A rooflight flashing kit is the set of preformed metal sections that weathers the join between the frame and the roof covering, and choosing the wrong one is the mistake you cannot correct without pulling the unit out. The kit you need is set by two things: the covering type, because the metal has to sit down into the tile or slate profile rather than bridge across it, and whether you are fitting a single unit or a run of them, because units side by side or stacked up the slope share a combination kit rather than each getting its own. There are recessed variants for flush installations too. Once the right kit is on site, it goes on in one order only: apron first at the bottom, side sections and soakers interleaved course by course up the sides, head flashing last under the covering above.
This page is about selecting and fitting the kit. The covering-by-covering profile table is on the main pitched roof skylight installation page, and the specific slate detail is on what flashing you need for a slate roof.
The four parts and what each does
Every flashing kit, whatever the covering, has the same four elements:
- The apron, the bottom flashing, sits below the window and is dressed down over the course beneath, throwing water clear onto the covering.
- The side sections and soakers run up the sides of the opening, interleaved with each course of tile or slate, so every course discharges onto the one below without water reaching the frame.
- The head flashing sits under the covering above the window and dresses down into its profile. Water arriving from above runs over it and is deflected around the unit.
- The drainage gutter behind the head, on most modern kits, catches anything that gets behind the head flashing and discharges it out to the sides.
Choosing the kit: by covering
The metalwork has to sit down into the profile of the covering. Bridge across a raised tile and water runs under. So the kit is matched to how deep and how profiled your covering is. In short:
- Flat coverings, natural or fibre cement slate, flat concrete tile and shingle, take a flat-profile kit with short soakers. This is the neatest and easiest to get right, and the standard on Victorian slate across central Ipswich. The specific slate interface is on the rooflight to slate roof interface.
- Plain tile, thicker than slate and double-lapped, takes a flat kit but sits slightly higher with longer soakers.
- Interlocking concrete tile, with a raised interlock rib up to about 45mm, takes a standard profiled kit deep enough to bridge the rib.
- Clay pantile and deep-profile coverings, with an S-curve of 50mm or more, need a high-profile kit with a deep-pressed apron that reaches into the trough of the tile. Suffolk is pantile country and this is where the most gets got wrong.
- Irregular handmade Suffolk pantile often needs individually dressed lead soakers rather than any boxed kit.
The full profile-depth table lives on the hub page so it is not repeated here. Fit a flat kit to pantiles and you leave a void under every roll, which someone fills with mortar, and that mortar cracks within three winters. That single error is behind a large share of the leaks covered on pitched rooflight flashing leaks.
Single, combination and recessed kits
Single kit
One unit on its own takes a single kit: one apron, two sets of side soakers, one head. Most jobs are this.
Combination kits
Where two or more units sit together, they do not each get a full single kit. They share a combination kit, which weathers the junction between the units as well as around the outside. There are two arrangements:
- Side by side, on the same course. A combination kit weathers the two outer sides and the covering strip between the units, keeping the gap between them narrow and neat. This is how a pair of units lighting one loft room is usually done.
- Stacked up the slope, one above the other. A combination kit weathers the junction between the head of the lower unit and the apron of the upper one, which is a detail a pair of single kits does not handle. This lets you run a tall glazed area up a slope without a leak between the units.
The gap between combined units is fixed by the kit, so it has to be designed in from the start. You cannot fit two single units close together and expect them to weather the gap. If you want a paired or stacked arrangement, we specify the combination kit at survey.
Recessed variants
A flush-fit unit sits lower in the roof, so it needs a recessed flashing kit with a deeper apron and head to reach from the dropped frame up onto the covering. This is a different kit from the standard one, not an adjustment of it. The flush detail is covered on flush-fit rooflights for pitched roofs, and on period and conservation roofs we more often dress lead throughout instead of using a proprietary recessed kit.
| Arrangement | Kit | Why |
|---|---|---|
| Single unit | Single kit for the covering | Weathers the four sides of one opening |
| Two or more side by side | Combination kit, same course | Weathers the covering strip between units |
| Two or more stacked up the slope | Combination kit, stacked | Weathers the junction between lower head and upper apron |
| Flush-fit recessed unit | Recessed kit or dressed lead | Deeper apron and head reach from the dropped frame to the covering |
| Conservation or listed roof | Dressed lead throughout | No visible aluminium, formed to an irregular covering |
The fitting sequence, up the slope
Flashing is fitted in one direction, from the bottom of the opening upward, so that every piece laps over the one below and water is always carried onto a lower course, never into a joint. Fit it out of order and you build laps that face uphill, which fill with water. The sequence:
- Set the frame first, at the right depth. The manufacturer specifies a fitting depth relative to the tile batten for each covering. That dimension is what makes the whole flashing geometry work. Set the frame too high and the head flashing bridges the covering above instead of dressing into it, which is the single most common cause of a leak. Check the frame square and level across both diagonals before fixing.
- Underfelt collar. Before any metal, the roofing underlay is cut to pattern, formed into a collar, taken up the outside of the frame, and dressed out over the underlay of the course below so the second line of defence is continuous. This is covered as one of the two collars on the hub page and it goes in first.
- Apron, at the bottom. The apron clips to the bottom of the frame and dresses down over the covering in the course below, throwing water clear.
- Side sections and soakers, course by course. As the covering is re-laid up each side of the opening, a soaker is interleaved with every course so each one discharges onto the course below. This is the slowest and most-skimped part, and short soakers work for about two years before they let go.
- Head flashing, last. The head goes under the covering above the opening and dresses down into its profile, with its drainage gutter behind it collecting anything that gets past.
- Cut tiles to the metal, not metal to the tiles. The covering is cut to fit neatly around the flashing rather than the flashing bent to fit the covering.
At the end of this stage the roof is watertight. Everything after, the insulation collar, the sash, the internal finish, is dry-side work.
Mortar is never the weathering. Mortar around a rooflight is a bedding and a finish, not a waterproofing material. It cracks. If you can see mortar filling a gap between a flashing and a tile, the wrong kit was fitted and the mortar is holding water out until it cracks. The right kit needs no mortar to weather. This is the tell we look for at survey on a leaking unit, and it is covered on flashing leak diagnosis.
Exposure and coastal detailing
On exposed and coastal slopes the standard kit lap dimensions, designed for inland gravity drainage, are not enough, because driven rain is being pushed at the slope rather than falling onto it. On the Suffolk and north Essex coast we increase the laps, mechanically fix at the head, and on the most exposed slopes dress lead at the apron rather than relying on a pressed aluminium section, because lead forms tighter to an irregular covering. We also fit 316L stainless fixings and isolate dissimilar metals to stop galvanic corrosion. Estuarine locations such as Woodbridge get upgraded fixings but not the full marine specification, because they carry moderate salt loading rather than open-sea exposure. The full coastal picture is on our Felixstowe page.
Common questions about flashing kits
Why does the flashing kit depend on my roof covering?
Because the flashing has to sit down into the profile of the covering, not bridge across it. Flat coverings like slate take a flat kit. Interlocking tile with a raised rib takes a profiled kit. Deep pantiles need a high-profile kit with a deep-pressed apron that reaches into the trough. Fit a flat kit to pantiles and you leave a void under every roll, which cracks the mortar someone uses to fill it within three winters.
Can I fit two rooflights close together with two separate kits?
No. Two units placed together share a combination kit that weathers the covering between them, whether they sit side by side on the same course or stacked up the slope. Two single kits cannot close the gap between the units, and the junction leaks. The combination arrangement fixes the spacing, so it has to be designed in from the start rather than added after.
In what order does a flashing kit go on?
From the bottom up, so every piece laps over the one below. Set the frame to the right depth, fit the underfelt collar, then the apron at the bottom, then the side soakers interleaved course by course up each side as the covering goes back, then the head flashing last under the covering above. Cut the tiles to fit the metal, not the other way round. At the end of that the roof is watertight.
Get the right flashing kit fitted
Tell us what the roof is covered with and whether you want one unit or several, and we will identify the covering profile at survey, specify the exact kit, single, combination or recessed, and include it in one written fixed price. That kit is on site before we start, because nothing goes on the roof until the correct flashing is in stock. Every installation carries a 10-year workmanship guarantee and the installers have 25 years fitting rooflights behind them.
Request a fixed quote for a pitched rooflight in Ipswich, Suffolk or north Essex, or read our published prices first.
Thinking about this job? We survey across Ipswich, Suffolk and north Essex and give you a fixed price before any work starts, with a 10-year workmanship guarantee.