Average Labour Cost/Price to Repair/Replace/Fit a Flat Roof





To clarify the following prices it is recommended that you read the article in the INFORMATION box below the PRICES…


(These prices are based on a tradesman’s rate of £150.00 per day and a labourer if required at £100.00 per day. This includes the cost of buying and collecting any materials, dumping any waste if necessary and any incidental materials they will need. The minimum price will usually be for a half day)



How Much Does it a Flat Roof Cost?


flat roof


Cost/Price For a Flat Roof/Asphalt/Torch On Felt



Job 1


The following is an actual quotation to put a new three layer “torchon” felt roof (that’s the one with its own integral bitumen) on a single size garage roof with one long edge being the junction with the house wall (lead flashings here).

It assumes 2 men working (the roofer and the labourer) at £150 and £100 per day. The job will take 2.5 days to complete.


Remove all existing felt and flashings, inspect timber deck for signs of rot and report on its condition. Should any replacement be necessary, this can be undertaken as an extra to the price.

Should the decking timbers be slatted boards as opposed to large sheets, it is likely that a great deal of black dust and particles will fall into the garage as work proceeds. If this is likely to cause concern to you, please ensure adequate covers are placed in position prior to commencement of work.

On roofs laid on absorbent decking, (chipboard etc.) if moisture is present under the felt, it is common for the top layer of board to come away with the felt as it is removed. Should this be the case, we will replace the affected board(s) with 18 mm weather proofed plywood sheets.

The charge for any unforeseeable timber replacement, will be £19.00 per man, per hour, plus materials and tipping etc. plus V.A.T.
On decking, fix any necessary "arris" fillets at junctions with house wall. Thoroughly nail down fibreglass bonding felt over entire area. This with galvanised clout nails at 200 mm centres.

(Arris fillets are triangular timber lengths which are placed in the right angle between roof and wall to give a slope for the felt to pass up, rather than a severe right angle).

Dress this over fillets, upstands, facias, drip battens etc. all laps to be 75 mm min.

(Drip battens are fixed to the top of the fascia boards so the felt can hang over them into the guttering).

On this lay "Torchon", plastomer polymer, pre bituminised black base felt. This to be heat bonded to primary layer as work proceeds.

On this lay "Torchon", plastomer polymer, heavy duty, pre bituminised green mineral felt. This to be heat bonded to secondary layer as work proceeds, with minimum 75 mm laps at joints.

Dress both layers of felt over fillets, upstands, facias, drip battens etc. and into guttering. Finish with "welted eaves".

(Welted eaves are an edging design, which thoroughly finishes the roof off, leaving no unsightly felt edges).

Fix code 4 lead flashings at junction with house wall. Each section to be no longer than 1500 mm. This to be dressed down over felt upstands, be well wedged and pointed in on completion in weatherstruck joint, alternatively make good any disturbed render or pebbledash as required.

flat roof repair/replace cost

PRICES


Job 1


The following is
an actual quotation to put a new three layer “torchon” felt roof (that’s the one with its own integral bitumen) on a single size garage roof with one long edge being the junction with the house wall (lead flashings here).

It assumes 2 men working (the roofer and the labourer) at £150 and £100 per day. The job will take 2.5 days to complete.


Remove all existing felt and flashings, inspect timber deck for signs of rot and report on its condition. Should any replacement be necessary, this can be undertaken as an extra to the price.

Should the decking timbers be slatted boards as opposed to large sheets, it is likely that a great deal of black dust and particles will fall into the garage as work proceeds. If this is likely to cause concern to you, please ensure adequate covers are placed in position prior to commencement of work.

On roofs laid on absorbent decking, (chipboard etc.) if moisture is present under the felt, it is common for the top layer of board to come away with the felt as it is removed. Should this be the case, we will replace the affected board(s) with 18 mm weather proofed plywood sheets.

The charge for any unforeseeable timber replacement, will be £19.00 per man, per hour, plus materials and tipping etc. plus V.A.T.
On decking, fix any necessary "arris" fillets at junctions with house wall. Thoroughly nail down fibreglass bonding felt over entire area. This with galvanised clout nails at 200 mm centres.

(Arris fillets are triangular timber lengths which are placed in the right angle between roof and wall to give a slope for the felt to pass up, rather than a severe right angle).

Dress this over fillets, upstands, facias, drip battens etc. all laps to be 75 mm min.

(Drip battens are fixed to the top of the fascia boards so the felt can hang over them into the guttering).

On this lay "Torchon", plastomer polymer, pre bituminised black base felt. This to be heat bonded to primary layer as work proceeds.

On this lay "Torchon", plastomer polymer, heavy duty, pre bituminised green mineral felt. This to be heat bonded to secondary layer as work proceeds, with minimum 75 mm laps at joints.

Dress both layers of felt over fillets, upstands, facias, drip battens etc. and into guttering. Finish with "welted eaves".

(Welted eaves are an edging design, which thoroughly finishes the roof off, leaving no unsightly felt edges).

Fix code 4 lead flashings at junction with house wall. Each section to be no longer than 1500 mm. This to be dressed down over felt upstands, be well wedged and pointed in on completion in weatherstruck joint, alternatively make good any disturbed render or pebbledash as required.

Price: £925.00 + V.A.T.


Breakdown

Labour
Strip the old roof, replace a small area of decking .5 day £125
Fix fillets and bonding felt, prepare for lead. .5 day £125
Torch on two top layers of felt, fit welted eaves. 1 day £250
Fit lead, clear up, go to tip. .5 day £125

Total labour £650
Materials and tipping £275


Should it prove necessary;- to replace all the newly exposed timber decking as work proceeds with 18 mm weather proofed plywood sheets, will cost an additional:-

Price: £385.00


Breakdown

Remove old rotten sheets, buy and fit new 1 day £250
Materials and tip £135




Job 2
Supply and fit a new lead flashing where the garage roof meets the house…….£135.00


Breakdown

Labour
Strip the old roof, replace a small area of decking 0.5 day £125
Fix fillets and bonding felt, prepare for lead. 0.5 day £125
Torch on two top layers of felt, fit welted eaves. 1 day £250
Fit lead, clear up, go to tip. 0.5 day £125

Total labour £650
Materials and tipping £275


Should it prove necessary;- to replace all the newly exposed timber decking as work proceeds with 18 mm weather proofed plywood sheets, will cost an additional:-


Price: £385.00


Breakdown

Remove old rotten sheets, buy and fit new 1 day £250
Materials and tip £135



Job 2

Supply and fit a new lead flashing where the garage roof meets the house

Price: £135.00


Material Information
Slaters Felt Underlay (15m x 1m) £20.00
Torchon Underlay (8m x 1m) £45.00
Torchon Green Mineral Capsheet (8m x 1m) £45.00
Roofing Grade Plywood sheet (1.2m x 2.4m) £20.00
Galvanised Roofing Tacks £7.00 per kg
Lead Flashing (240mm x 3m) £80.00
Arris Rail (75mm x 75mm) £2.00 per metre.
Skip £150-£300


*With Flat Roofing we always advise you get a price for the complete job as opposed to a day rate - unless you know the roofer very well.








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A Price Guide and Information Sheet on the Cost of Repairing a Flat Roof



Don’t ask
if a flat roof will leak but when will it leak. 15 years is doing well!

Felted Roofs



information
“Standard” flat roofs are made up of 3 layers of felt on top of a slightly sloping wooden deck (they should never actually be flat). The top layer should have protection from the sun’s ultra violet rays and sparks from bonfires etc. This is usually in the form of an integral layer of mineral flakes (usually green) or 2” (50mm) of small stone chippings.

The former do the job perfectly well, the latter add ¼ ton to the roof, (and that’s when dry), BUT they are very good at hiding standing water from prying eyes (you), if a builder hasn’t put a proper fall on the roof .
The standard requirement is a fall of only 1:80, which is pretty flat but most builders go for 1:40.

There are basically 2 methods of sticking the felt to the roof and to itself.

The oldest way and one which is still extensively used is by heating blocks of bitumen
in a gas fired boiler placed close to the job, hauling buckets of the boiling black stuff up onto the roof and spreading it around with brushes before it “goes off” (man’s work).

The newer way is to use “torchon” felt which is pre-bituminised. This is heated in situ. on the roof with a gas fired burner.

Both are effective provided you know what you’re doing!

There are other types of flat roofing systems, some of which you see advertised by some aging “has been” in the colour supplements. These tend to be formed plastic layers moulded and heat sealed to the roof. (the covering, not the spray-tanned celeb). They are preceded by salesmen in shiny suits with brochures showing ludicrously happy people who don’t seem to mind one bit that they have just forked out £3500 to stick a roof on the
garage.

Mastic Asphalt Roof


This is the “Rolls Royce” of flat roofing (if you ignore what the men in suits will tell you). Here, a good thick layer of very hot thick asphalt is hand spread over the entire roof with no seams at all, it even continues up adjoining walls etc. for 6” (150mm) and is forced into a suitable
mortar bed in the brickwork. It is expensive, specialist work, but if you want a flat roof to last 50 years………….


All roofs, flat and pitched tend to leak where they meet other things such as house walls and chimneys, vent pipes, roof windows, parapet walls etc. (Parapet walls are short upward extensions of the normal wall which forms the side of the house. They are common on Victorian houses particularly when two neighbouring roofs meet. They are one way of forming an edge to roofs).

There are two reasons for this. The obvious one is the abrupt change of angle, which requires a joint to be made. The other which is relevant to felted roofs is called thermal difference (but it’s unlikely your roofer will have this phrase in his vocabulary)!

Basically, different materials expand and contract at different speeds, bricks and felt are no exception and when stuck together to form a joint between a garage roof and the house wall for instance, they will eventually crack apart and rain does love a crack! Anywhere a felted roof meets an obstacle (an upstand in builders parlance) it can eventually leak. If you are lucky and it doesn’t then after 20 years the ultra violet will eventually win, blisters will form, and the rain, which pays the roofers mortgage will triumph!

Upstands have to be given special attention. Very often these are made using the same felt as the roof but they don’t last very long. By far the best material to use is
lead, it’s good for 100 years if it’s fixed properly.


Replacing a Flat Roof


It’s false economy to attempt to patch a flat roof except in the following instances.

Replacing leaking felt upstands with a lead flashing.
Sticking a layer of (mineral) felt on top of a very old mastic asphalt roof.

If your flat roof leaks somewhere in the middle, its time to replace it. This is done by completely removing the existing felt to expose the timber decking (sometimes called sarking). You will be surprised to discover this is done with spades. Hopefully the sarking will be sound and dry but if you had a leak it’s likely it won’t be!

So, what state is it in? There are many types of decking that can be revealed. If you are lucky and it’s wooden planks (just like floorboards), sections of them can be easily replaced. If the deck comprises (
roofing grade, plywood ) timber sheets, then it may be possible to replace a small section of one or even one complete sheet.

However if the decking is chipboard, it is very likely that the top layer of it will lift with the last layer of felt and it will all have to be replaced.

The decking maybe a composite, straw like insulation material (from the 70’s) about 3” (75mm) thick. In this case the roofer will have a problem which is best solved by covering it with new plywood and roofing on top but this may cause problems with heights of fascia boards etc. (
Fascia boards are the timbers which line the edges of most roofs which guttering is usually fixed to).

The roof may be concrete but in this case the roofer should have already worked this out and stated in his quote that he will need to apply primer before felting.

Essentially no roofer with any sense wants to find any problem when he removes the felt. He has just one day to get the old roof off and the new one on, at least to a watertight situation, before he leaves for the night because it
will rain and no amount of covering with tarpaulins will stop it getting in!



Questions to ask the roofer during his quotation visit.


questions
Why hasn’t he got on the roof to have a look?
He must at least get up and look at the roof, if he says it’s not necessary, he’s going to charge you so much, that no matter what he finds when he does the job, he still can’t lose money! (you probably won’t want to employ him).

Will he be removing all the felt?
This is essential, don’t allow any roofer to felt on top of old stuff.

Will he put a tarpaulin down to protect your new “paviour” driveway and white house walls?
He will be chucking the old felt off the roof because time is of the essence and it will mark everything it smashes into.

What sort of decking do you expect to discover and how will you be including the cost of any probably repair/renewal work in your quotation?
He probably won’t know what decking it is until he gets the felt off, so he can’t give an accurate price but he must tell you in writing how much per hour, per man, he will charge for repair or replacement work. There may also be extra materials to buy, he will charge you for these but you have a right to see the invoices.

Note
He will have paid VAT on these materials and so will you when you pay him for them. Be careful he doesn’t include them at the gross price in his invoice, because if he is charging you VAT as well, then you will be paying this bit twice!

What he
can quote for relevant to unforeseen work is to remove all the newly exposed decking and replace it with new roofing grade plywood (or a special timber roofing sheet called “Sterling Board”), plus any allied works associated with complete deck replacement such as replacing damaged fascias, guttering etc. Then you will know the maximum price you can possibly be charged.

What type of solar protection will he use? (mineral felt or chippings)

If he leaves the top surface as black felt, he doesn’t know his job. Even a black top painted with solar reflective paint will be a second rate job because it will weather off in 2 years.

What type of upstands will he be creating?
As mentioned, lead is by far the best material. If he uses lead ( it’s called “flashing” ) then he should use code 4 lead which he must cut into lengths not exceeding 60” (1500mm) because longer lengths will buckle over time as they expand and contract. This must be fixed into a thoroughly raked out mortar joint between two courses of brickwork with lead wedges and then pointed with mortar to finish.

He may however have to use his roofing felt around any roof windows, as there may be no possible fixing point for lead.




A-Z of Job Pricing