VELUX flashing types: matching EDW and EDL to your roof

A flashing code is not a quality grade. It names a roof covering, so one set of letters is no better or worse than another.

A VELUX roof window is sold in two parts that are easy to confuse. The window has a size code, such as the ones explained in how to read a VELUX size code. The flashing is ordered separately, and its code is written with the same size letters, so a kit is described as a flashing for a given covering type and a given window size. The window and the flashing have to agree on size. They also have to agree with the roof.

That second agreement is where mistakes happen. A homeowner measuring up from a brochure often gets the window size right and never asks what the covering is. The window then arrives with a kit that cannot be dressed into the tiles already on the roof.

Two codes are widely published and are the ones this page names. EDW is the kit for profiled tiles, meaning tiles with a pronounced wave or roll, such as concrete interlocking tiles and pantiles. EDL is the kit for flat coverings, meaning slates and thin, flat tiles that lie in even courses. Other kits exist for other situations, including recessed fitting and unusual coverings. Those are described by what they do in the sections below. The exact letters and the depth limits printed on each kit should be read from the current VELUX catalogue for the specific window, not from a web page.

Profiled tiles have hills and valleys across their width. Flat slates have neither. The two kits exist because the gap they must close is a different shape.

Take a concrete interlocking tile. Its surface rises and falls, and the valleys between the rolls carry water down the slope in narrow channels. A flashing for that surface has to stop those channels at the frame and pass the water round it. The EDW kit does this with a flexible lower apron and side pieces that can be moulded into the profile, so the metal follows the wave instead of bridging it.

A slate roof behaves differently. Each slate overlaps the one below, and water runs over the whole surface in a thin, even sheet. There are no valleys to follow. The EDL kit therefore uses a flatter set of pieces that slide beneath the slates at the sides and lie over the slates at the bottom, like an extra course of the roof.

The table sets the two side by side, which is the comparison behind a search for VELUX EDW vs EDL.

If a roof is half one material and half another, the kit follows the material the window sits in, and the survey records which one that is. The kit is never a compromise between the two.

Crawley grew as a New Town from 1947, and its housing shows it. Brick semis with concrete interlocking tiles are the common picture in the neighbourhoods built in the post-war decades, which points toward EDW for the lofts converted since.

That is a starting guess, never a decision. A tile that looks profiled from the pavement can turn out to be a shallow double roll, a plain clay tile laid in the old way, or a mixed covering after an earlier change to the roofline. Older tile-hung cottages toward the Weald can carry handmade clay plain tiles, which are flat in section and behave more like slate for flashing purposes. The eye from the ground is not enough, and this is why the loft hatch and the ladder both come into the survey.

The covering is checked at the exact spot the window will sit. A roof can change tile type at a ridge, at a dormer cheek or at an old extension line, and a window placed across such a change needs a different conversation. The general principles of dressing a kit to tiles and slates are covered in the roof window pages. This page stays with the codes and with the decision between them.

Slate asks for the most careful dressing, because the lap between slates is thin and the roof has no valleys to hide a poor junction.

Natural slate and fibre cement slate both count. They are laid in regular courses with each slate covering the joint of the two below, and the flashing has to work with that logic. The side pieces are slid under the slates that run alongside the frame. The apron at the bottom sits on top of the slates below the window and is shaped to their thickness, so water running off it lands on the roof surface and does not get behind it.

A few slate conditions call for a pause:

• Old slates that are brittle at the edges and may crack when lifted.
• Slates laid to a very low pitch, where water moves slowly and the lap becomes critical.
• Reclaimed or mixed-thickness slates, where the apron cannot sit evenly.
• A home in a conservation area, where the covering is often protected and the choice of window is part of the approval. The conservation rooflight installation hub covers that side.

In each case the flashing type is still EDL, but the way it is fitted changes. That is the difference between a kit and an installation.

A standard VELUX sits on the rafters with the frame standing proud of the roof covering. A recessed fit sinks the window lower so the glass lies closer to the plane of the roof.

The appeal is appearance. A recessed window looks tidier from the street and sits lower against the tiles, which matters to people who dislike the raised frame, and to planning officers in sensitive roofs. It also changes the geometry of the water path, so the ordinary flashing is not used. A recessed installation has its own kit, its own support brackets and its own depth limits, and these are set out in VELUX documentation for each window size.

Two practical points follow. First, recessing a window changes the depth of the roof build-up around it, so the insulation has to be planned with care. The page on the VELUX insulation collar and underfelt collar explains the layers that sit beneath the flashing. Second, the roof opening does not change. A frame that was right for a standard fit will not always suit a recess, so the decision is made at the order stage, not on the day.

Every flashing kit is made for a range of covering depths and a range of roof pitches. A kit used outside those limits is one that has not been designed for the job.

Depth is the thickness of the covering, measured from the top of the battens to the highest point of the tiles. A deep, rolled concrete tile sits higher than a thin slate, and the kits are made to match. Pitch matters because water moves faster on a steep roof and slower on a shallow one. A shallow roof needs a more generous lap at the head and the sides, since wind can push water sideways and upslope as well as down.

The range of pitches the window itself accepts is covered in which VELUX is best for a low-pitched roof. When the pitch is at the lower edge of what the window allows, the flashing choice becomes more sensitive, and the survey takes more care with the underfelt and the tray behind the head of the frame.

Depth is also where a re-covered roof catches people out. If the original tiles were replaced with a thicker or thinner product after the window went in, the old kit may now sit outside its range. That is one of the first things to check when a window is being swapped.

The metal on a finished roof window is seen every day from the garden, so its colour and its dressing matter more than people expect.

Flashing kits are offered in a small range of finishes, commonly a dark grey, chosen to sit against tiles and slates. Dark grey suits slates and dark concrete tiles. A warmer tile sometimes suggests a brown or red-toned option. It is a matter of judging the roof as it looks now, not as it looked when laid, because weathered tiles are lighter and more varied than a brochure sample.

The finished junction should show three things from ground level:

1. A neat line of metal at the head, tight to the covering, with no daylight showing under it.
2. Side pieces that follow the tile profile, or lie straight against slate, without buckling.
3. An apron at the bottom that rests evenly on the covering below and is not lifted by a slipped tile.

A window that looks crooked on the roof has often been fitted with a flashing that was forced. A kit that matches the covering falls into place with little coaxing.

Rain falling on a metal apron and on glass makes a sound inside the loft, and the flashing is part of that story. It does not decide it.

The sound of rain in a loft bedroom comes mostly from the glass. A laminated acoustic inner pane and well fitted seals calm it far more than any flashing will. The flashing has a smaller part. A properly fixed, well supported apron does not rattle in the wind and does not tick as it warms and cools. A loose one does.

So the choice is made in a set order. The glazing is chosen for the noise the room hears, as laid out in the VELUX glazing options for a quieter loft. The flashing is chosen to suit the roof and then fixed firmly. The written quiet spec that comes with every quote records the glazing and seals, and the survey note beside it records the covering the flashing must suit.

Replacing a VELUX in an existing opening raises a practical question: is the old flashing still the right one?

Sometimes the answer is to renew the flashing with the window. A flashing that has sat in the weather for years can lose its flexibility, and an old apron does not always lie down as it should against a new frame. A new window in an old kit asks two generations of product to work together. Whether a new unit goes into an old hole is handled in will a new VELUX fit my old VELUX opening.

The survey looks at the old kit for three things: whether its code matches the covering, whether the pieces are intact, and whether the roof was re-covered since the window went in. A roof re-tiled with a different product around an older window is a common cause of a mismatch. The old kit was right for the old roof and is wrong for the new one.

When the answer is to renew, it is written into the quote as a line of its own so you can see it.

A flashing quote begins with a short list of observations, and each one is written down so the order matches the roof.

• The covering type at the exact window position, with a photograph of it.
• The approximate depth of the covering and whether it is uniform.
• The roof pitch, taken from the loft, not guessed from below.
• Whether the fit is standard or recessed.
• The finish that suits the roof as it looks today.
• Any earlier window, flashing or re-covering visible on the slope.

These go onto the order and into the job file. The work is installed to current Building Regulations, and where it is notifiable we handle the Building Control notification. If the window is part of a wider loft plan, the VELUX window installation hub shows how the pieces fit together, from size to glazing to finish. To start the conversation, use the quote form or send a photo of the roof by WhatsApp.

These are the points that come up when someone is comparing a kit on paper with the roof in front of them.

Can an EDW kit be used on a slate roof?

No, and there is no reason to try. The profiled kit is shaped for waves and rolls. On slate it would sit proud and leave gaps under the aprons. Use the kit made for flat coverings.

Is EDL only for natural slate?

The published description covers flat coverings in general, so fibre cement slates and thin flat tiles fall under it as well. The deciding factor is how the covering is laid and how deep it is, which the survey measures on the roof itself.

Does the flashing code affect the window's glazing?

No. They are separate choices. The glazing is picked for light, heat and sound, and the flashing is picked for the roof. Both are listed on the quote, along with the size code, so nothing is assumed.

How do I find out what flashing my existing window has?

Look for the data plate on the frame, as described in where the data plate is on a VELUX window. The plate gives the window size and type. The flashing is identified from the roof and from any marking on the metal, and a photograph of the junction is usually enough to confirm it.