Flat Roof vs. Pitched Roof: Which Is Better?

Flat Roof vs. Pitched Roof: Which Is Better?

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We all need a roof on top of our home, our extension, or the workshop or garage that we are planning to build, but what kind of roof will be the right one to plan for? Is a pitched roof the right one to build, or would a flat roof be more appropriate?

Before you commit, take a look at some of the areas where a flat roof might come out top over a pitched roof, and vice versa.

What Is a Flat Roof?

A flat roof is technically speaking a ‘low slope’ roof, as a roof will still need to drain rainwater from its surface. It is usually constructed using a heavy bitumen felt covering that is welded together using a torch or heat gun.

More modern materials such as single-ply polymers are also popular with commercial builds. These are glued and sealed with a heat gun. Other flat roofs are made in one piece from GRP (Glass Reinforced Plastic) and are often seen on tract housing or kit-form extensions or outbuildings.

In a separate article, we wrote more about the advantages and disadvantages of flat roofs.

What Is a Pitched Roof?

A pitched roof is the most common, traditional roof construction, seen right across the US on many buildings. Pitched roofs are oftentimes covered in either concrete tiles, natural slate, or cedar shingles bringing a choice of finish, color, and style to a neighborhood.

This construction is usually built with a definite slope in one or more directions. It can be an incredibly strong triangular design that is resistant to wind, snowfall, and heavy rain and is sometimes made to order as structural trusses in a factory, delivered to the site, and erected very quickly.

In a separate article, we wrote more about the advantages and disadvantages of pitched roofs.

Flat Roof vs. Pitched Roof: What Are the Differences?

Below, we’ll look at the differences between these two types of roofs.

Durability: How Long Will My Roof Last?

Flat roofs are usually expected to need their covering renewed every 10-15 years for a bitumen-based product. A single-ply polymer is normally guaranteed for at least 20 years, while a GRP roofing system can have a manufacturer’s guarantee from 20-40 years depending upon the final product.

A pitched roof is a different thing altogether. A concrete tile roof, if properly maintained, should last the lifetime of the building, which is normally estimated at 75-100 years. A natural slate roof, exposed to an average level of weather, will have a lifetime of approximately 50 years, sometimes longer.

Cedar shingles look amazing and are a sustainable way to cover a roof if they are suitable for your project in terms of location. Manufacturers claim they will last up to 50 years if properly maintained, but they are prone to rot, warping, and splitting.

Maintenance: Looking After Your Roof

A flat roof can suffer from ponding, where water simply won’t drain away. This is usually due to either an ice dam build-up or leaves clogging the outlets, so regular inspections will be required as you head into autumn.

A pitched roof may also suffer from clogged outlets; however, the water will not remain trapped on the roof surface, and the issue will be confined to your gutters and downspouts. If left for too long, water on a flat roof may find its way through the joins on your membrane.

Standing water also encourages bugs and wildlife, and eventually, you might see plants growing on your flat roof. Plant roots can be very invasive, and hard to get rid of. If there is a route through the roofing membrane, nature will find a way.

Up-Front Costs: What Will I Pay?

The straight answer is that a pitched roof will have a bigger up-front cost. To start with, you will be paying more for the foundation concrete before you get anywhere near cutting the first rafter. A pitched roof will require more of everything, more timber, more roof covering, and more time to build.

If it is used to house additional storage or living spaces then the cost can perhaps be justified and will have to be budgeted for, but a flat roof will always be the most economical up-front cost choice.

Flexibility: Unlocking Future Potential

A flat roof has unlimited potential. It could be the launchpad for another story on a building if the foundations are solid enough and comply with codes. Or it could be an elevated outdoor space, perhaps a terrace for entertaining, or maybe an urban garden.

You might even consider putting a glass house or lightweight conservatory extension over your flat roof to make it a year-round space to enjoy the views, the light, and your plants.

A pitched roof, on the other hand, is there to stay. It can only really be converted into additional usable living space if there is the height to do so. Insulation requirements for attic conversions are rigorous, requiring an R-value of up to 60 in Northern US climate zones, which will impact available headroom.

It pays to think ahead if you see yourself expanding into the attic in the future and adjusting the pitch to suit. Perhaps ask your architect to take this potential into account. If it takes the budget up too far then it might be more sensible to choose a flat roof. In a decade or so, when it needs replacing, the budget might be ready for that second-story extension.

Flat Roof vs. Pitched Roof: Which Is Better?

When your project is on a limited budget all the advice will be to push for the best quality affordable at that level. Pitched roofs are expensive, so opting for a flat roof should help to retain focus on doing the job as well as possible, rather than cutting corners.

A pitched roof has its strengths in that it could be used as additional living space if it is large enough and insulated properly. A low-pitched roof could also be a great space for services, such as an HVAC system.

Flat Roof vs. Pitched Roof: Which Is More Common?

If you are considering a single-story extension then it is probably sensible to pick a flat roof over a pitched roof, as you will incur less expense on foundations and roof structure, but there are other things to consider beyond the budget.

Take a look at the local neighborhood. What is the most common form of roof construction locally? Whatever it is there’s likely a good reason for it, as local climate, materials, and aesthetics all play a part.

In Southern states, especially in desert regions and close to the border with Mexico, a flat roof might be more common, used as an outside space for drying laundry or perhaps just hanging out and enjoying the view. However, it’s very unlikely that much carpentry went into their construction!

Across most of the USA, however, it’s most likely that you will see pitched roofs gracing the tops of most residential buildings due to their practicality and long-term durability, which is usually expected to offset the initial high costs.


At the end of the day, it really comes down to budget and expectations. When building a small-scale extension it is probably more cost-effective to go with a flat roof design, as the urgency to complete such a project likely outweighs most other considerations.

If you are after a modern, cube-house look, then the additional cost of a resin-based flat roofing system that lasts longer than a traditional bitumen-based product, is probably worth it to achieve the right curb-side appeal, durability, and guarantees.

A pitched roof for a new-build house is the expected route for most self-builders and contractors as it is the traditional time-served roofing solution that works for almost all building designs. Its long-term durability and design adaptability make it the top choice for most projects, but ultimately, it’s up to you.