Pipe flashing is designed to create a flexible weatherproof seal around pipes and other roof elements such as chimneys. To make sure your roof pipe flashing is doing its job properly, you need the right size for your pipework.

The question is:

What size flashing do I need?

To help you figure this out, at Roofing Superstore we’ve put together a pipe flashing size guide to popular brands, including Dektite ranges and Aztec Master Flash.

Here’s what we have in store for you.

Table of contents:

What thickness are flashings?

The International Building Code, 2015 Edition, Section 1503.2-Flashings stipulates that roof flashing must be installed at roof intersections in such a way as to prevent moisture from entering the roof and wall of a building.

When it comes to metal flashing, the metal must be resistant to corrosion and at least 0.019″/0.483mm thick (no.26 galvanised steel). But wait! There’s more:

The nominal thickness of the flashing will vary depending on the material. As per the Metal Cladding & Roofing Manufacturers Association, the typical thickness of steel flashing in the UK is 0.7mm, while the corresponding figure for aluminium is slightly higher at 0.9mm.

How many inches should flashing overlap?

When installing flashings, you should make sure they overlap by at least 4″/102mm.

However, keep in mind that under some circumstances, such as high winds, you might want a bigger overlap to prevent water from creeping in.

In addition, roof valley flashing requires a bigger overlap of at least 6″/152mm. If in doubt, always contact the manufacturer.

Having addressed some of the most common questions that pop up when discussing pipe flashing sizes, let’s take a closer look at some specific examples.

Dektite roof flashing

Dektite offers a highly versatile range of pipe flashings you can use to seal gaps or connections on your roof quickly and easily. Featuring a tough watertight seal and a strong base, they come in different shapes and sizes to accommodate various applications.

Dektite Premium and Dektite EZi-Seal size chart

Available in EPDM or silicone and edged with a flexible aluminium band, Dektite Premium is perfect for flashing pipes on metal roofs. Dektite EZi-Seal features a highly innovative, non-absorbent and non-porous sponge gasket which seals through compression.

Both types are available in the same size range.

Pipe ExternalRoof Pitch
0-35mm0-45°100 x 100mm
5-55mm0-45°139 x 139mm
5-76mm0-45°178 x 178mm
5-127mm0-45°221 x 221mm
75-175mm0-45°280 x 280mm
100-200mm0-45°310 x 310mm
125-230mm0-45°363 x 363mm
150-300mm0-45°456 x 456mm
170-355mm0-45°496 x 496mm
230-508mm0-45°681 x 681mm

Dektite Diverter size chart

Dektite Diverter is designed to reduce and divert rainwater pooling on very high- or low-pitched roofs. It’s available in the following sizes in either grey EPDM or red silicone.

Pipe External Roof PitchBase Size
75-155mm0-60°410 x 360mm
114-254mm0-60°485 x 460mm
254-406mm0-60°708 x 635mm
380-610mm0-60°1006 x 905mm
235-425mm0-40°750 x 660mm

Dektite Combo size chart

Another popular choice with professionals and homeowners alike, Dektite Combo allows you to flash over or around for maximum flexibility and convenience. You can get it in grey EPDM, black EPDM or red silicone in a wide range of sizes.

Pipe External Roof PitchBase Size
5 - 60mm0-40°139 x 139mm
45 - 85mm0-40°177 x 177mm
5 - 127mm0-40°218 x 218mm
75 - 175mm0-40°285 x 285mm
108 – 190mm0-40°365 x 365mm
125 - 230mm0-40°365 x 365mm
150 - 280mm0-40°454 x 454mm
175 - 330mm0-40°454 x 454mm
240-508mm0-40°685 x 685mm
350 - 760mm350-500mm cut is <30°1000 x 1045mm

Aztec Master Flash sizing chart

Aztec Master Flash standard roof flashing for pipe is an ideal solution to for waterproofing various pipe fixings. They’re suitable for use on different roof structure types regardless of the location of the pipework. The following sizes are available in either EPDM or silicone.

Model Pipe SizePipe SizeTop Opening Diameter Cut to Suit Pipe SizeBase Dimensions
#222-101mm22mm 22-101mm152mm
#6121-254mm95mm 121-254mm304mm
#9241-520mm203mm 241-520mm635mm

Final thoughts

Pipe flashings come in a huge range of shapes and sizes in order to accommodate various applications.

That’s why you need to be absolutely sure what size you’re going to need before you purchase roof pipe flashing for your next roofing project and go on to install it.

What’s more:

Pay attention to the roof pitch specifications since not all flashings can be used on very high or very low roof pitches.

The bottom line is:

Measure your roof pipe size carefully, consider your roof pitch and explore the available lead, EPDM and silicone roof flashing for pipe options carefully.

If you have further questions about the size of the pipe flashing you’ll need for your next roofing project, feel free to give us a call at 01752 692 760. Alternatively, open the chat box in the bottom right-hand corner of your screen to speak to our experts.

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