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Garage Roof Replacement Cost

Do you need a garage roof replacement? Are you perhaps worried about the cost of a new garage roof? This article will breakdown garage roof prices by material and look at all aspects of replacing and installing a new garage roof.

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Introduction to Garage Roof Replacement

Garages are good places to store many things. Builders will install flat roofs that last 10 or 15 years and cost far less than a pitched roof with tile or slate, which might last 50 years. Sometimes a cheap roof is all you need.

A bitumen felt garage roof replacement will cost about £450 for supplies and £350 for labour. This makes the total cost of a new garage roof in the UK is about £900 to £1000.

A flat roof garage is cheaper, lightweight and needs shallower foundations than pitch roofs because they're supporting less weight.

Flat garage roofing has a slight slope to allow rainwater to run off. However, even then, the bitumen felt will degrade over time.

The felt will become brittle and crack, allowing water to leak onto the timber underneath. You will have to remove the felt to find out whether the timber roof structure is rotten.

Check on the state of the felt regularly and replace the roof when it turns brittle. This is the best way to keep your roof's maintenance up to date.

In this article, we look at the costs and more associated with replacing a garage roof.

How Much Does It Cost to Replace a Garage Roof?

It's important to remove and replace the roof covering to check that all timber is sound underneath. If it isn't, it is essential to replace the wood before re-felting it.

If you find it is necessary to replace any garage roof sheets, add an extra £40 for every 2.4m x 1.2m plywood board.

Bitumen felt and asphalt is used to be used on most flat roofs. But, in recent years more flat-roofed garages use EPDM (an efficient rubberised membrane) and GRP Fibreglass.

Felt and asphalt roofs have improved with technology advances and are no longer the problem materials they used to be.

If you are uncertain about tackling the job, either employ a roofer or seek some professional garage roof replacement advice before starting the job.

A garage roof refurbishment will cost a lot of money to do properly, so it makes sense to hire a suitably qualified merchant to replace the roof.

Some of the most important questions to ask your contractor before hiring them are:-

  • Does the roofer have references or recommendations readily available? It makes sense to follow these up - ask the customer whether they were satisfied with the completed work. Roofers can obviously install slates and tiles, but if you want a flat roof using one of the new technologies, the roofer must be trained and suitably qualified.
  • Ask whether the roofing company is a member of the National Federation of Roofing Contractors (NFRC)?
  • The company should adhere to a code of practice that members are expected to adhere to.
  • Ask for quotes from at least three different contractors. Ensure the roofers visit and inspect the site to give a good, comprehensive quotation. Avoid rough estimates over the phone as they cannot take into account any unforeseen problems unless they actually see them. They will simply have given you the basic price and probably expects to add more items onto the bill at the end.

Please remember that the cheapest quotation will not necessarily the best. Be prepared to expect added extras on a job like this, it is usually unavoidable.

Other expenditure doesn't come to light until they remove the existing roof—for example, water–damaged plywood or rotten joists will obviously add to the costs.

However, a reputable merchant will already know that and should make you aware of any problems right from the start, adding them into their quote.

The following table will show you the typical costs for single and double garages, using some different roof coverings.

If your garage is a different size, don't be concerned, as you can calculate the cost of your replacement garage roof simply by multiplying the cost per square metre by the area of your garage roof.

Type of Garage Task Cost/m2 Estimated Cost
Standard Double garage 6m x 6m Fibreglass roof £100 £3,600
EPDM Rubber roof £90 £3,240
Felt roof £50 £1,800
A medium single garage 2.7m x 5.5m Fibreglass roof £100 £1,485
EPDM Rubber roof £90 £1,336
Felt roof £50 £742

The most common roof coverings are:-

Felt Garage Roof

Low–cost roof covering with proven results and suits almost any roof size. However, it needs heat for application and is not suitable for a DIY roof, as it's not strong enough to walk on.

EPDM Rubber Roof

This roof covering is lightweight, flexible and hardwearing. Also, you don't need heat during the application, and it'll last a long time.

However, it might shrink with age and isn't good for fiddly roofs. As it doesn't need special equipment to install, it sometimes attracts dodgy installers.

GRP Fibreglass Roof

Lightweight and hardwearing, you don't need heat to install it, and it has no joints. It is very vandal-proof, looks good, with a long lifespan.

If you have DIY skills, this roof is for you. But the covering isn't flexible and isn't a great choice for large areas and can be slippery when it's first installed.

So, if your main concern is the price, then simply choose a cheaper felt roof option. If you want a hardwearing roof, GRP fibreglass or EPDM rubber is probably the best long-lasting and most durable material.

Remember that ensuring you have a weather-tight garage roof is essential if you want to use a garage to its fullest potential, and it can also add value to your home.

Here is a table of average costs for replacing a flat roof:

Single Garage No £700
Double Garage No £900
2-storey Extension Yes £1200

Here are the different roof materials and their costs:

Felt roof £40-£60
Rubber roof £80-£90
Fibreglass roof £70-£90
Lead bay roof £90-£105
Fibreglass bay roof £95-£120

Replacing a Flat Roof

Felt £2 to £10 per m2
Rubber £9 to £12 per m2
Fibreglass £2 to £3 per m2
Lead £2 to £4 per kg
Fibreglass insulation £6 to £10 per m2
PIR Insulation boards £5 to £15 per m2
Spray foam insulation £5 to £12 per can

Types of Garage Roof

Here is a list of typical garage roofs:

Flat Garage Roof

The most common support structure for a flat roof uses 150mm x 75mm joists set 450mm apart, and the slope must comply with BS6229 and BS8217 to produce a minimum gradient of 1:40 and a maximum of 1:80, allowing the roof to shed water easily.

Use wedge-shaped nails or 'furring pieces' the same length as the joist, onto each joist, then nail 25mm thick plywood to support the covering.

Some flat garage roofs use concrete instead of timber. Concrete garage roofs use steel RSJs or concrete lintels instead of timber joists.

Standard concrete blocks fill the joists' gaps, then a layer of screed covers the concrete structure to seal all joints and gaps. The surface is then ready to apply the waterproof covering of your choice.

There are several types of roof coverings available on the market and easily sourced.

Corrugated Garage Roof

Corrugated roofing uses timber joists to provide the main structure, then covered by corrugated plastic or metal sheets.

Metal garage roofs using corrugated iron used to be very common in the past. Today however, corrugated clear PVC or Polycarbonate sheets are more common.

Pitched Garage Roof

Garages with pitched roofs are often seen in detached properties and have timber rafters covered in tiles or slates, similar to the house.

However, corrugated iron is also a favourite covering. Large single and double garages won't generally have a pitched roof, but, if it does, the pitch should match and compliment the house's roof.


  • During the winter months, a flat roof absorbs the sun's warmth, which transfers to the inside of the building.
  • A flat roof is easier to stand and walk about on during maintenance.
  • A flat roof uses fewer materials and takes less time to build than a pitched roof, so it is considerably cheaper.
  • Space on the roof would normally be wasted. However, a strong flat roof can double as a garden, patio or green roof for insects to thrive.

What Does Replacing a Garage Roof Involve?

Replacing a garage roof isn't; you may consider hiring a professional tradesperson to do the work instead.

A simple guide for replacing your roof using corrugated sheets.

  • Take away the old roofing; this is usually a two-person job, especially with heavy asphalt shingles.
  • After removing the old roof material and the layers underneath, you need to check the roof's foundations, especially if it is timber. Don't place a new roof on already rotting timber. Replacement is worth tackling whilst you have the chance.
  • Next, lay down your replacement roofing. Make sure the roof slopes slightly towards the guttering for the water to run. If you are replacing a flat roof with another, the joists should already be in place. You may need to replace it if the timber has warped. If you are using corrugated sheets, this will be the best time to ask for help as these sheets will need to be straight when nailing into the joists.
  • Nails should be placed every 2-3 bumps apart. Make sure they are nailed into the corrugated sheets' top bumps, not in the grooves because this where the water will run. Ask for some assistance, as this can be quite a strenuous job and not one to tackle if you do not have a head for heights!

There are many reasons why a garage roof could need replacing. It may just be years in the open with the unforgiving Great British weather, damage or accident.

Consider replacing an older garage roof, as it is could contain asbestos – dangerous, getting into your lungs and cause health risks and even deaths in later years. A specialist is needed to remove it, and it will be costly, but do not attempt this yourself.

A leak or moisture will be a significant problem if the garage is connected to the main building, as it can lead to the spread of damp and mould to your home. A damaged, leaking garage roof may also create hazardous problems, such as slippery surfaces and rotting timber.

A flat garage can collect or pool water if not designed and constructed properly, as it has no natural drainage—slopes, allowing water and debris to run off the roof.

If you are considering changing a flat roof to a pitched roof means you will need other foundations to help support the roof. Keeping a flat roof will probably be the better option.

Several factors will come into play when choosing the type of material for your garage roof. This will include durability, weather resistance, waterproof capabilities and cost. Consider what you intend to use the garage for in the future. If you are simply garaging your car, you could use cheaper materials.

If your garage has a pitched roof, most specialists would probably recommend using corrugated metal sheet as it is cheap and effective. Corrugated materials are weatherproof and lightweight; the groove adds to the durability, helping water drain away, as it collects and runs along its ridges.

You have a few options for flat roofs, one being stick-on bitumen felt, layered on using a flame. This material comes in different prices and is highly regarded due to its durability but shouldn't be attempted as a DIY project.

When hiring a specialist to carry out the job, you can hire a trained roofer, a builder, or a specialist roofing company, but get quotes before deciding.

DIY Garage Roof Replacement

Replacing your garage roof yourself is not recommended, as it is heavy and sometimes very dangerous work. Bulky materials will need to be carried up to the roof.

This is a tiresome job, involving climbing ladders, (unless you have a scaffolding tower, which will ease the job slightly).

If you do feel confident enough to take on the task on yourself, remember to ask someone to give you a helping hand from one or two more people, ideally an experienced roofer.

Replacing a roof on a 2-storey garage extension yourself, you could save around £300. But, it can be a dangerous job, so think twice before committing to it.

Most flat roofs are constructed to incorporate a slight slope running from one end to the other. This lets rainwater run off the roof into the gutter. This may be a tricky job to undertake yourself successfully.

If you are considering replacing your garage roof you will probably not need planning permission. A normal garage roof falls under a Permitted Development (PD), but it is always a good idea to check with your local Gov. Planning dept. However, the permissions do differ depending on your requirements.

Flat roofs repairs won't need to comply with building regulations. However, suppose you are completely replacing the roof and incorporating integral insulation.

In that case, you might need to upgrade the garage's thermal element, reducing the heat loss by using a thicker layer of insulation.

If you're retaining the roof's overall height or shape, Planning Permission won't usually be necessary. Check with the local Planning and Building Control Offices in your area for guidance.

British Standards Codes of Practice

A flat roof on your garage must comply with Codes of Practice - BS6229 and BS8217. These Codes of Practice are specifically for the construction of the roof.

A minimum gradient of 1:40 is necessary on a flat roof,with a maximum slope of 1:80. This slope will provide the optimum slope range so that rain sheds easily, carrying as much leaves and debris as possible.

Use breather membranes or a vapour control membrane They also specify the best way to allow water vapour to escape.

You will not need planning permission for repairs or partial replacement of less than 25% of your roof.

You will however need to apply if you are planning to carry out any of the following:

  • Replacing or repairing more than 25% of the roof, requires the insulation to be improved, and any structural alterations will need to be undertaken.
  • The quality of the roof material will need to be drastically improved if you require planning permission, and your bill could be anywhere between £206 to £462 depending on the extent of the roof work.

Suppose you intend to replace a pitched roof covering a different material, such as slates or tiles.

You must then comply with Building Regulations regarding structural strength and stability. You must strictly comply with fire safety and energy efficiency requirements. For more advice on these matters, contact the Building Control Office.

There are numerous planning regulations regarding changes in appearance and height, so ask for guidance from your local Planning Department.

Potential Problems and Pitfalls

  • Depending on the construction materials, your garage roof's lifespan could be just 10 to 15 years.
  • The drainage of rainwater and other debris from flat roofs can be a problem. If the roof isn't regularly cleaned, the covering material could deteriorate quickly .
  • Flat roofs require more maintenance than a pitched roof. Consider the implications before choosing to build one.
  • You may also have a limited number of suitable covering materials, you have a limited style range for your flat roof.

If your home just happens to have a garage with a flat roof, you will soon realise that it often requires more work than other types of roofs.

It may have been easier to build, but it will require many maintenance and inspections to keep it in good repair, making sure everything is functioning as it should.

One of the most difficult things about a flat roof is knowing when you need to replace it or whether it simply needs some minor repairs.

Here are the most common problems that happen in flat roofs and how best to deal with these issues if and when they arise:


This is one of the surest signs that your flat roof needs replacement is a phenomenon called alligatoring.

This happens when the asphalt used to build your flat roof has aged and lost its elasticity, causing the roof covering to crack and bubble - looking something an alligator's skin.

If this is the case, your asphalt flat roof has deteriorated past the point of no return and will be replaced before it damages the underlying timbers.

Leaks and Moisture

Leaks and lingering moisture are probably the most common problems with flat roofs but can be dealt with effectively, as long as you stay on top of them.

A flat roof will develop leaks, just as any roof can, but since it's flat, the water can't run away as it doesn't have anywhere to go except straight down.

The water will seep into the roof itself, causing problems such as mould and fungus. To deal with this most effectively, make sure your roof is inspected regularly and any issues are dealt with swiftly.

Buckle in the Membrane

Most asphalt flat roofs are constructed in a similar way to shingled roofs - made up of a membrane soaked in asphalt.

They are then laid across the building's top to make the roof; the membrane on a flat roof is all one piece. Over time, your garage shifts and settles, as will your roof. More excessive movements can result in buckling appearing in the membrane.

This is a bad sign and means the end of your flat. A buckling roof is unsafe and can cause major problems down the line. It's a good idea to consider replacing it quickly.

Pooling Water

On a flat there is nowhere for water to escape when it rains or snows. As your garage settles over time, the roof itself will shift slightly The garage might not be as level as when it was new, which may cause water to pool in dips and uneven parts of your roof.

Most materials these days are manufactured to hold a limited amount of moisture and water, but it's recommended to drain these pools as soon as possible, checking carefully to make sure that water hasn't seeped into the timbers of the roof.

If pooling is allowed to stand for long periods of time, it's will deteriorate the outside of your roof, and shortening its lifetime.

Crack in the Roof

Because flat roofs tend to have more pressure exerted on them, they are not slanted. Sometimes this pressure can build up, and the stress becomes excessive, which can quickly cause your roof to crack.

Call a professional immediately if your roof does crack. Exposing the garage to the weather, a crack in the roof is often a sign that your roof is structurally compromised. It's time for a new one.


Just like most other materials, flat asphalt roofs tend to expand and contract with the weather and changing temperatures.

Over time, this expansion and contraction can result in the flashing pulling away from the edges of your roof. This may lead to leaks and moisture getting trapped inside your roof. To avoid this, inspect and maintain your flat roof regularly.

It will save you the far more considerable cost of installing a new roof. If the leaks are significant, or if you have a lot of deterioration in the flashing, you will need to install a new roof.

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Sam J

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