Roof Flashing for a Pipe: flat pattern

The flashing where a flue or vent passes through a pitched roof: the base plate on the slope with its hole, and the sleeve cut to the pitch. The flashing where a flue, vent or exhaust pipe passes through a pitched roof: a flat base plate on the slope with the hole cut to it, and an upstand sleeve, straight or narrowing to the pipe, cut to the pitch at its foot.

Configurations

• Cone sleeve. The sleeve narrows from its foot on the roof up to the pipe, so water runs off it and down the slope.
• Straight sleeve. The sleeve is a plain cylinder round the pipe, cut to the pitch at its foot.

A worked example

The cone sleeve configuration with the sizes SheetMorph opens with, in mm. Two plates: the sleeve, cut to the pitch at its foot, and the base plate with the hole: 2 parts, 2 seams.

How it is developed

Development of a cone cut by a plane, and a flat plate. This is an exact development: the surface unfolds without stretching, so the pattern closes exactly.

• The sleeve is a cone cut by the plane of the roof: its lines are longest on the down-slope side, where its seam is, and shortest up the slope.
• The hole in the base plate is the foot of the sleeve laid on the plate: longer up the slope than across it.
• Lay the upper part of the base plate under the roofing above the pipe and the lower part over the roofing below, then fit the storm collar round the pipe on top of the sleeve.

Checked before it can be exported

Every pattern SheetMorph draws is checked against the 3D part it comes from. For this example:

• Surface connectivity (passed): 66 facets form a sleeve standing on a base plate: every edge inside a part joins exactly two facets, every open edge one (V - E + F = 1).
• Developed edges equal true 3D lengths (passed): 198 facet edges compared between the 3D surface and the flat pattern (max deviation 5.12e-13).
• Shared edges and seam closure (passed): 64 internal edges are shared vertex-for-vertex between adjacent facets; 1 seam(s) have mating edges of equal true length (max deviation 5.68e-14).
• Developed facets consistently oriented (passed): All developed facets are counter-clockwise (outside face up); none is mirrored or degenerate.
• Developed area equals surface area (passed): Facet area in 3D and in the flat pattern agree (difference 1.16e-10).
• Cut outlines closed and non-overlapping (passed): 2 closed outline(s); no outline crosses itself or another outline.
• HOLE-SLEEVE lies within its plate (passed): 128 points of the hole compared with the edges of the plate; its developed area is 84818.9159.

Assumptions

• The pattern is developed on the mid-thickness surface; inside or outside sizes are converted to it by the thickness.
• Curves are chains of chords between division points.
• No seam, lap, weld-preparation or pressing allowance is added.

Limits of this module

• The roof is one plane; a flashing on a ridge, a hip or in a valley is not modelled.
• The base plate is a plain rectangle centred on the pipe; a plate set further up the slope, or with turned-up sides, is not drawn.
• The storm collar, the clamp and any sealant are not modelled.
• The sleeve is joined to the plate on the line of its foot: no flange is turned on the sleeve to lie on the plate (add one with Fabrication).
• Curves are chains of straight chords between division points.
• No seam, lap, weld-preparation or pressing allowance is added, and plates are not nested onto stock sheets.

Conventions

Coordinate system. The part stands on the Z axis with End A at Z = 0. Angles round the axis are measured from +X toward +Y, counter-clockwise seen from +Z.

Divisions and thickness. A circle is divided into 4N equal chords. Sizes are inside, mid-thickness or outside sizes; the pattern is developed on the mid-thickness surface and the views show the sizes as entered.

Roof and pipe. The pipe stands on the Z axis. The roof rises toward +X at the pitch given, and its plane passes through the origin where the pipe meets it. The sleeve’s height is measured along the axis, from the roof to its top, which is level.

Sleeve. The sleeve’s top is as wide as given, to take the storm collar round the pipe. A cone sleeve is as wide as its base diameter where its axis meets the roof; it is longest on the down-slope side, where its seam is, and shortest up the slope.

Base plate. The base plate lies on the roof, centred on the pipe, its length measured up the slope. The hole in it is where the sleeve stands on it: longer up the slope than across, by the pitch.

Laying. The upper part of the base plate is laid under the roofing above the pipe and the lower part over the roofing below, so that water runs over it. Lap, solder or seal the sleeve to the plate as the roofing needs.

Change the sizes to your own in SheetMorph, check the drawing, add seam and flange allowances, and export DXF, PDF, SVG, CSV or G-code. Check every pattern against your own standards before cutting.

Other pipe ends and nozzles

• Angled Cut: A length of round pipe with one or both ends cut at an angle: mitered ends, wedges and oblique lengths.
• Pipe on Plate: A round pipe standing on a flat or sloping plate, such as a roof: the pipe cut to the slope, and the plate with its hole.
• Nozzle on Head: A round nozzle set onto a dished or hemispherical head, on its centre or off it: the nozzle unrolled with its saddle cut.
• Pipe on Elbow: A round branch set onto a segmented bend, on its outside or on its side: the branch unrolled with the saddle that fits the gores.
• Nozzle on Sphere: A round nozzle on a sphere made in zones, radial or upright: the nozzle unrolled with its cut, and the zone it stands on with the hole marked.
• Bellmouth: A flared inlet to a round duct or a fan, with a straight spigot: made in rings, each part of a cone, or in petals pressed to the curve.