Can a rooflight be moved to a different part of the roof?
Yes, and it is best understood as two separate pieces of work rather than one. Forming the new opening is an ordinary installation. Closing the old one is a full reinstatement of roof structure, underlay, covering, insulation and ceiling, and it is usually the larger and more awkward half, because the roof has to end up looking as though the window was never there. Both halves happen under the same scaffold, on the same visit, which is the one economy available. People ask this question when a loft has been converted around a badly placed unit, when a kitchen island has landed under the wrong part of the ceiling, or when an escape window turns out to be in the wrong position, and in all three cases moving it is the correct answer. The general work is described on the roof window installation page.
Two jobs under one scaffold, and which is the bigger one
Set out plainly, a move consists of: forming and trimming a new opening, setting and weathering a new or re-used unit, building a new internal reveal, then taking out the old frame, reinstating the cut rafter, closing the deck and underlay, re-laying the covering over the old position, insulating the old opening and closing the ceiling below it.
The second list is longer than the first. It also carries more risk of a visible result, because a re-laid area of covering over an old opening is the thing a critical eye finds from the garden. On a concrete interlocking tile roof it can be made invisible. On a two hundred year old Cotswold stone slate roof it takes real care and matched reclaimed material.
Reinstating the structure where the old opening was
An existing opening has a cut rafter, a head trimmer and a cill trimmer, and the load from the cut member has been running through those trimmers into the rafters either side for as long as the window has been there.
Closing it means restoring the original load path. The cut rafter is made continuous again, either with a new full length member alongside the old one, scarfed and bolted through, or with a new rafter run from wall plate to ridge in the same bay where access allows. The trimmers usually stay, since removing them achieves nothing and they now simply carry battens. Battens are run across at the correct gauge for the covering, and any counter battens reinstated. Occasionally the old opening turns out to have had no trimmer at all, which is a structural finding in its own right and gets put in writing before anything else proceeds.
The underlay, and why the closed area is the vulnerable one
A closed opening is a place where the membrane has a joint in the middle of a slope, and that is the detail that decides whether the area stays quiet for the next thirty years.
New membrane is lapped over the sheet below and under the sheet above, in the direction of flow, with a generous lap and support under it so it does not sag into a pond between battens. Where the original underlay is brittle 1930s bitumen felt, and around Gloucester and Tewkesbury a great deal of it is, the sound approach is to take it back further than the opening itself and land the new laps on solid material rather than on something that crumbles when it is lifted. Sarking boarded roofs in the Forest of Dean need the deck made continuous first, with the new boards supported off the rafters rather than nailed to the trimmer ends.
Making the covering match over the old position
This is the part homeowners judge the job on, and it is entirely a materials question.
Concrete interlocking tiles from the last forty years are still made and weather to a similar tone within a season or two, so the area disappears quickly. Clay plain tiles and pantiles are harder, because handmade and older machine made tiles vary in colour and texture, and new ones read as new for a long time. Welsh slate needs matching in size and thickness, and old slates are brittle at the nail holes so more come out broken than expected. Cotswold stone slate is the extreme case: the courses run in a diminishing gauge that changes continuously up the slope, so the re-laid area has to re-establish the exact gauge of its neighbours, in reclaimed stone matched for thickness and weathering colour. Sourcing that takes weeks, and it is planned before the scaffold is booked.
Inside: the ceiling, the insulation line and the reveal
Below the old opening there is a hole in the ceiling with a plastered reveal around it, and closing that properly is a plasterer’s job rather than a roofer’s.
Insulation is reinstated between and, where the build up allows, over the rafters, continuous with the insulation either side and with no void left where the reveal used to be. The vapour control layer is taped back into the layer around it so warm room air is not driven into the closed construction. Then plasterboard, scrim, skim and decoration. On a lath and plaster ceiling in a Victorian terrace the finished area will be flatter than its surroundings unless the whole ceiling is skimmed, which is worth raising early because it changes the scope of the internal work. In a finished loft bedroom the room is sheeted and floors protected throughout.
Whether the existing unit can be re-used
Sometimes, and it depends on its age and what comes off with it. A unit under about ten years old, in sound condition, with its sash true and its gaskets supple, can be lifted out and re-set into the new opening. The frame is checked for square, the hinges and the pane are inspected, and the flashing kit is renewed rather than re-used, since the pieces are dressed to the covering they came out of and rarely sit properly a second time.
An older unit is a different calculation. At fifteen to twenty-five years the sealed unit is approaching the end of its service life, the gaskets are hardening and the timber may be tired, and re-setting it means paying for all the labour of a new installation around glass that will mist within a few years. Where that is the finding it is set out at survey. The reasoning is on replacing a failed or misted rooflight.
Choosing the new position, and what tends to block it
A move is a rare chance to place a window where the room actually wants it, so the setting out is done from inside first and transferred outside by drilling through at the corners.
What gets in the way is usually the same short list. A purlin crossing the slope at mid height divides an interwar semi’s roof into two usable zones. A hip narrows the slope towards the corner, so on a Longlevens or Warden Hill semi the clear rectangle is smaller than the roof looks from the garden. A chimney stack and its back gutter rule out the run of water above it, covered at whether a rooflight can go near a chimney. Rafter centres decide whether the new position needs a cut rafter at all, set out at what size rooflight fits between rafters. On a trussed estate roof the new position has to respect the same bays the old one did.
When a move is worth doing, and when a second unit is better
Moving is clearly right where the existing position causes a problem that cannot be solved any other way: a unit sitting over a stairwell void so the light never reaches the room, an escape window in a loft bedroom that no longer meets the clear opening requirements after a layout change, or a unit above a fitted wardrobe that a conversion has since built underneath it.
Where the complaint is simply that the room is not bright enough, adding a second unit in another bay often gives a better result than relocating the first, because two positions light a room more evenly than one and there is no old opening to close. That comparison is made at survey with the room and the roof both measured, and it is worth having honestly rather than assuming the move is the only option. How the numbers move is set out at how much a pitched roof rooflight costs.
Building Control, permissions and how a move starts
Both halves are notifiable. Forming a new opening is structural work and so is reinstating a cut rafter, and the insulation continuity at both positions falls under the conservation of fuel and power requirements. Where the window is the escape from a loft room, the new position has to meet the clear openable area and the height above floor level, which is one of the more common reasons a move is being done at all. The notification is submitted, inspections booked, and the completion certificate comes back in the homeowner’s name.
Planning matters where the property is listed or in a conservation area, because closing an opening on a visible slope and forming a new one is an alteration in both directions, and a conservation officer will want to see both. On a Cotswold or central Cheltenham address that conversation happens before a unit is ordered. To start, email info@severnskylightsgloucester.co.uk with photographs of the existing unit inside and out, the slope you have in mind, and the address. Further reading is collected in the guides.
Next on this subject.
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