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Cost Check: Flat Roof vs Pitched Roof, Which is cheaper?

Cost Check: Flat Roof vs Pitched Roof, Which is cheaper?

Modern Flat Roof Design

If you’re wondering whether to go for a flat roof or pitched roof on your building, there are three things you’ll need to consider: cost, aesthetics, and functionality.

Flat Roof

Flat roofs are a popular choice in many contemporary buildings. The flat roof offers a neat, sleek, and compact appeal. It especially resonates with those whose architectural style leans towards minimalism and modernity.

The space on top of the flat roof can be utilized as an additional space either as a roof terrace or roof garden.

In essence, no roof is “flat” per se, since any roof must have a slope for rainwater to successfully drain away. A roof is considered flat if its slope (pitch) does not exceed 10 degrees from the horizontal. This angle is not easily noticeable by the human eye.

Pitched Roof

The alternative to a flat roof would be a sloped (also known as pitched) roof.

The pitched roof is one of the most common types of roofs found on buildings. The sloping surfaces of such roofs will have an angle usually over 20 degrees but not more than 70 degrees. Anything above 70 degrees pitch is considered a wall.

Pitched roofs have a more classical appearance and are considered ‘traditional’. The space underneath such a roof can be utilized either as an attic floor or loft if the pitch is really steep.

The steepness of the roof can also be used to control cost. The more steep the roof, the more the surface area and hence the more the cost. 

Comparing the cost of Flat roof vs Pitched Roof

Assume you are roofing an area with a coverage of 100 square meters.( 10mX10m)

For the flat roof, you need to consider the cost of RC works as well as waterproofing. Below is a breakdown of this

  1. Cost of formwork. sides and soffits of the slab.
    • Rate: KSH 560 per SM,
    • Formwork will cost KSH 59,360
  2. Cost of steel reinforcement.
    • Rate: KSH 140 per kg,
    • Assume 80kgs reinforcement per cubic meter
    • Reinforcement will cost KSH 168,000
  3. Cost of concrete works for 150mm thick slab.
    • Rate: KSH 13,800 per cubic meter,
    • Concrete works will cost KSH 207,000
  4. Cost of waterproofing: EPDM rubber for flat roof
    • Rate: KSH 1,780 per square meter
    • EPDM rubber waterproofing will cost KSH 178,000

Total Cost for flat foof= KSH 612,360

Let us now consider the cost of a pitched roof, assuming a 22-degree pitch.

Our cost will include the cost of steel trusses, cypress battens, and roof covering in the form of stone-coated (decra) tiles. For this, we’ll use an all-in rate of KSH 7,500 per square meter.

Total Cost of Pitched Roof= KSH 960,327

Sample Pitched Roof Plan
Sample Pitched Roof Plan

Conclusion

It is clear that the initial cost of construction of a pitched roof is comparatively higher. However, it is important to remember that the drainage of the pitched roof is more efficient.

This means that there is a higher likelihood of the flat roof leaking as compared to the pitched roof. So property owners in areas that see heavy or prolonged rainfall may need to think twice about this.

Whatever your choice of roofing style be sure to engage a professional roofing contractor to ensure you get the most out of it.

Cover image courtesy of gambrick.com

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