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Roof Height.....

Discussion in 'Building' started by limerockconstruction, 23 Jan 2015.

  1. limerockconstruction

    limerockconstruction

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    Chaps - can someone help me?

    Building an extension at the moment, lean to at the back of the house, standard stuff.

    It has a lean to roof on it naturally, its been specified as 17.5 degree pitch and the extension is 4.2m to the outside face of B/W.

    9x2's

    What height will the roof rise up the back wall?
     
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  3. tony1851

    tony1851

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    Not a clue mate - tell us. :LOL:
     
  4. limerockconstruction

    limerockconstruction

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    I thought of all people you would have been the man with Answer Tony!
     
  5. catlad

    catlad

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    At a guess I would say you would struggle to get it in under the first floor windows.
     
  6. noseall

    noseall

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    A right angled triangle with a bottom line of 4200mm and an angle of 17.5 degrees will have a rise of 1324mm.

    Fiddling with those figures it looks as though you will need about 1450mm from the top of the rafter down (vertically) to the top of the plate.

    Or if you were to measure from the external ground level (assuming G/L is 150mm below DPC) and a typical 2400mm floor to ceiling, your rafter top will pitch at aboot 4050mm up from the soil/slabs etc.

    Reduce the ceiling height (wall plate height) and you reduce the rafter height also. It will be those pesky deep lintels over those pesky standard 2100mm high patio doors you need to watch!
     
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  8. tony1851

    tony1851

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    Sorry!
    As per the others, think you will struggle to get it under the cills. You might have to do a cut-out below the cill.
    Could you reduce the pitch to 15?
    You can also thin the rafter down over the wall plate without compromising its strength.

     
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  9. limerockconstruction

    limerockconstruction

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    Sorry for the delayed response - thanks chaps - perfect information.

    This is a bit of a favour for a mate, so not really got any proper drawings to relate too.

    I could come down in pitch to 15 I suppose, thats as low as Velux will guarantee from memory.

    Does that dramatically alter things? My wall plate will be at 2.4m because of the whopping great lintel we have to out over the 4m doors. its a 225mm up-stand.

    Be interested if you could remind me of the equation to work this out.....school seems so long ago!
     
  10. tony1851

    tony1851

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    Dropping to 15 deg. will bring you down approx. 190mm.

    It's a lllllong time since i left school, but I seem to remember something like 'opposite over adjacent = tangent of the angle',
    so horizontal distance x tangent of the angle = the rise.

    (We had log tables then, which made looking-up the tan. easy. Then in the 6th we graduated to slide rules!!! Hand-held calculators were far into the future).
    and tv was 'Supercar' and 'Fireball XL5'; and we had snakebelts and catapults weren't a H&S issue.. and ten-shilling notes....and.........doh!...
     
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  11. theoldun

    theoldun

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    limerockconstruction
    If you only ask half a question then you will only get half an answer.
    You do not state if external wall plate is sat on half brick wall, a one brick wall or 300mm cavity wall. Where your lower plate sits determines your half span.
    Assume your half span is 4200, less 50mm for top pole plate = 4150 half span at 17,5 = true hypotenuses of 4403 (pitch line) and rise of 1308.
    Remember your pitch line (hypot) is not your total rise. Your total rise will also include the depth of timber left above the sole cut on the plimb line of heel cut.
    If you have a standard house with first floor cills at 3250 above DPC then you will not get in a 15 or 17.5 degree pitch. Hpw evaer there are ways to overcome this problem.
    Regards oldun













































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































    limerockconstru
     
  12. freddiemercurystwin

    freddiemercurystwin

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