Shared Knowledge
"Home Roof Gutter - Minor Change in Flow"
26 September 2005
Updated: 30 Nov 2012
Summary: by inserting a small metal dam/spillway into a gutter, you can slightly change water flow in a gutter system.
Background:
Whole house renovation 1990-91.
Moved in March 1991.
When high voltage air conditioning (HVAC) switched on, found I had a water stream running through back patio from HVAC condensate.
Gutter on back some 60 feet long and needed both downspouts but did not want HVAC condensate stream on patio either.
Changing gutter flow:
Because condensate a slow steady flow, decided to create a dam in gutter and then route condensate to other side of dam such that "stream" would be sent down downspout that does not dump onto patio.
To do this, I bought a small piece of flat, thin, aluminum, sold as roof flashing and cut it to match the interior cross section of my gutter.
As I ok with water flowing on ratio during a heavy rain storm and sure a single downspout would not be able to handle all water off my long roof, I cut the flat aluminum such that it was shorter than gutter cross section.
With aluminum dam shorter than cross section of gutter, idea was to force condensate down the far downspout but when the gutter got full from rain, allow it to spill over to the other downspout that dumps onto my patio.
Then using Henry 108R roof caulk, caulked my dam/spillway in place beyond the downspout that dumps onto my patio.
I then attached a piece of PVC pipe to my HVAC condensate pipe and routed it just beyond my gutter dam/spillway.
Now all HVAC condensate does down the far downspout and not onto my patio.
Damn/spillway:
My reason to modify gutter water flow was HVAC condensate but the a dam/spillway inserted into a gutter could help with many gutter flow situations.
I have a 60 foot long, seamless gutter on the front of my home that has only 1 downspout. My thoughts are to add a second downspout but as removal of entire gutter is a chore and a half, simply insert a dam/spillway in the middle of the gutter run and try to force some water down my newly installed downspout.