Roof Window and Insulation Costs: Upgrade Options UK

Getting a handle on roof window and insulation cost before you call anyone is the difference between judging a quote and just accepting it. The three upgrades homeowners ask about most, roof windows, dormers and loft insulation, sit at very different price points: a single Velux-style roof window is usually a four-figure job, a dormer runs into several thousand pounds, and loft insulation is the cheapest of the lot while paying you back on heating bills. This overview gives real 2026 UK ranges for each, explains what pushes the number up, and points to the deeper cost guides for the one you are planning.

Every figure here is an indicative range to help you sense-check a price, not a quote. Nobody honest prices roof work without seeing the pitch, the access and what is behind the existing structure.

Roof windows (Velux and skylights)

A standard roof window fitted into an existing pitched tile or slate roof typically costs between roughly £900 and £1,800 per unit in 2026, supplied and fitted. Of that, the window itself is often £350 to £900, flashing kits £100 to £250, and labour £350 to £600 for a one to one-and-a-half day install. Larger, electric or complex installations, or jobs needing scaffolding and structural alteration, can push a single window past £2,500 and occasionally beyond £4,000.

The things that move the price are size and glazing, whether the opening already exists or a new one must be cut, the roof covering (slate is fiddlier than plain tile), the height and access, and whether you need scaffolding. Scaffolding alone is a meaningful line item; our roof scaffolding cost guide covers what to expect there.

Dormers

A dormer is a bigger job because it changes the roof structure, not just the covering. Adding a single dormer window commonly ranges from about £1,500 to £4,000 for a modest, simpler installation, but the figure climbs quickly with size and complexity. Converting a rooflight setup into a full dormer, which adds headroom and floor space, typically runs from around £6,000 to £17,000, and a large dormer as part of a loft conversion is a far larger project again.

What you are paying for with a dormer is carpentry and structure: the framing, the roof and wall finishes, the window, flashing and making everything weathertight. Because it alters the roofline, it is also the upgrade most likely to need building regulations sign-off and, in some cases, planning permission, so factor those in.

Loft and roof insulation

Insulation is the cheapest of the three and the only one that pays you back. Standard blanket (mineral wool) loft insulation costs roughly £5 to £17.50 per square metre for materials, and a typical professionally insulated three-bedroom semi comes in at around £930 all in. Rigid PIR insulation board and spray foam are considerably more per square metre, and are used where you are insulating at rafter level (a warm roof) rather than laying quilt across the loft floor (a cold roof).

The cold roof versus warm roof choice is the key decision and it depends on whether you use the loft space. Insulating the floor (cold roof) is cheapest and suits an unused loft; insulating at the rafters (warm roof) costs more but keeps the loft itself usable and is what you need under a converted or dormer loft. The Energy Saving Trust sets out the savings and any current grants, and it is worth checking before you pay, as insulation is the upgrade most likely to qualify for support.

Which upgrade is worth it?

It depends what you are trying to fix. If the loft is dark and you want light without changing the structure, a roof window is the simplest and cheapest of the structural options. If you need usable headroom and floor space, a dormer is the bigger spend that actually creates room. If your aim is a warmer house and lower bills, insulation is the clear-value choice and often the one to do first, because there is little sense heating a loft you have just added windows to. Many homeowners doing a loft do all three together, and combining the work saves on access and scaffolding.

For the wider picture on roof costs and how a full re-roof compares, see our guides to new roof cost in the UK and roof cost per square metre. If you are adding windows or converting a loft, do not overlook airflow: our roof ventilation guide explains why a warm roof still needs to breathe.

Frequently asked questions

How much does it cost to fit a roof window in the UK? A standard roof window fitted into an existing pitched roof typically costs between about £900 and £1,800 per unit in 2026, supplied and fitted. Larger, electric or complex installs, or jobs needing scaffolding and a new opening cut, can rise past £2,500 and occasionally beyond £4,000.

How much does a dormer cost? Adding a single dormer window commonly ranges from around £1,500 to £4,000 for a simpler installation, while converting a rooflight into a full dormer for extra headroom typically runs from about £6,000 to £17,000. A large dormer as part of a loft conversion costs considerably more.

How much is loft insulation? Blanket mineral wool loft insulation costs roughly £5 to £17.50 per square metre for materials, and a typical three-bedroom semi comes in around £930 fitted. Rigid PIR board and spray foam cost more per square metre and are used for insulating at rafter level rather than the loft floor.

What is the difference between a cold roof and a warm roof? A cold roof is insulated at the loft floor, which is cheapest and suits an unused loft. A warm roof is insulated at the rafters, keeping the loft space itself usable, and is what you need under a converted or dormer loft. The warm roof costs more but is essential if you want to use the room.

Which roof upgrade adds the most value? It depends on the goal. A dormer adds usable floor space and headroom, so it tends to add the most to a home where extra room is valuable. A roof window adds light cheaply, and insulation adds comfort and lower bills. For resale, usable space from a dormer or loft conversion usually has the biggest impact.

Should I insulate before adding roof windows? Often, yes. Insulation is the cheapest upgrade and cuts heating bills, so it makes sense to sort it first or at the same time, especially if you are converting the loft. There is little value in adding windows to a loft that then leaks heat, and combining the jobs saves on scaffolding and access.