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“Marking out the roof” is laying
the tiles perfectly straight implies a knowledge of right angles. |
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Trait carré /Right angle |
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Definition |
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To use terms proper to geometry,
the right angle is a line drawn perpendicular to another straight
line.
This straight line is a horizontal line defined as level
in various ways.
This line is parallel to the gutter
when the latter is recognised as being horizontal.
This line can be defined as the line
drawn between two points on the rafters with the help of a spirit
level, well known to builders (A very reliable method
especially when the gutter and the ridge are not level).
This line can be determined by taking
a straight edge in wood or even better in aluminium on which
is placed a spirit level. (slightly less precise when
the roof is not perfectly level).
Generally the squareness of the perpendicular
can be checked by measuring 60cm along the base line and 80cm
on the vertical and the diagonal (Hypotenuse) should measure
1m. |
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Method |
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• Once the level has been drawn you
trace parallel lines to this line which will allow you to line
up the battens.
• On the side of a batten draw
a line x-y parallel to the top edge of the batten. Anywhere
on this line mark a point A from which will be drawn the perpendicular.
From this point mark two points B and
C equidistant from A with a bradawl.
• Using a batten with
a nail at either end, make two arcs from point B and from point
C. |
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Tips: |
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To be certain that these two
arcs intersect on the supports, it is recommended that you nail
two pieces of plywood or metal at the place where you presume
the arcs will intersect.The straight line joining these intersections
should be marked with a builder’s chalk line.This is how
the perpendicular is drawn and this represents the line of greatest
fall. |
Measure and mark out the roof
