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CallMeVilla 10-19-2013 09:44 AM

Re-bending Flashing
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Remember whining about math? “When will I ever use this in real life?” Well, I had one of those moments proving how math is important in real life …

Problem: Standard L-flashing needs to be re-bent to a different angle to provide a runoff slope for rain. How do you determine the proper angle and (practically) how do you bend the 10 foot long flashing segments easily in the field without a metal break? The original flashing is 3” x 3”, bent at 90 degrees.

Answers: The flashing is being applied to a wall and a horizontal ledge. An obtuse angle will allow for a good slope to shed rain water from the roof above it. The decision was to put a ½” lift on the wall side. This requires a new angle on the flashing because 90 degrees will not shed the water. Using my smart phone, I located a site that could calculate the sides and angles for a triangle with a 0.5” side and a 3” hypotenuse.

The website calculated the interior angles of the triangle ABC. The interior angle at B was about 81 degrees, making the outside angle at B equal to 99 degrees. The field solution (rounded) is to add 10 degrees to the L-flashing (totaling 100 degrees)

Bending: Without a sheet metal break, how do you open the angle on the long flashing segments accurately? Original Euclidian geometry and early trigonometry was based on lines intersecting a circle. The answer to opening up the angle is easy.

Using a common 4” diameter length of ABS pipe, simply lay the L-flashing on top of it. Using a 2x4 lengthwise along the flashing, press down firmly along the corner to re-bend the flashing. Using a protractor, measure until the angle is 100 degrees.

Then we finished the application of the flashing to the wall !

PangioneDevelopers 10-19-2013 10:17 AM

Bending flashing is simple.... First toss out all the calculation mumbo jumbo and lets get basic
Simple is good....

Lay your metal stock down on a 2piece of plywood or flat surface. Sandwich the metal at point of bend with 2- 2x4's or 2x6's the length of the metal. ( This is why a metal brake was created)
with someones help, squeeze the 2 2x's together while you proceed to bend metal to the angle that you need.
As you are bending, you will want to actually tilt the sandwich up slightly while you are pressing the bending angle down and against the flat surface. A long piece of plywood or another 2x8 makes a good surface.
This is justfor those that cannot and will not have access to a brake bender.

Good Luck

CallMeVilla 10-19-2013 12:42 PM

Oh, forgot to mention ... I did this by myself, without a helper, without a bender, without clamps, without anything except the pipe and 2x4 ... just good math sense and creativity. :D

oldognewtrick 10-19-2013 05:09 PM

Get some big "C" clamps to secure the ends and the middle of your 2X's if the metal doesn't interfere.

firehawkmph 10-23-2013 08:13 PM

Funny stuff. I've owned several siding brakes over the years since 1978. Sided a lot of houses, bent a ton of flashing for all different applications, long before smart phones came out. Never once had to get a computer to tell me to bend a piece of flashing less than 90 degrees to get it to shed water. I could look at it in the brake as I bent it and know if it was right or not. Your eyes are one of the best tools you have.
Mike Hawkins:)

nealtw 10-23-2013 09:45 PM

Villa: don't look now but I think a few of us were amused at your need for technical help.

CallMeVilla 10-23-2013 11:10 PM

Thanks guys ... I have a technical/mathematical side and just got into the problem solving thing ... Ended up doing the "looks good by eye" thing afterall ... but I did use the ABS pipe as a device and it worked great.

Was by myself, so I needed a solution ... wasn't even drinking when the idea came to me.


oldognewtrick 10-24-2013 05:27 AM


Originally Posted by CallMeVilla (Post 92792)
Was by myself, so I needed a solution ... wasn't even drinking when the idea came to me.


Well, that explains everything...;)

Necessity is the mother of invention.

firehawkmph 10-24-2013 11:50 AM

this reminds me of another story. Years ago, when I was a firefighter in a fairly wealthy community, there was a big party going on with two Lifeflight helicopters on display, along with their crews being there, and other hospital dignitaries. An emergency call came in for the copters, and this again was before smart phones. One of the pilots was an ex Vietnam pilot, the other was a college kid trained over here, non-military. The kid runs in the house, gets on the phone to get all the latest weather conditions, wind speeds, etc. Before he even connected the call, the Vietnam vet had jumped in his copter, fired it up and was gone in no time at all, leaving the kid still waiting on the phone. We all got a good laugh at it at the time. Glad to here your flashing thing worked out.
Mike Hawkins:)

BridgeMan 10-25-2013 08:15 PM

The actual amount to add to 90 degrees is the arcsin 0.5" / 3" = arcsin 0.16666667 = 9.594068 degrees. That is, if one wants to be sloppy, and just carry out the calculations to 6 places.

Man, I love that "mumbo-jumbo"! Guess that's why I was considered the teacher's pet in sophomore geometry class, when the instructor asked me to help him tutor some of the other kids who were a bit slow in catching on.

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