Page 540 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

ACTIVITY

Calculation of effective roof area
Using the formula given above, calculate the following effective roof areas.
1 A roof has a length of 12 m, a width of 7 m and a height of 3 m.
2 A roof has a length of 8 m, a width of 8 m and a height of 4 m.
3 A roof has a length of 10 m, a width of 8 m and a height of 4 m.
INDUSTRY TIP
The area of a flat roof should be regarded as the total plan area. If the roof has a
The Building Regulations complex layout, with different spans and pitches, each area should be calculated
2010 Document H3 can be separately.
accessed at: www.gov.uk/
government/uploads/system/ Building Regulations Document H3 gives an acceptable alternative for the
uploads/attachment_data/ calculation of roof area where the area of the roof is multiplied by a pitch factor.
file/442889/BR_PDF_AD_ This is detailed in Table 8.6. For this calculation, only the length of the roof and
H_2015.pdf the span are required.

 Table 8.6

Type of surface Design area (m )
2
Flat roof Plan area of relevant portion
Pitched roof at 30° Plan area of portion × 1.29
Pitched roof at 45° Plan area of portion × 1.50

H Pitched roof at 60° Plan area of portion × 1.87
Pitched roof over 70° or any wall Elevational area × 0.5
To calculate flow in litres/second for 75 mm/hour
intensity, multiply effective roof area m 2 by 0.0208
W
p Figure 8.6 Elevational area
Source: The Building Regulations 2010 Approved Document H

IMPROVE YOUR MATHS
In this instance, if the angle of the pitch of the roof is known, the calculation is
simplified. For example, if we use the data from the previous example, we arrive
at the following.
Example 2
A roof has a length of 10 m and a width of 6 m. Calculate the effective area of
the roof if the pitch of the roof is 30°.
Length of roof = 10 m
Width of roof = 6 m
The pitch factor from the table = 1.29
Therefore:

10 × 6 × 1.29 = 77.4 m 2

528

9781510416482.indb 528 29/03/19 9:04 PM