The answer
Yes, in the right roof it can, but a bigger window means a bigger opening, and that changes the roof structure. Rafters are cut and trimmed, the flashing is changed and the lining inside is remade. Whether it works depends on the rafter spacing, the roof pitch and the room below, so a survey comes before any promise.
Why a larger window is a different job
A like for like replacement drops a new unit into the opening that already exists. A larger window cannot do that, because the hole is too small. The roof has to be opened wider, and that touches the structure that carries the weight of the tiles.
The size code on your frame tells you what is there now. The letter is the width and the digits are the height, so a code such as MK04 describes a particular opening. Our size code guide shows how to read yours, which is the first step in choosing something larger.
What the rafters allow
Rafters run down the slope at set spacings. A window between two rafters can grow in height without cutting any, but widening it past a rafter means cutting that timber and carrying its load round the new opening. This is done with trimmers, extra timbers fixed across the gap, and it is work for a fitter who has done it before.
Sometimes the answer is two windows side by side rather than one wide one, because two units sit within the existing rafter pattern. Other roofs need a structural calculation before the first tile is lifted. Once we have seen the roof from inside the loft, we can tell you what is possible.
Pitch, flashing and the covering around it
A larger opening also disturbs more of the roof covering. The tiles or slates round the window are lifted, relaid and sealed with a new flashing kit sized for the bigger frame. The pitch of the roof matters here, because each window is designed to work within a range of slopes, and a low pitch asks more of the weatherproofing.
If the new window replaces an old one, the old flashing cannot be reused with a different frame. The two have to match, so the whole set is changed. Read more in replacing a VELUX window: like for like or upgrade.
What a larger window does to the room
More glass means more of the sky comes into the room, and the light reaches further across the floor. In a loft bedroom or a landing, a wider window can make a small room feel less like an attic and more like a lit space of its own. The ceiling needs thought too. A bigger opening means a deeper splay, the sloped lining that carries the light down into the room, and that is finished by us as part of the job.
Bigger is not always better. A very large window on a south-facing slope can bring in strong sun in summer, and a blind or solar-control glass keeps it comfortable. Opening style matters as well, since a larger sash is heavier to move and may suit an electric opener. We talk through these choices at the survey, with the roof in view.
Rules, planning and the room below
The size you want has to sit within the rules. Part L asks the larger window to reach the same U-value of 1.4 W/m²K, or Window Energy Rating band B, as a smaller one. Where the work has to be notified, Building Control hears from us. Planning is a separate question, and our planning permission guide for Milton Keynes is the place to start.
Indoors, a bigger opening means a bigger lining and a different patch of ceiling to finish. A loft room can gain a lot from more sky overhead, because the light then falls from above and reaches the far wall as well as the floor. Straight up is clear, whatever the street offers at the sides, and a larger window simply shows more of that sky.
Before you ask for a larger window
- What is the size code on the frame today?
- Which way do the rafters run, and how far apart?
- How much wall or ceiling is beside the opening?
- Is the roof in a conservation area?
- Would two windows suit better than one?
Glass, blinds and the other choices
Enlarging the opening is a good moment to rethink the rest. Glass can be chosen for sound, for strength or for sun control. Blinds can be fitted to match, manual or electric. A rain sensor on an electric window closes it when the weather turns, which matters on a larger sash that is harder to reach. These parts are easiest to fit when the window is new.
From survey to a decision
The free survey is where this gets answered. The opening is measured, the rafters are checked from the loft and the covering is read from outside. The quote is written down and holds on the day, and a 10-year workmanship guarantee is given in writing. The wider range of units and options is on our VELUX windows hub.
A photo of the window and its label, sent on WhatsApp (07880 284133) or to info@vertexskylightsmiltonkeynes.co.uk, lets us say a good deal before we visit.
Related questions
Does the same apply to a flat rooflight?
A rooflight on a flat roof stands on an upstand, and its size depends on the joists below and the falls of the roof. The same survey checks both, with the same questions about structure.
Will a bigger window make the room colder?
A new unit is built to meet the energy limits, so a larger one need not leave the room draughty. Glass choice and a good fit decide how it feels, as explained in when to replace a VELUX window.
How long would the work take?
A new opening takes longer than a swap. See how long a VELUX installation takes for what sets the time.
