posted by WP&P View Post
    I don't bother with calculations; rather I lay things out based on the things I can measure directly.
    - What he said...
    Last edited by Jugtown Modeler; 12th Jun 2019 at 08:34 AM. Reason: Just read WP&P
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    Sorry, I should've mentioned that the right roof is already done (do the easy stuff first, right?)

    I think what I'll do now is make the rectangular portion of the left roof first (the easy part) and then play around with paper mockups for the angled pieces until I get something that fits.

    Thanks!
    -Mark

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    I tend to design most of my structures in 3D in Sketchup, then use the Flattery plugin to 'unfold' the 3D model into a 2D printable cardstock model. This method works well for simplistic modern structures. That works well for the unusual roof pieces as well.
    IMG_20150728_144019.jpg

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    You can always cut a few templates out of paper or a heavy card stock until you find the correct angle of the roof, then trace the one you like onto the material your using for the roof.
    Seanifer

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    Agree with the other posters, it seems to come down to trial and error. However, if you want a simple online calculator I have used this before.

    https://www.calculator.net/triangle-calculator.html

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    Not that hard to do but much harder trying to write out all the steps and simple math required. That is a simple valley cut, now this one was fun not a square corner and hips both ends.
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    It looks great with 90% of the roof installed. I wonder if the employees would enjoy the extra fresh air if I just skipped the stupid triangles?

    -Mark

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    Not in WINTER!!!

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    did this fast will work on most roofs. Fast and easy and will work on most roofs
    rich
    www.rslaserkits.com
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    I did something similar but no math, similar to WP&P. I don't trust the accuracy of my cuts enough to use math.
    Hardest part for me was beveling the roof sheets' ridge edges because if you go too far you get gaps, and if you don't go far enuf you get gaps.

    The gable walls determine the width of the roof sheets just like the eave walls determine ridge length. So build the walls and glue them up square and sturdy, then measure off them and add eave and gable overhangs to make the roof sheets.

    For the valley sheets its no different; its just as easy to measure the eave lengths off the walls as is it to measure the ridge lengths once the walls are in place. At least you don't have to bevel them.

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    Quote Originally Posted by nicki6 View Post
    Not in WINTER!!!
    That's the beauty of model railroads - the seasons never change and it's forever summer in Hope!

    -Mark
    Last edited by Spookshow; 12th Jun 2019 at 07:20 PM.

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    So, at the end of the day it was still a lot of trial and error. But the suggestions were very helpful and I did make good use of them



    Thanks boys, good team effort!

    -Mark

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    Looks great Mark. I'm always impressed with your builds.

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