How much does it cost to replace your flat roof with a pitched roof?
Because of the variability in design and the possible choice of materials, sometimes it is easier to work to an average price per square metre. For a shallow pitched roof, work on a baseline cost of about £25 per square metre. The average cost for conversion from flat to a pitched roof is between £3,000-£5,000 depending on the roof size and choice of materials. Despite the new generation of materials available for a flat roof, many homeowners do look to upgrade a flat roof to a solid pitched roof if they can.
Last Updated: October 2022
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Why are homeowners replacing their flat roof with a pitched roof?
Flat roofs are sometimes a necessity because there isn’t the space to accommodate a pitched roof or, a traditional style roof would interfere with the storeys above or even a neighbouring property. Flat roofs are generally less expensive and quicker to install than a pitched roof but they can have significant disadvantages which is why many property owners will choose to upgrade an existing flat roof with a pitched roof.
A common trigger point is when the flat roof has reached the end of its natural life and costs of roof leak repair are becoming too high. This often prompts the conversation whether to replace with a flat roof again or opt for a new pitched and solid roof instead.
What are your pitched roof options?
You can either work with the roof that you have providing it is in good order and install a new shallow-pitched roof over the top or, you can construct a completely new roof with a greater degree of pitch and a new floor below it. if you don’t build a new floor then it can limit your options for the new roof as the ceiling joists will affect the installation.
The most popular option is to convert a flat roof to a pitched roof by installing a trussed roof. A framework of angled beams is placed above your flat roof to bridge the gap and to provide the new shape whilst supporting your roof materials. This is a long-lasting and durable choice with very little maintenance required particularly compared to a flat roof but there is no roof void so this option does not add extra space. A shallow pitch is usually quicker and easier to install and complete than a steeper one. Some planning authorities are less concerned about permission for a roof with a more gentle slope than something very angled and extreme.
A gable roof with its triangular shape is also a popular option providing attic space for storage or conversion and affording good ventilation without being hugely expensive.
A hip roof features a downward slope on each side and will cost more than a gable roof and a further variation on this theme is a pyramid hip roof which is much more complex in structure and consequently more expensive. A pyramid hip roof is incredibly durable in adverse weather conditions, more so than a standard gable roof so a good choice for homes in exposed locations.
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Pitched roof versus flat roof
Here is a comparison between the two roofing styles, a summary of the main advantages and disadvantages.
Flat roof pros
- A much cheaper and inexpensive roofing option compared to a solid roof
- Installation is quick
- A competent householder can do this job themselves
- You can make more of a contemporary design statement with a flat roof particularly with new modern materials and finishes
Flat roof cons
- Even with excellent workmanship, flat roofs can be prone to leaks because of the minimal slope of no more than ten degrees
- Flat roofs require regular care, attention and maintenance
- They have a shorter lifespan than other roofs
- Repairs can become costly
Pitched roof pros
- A pitched roof has a solid and traditional design which can be more pleasing aesthetically
- They are easier to maintain
- The slope affords better drainage capacity so they are less prone to leaking
- Pitched roofs usually have a very long lifespan
- They offer high-quality ventilation which promotes energy efficiency rather than energy wastage
- The pitched slopes offer the opportunity to install solar panels
- The correct choice of design will offer space within the roof which can be either used for storage or converted to form further accommodation
- A structural change to a pitched roof from a flat roof will add value to your home
Pitched roof cons
- The price of a pitched roof is significantly more expensive than a flat roof
- There is a longer installation process
- Construction can be complex
- This is unlikely to be a project you will be able to undertake yourself
- There is a level of disruption to the property and sometimes adjoining properties when a pitched roof is installed due to the complexity of the work and the time taken
Other cost factors
There will be other factors associated with the conversion and general cost of re-roofing a house including:
- Changing from a flat roof to a solid, pitched roof construction is a major structural change and so will require the services of either an architect or structural engineer who will charge professional fees. They will need to draw up plans which comply with Building Regulations and obtain planning permission for which the local authority fee is around £200
- The larger the roof or the higher the pitch, the greater the cost
- The state of the original roof once the original roofing materials are stripped off – you may need to repair or upgrade the structure before work can carry on – if the worst comes to the worst, you could need a completely new roof before the project continues but this should be picked up at the survey stage ideally and not appear as an unexpected cost. The material you choose will also be a cost factor, for example, slate roof costs are likely to be slightly more expensive than other materials.
- Your new pitched roof will require insulation and the type of insulation you choose will impact on the cost – spray foam insulation is between £20 and £50 per metre whilst roof insulation panels around £25 per square metre
- Rainwater goods may need complete renewal to fit your new roof, work on a figure of around £30 per metre but if you have a period property and are opting for cast iron fittings, then these can retail at up to £75 per metre
What is the process of changing a flat roof to a pitched roof?
This is the outline of a fairly standard schedule of works to convert a flat roof to a pitched roof:
- The old flat roof is removed so any tiles or the coverings plus the roof battens. This is the first point at which the roof can be fully checked for rot or other damage and which will need to be remedied before the installation can continue
- The joists are checked including their spacing to make sure they are suitable for the new roof
- Roof trusses are placed over every second joist and connected to the supporting wall
- Gable ends are measured and added and then typically plywood laid over the entire roof to cover it before being hammered onto the trusses to form the new shape
- The roof receives a waterproof layer at this point, most commonly tarpaper which is laid along the length of the roof up to the peak. This is nailed in place
- The ridge boards are installed followed by the tiles
- Finally, the gable ends are covered using a siding material which is secured onto the wooden structure. This is then primed and waterproofed
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Frequently Asked Questions
How long will the roof replacement take?
This depends on the size of the roof and how many people are working on it but usually, a roof replacement will take between 2-4 days.
What is the actual mathematical difference between a flat roof and a pitched roof?
A flat roof is defined as a roof that is almost completely level, it will have an almost imperceptible slope of ten degrees or less to prevent rainwater ponding. A pitched roof is a roof with a slope of 12.5 degrees or more. It is usually easier to get planning permission with a more shallow pitch to a roof than something very steep.
Can I add my pitched roof myself?
Even for the most ardent of DIY enthusiasts, installing your own roof is often a bridge too far. A new roof is a major structural change and the works will be subject to regular inspections by the Building Control Officer. If you have the time and some skill, it may be better to offer to do some labouring or you could even remove the old roofing material yourself ahead of the main works to save costs.
Do I need planning permission to change my flat roof to a pitched roof?
Because the conversion is classified as an architectural change, you will need to obtain planning permission from your local planning authority. The biting point is whether your project is going to be more than 150mm from the existing roof and whether the alteration be will be higher than the roof’s current highest point. You will also need to apply if the total roof volume is more than 40 cubic metres and your house is a terraced property or 50 cubic metres for a semi-detached home. You could also need to seek Building Regulations approval but your engineer or architect can advise you on this – it will depend on the scope of the works. If your property is listed or in a conservation area then any conversion to the roof shape and type will require planning permission.
How can I finance my roof?
If you have a mortgage then you may be able to apply to your lender for a Home Improvement Loan or Further Advance to fund this and other home improvements. You will need sufficient residual equity in the property to support the funds and pass an affordability test for the increased mortgage payments. If money is forthcoming then your lender may require evidence of the works and that you have actually spent the money on home improvements. Older people who are mortgage-free may want to look at some of the Equity Release schemes available to fund this and other works to their property.
Some building contractors work in tandem with finance companies and can offer you a quote for finance which will help spread the cost. Always compare finance options thoroughly as there may be a cheaper provider in the marketplace. Many of the finance packages will come from the main banks and will be a name you are familiar with. Some schemes are even interest-free but can require a deposit of 50% with the bank funding the rest. The most attractive zero or low-interest options are usually only available to people with a very good credit score. The advantage of these schemes compared to a Home Improvement Loan from your finance company, is that they are quite short-lived, usually two to five years but you can often run them for up to twelve years to help keep the monthly cost lower. The mortgage company schemes are commonly spread over the remaining years the mortgage has to run so you will end up paying more in the long run.
Thanks for reading - hopefully, you'll have a better idea of the costs of adding a pitched roof! For more information on planning permission, see guidance from the HomeOwners Alliance, and Planning Portal on planning permission for roofing projects.