Steep Roof Flashing (Part 1)
Flashing is an every day concern for roofing contractors. It can easily be misunderstood or ignored because it is usually he slow, non-interesting part of the roofing project. Many times roofers want to install the showy, fast moving part of the roof and may not have the most experienced person installing the most important aspect of the roof.
Flashing should always be approached with a water-prevention mindset. New employees may not have that mindset or understanding developed yet. Flashing has a different meaning for each person here, depending on your relationship to the building:
* If you are the owner, you want a leak free building.
* If you are the architect or designer, you want it to perform
a function well and be aesthetically pleasing.
* If you are the engineer, you don’t want it to interfere with
the integrity of the structure.
* If you are the general contractor, you want it to fit the construction
budget.
* If you are the roofing contractor, you want it to complete
and protect your roof and prevent callbacks.
So you see, while each may have a different interest or role, all have to be a team with the same goal in mind of our customer expectation.
A high percentage of owners or managers of commercial buildings, churches, schools and residences almost never have their building checked until problems arise. Unfortunately, many times flashing and waterproofing is taken for granted, or ignored altogether. The result of the absence of flashing can make itself known subtly or in a major way.
1. Wet ceilings causing dark spots.
2. Wood buckling or splitting, or completely deteriorated.
3. Plaster spalling or powdery patches.
4. Mold
5. Water dripping between the fascia and gutter.
6. Water trails down the brick walls at coping joints or gravel stop joints.
Rarely do leaks correct themselves. Water in the wrong place can be the enemy of a building. This is assuming the insulation and humidity levels of the interior are OK.
Flashing is not the area to cut costs, or value engineer out, or minimize. There is too high a price to be paid for this after the fact.
WHO IS RESPONSIBLE FOR DECIDING WHEN AND WHERE FLASHING IS NEEDED?
The first answer is usually the designer who has to understand the progression of infiltrated water in the building, and design flashing as an integral part of the building.
Unfortunately, many times we are told not to allow flashing to be exposed. A given is that many times, in the proper order of the way water flows; it may not always be possible to hide good flashing. Case in point, if apron flashing is installed under the last roofing course, then it has to be nailed through for the well being of the structure.
The roofing contractor should address the flashing related to their roof installation; but very few that I know of will get involved in other areas of the flashing. We will cover these later.
Up until recently, we depended on the general contractor to inform us of needed extra flashing. What we found out was that beyond window flashing, most general contractors are not astute to flashing needs. I made a commitment to our customers
that in the future we would determine where unspecified flashing is needed and give a broken-out price for it. This all came about when we bid a large residence and included our standard counter-flashing on what we thought was a large wall. During construction, we kept getting calls about wet floors on the lower floor. We realized immediately that the wall had doorways, inset windows and other openings. This required a through-wall flashing, about $6,000.00, frayed nerves and a lot of finger-pointing to get resolved. We made the decision then to get involved in the total flashing aspects of our customers.
The owner doesn’t always know where flashing is needed. Many masonry contractors understand the need for flashing at window openings, but not other areas.
A. Flashing is the termination, or last, step in the roofing process to keep water out of the building and roofing assembly.
B. Flashing should be installed at any point where water can blow or soak into a wall assembly. In some instances you cannot prevent water from migrating in. Examples would be masonry, stone, and hard-coat stucco after it checks and cracks. The key is to control the progression as the water migrates downward in the wall. Water usually takes the path of least resistance as it moves. We want to block this water and send it where we want it to go rather than where it wants to go.
Some areas where flashing is needed would be:
• Chimneys • Crickets
• Walls • Expansion joints
• Windows • Eave strip
• Vent pipes • Under the gutter
• All roof penetrations • Masonry projects
• Chimney tops • Thresholds
• Decks, wood, concrete, and also waterproofing.
C. WHAT PRODUCTS TO USE FOR FLASHING:
(1) First of all, anything is better than nothing (intellectual insight statement) … well almost.
(2) Surface mounted counter flashing can be most of the metals since it is isolated by strip tape or sealant.
(3) Cut-in counter flashing can be most metals, copper, lead coated copper, terne coated stainless, Kynar finish aluminum or galvanized, etc. Mill finished aluminum can react with mortar, so be cautious.
(4) Through-wall flashing can be copper, lead coated copper, terne coated stainless steel, or stainless steel.
(5) Wall moisture barrier above the flashing can by Tyvec type, or felt for wood walls. Use self-adhering modified bitumen two-feet above through-wall flashing and Tuyvec
type above that. Use self-adhering MB on chimneys behind stone. Also two-part liquid membranes can be used. With all this information available, why are building owners and insurance companies paying out millions of dollars each year to correct poorly installed work? Where is the accountability?
HOW OR WHEN DO YOU START OR PREP FOR FLASHING?
Flashing begins at dry-in time. When the steep roof has the underlayment such as 15# or 30# felt, fully adhered MB, SBS modified bitumen or 90# granulated roll roofing, or the new underlayments appearing on the market are installed and ready
for the finish roof product.
On flat roofs, you don’t typically dry them in. Depending on the material to be used, such as Built-up roofing, EPDM, TPO, Modified Bitumen, the new coating-type roofs, the flat metal roofs with stretch screws at 3” OC into hot sections, low slope standing seam metal panels or others.
In this modern, enlightened day there is unlimited knowledge from many sources, such as the manufacturer’s instructions, Roof Consultants Institute, NRCA waterproofing manuals, courses taught by your local roofing contractors’ associations, trade magazines such as Professional Roofing, SNIPS, RSI, SMACNA Manual, Slate Bible, and the internet to name only a few.
Remember: installing flashing after the building is finished is very costly. Flashing will be continued in future magazines, because the subject is too large for one issue.