Replacing the roof on a detached four-bedroom house costs £17,000 to £27,000 including VAT in London for concrete tile, and £24,000 to £39,000 for natural slate. Outside London and before VAT, the same job is £11,500 to £18,000 and £16,000 to £26,000.
Why the two sets of numbers look so different
They are not disagreeing. They are measured differently, and both differences run the same way.
The first is VAT. Published cost guides such as Checkatrade and Which? headline figures that exclude it. A homeowner's quote normally includes it. Reading an ex-VAT figure as your bill understates the real cost by a fifth: on the UK concrete-tile range above, £11,500 to £18,000 before VAT, that is £2,300 to £3,600 of error.
The second is region. London labour, waste disposal and access all cost more, and the composites above carry a 20 to 25% London uplift over the UK baseline. Neither adjustment is optional, and a page that quotes one national number without saying which basis it is on is not much use to anyone in SE or SW postcodes.
The area assumption behind every figure here
A detached four-bed carries roughly 100 to 120 square metres of roof, against 45 to 60 on a three-bed terrace. The area roughly doubles. The cost does not: our London concrete-tile figures run £6,500 to £12,000 including VAT on a terrace and £17,000 to £27,000 on the four-bed, which is 2.25 to 2.6 times the terrace on twice the area. Cost rises faster than floor area on a roof.
What drives that is detail rather than field. A detached house has four exposed elevations, which usually means more verge, more hip, more valley and more flashing per square metre than a mid-terrace protected on both sides by its neighbours. Those are the slowest square metres on any roof.
So the 100 to 120 figure is the first thing to check against your own house. A simple two-plane gable sits at the bottom of it; a hipped roof with dormers and two stacks sits at the top and carries more of the expensive detail as well.
What the money buys
Expect a job of this size to break down roughly as follows. The component figures below are published cost-guide ranges and exclude VAT.
Materials account for around 45%: tiles or slates at £2,500 to £8,500, membrane £350 to £600, battens £180 to £350, dry-fix ridge and hip £250 to £600, lead flashings £200 to £500, sundries £150 to £300.
Labour and services take the other 55% or so: roofer labour £2,000 to £4,500 for a two-person team over five to ten days, scaffolding £900 to £1,800, skips £350 to £650, guttering £300 to £800, soffit and fascia £800 to £2,500, and certification anywhere from nothing to £250.
Two cautions on reading that. The £2,000 to £4,500 is a bare wage line from an itemised schedule, and it is not the same measure as the roughly £130 per square metre Checkatrade publishes as an installed labour rate. That one carries overhead, insurance and margin as well as wages, and over this area implies £13,000 to £15,600. The two are different bases and cannot be compared or added. The scaffolding figure also sits above the £800 to £1,500 usual on a London terrace, because a detached house has to be scaffolded on four elevations rather than two.
What the breakdown hides is the edges. A detached house has fascia and soffit on four sides at around £150 per linear metre, far cheaper done while the scaffold is up than revisited later. Rotten rafter ends only appear once the covering is off, at around £25 per metre to repair, so a quote carrying no provisional sum for timber is incomplete rather than cheap. And a Velux replacement starts at £1,000, which detached four-beds often need several of.
Scaffolding has to go round four sides
Checkatrade's scaffolding guide prices by the number of walls, which is where the detached penalty shows plainly: a two-storey terrace over two walls is £800 a month, a two-storey semi over three walls £875, and a three-storey semi over three walls £1,100, all excluding VAT. A mid-terrace only ever needs two elevations scaffolded because its flank walls are party walls. A detached house needs four.
Duration compounds it. A three-bed concrete-tile re-roof is three to four days of roofing, or about a week with guttering and fascia. A four-bed detached is the five to ten days the labour line above assumes, and the scaffold is on hire for all of it.
On this one line the shape of your house sets the price rather than the roofer's rate. That makes it a poor place to hunt for savings and a good place to check that two quotes have priced the same structure.
Slate changes the arithmetic more at this scale
Which line leads on a tiled roof depends on the measure, and the published sources disagree. Checkatrade's installed rate of around £130 per square metre against roughly £50 for material supply puts labour well ahead; the itemised breakdown above puts materials ahead. Both are ex-VAT and neither is wrong, but they are different bases.
Natural slate settles it at this scale on either reading. At 100 to 120 square metres the covering line reaches £8,500 at the top of its range, comfortably above what the £50 per square metre material rate allows over the same area and several times the itemised wage line. The slate itself becomes the biggest number on the page.
It is also most of the gap between the two headline ranges: £24,000 to £39,000 for slate against £17,000 to £27,000 for concrete, both including VAT. So on a four-bed slate quote the question worth asking is whether the price assumes salvaged slate off your own roof or an all-new order, rather than what the day rate is. Over this area the two answers are thousands apart.
A roof this size is the wrong one to buy on a headline total.