1-10 degrees1-10 degrees. That means flat roofs aren’t actually flat. It may look horizontal but often has a minimum slope of 1/4 inch per foot. This allows water to run off the roof to prevent damage.

What angle is a flat roof?

between 1° and 10°

Flat Roofing

A roof is still considered a flat roof if it has an angle between 1° and 10° and even though they aren’t suitable for all buildings they are a popular choice for extensions, porches and garages.

How do you calculate the slope of a flat roof?

Quote from Youtube video: One we should plan a minimum slope of 3 degrees for flat roofs or 5.7 degrees for profile roofs an easier way to calculate the slope is to convert degrees. Into percentage of the length.

How shallow can a flat roof be?



A flat roof is defined by BS6229:1982 as being 10˚ (1in6) or shallower. In reality most people refer to flat roofs as being much flatter than this, and pitches up to 10˚ usually being referred to as shallow pitch roofs.

What is the maximum slope given to the flat roof?

The slope of a roof is properly known as its pitch and flat roofs have up to approximately 10°. Flat roofs are an ancient form mostly used in arid climates and allow the roof space to be used as a living space or a living roof.

Is 2 degrees enough for flat roof?

A flat roof is between 0 and 2 degrees and, as long as there is no ponding, a flat roof will still discharge rainwater to a gutter. A slope is best though, the greater, the better, as materials can settle and ponding can occur.

What is the minimum fall for a flat roof?


According to BS 6229 & BS 8217, flat roofs should be designed with minimum falls of 1:40 to ensure a finished fall of 1:80 can be achieved, allowing for any inaccuracies in the construction. This applies to general roof areas along with any internal gutters.

What is the best pitch of a roof?

Conventional slope roofs, with a pitch between 4/12 and 9/12, are the most common in residential work. Roofs with a pitch exceeding 9/12 (37 degrees) are termed steep slope roofs. In commercial work, low-slope roofs (with a pitch between 2/12 and 4/12) are most common.

What are standard roof pitches?

Conventional slope roofs are most common with residential roofs. This means the slope has a pitch between 4/12 and 9/12 on most homes.

What roof pitch is 30 degrees?

7/12 roof

A 30° roof pitch is roughly the same as a 7/12 roof pitch. To convert from degrees to the American ratio: Find the tangent of the angle, tan(angle). This gives you the pitch of the roof.

What is the minimum slope for water drainage?

For efficient drainage, paved surfaces should have a minimum 1-percent slope. Turf or landscaped areas should have a minimum slope of 2 percent.

What angle is a 1 in 40 slope?

Slopes vs. gradients vs. % grades

Angle (degrees) Gradient
39 1 1.235
40 1 1.192
41 1 1.150

What’s the minimum slope for a roof?

2:12 pitch

The minimum roof pitch for shingles is a 2:12 pitch.

If your roof is less than 2 vertical units (inches or feet) up for every 12 horizontal units out, it’s considered low slope.

What is the minimum drop on a 12 ft flat roof?

Flat Roof Slope Minimum

According to the International Building Code, the typical built-up flat roof that uses tar or asphalt goes by the guideline that for every foot (12 inches) of a flat roof, a minimum of ¼ inch must step up or down.

Do I need guttering on a flat roof?

Most modern flat roofs are covered by a membrane that prevents water leaking into your property. But if your roof has a slight slope it will need gutters to ensure proper drainage.

Where does water go on flat roof?

Interior Drains

These drains are placed in areas of the roof that collect the most water, and they lead the water into a system of pipes that is installed below the roof. The water travels through these pipes until it is dispensed into a gutter or downspout at the side of the building.

What are the problems with flat roofs?

Here are 11 flat roof problems to look out for:

  • Ponding. As the name suggests, a pond of water on your roof is a very bad sign. …
  • Watermarks. …
  • Vegetation. …
  • Cracking or stretching at joints or corners. …
  • Blistering. …
  • Movement. …
  • Rusted or missing roof nails. …
  • Dodgy repairs.

How do you divert water from a flat roof?

Quote from the video:
Quote from Youtube video: All right well since I cut out the boards here. I am able to lower the channel to where I want it to be. But I come now to the fascia board here we just usually the side of the roof. And this is where

Is standing water on a flat roof OK?

Standing water on a flat roof for 12-36 hours after a rain storm can be normal, but according to the National Roofing Contractors Association, any water found ponding on flat roofs for longer than 2 full days should be examined by a professional commercial roofing contractor.

How do you stop ponding on a flat roof?

The easiest way to prevent water ponding is to clean the drains, rain gutters, and downspouts on the roof. By removing debris such as leaves, sticks, and branches, the water can flow more easily from the roof.