Step Flashing Curiosity

**Stuart Brooks** · 05-09-2013, 09:31 AM

I never seen step flashing installed on the back side of exterior siding. The picture shows the the roof step flashing at the point where the garage roof abuts the gable end of the house. The plywood sheathing is the exterior finished siding of cedar T1-11 siding. Noting the water stains on the plywood, the siding must go down to the roof surface. The exterior cedar trim running down the roof does and is rotting in places where it was in direct contact with the roof surface. I want to call it as an improper installation and call for correction of the flashing installation and repair of damaged siding and trim. But, when you think about it when the sheathing is nothing but foam or Thermo-ply material, there isn't much difference. P001A.jpg

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**John Kogel** · 05-09-2013, 12:30 PM

They should have trimmed the sheathing so it was 2" above the bottom of those flashings. I can see them flashing that way for a decorative plywood sheathing, one layer.
They should have used a flashing with a higher rise than what they have there.

I think you are right to call it out for a repair. It will probably go to the bottom of the list, fix it when the rot gets worse.

**Lon Henderson** · 05-09-2013, 05:50 PM

That flashing is wrong. Plywood sheathing isn't meant to be exposed to recurring water and it appears that the bottom of the plywood would be getting wet on a regular basis.

**Gunnar Alquist** · 05-09-2013, 05:53 PM

Originally Posted by Stuart Brooks

I never seen step flashing installed on the back side of exterior siding. The picture shows the the roof step flashing at the point where the garage roof abuts the gable end of the house. The plywood sheathing is the exterior finished siding of cedar T1-11 siding. Noting the water stains on the plywood, the siding must go down to the roof surface. The exterior cedar trim running down the roof does and is rotting in places where it was in direct contact with the roof surface. I want to call it as an improper installation and call for correction of the flashing installation and repair of damaged siding and trim. But, when you think about it when the sheathing is nothing but foam or Thermo-ply material, there isn't much difference.

Stuart,

The reason you may not have seen step flashing on the back side of siding is because there should be a building paper between the siding and studs. Stains on the siding are common due to capillary action. Not sure about the lap requirements of the step flashing.

**Billy Stephens** · 05-09-2013, 06:15 PM

Originally Posted by Stuart Brooks

I never seen step flashing installed on the back side

But, when you think about it when the sheathing is nothing but foam or Thermo-ply material, there isn't much difference. P001A.jpg

Yes Much, There is Much Difference if the Step fashing is incorrectly installed under and not on top of a proper moisture barrier.

**Mike Kleisch** · 05-10-2013, 08:00 AM

I see this from time to time where the T1 is the siding and sheathing, done it myself. Like others pointed out it is not done proper, larger step flashing should have been used and the T1 should have been 1-2 inches above the roofing. I’ve also done a saw kerf and installed counter flashing, thought it would help a roofer down the road, but think that causes more of a maintenance issue with caulking it in and maintaining it.

I tried installing a 2” gap one time and the owner had a fit about the gap he could see, tried to explain the reason for it, but to no avail, 1” it was. I was going to run Cedar trim anyway, so the T1 stayed at 2” and set the cedar at 1” and done. I would have installed blocking between the studs for the step flashing to push against, as well as the T1, and you would have not seen how it was done…

**Jim Hintz** · 05-11-2013, 08:58 AM

Another thing to consider: the flashing may have been fine with only the initial roof surface installed, but an overlay narrows the distance between the roof surface and the drip edge, making is easier for dirt and debris to collect under the drip edge which leads to wicking. How many roof surfaces were there?

**Robert Sole** · 05-11-2013, 09:33 AM

Originally Posted by Stuart Brooks

I never seen step flashing installed on the back side of exterior siding. The picture shows the the roof step flashing at the point where the garage roof abuts the gable end of the house. The plywood sheathing is the exterior finished siding of cedar T1-11 siding. Noting the water stains on the plywood, the siding must go down to the roof surface. The exterior cedar trim running down the roof does and is rotting in places where it was in direct contact with the roof surface. I want to call it as an improper installation and call for correction of the flashing installation and repair of damaged siding and trim. But, when you think about it when the sheathing is nothing but foam or Thermo-ply material, there isn't much difference. P001A.jpg

There are a number of things wrong with that flashing. First the flashing only appears to go up the wall about 2 to 2 1/2 inches. The flashing should be at least 3" by 5 " with the 5" up the wall.

Second the flashing is not properly supported along the bottom. Note in the photos how the up slope side is hanging down. That will allow water to run back into the attic.

Also the flashing does not have enough overlap. That 2 inch lap will not stop wind driven rain from blowing back up past the next piece of flashing.

The flashing should also be against a solid backing or blocking. That supports the flashing and gives you something to nail the top edge to. Notice in the first photo, the second piece of flashing to the left of the 2X4 is leaning into the attic.

As to the water stains on the plywood. If the bottom edge of the plywood is not sealed, water will wick up into the plywood even if there is adequate space between the siding and the roof. By the look of the photos, I would not expect to see much, if any gap on the outside.