The short answer
Yes, VELUX roof windows can be fitted side by side, and it is a standard arrangement. The pair shares a combination flashing made for that layout, and a rafter sits in the gap between the two frames. The width of that gap follows the flashing you choose and the rafter spacing, so it is set at survey and checked against current VELUX data before anything is cut.
What a pair of windows needs from the roof
Two windows in one opening behave as one detail. They need one weatherproof collar around both, and the structure under the gap has to carry the load that two holes remove.
A single roof window sits between two rafters, with short timbers called trimmers across the top and bottom of the opening. A pair is the same idea stretched wider. The two frames are set close together, and the flashing that surrounds them is made as one piece with a shared strip in the middle. That strip covers the joint between the frames, so rain has no seam of its own to find.
The gap matters because something has to fill it. In a well planned pair that something is a rafter, left in place. Keeping it means the roof is not weakened where the two windows meet, and it gives the lining inside a solid line to finish against. Where the rafters do not fall in the right place, the framing is altered instead, with new trimmers and doubled timbers. That is a structural change and it is planned on paper first.
The two windows do not have to match in size, but a pair of identical sizes is easier to flash, easier to line and easier to live with. Two different heights side by side leave a stepped edge that somebody has to detail. We raise that at survey, because it changes the quote.
For the flashing families themselves, see our page on VELUX flashing types. The combination kits are an extension of those.
How the combination flashing holds two windows together
A combination flashing is sold for a chosen roof covering and a chosen layout. It is not a universal part, so the covering on your roof decides the code.
The kit is made up of the individual side and corner pieces you would use on one window, plus a connecting piece that bridges the space between the frames. The installer slides it in sequence with the tiles or slates, lapping each piece over the one below, so that water always runs onto the next layer rather than behind it. Laps go from the bottom of the opening upward, and the top apron goes on last.
Two points catch people out. First, the flashing for a pair is chosen for the roof covering, such as plain tile, pantile or slate, and the wrong one will not lap correctly. Second, each layout has its own kit: side by side is one product family, and one window above another is a different one. The two cannot be mixed, so the layout is agreed before the order is placed.
Roofs around Crawley include concrete interlocking tiles from the New Town years and clay plain tiles on older houses. Each of those needs the matching flashing variant, and the batten gauge has to suit it. We record the covering and the batten gauge in the survey notes so the right kit arrives.
Setting the gap for the lining inside
The space between the two frames is decided from inside the room as much as from the roof. The lining is the part you will see every day.
Inside, each window has a lining that runs from the frame to the plasterboard ceiling or sloping wall. With a pair, there is a short section of wall or ceiling left between the two linings. If the gap is wide, that section is generous and needs its own plastering and painting. If it is narrow, the linings almost meet and the finish is neat and quick.
There are three practical choices, and the table sets them out.
| Gap choice | Inside look | Roof side |
|---|---|---|
| Narrow, at the kit minimum | Linings almost touching, one wide glazed band | Least flashing exposed, a rafter may be cut back |
| Set to a rafter | A clean strip of wall between the windows | Structure untouched, simplest framing |
| Wide, set by the room | Windows centred on a bed or desk | Extra framing, more lining work |
The middle row is the one that tends to win. Setting the gap to fall on an existing rafter keeps the roof structure intact and the framing simple. The narrow option gives the most glass for the width but may mean altering the timber. The wide option is chosen when the room layout insists on it, for example two windows centred over a pair of bedside tables.
Insulation goes into the gap too. The collar and the underfelt collar that come with a window frame carry the thermal and weather line around each frame, and in a pair they have to meet properly in the middle. Our page on the insulation collar and underfelt collar explains the two parts.
Sound, light and the pair
Two windows bring more glass, and more glass means more light. It also means more roof surface for the sky to reach. That is where the quiet spec applies.
Two panes beside each other each hear the weather. Rain and aircraft reach both, and a loft bedroom with a pair above the bed has twice the glass facing the sky. The answer is the same as for a single window: choose the glazing build for the noise in the room, most usefully a laminated acoustic pane with well fitted seals. Choosing one build for both windows also keeps the sound of the pair even, so one does not ring while the other stays dull. Our page on glazing options for a quieter loft goes through the choices, and the written quiet spec records the one we propose for your room.
Daylight comes first, of course. Two windows side by side spread light along a wall, which suits a long room or a loft with a low eaves edge. They are a good answer where a single large window would be too tall for the roof pitch or too heavy to open comfortably.
What a survey looks at before a pair goes in
A pair is straightforward once the facts are in. The survey collects them so nothing is decided on the roof with the tiles already off.
- The roof covering, and the batten gauge under it.
- Where the rafters fall, and how far apart they are.
- The pitch of the roof, because each window has a range it suits.
- The ceiling and wall finish inside, which sets the lining detail.
- Where beds and desks will stand, so the windows line up with real life.
The work is installed to current Building Regulations, and we handle the Building Control notification where the work is notifiable. Structural alteration to the rafters, where needed, is part of that assessment. Replacing an existing single window with a pair is a larger job than a like for like swap, because it reopens the roof structure. Whether a new VELUX fits the old opening is a separate question, covered on its own page.
Sizes are read from the code on the window, and choosing two that suit the roof comes down to that reading. See how to read a VELUX size code if you want to work out candidates before we visit. To talk it through for your roof, use the quote form, and the parent page on VELUX window installation in Crawley shows the wider service.
Questions about fitting two VELUX windows together
Can the two windows be different sizes?
They can, but the flashing and the lining both become more complicated. Matching sizes give a level top and bottom edge. Different heights leave a step that has to be detailed separately, so we agree it at survey.
Does fitting a pair need a new rafter layout?
Not always. When the gap can be set to fall on an existing rafter, the structure stays as it is. When the rafters are in the wrong place for the room, the framing is altered with new timbers, and that is planned before work starts.
Can I stack one window above another instead?
Yes. That arrangement uses a different flashing family from side by side. It suits a room where the roof is long from eaves to ridge and you want the glass to run up the slope. Both layouts are assessed in the same survey.
Do two windows mean double the noise?
They mean more glass exposed to the weather, so the glazing choice matters more. A laminated acoustic pane in both windows, with the seals checked, keeps the room calm. The size of window for a loft bedroom and the glazing are decided together.