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Gutter Downspouts

Well all that water had to get out of your gutters somehow right?  That is where downspouts come in. Choosing the proper location for downspouts is extremely important aspect of water management on your property.  Also sizing the downspouts correctly for the potential amount of water coming off of your roof is vital.

Proper Sizing / Water Handling Capacity Downspouts

Perhaps the most vital part of your gutter system is making sure thats the water captured by the gutters can quickly and efficiently exit the roof.  Use the below chart for the most common kinds of downspouts and the recommended capacity.

Down Spout Size Max Area of Roof draining to one down
2x3
400
Sq Ft
3x4
650
Sq Ft
4x5
1000
Sq Ft
3" Round
450
Sq Ft
4" Round
700
Sq Ft
5" Round
1200
Sq Ft
(Safe for maximum rainfall)  
* Reduce by 10% per 90 degree turn in gutter
Assumes proper pitch and no obstructions or turns

 

Where to place gutter downspouts

Every home and property has unique issues with where to place your downspouts. There is no one right answer as to the locations of your downspout other than to say that they must be at a low point of the gutter as water doesn't run up hill. 

Here are some common guidelines.

1)The more downspouts you have the more margin for error you will have when something goes wrong.  For example two 2x3 downspouts will in general more efficiently drain water on a long run than a single 3x4 that would do the job.

2)Relating to #1 debris in the gutters is a downspouts worst enemy.  Most debris suck as leaves, twigs, seeds and pine needles get washed towards the downspouts and can easily clog the opening.

3) Make sure the water exiting your downspouts can't drain back towards the foundation of your home.  Try to locate the downspouts on a downslope or add downspout extentions to get the water a MINIMUM of 4ft away from your foundation.

4) If at all possible do not drain downspouts to concrete or masonry of any kind.  A concentrated amount of water will hit these areas and therefore erode those surfaces.

5) Do not drain downspout onto roofs. Some contractors will draing downspouts onto lower roofing slopes.  The problem is those shingles get eroded quicker as a large directed portion of water beats down on them.