How Much Does It Cost to Fit a New Roof Window in a Loft?
Fitting a brand-new roof window into a loft in Ipswich costs £1,900 to £2,700 for a unit up to MK06 in a cut roof, £2,300 to £3,300 for a PK10 or larger, and £2,400 to £3,500 for an escape-rated top-hung unit. A new opening in a trussed roof is quoted individually after an engineer’s design. It costs materially more than a like-for-like swap because you are building the opening, not reusing one.
Installed prices for a new opening
These ranges are supply and fit for a modern, thermally efficient roof window, including the flashing kit matched to your covering, the insulation collar, the underfelt collar, all fixings and reinstatement of the covering, plus the structural trimming, the internal lining and the making-good the new opening needs. They assume a traditional cut roof with sound timber.
| Job | Installed supply and fit | Days on site | Guarantee |
|---|---|---|---|
| New opening, cut roof, single unit up to MK06 | £1,900 to £2,700 | 2 | 10 years |
| New opening, cut roof, PK10 or larger | £2,300 to £3,300 | 2 | 10 years |
| Escape-rated top-hung unit, new opening | £2,400 to £3,500 | 2 | 10 years |
| New opening in a trussed roof | Quoted individually after engineer’s design | 2 to 4 | 10 years |
Cut-roof figures assume single-length rafters and no engineer required. Trussed roofs are priced only after the designed solution. Your survey fixes the price.
Why it costs more than replacing an existing window
A like-for-like swap reuses the hole. A new opening builds one, and every stage of building it adds cost that a swap never touches.
Structural trimming
Cutting a roof window into an existing pitched roof means removing part of a rafter and transferring its load into doubled trimmers above and below the opening, then into the rafters either side. On a traditional cut roof with 100 by 50mm rafters at 400mm centres, one rafter can normally be trimmed for a window up to about 940mm wide without an engineer. That is real structural carpentry, and it is the first day of a two-day job before the window itself goes anywhere near the roof.
Plastering, lining and decoration
A replacement drops into a reveal that already exists. A new opening has no reveal at all, so we form one: plasterboard, a vertical lining at the head, a horizontal lining at the sill, then skim and decoration. The splayed reveal is not just finishing, it throws daylight further into the room and lets warm air wash up the glass to cut condensation. That work, materials and time, is priced in and it is a meaningful part of the difference.
Building Control
A new opening is a structural alteration as well as a thermal element change, so it is notifiable in its own right. We handle the Building Control notification for you: notifiable work goes to your local authority Building Control as a building notice, to Ipswich Borough, East Suffolk, Mid Suffolk, Babergh or Colchester depending on where you are. We take care of that notification where it is required and tell you at survey which route your job needs.
Escape windows are a Part B job, not a size choice. A habitable loft bedroom generally needs an escape window: a clear openable area of at least 0.33 square metres, no dimension under 450mm, and the bottom of the opening no higher than 1100mm above the floor. A centre-pivot cannot serve, because the pivot blocks the opening, so an escape-rated top-hung unit is required. That is why the escape figure sits above the standard new-opening price.
The trussed-roof exception
The cut-roof prices above assume single-length rafters running wall-plate to ridge, which is what most older Ipswich housing has. Trussed rafters are different. Almost every roof built after about 1970, including most of the estates around Kesgrave, Martlesham and Grange Farm, uses engineered trusses in a W or M pattern with metal plates at the joints. You cannot cut one without a designed solution from a structural engineer. Any opening over roughly 1.2 metres wide, or any roof with irregular rafters, also needs an engineer, and the timber-framed cottages inland from Ipswich fall into that category almost every time.
We work to the engineer’s design and we will not tell you a truss can be cut because it makes the quote simpler. That is why a trussed-roof opening is priced individually: the design decides the cost, not a standard rate. The structural background is on our installation process page, and if this is part of a wider conversion, our loft conversion rooflight page covers getting the windows right at design stage.
What it means for your budget
If you are adding light to a loft that never had a roof window, expect the new-opening figures, not the swap figures. If you are replacing a window that already exists, you are on the cheaper replacement cost page instead, because nobody cuts the roof. The gap between the two is the trimming, the lining and the notification, and it is real. For the full specification background behind every figure, see our roof window installation cost guide, and the published menu across every service is on our costs page.
Whichever job yours is, the survey confirms the exact price and then fixes it. You get one written figure with the U-value stated, and it does not move unless you change the specification.
Request a fixed quote for a new roof window opening in your Ipswich, Suffolk or north Essex loft, and we will confirm the figure after survey.
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.