Yes, using the flat roof range rather than a pitched roof window. Those are a different product: a glazed unit made to sit on a kerb on a shallow fall, with a separate top cover in flat or curved glass that sheds the water. Fitting a pitched roof window to a flat roof is a different question, and it needs a kerb built up to a slope.
Why a pitched window will not simply sit on a flat roof
Because of the minimum pitch, and the reasoning is on can you fit a roof window to a flat roof.
What that page does not cover is the product family made specifically for the flat case, which is what follows.
What the flat roof product is
A kerb mounted unit in two parts.
A glazed base unit sits on the upstand and is weathered into the roof covering, and a top cover sits over it and does the shedding.
It is designed around water lying rather than running.
The top cover
The part that distinguishes it, and it comes two ways.
A curved cover in a clear polymer sheds water by its own shape and is the more forgiving on a very shallow fall. A flat glass cover looks considerably better from an upper window and asks a little more of the fall.
Which one suits is usually decided by what overlooks the roof.
Why a curved cover works on almost nothing
Because the curve makes its own pitch.
Water runs off a domed surface regardless of what the roof beneath it is doing, which is why the curved version is specified where the fall is minimal or uncertain.
Why a flat cover looks better
Because it reads as a pane rather than as a dome.
Seen from a bedroom window above a rear extension, a flat cover is a quiet rectangle where a curved one is a bubble, and on a house where the roof is overlooked that decides it.
The kerb
Common to every flat roof rooflight, whatever the brand.
How high it should be, how it is insulated and how the covering is dressed up it are set out on how high should a rooflight kerb be.
A flat roof window is a product that sits on a kerb, not a product that replaces one.
Fixed and opening versions
Both exist, and the opening ones are worth considering.
Manual, electric and solar opening versions are made, which turns a rooflight into ventilation for a kitchen or a shower room without any other work.
What that adds is on the electric rooflight installation page.
Sizes
Fewer than the pitched range, and it matters.
The flat roof family runs to a set of standard sizes rather than the full size code grid, so the opening is set out to the product rather than the product found for the opening.
It is checked before a kerb is built.
Where a bespoke flat rooflight is better
On a larger opening.
Above the standard sizes, a made to measure flat rooflight with a slim frame is generally the better answer visually and dimensionally.
That product is on the flat roof rooflight installation page.
The insulation at the kerb
Where a flat roof installation is most often let down.
A kerb insulated on the outside face only leaves a cold ring under the unit, and that is where the condensation appears in a kitchen in January.
It is the same failure whatever product sits on top.
Ventilation of the roof build up
Worth raising, because it depends on the roof.
A warm deck and a cold deck flat roof handle moisture differently, and cutting an opening into one that was built as the other is where problems start.
Which one is there is established before anything is cut.
Fitting to an existing flat roof
Entirely possible, with the covering as the question.
A new kerb is built into the existing deck and the covering is dressed up it, which on felt means a torched detail and on a single ply means a welded one.
That is covered on can a rooflight be fitted to an existing flat roof.
Walking on it
Neither cover is a floor.
A standard top cover is not made to be walked on, and where a roof is used as a terrace the product is a walk on unit designed for imposed load.
That range is on the walk on rooflight installation page.
Cleaning it
Easier than a pitched window and it needs doing more often.
A shallow pane collects what the wind brings and does not shed it, so a flat roof unit wants clearing a couple of times a year where a steep pitched one largely cleans itself.
When a pitched unit on a kerb is still right
Where escape is the requirement.
Where a flat roof unit cannot provide a compliant clear opening and a room needs one, a kerb built to the minimum pitch and a top hung window is the route.
Condensation on the underside
Common on a flat unit and it is not a fault.
A shallow pane over a kitchen collects the moisture the room produces, and because the surface is nearly level the water sits rather than running to an edge.
Why that happens is on why is there condensation on my flat rooflight.
Noise in heavy rain
A fair question about a curved polymer cover.
A domed sheet over a bedroom is audible in a downpour where a glass cover is not, which is one reason the flat glass version is usually specified over a room somebody sleeps in.
Where two units are better than one
On a wide flat roof, and for the same reason as on a pitched one.
Two standard units spaced across an extension roof light the space more evenly than one in the middle, and they stay within the standard sizes rather than pushing into bespoke.
How many a roof wants is on how many rooflights does a flat roof extension need.
What we take on a VELUX
We take the fall with a gauge and look at what overlooks the roof before choosing between a curved and a flat cover, because those two decisions between them settle the product.
The rest is on the VELUX window installation page.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.