Steep Roof Flashing (Part 2)

In Part I we covered expectations of each person associated in some way with the building. Who is responsible for deciding when and where flashing is needed? What products are to be used for flashing? When and how do you start or prep for flashing? In this part, we will see how to relate the importance of flashing to the different conditions. We will also note how to relate to historical buildings. First of all, what is flashing? For the benefit of these articles, we will say that flashing is any permanent material fabricated and/or installed between the roofing or siding and the sub-components to prevent water intrusion. Earlier on this meant metal, and in most instances still does. It could also be one of a number of new flexible items.

 

Does flashing change from one type of construction to another?

Basically, the function of flashing is the same in all cases…that is to prevent or control water on or in the structure. There are conditions that relate to different areas; for instance:

  1. Most houses in a residential development will have basic flashing. That is chimneys, vent pipes and maybe a wall or two.
  2. Commercial buildings have different requirements such as flat roofs, copings, window walls, precast walls, unusual brick work, expansion and contraction considerations.

 

 

Churches have many unique features:

  1. Steeples with openings in them usually over the entry.
  2. Parapet wall at the gable ends with base and counter flashing cut in. The walls are capped with limestone, stone or other hard cap. The joints are mortared or sealed with sealant. In most cases a through-wall flashing is installed. As a rule, the flashing does not extend out far enough to get water away from the wall. As a result you notice black streaks down the face of the wall at each joint in the cap.
  3. At the eave of the roof is often a built-in gutter or
    cricket area to drain water to scuppers and downspouts.

What are the different types of flashing? Where are they used?

 

Reglet Flashing was formerly the primary method of counter flashing. The reglet is formed by removing the mortar from a masonry wall approximately one and one-quarter inches deep, fabricating metal flashing to fit over base flashing into the reglet joint one to one and a quarter inches with a one-quarter inch leg turned up and held in with wall wedges. The mortar joint was then repointed with compatible mortar the same color as original. Now most reglets are cut in with a dry diamond saw or side grinder, the counter flashing is inserted and caulked. Most sealant manufacturers say pre-priming is unnecessary. The dust created by grinding should be brushed out. If dust remains, priming is a way to allow the sealant to perform more efficiently. Care should be taken to insure the sealant bonds to the insert flashing as well as the mortar joint. Nail-on or Surface Mounted Flashing is used where it is impractical to cut a reglet or where a reglet is not provided, for example, pre-cast walls. With the coming of single-plies, termination bars became popular. This varies with different manufacturers and can be plastic or aluminum. Care should be taken to seal between the membrane and the substraight. The term bar is the force that holds the membrane to the wall.

 

Surface mounted counter flashing will require as much consideration as any other method because with the water running down, the wall can become saturated and find any unsealed section to bypass the termination bar. Thought should be given to wire brushing dust from the substraight surface. A compatible primer will enhance the bonding ability of the butyl strip tape. Fasten in all holes as recommended by the manufacturer. The fastener is usually a drive pin anchor such as zamac or tapcon screws. Fiber or plastic plugs can be used with appropriate screw. We don’t use nylon drive plugs for this because of the degrading by the sun and heads breaking off, which allows the term bar to fall off the wall.

 

Through-Wall Flashing (or Built-in Flashing) is by far the most expensive of all the flashings. When it is omitted, or improperly installed, the cost can be staggering.

Why does flashing need to be through-wall? All walls or chimneys don’t have to be through-wall. It depends on the wall covering.

 

Let’s consider a few:

  1. Stucco (hard coat) – Usually has a vapor barrier behind it so the flashing can turn up behind the underlayment. The reason for this is because of the checking and cracking of the hard coat stucco. We usually see this on chimneys. Elastomeric coating is usually the most economical method of stopping this leak.
  2. EIFS – As a rule the flashing is installed against the backer. The Styrofoam is then adhered above the flashing. We try not to install the flashing before the backer is installed because of the potential for water to soak into the backer board.
  3. Wood – When flashing is installed under wood, it should be as near the finish surface as possible. Example: lap siding, board and batten, tongue and groove, V siding, plywood, etc. The flashing needs only extend up behind the finish ply. Also behind the wall moisture ply which can be roofing felt, Tyvec or other good underlayment. There again, you want to keep the water away from the framing membrane. NOTE: this can also apply to other forms of siding such as vinyl.
  4. Stone should always be through-wall flashing if it is part of the interior heated and living area. We are dealing with a chimney now that has just begun to give problems after 75 plus years because of cracks that channel water in due to the irregularity of the stone and the shelf forming characteristics.

Folks, of all the flashing that we talk about here, through-wall flashing can have the most expensive, devastating effect when either omitted or incorrectly installed.

We received a call to check leaks around a tall stone chimney. It was laid in the dry stack method. After removing a couple of the stone, it was immediately apparent that there was inadequate flashing. The copper was laid in flat and sealed with acetic-based silicon (NOTE: DO NOT use this on copper. It usually turns green and then loose.) The concrete block base was not waterproofed. Now was the time to be the bearer of bad news. The stone had to be removed to reflash the chimney. We estimated 80 tons of stone. The cedar shake roof was removed around the chimney as well. This chimney had to have through-wall flashing. It was only about three feet by six feet, but it took 12 sheets of copper to flash it all the way around. Then we ran the bituthene self-adhering membrane to the concrete block. The stone was then relaid. The cost of this omission at time of construction was $14,000 for the flashing and approximately $30,000 for stonework.

 

As devastating as this example sounds, it happens also on commercial buildings. How do we know where throughwall flashing should be? If a masonry wall has openings cut through where migrating water can enter, a throughwall flashing is needed. Water in a wall will continue downward until it is stopped by an opening or shelf angle needs through-wall flashing.

 

This type of flashing should always be designed and installed by a person who understands water migration. Through-wall flashing should always be sealed or soldered at the joints. Same as exterior flashing: It should be sealed to the sub-structure. In case of brick or stone, it will be the concrete block.

 

Other Areas of Flashing:

Kick-out flashing is needed at any point where the bottom of a base-flashing run terminates behind the finish material of a wall. The kick-out stops the water flow downward and channels it out onto the roof. The omission of a $5.00 kickout can result in $60,000 – $85,000 repairs

 

Window flashing. This is usually window and door top flashing. It should turn up behind the wall underlayment. The ends should turn up to form dams that channel the water out rather than dripping down the ends. Brick masons and carpenters don’t like this because they have to fit over the dam.

 

Gutter flashing. Occasionally yet, we get a project that has the gutter setting on a shelf. An under-gutter flashing is needed here to prevent water from soaking into the framing. I saw an entire three-story EIFS wall pull away from the wet gyp backer board due to water running under the gutter.

 

In conclusion we have dealt with only a few methods of flashing. There will surely be more complex needs for usually and unusual flashing required as buildings get more extraordinary.

 

When I thought I had seen all weird ways of what passed as flashing, one more arose. We were installing the cornice work on a building. Another roofing company was installing the shingles. I happened to be on the jobsite when the other roofer was getting ready to install the counter flashing. He had the ladder set up, had his apron on, hammer in the hammer holder, caulking gun in hand and started up the ladder. I asked, “where is your flashing?” He said, “oh, I have it.” And continued to climb. To say I was curious is an understatement. When we install counter flashing, the joints are cut out. The flashing is either precut to fit or in 10-foot lengths to custom cut on the roof.

 

Always willing to learn a new method, I wanted to see what this guy was going to do. What happened next is too unbelievable to write about. You would need to see for yourself. As I watched, this “roofer” reached into his shirt pocket and took out a triangle shaped piece of trim sheet, laid it on the wall, hammered in two nails and caulked the top. This continued up the roof. The warranty on these shingles was 50 years. Before we finished our work, I checked out this new method and found the majority of the caulking had turned loose. The other roofers were long gone.