The size of the roof gutter depends upon the following** 4 factors.**

1. Surface drainage area of a pitched roof.

2. Pitch of a particular roof.

3. Maximum intensity of rainfall in that region.

4. Type or style of the roof gutter.

Now, let us understand the calculation steps in detail.

**Calculation formula:**

First, we have to calculate the adjusted square footage for the given roof by the formula,

**The adjusted square footage**

= [(roof drainage area) 🇽 roof pitch multiply factor 🇽 maximum rainfall intensity]

After calculating the adjusted square footage, we can select the required roof gutter size from the charts or tables.

**Calculation procedure:**

**1. Drainage area:**

The drainage area of a roof is determined as shown below.

Drainage area = [roof length 🇽 roof breadth]

**Note:**

a. If the roof has multiple facets, we have to add all the areas.

b. If the drained water from the 2nd-floor roofing comes over the roof of the 1st-floor, the total roof area of both should be considered.

**2. Roof pitch:**

The pitch of a roof is the ratio of no. of units it rises for every 12 units of horizontal run.

**roof pitch multiplying factor**for a different

**roof pitch**ratio is given in the following table.

**3. Maximum rainfall intensity:**

**4. Roof gutter size:**

**Eg:**

__Given data:__From the above-given table, the roof pitch multiply factor for 8/12 pitch is = 1.1

**Calculation:**

**The adjusted square footage**

= [(roof drainage area) 🇽 roof pitch multiply factor 🇽 maximum rainfall intensity]

= [ (19.68 х 16.40 ) х 1.1 х 6.5]

= **2307 < 2500**

**Therefore, we can select half round gutter of 5" in size.**

( Taken from the above-given table)

**Thank you for going through these calculation steps❤. Have a good day 😄.**