COP v3.0:penetrations; boot-flashings

9.5 Boot Flashings 

A boot flashing is a proprietary EPDM flashing designed to weatherproof cylindrical penetrations protruding from a roof or wall. The top is trimmed to form a tight weatherproof collar around the penetration, and the base is formed with a series of concentric rings to the underside and a malleable stiffener of aluminium which is dressed to conform to the shape of the roofing profile. It is generally top-fixed to the roof surface with screws or rivets, and sealant.

The Profiled Metal Roofing COP allows pipe penetration flashings to be fitted directly to the profile or on to an over flashing. Pitch limitations depend on the method used and the cladding profile.

Direct-fixed options are pitch sensitive. When laid directly on to the profile at too low a pitch, they will entrap water rather than allow it to discharge over the profile crests that they traverse. The practical limits of direct-fixed boot flashings that cross an entire pan are 8° for standard corrugated and 10° for low rib trapezoidal products. Where the base of a boot does not obstruct a pan it can be direct-fixed to the minimum pitch for that profile.

Direct fixed applications for high rib trapezoidal profiles and trough sections vary according to the profile, and the size and position of the penetration. For these applications, the manufacturer should be consulted or the flashing can be attached to an over flashing, or a top fixed soaker type can be used.

Where the penetration is wide such as a chimney flue casing, and the penetration is far from the apex, soaker flashings may be used where the profile ribs are cut back so water can divert into the adjacent pan.

Where overall width is not a constraint, directly fixed boot flashings should be installed with their edges diagonal to the fall of water. Where this is not practical, they may be laid square at pitches of 10° or more.

Where boot flashings traverse a lap, the lap must be fully sealed or other actions must be taken to avoid leaks through capillary action. Where possible the fixing of a boot flashing over a lap should be avoided

The vertical sections of a boot flashing must not constrict the free flow of water. Where more than 50% blockage of the pan occurs other penetrations must be considered, or catchment calculations of the capacity of the remaining pan area should be made. (See 5.4.7 Gutter Capacity Calculator)



9.5.1 Boot Flashings to an Over Flashing 

Boot flashings fitted to an over flashing are acceptable at pitches down to the minimum of that allowed for the profile. Typically, this is 8° for standard corrugated, and 3° for trapezoidal and trough sections. These boot flashings must be fixed diagonally to the fall of the roof at pitches below 10°.

Over flashings can be continuous to the apex, or terminate with a soaker at the upper edge.

9.5.2 Other Applications for Boot Flashings Plant Room And Conduit Penetrations 

Where flexible power conduits or telecommunication cables are required to penetrate the roof cladding, accessibility can be improved by using P.V.C pipe fittings and an E.P.D.M. flashing to weather a number of conduits.

Cable penetration flashings must be goose-necked. It is not acceptable to exit cables through a vertical flashing such as a boot flashing where sealant is the only barrier to water leakage. PVC and E.P.D.M Flashing

This flashing should be fixed next to the purlin for support.


Safety bollards for fall arrest anchorages are required where regular maintenance is required, and these can also be weathered by E.P.D.M. flashings. Mechanical Services 

Where plant room supports are required to penetrate the roof cladding, the designer should provide the support framing from Circular Hollow Sections (CHS) in preference to Rectangular Hollow Sections (RHS) or other hot rolled steel sections, because it is easy to flash the CRS with E.P.D.M. flashings. This procedure allows the E.P.D.M. flashings to be slid over the pipe framing during erection, and avoid the necessity of using retrofitting types.

The support framing should be in place, but below the top of the purlin, before installing the roof cladding. That allows the cladding installation to proceed without having to weatherproof multiple penetrations at the same time.


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Proprietary support systems are available for lightweight support through to the purlins.


These types of supports provide clearance for cleaning but should not create an unwashed area underneath them.




9.5.3 Flush Penetrations 

Penetrations such as roof window may be mounted flush with the crests of the roofing profile.  In such cases, the side flashing onto the roof shall be the same as required for a barge cover. The flashing termination onto the roof window shall be as per window manufacturers requirements