Most of us don't think much about our homes' roofs, so we don't know much about roofing terms. But one of the most important things a house does is protect us from the weather. This includes keeping water out, which your roof does a great job of.
If your roof is fully waterproofed, you won't have to worry about problems like rot, mould, and structural damage. Flashing is one of the materials and design features built into a house's roof to make it waterproof and keep this damaging water out. In this article, we'll talk about roof flashing, including what it is, why it's important, and what it's made of.
Where a roof meets a vertical structure, there are natural weak spots, such as joints and places where you can get inside. Penetrable sections are holes or openings in the surface of a roof that make it possible for things like chimneys, skylights, vents, and flues to be built. There are joints in places like gutters, walls that touch roofs, and the frames around doors and windows.
All of these can let water in if they are not properly sealed. But it can be hard to make a completely waterproof joint between two metal products or between a metal product and a wood product. Sealing places where pipes pass through can also be difficult because the joints can shrink or expand as humidity or temperature changes.
So instead of just using sealants, roofers use roof flashing as part of a home's overall system of weather-resistant barriers. Flashing is a piece of equipment and a way to keep water out of a building and keep everything sealed while still letting it move. It forms the ends and connections of surfaces and roofing systems. It usually comes in thin waterproof material placed at strategic points on a roof to make a more weatherproof envelope.
Roof Flashing gets its name from how it looks and what it is used for. Different types of a roof flashing are also used in different parts of the world. Each type is made to fit a certain style of roof or building. Among them are:
Roof flashing is put around anything that sticks out from the roof of a building or where there is a break in the roof. This is done to keep water from getting into valleys or seams where water runs off.
A shallow gutter that fits the angle between two slopes inside a roof. Most of the time, it will have a return at each edge to prevent water from getting into the roof space. Depending on the size and purpose, more stiffening ribs may be inside.
Wall flashing is usually found near windows and points of structural support. It can be built into a wall to keep water from getting in or to send water that has gotten in the back outside.
Cap flashing is a hidden flashing that goes above doors and windows to keep water out of the walls.
Sill flashing is a hidden flashing that is put under doors or windows to keep water from getting into the wall.
Through-wall flashing: This type of flashing goes through a wall and guides water to small drainage holes.
Kickout flashing is used to keep water away from a wall. It is found at the bottom of a wall or roof intersection.
Roof penetration flashing keeps pipes, cables, supports, cables, and other things that stick out from the roof from getting wet.
Channel flashing: Made in a "U" to catch water where a roof edge meets a wall.
Apron flashing sends water from a vertical surface to a gutter or covers the joint between a vertical surface and a roof with a slope (at the lower edge of a chimney, for example).
The valley flashing protects the middle part of the roof where two sections meet and direct water away from the roof.
Roll-top ridge flashing: Covers the ridge (or high point) where two tiled or metal roof surfaces meet.
Flat ridge flashing is like roll-top ridge flashing, except the ridge is flatter.
Barge capping flashing is like roll-top flashing and flat ridge flashing, but it is in the shape of a box.
A square or rectangle-shaped gutter that goes around the edge of the roof. It can be made between two roof surfaces or between a roof surface and a parapet wall. Edges can be folded in, out, splashback, or squash fold. A box gutters board usually holds up this gutter to make it stronger and stiffer and reduce damage from roof traffic.
Fascia flashing is attached to the fascia and gives the roof's edge a nice look.
Parapet flashing is a covering used on roofs and walls to keep water out and finish off the ends of masonry walls or vertical sheets.
Pipe flashing is a thin piece of waterproof flashing that is made to fit the shape of pipes and tubes.
Step flashing is made of pieces of flashing that overlap in "steps."
Flashing keeps water from getting into a roof structure in three ways: gravity, wind pressure, and surface tension. It can be put up like shingles, with one piece on top of the next, or it can be sealed to work as one smooth surface. In either case, it uses surface tension to keep water from getting into a house.
Depending on how it's used, flashing keeps water, penetrating damp, and debris buildup away from places where they could get in. It is also used on surfaces that are likely to leak, to protect wall cladding from the weather, and to keep gutters from getting too full, which can cause damage and let toxic moulds grow.
Flashing materials can be very different and chosen based on cost, architectural design, and how well they work with other materials. Flashing should keep water out and fit in with the rest of a building's design. It should also be flexible enough to fit into the cracks and curves of a building where flashings are needed.
Most roof flashing materials are made of metal or rubber these days. Metal flashings can be made of aluminium, copper, zinc alloy, stainless steel, lead, or coated metals like lead-coated copper, galvanised steel, and anodized aluminium. Acrylic, rubber, rubberized asphalt, and butyl rubber are flexible flashing materials. Flashing can be bought as a roll or a membrane, making it easier to put up around roof projections.
The most common types of flashing in Australia are exposed and hidden. Most exposed flashing is made of sheet metal, while hidden flashing is usually made of metal or flexible material and is used around wall openings like doors and windows. Most exposed flashing is either Colorbond® roof flashing, which is steel that has already been painted, or Zincalume® aluminium/zinc alloy-coated steel that has not been painted. Most people use lead substitutes like Wakaflex, rubber, or rubberized asphalt for hidden flashing.
Flashings are a practical and aesthetically important part of the design or renovation of any building. When metal roofing flashing needs to be designed, cut, and fastened, qualified roofers, are an important part of the process. They know what kinds of flashings will work best in different climates and environments, and they can instal them quickly, effectively, and safely. Roofing professionals also follow the standards of the Building Code of Australia. For example, the Installation Code for Metal Roof and Wall Cladding has rules about flashing (HB39-1997). Some important things that these rules cover are:
Even though different cladding profiles use similar metal roofing flashing methods, flashings (other than standard ridging) are usually made from a coil or a flat sheet and shaped to fit each application. If flashings need to match the colour of the cladding sheets, they should be made from pre-painted coils or flat sheets by the same manufacturer using the same process. This will keep the colour from fading and ensure the colours match well.
Flashings and other metal roofing building parts should be made of the same material as the roof or walls. Coated steel products can get damaged and rust faster if they get wet from or come into contact with materials that don't work well together, like treated wood, chemicals, and cleaning products. Galvanic corrosion can also happen when two metals that don't get along are put together. This can happen when lead and copper come into contact with zinc, aluminium, or coated steel; zinc and aluminium flashing with pressure-treated wood, and aluminium with wet plaster or mortar.
The wind puts a lot of force on both the top and bottom of the metal roofing cladding. The roof cladding can collapse inwards if forces come from the inside. Positive wind pressure inside the building and negative wind pressure from outside the building cause forces that push the building away from them. It can separate the siding from the building's frame and the roof from the rest of the building. Because of this, it is very important to fix the roof framing, battens, claddings, and flashings so they can stand up to these forces.
Wind gusts can also cause air pressure differences between the inside and outside walls or the roof. This can make the flashing move back and forth, or "pump," Water can get sucked into a space or joint it is covering. All flashing edges close to the wall cladding or roof should have a sealant, a gap of up to 5 millimetres, or an anti-capillary offset fold to stop water from getting in. Flashing should also have expansion joints on long runs to protect against damage when the walls or roof shrink and grow.
Roof Flashings fasteners keep the metal cladding from flapping, making noise, and bending or cracking when the load changes.
All roof cladding edges that aren't at gutters must have flashing fasteners on both sides. The "wind load" of a building determines how many and how far apart these fasteners should be.