![\"\"](\"https:\/\/www.nedzink.com\/wp-content\/uploads\/import\/cms\/userfiles\/images\/divers\/tabel1eng.jpg\")
<\/p>\nTheoretical results show that in the Netherlands the maximum rainfall intensity at our geographical width is 540 – 600 (l\/s)\/ha). If the rainwater-drainage system of a building or house is based thereon then a rainwater-drainage system will never overflow. Within the standardisation the question has been raised if it is realistic that the costs of the size of a gutter for such a heavy rainfall intensity offset the inconvenience of a rare overflow.
\nIt should be taken into account that the capacity of the public sewer will not be sufficient.
\nIt is expected that once every 5 years the rainwater-drainage system may overflow, which is considered acceptable. This risk entails a rain intensity of 0.03 (l\/s)\/m² or 1.8 (l \/min)\/m².<\/p>\n
The quantity of rainfall on a roof surface is determined by the effective roof surface in m² to be multiplied by the rain intensity (i) l\/min. The dimensions of the rainwater-drainage system can be calculated by means of this quantity of rainfall to discharge per unit of time.<\/p>\n
In the calculation of the rainwater-drainage capacity of a roof the dimensions of the rainwater downpipes and the number of rainwater downpipes are determinable. The choice for the (standard) gutter is to be made on the basis thereof. The standards NEN 3215 and NTR 3216 serve as guideline for the calculations.<\/p>\n
Determination of the quantity of rainfall (Qh) on a roof is made with the formula:<\/p>\n
Qh = ( α x i ) x ( ß x F ) formula 1
\nQh = the rainwater load in litres\/minute (l\/min.)<\/p>\n
<\/p>\n
Roof examples see figs. 1 and 2.<\/p>\n
\nα = the reduction factor for the rain intensity for flat roofs
\nα = 0.60 flat roof with ballast of gravel
\nα = 0.75 for the other flat roofs
\n As flat roofs discharge the water at a slower pace, for all other cases (therefore all pitched roofs)
\n applies α = 1,
\ni = rain intensity and is 1.8 (litre \/ minute)\/ m²
\nß = reduction factor for the roof width is determined by the pitch of the roof
\nF = surface of the roof
\n <\/p>\n
Figures 1 and 2 show different roof forms.<\/p>\n
Determination of the roof surface “F”<\/p>\n
The roof surface is determined by the product of the length (l) and the effective width (b) of the roof surface. The effective width is determined by the reduction factor ß.<\/p>\n
Effective width of the roof and the reduction factor ß
\nThe roof pitch ε determines the reduction factor ß. Walls also contribute to the discharge of rainwater
\n( ß = 0.3). It is indicated in the standard that no horizontal projection is applied. Table 1 gives the reduction factors for the various roof pitches.<\/p>\n
Reduction factor α for flat roofs
\nFor flat roofs the discharge of the rainwater to the roof outlet is slowed down. To this end, the rain intensity (i) of 1.8 (l\/min)\/ m² is multiplied by the factor α. See table 1.<\/p>\n
The reduction factors α and ß are summarised in table 1.<\/p>\n
The number of rainwater downpipes (n) must first be determined. The quantity of rainwater to be discharged in l\/min is known from formula 1.<\/p>\n
Prior conditions:<\/p>\n
<\/p>\n
The number is first determined by the structural design.<\/strong><\/p>\n Roof surface<\/p>\n<\/td>\n Number of roof outlets<\/p>\n<\/td>\n<\/tr>\n <100 m² <\/p>\n<\/td>\n min. 1<\/p>\n<\/td>\n<\/tr>\n >100 m² <\/p>\n<\/td>\n min. 2<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n For flat roofs: The quantity of water to be discharged per rainwater downpipe is “Qh : n” in l\/min. <\/p>\n Depending on the circumstances the number of rainwater downpipes can be increased.<\/p>\n Gutters larger than the required minimum dimensions can always be applied.<\/p>\n The roof gutter must lie of course on slope and be installed from low to high.<\/p>\n For more information on the installation of roof gutters and rainwater downpipes, see NedZink Advice TZ1.<\/p>\n <\/p>\n Example Figure 1<\/p>\n Dimensions.<\/p>\n (L) = 22 m, (b) = 5 m, Roof pitch ε = 40° \nNumber of rainwater downpipes: Choice of rainwater downpipes: Choice of roof gutter is box gutter B37 or suspended \nTabel 4<\/p>\n Max. quantity<\/p>\n Rainwater<\/p>\n Qh in l\/min<\/p>\n<\/td>\n Ø Downpipe Min.cross-section (A)<\/p>\n of the gutter Smallest type * standard rainwater downpipes Quantity of rainfall. Theoretical results show that in the Netherlands the maximum rainfall intensity at our geographical width is 540 – 600 (l\/s)\/ha). If the rainwater-drainage system of a building or house is based thereon then a rainwater-drainage system will never overflow. Within the standardisation the question has been raised if it is realistic that […]<\/p>\n","protected":false},"author":9,"featured_media":0,"parent":0,"menu_order":1120,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"class_list":["post-47808","page","type-page","status-publish","hentry"],"acf":[],"yoast_head":"\n\n\n
\n \n \n \n <\/td>\n <\/td>\n<\/tr>\n \n \n \n \n \n \n
\nDistance between 2 roof outlets must be limited from 10 to 20 metres. Place the roof outlet at
\nleast 1 metre from the corner of the flat roof.<\/p>\n
\n(n) = number of outlets.<\/p>\nTable 4 shows the choice of the accompanying smallest
\nstandard roof gutter.<\/h3>\n![](\"https:\/\/www.nedzink.com\/wp-content\/uploads\/import\/cms\/userfiles\/images\/tz3_fig1.jpg\")
<\/p>\nArithmetical examples<\/h3>\n
\nSingle roof α = 1 and ß = 1, see table 1
\nCalculating the quantity of rainwater
\nQh = α x i x ß x F
\n= 1 x 1,8 x 1 x (22 x 5)
\n= 198 l\/min.<\/p>\n
\nPrior conditions,<\/p>\n\n
\n\tRoof surface (F) = 110 m2 => min. 2 rainwater downpipes, see table 3<\/li>\n
\n\tGutter length 22 metres => min. 2 downpipes Ø 80 mm, see table 2. (Expansion device required).<\/li>\n<\/ol>\n
\n2 rainwater downpipes => 99 l\/min => table 4 => Ø 80 mm<\/p>\n
\ngutter M37, see table 4 (37 indicated the developed width in cm.).<\/p>\n\n\n
\n \n \n
\n\t\t\td in mm<\/p>\n<\/td>\n\n
\n\t\t\tA ≥ 1.3 di² in cm²<\/p>\n<\/td>\n\n
\n\t\t\tStandard gutter **<\/p>\n<\/td>\n<\/tr>\n\n \n 117<\/h3>\n<\/td>\n
\n 80*<\/h3>\n<\/td>\n
\n 79<\/h3>\n<\/td>\n
\n B37 or M37<\/h3>\n<\/td>\n<\/tr>\n
\n \n 210<\/h3>\n<\/td>\n
\n 100*<\/h3>\n<\/td>\n
\n 125<\/h3>\n<\/td>\n
\n <\/h3>\n
B44 or M44<\/h3>\n<\/td>\n<\/tr>\n
\n \n 338<\/h3>\n<\/td>\n
\n 120*<\/h3>\n<\/td>\n
\n 181<\/h3>\n<\/td>\n
\n B55<\/h3>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n** B = box gutter 37\/44\/55 = developed width in cm.
\n M = suspended gutter
\n The outlet piece for a rainwater downpipe has an inner diameter (di) that is at least 4 millimetres
\n smaller than the nominal size of the rainwater downpipe. This inner diameter of the outlet piece
\n determines the inflow capacity of the rainwater downpipe.<\/p>\n","protected":false},"excerpt":{"rendered":"