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PHOTO 1: The through-wall flashing stainless-steel drip can be observed projecting nicely from the wall\u2014but the termination of the roof base flashing more than 1-inch below resulted in a section of the brick wall that allows water to pass into the wall below the through-wall flashing and behind the roof base flashing, resulting in the damage seen in Photo 2.<\/p><\/div>Projects are perceived to be successful by their ability to prevent disturbance from weather, including rain. Have you ever heard two architects talking about Frank Lloyd Wright?<\/p>\n
\u201cWhat a genius! His spatial conception is magnificent, even after 100 years.\u201d<\/p>\n
“But all his buildings leak!”<\/p>\n
I used to give a talk to University of Illinois architecture students in which I told them the quickest way to go out of business is to be sued. The quickest way to be sued is to have a building allow moisture intrusion. If he were alive today, Frank Lloyd Wright\u2014God rest his soul\u2014would be in jail (and a few current architects may be well on their way). Owners are not very kind when their \u201cbabies\u201d leak.<\/p>\n
Many roof termination interfaces are never even thought about by designers and are left to the roofing contractor to work out. This is not a recommended practice. One such condition\u2014that every architect should be able to detail\u2014is how the roof base flashing terminates at a masonry wall that has through-wall flashing and weeps at the base of the wall above the roof. I believe so fervently that architects should be proficient in detailing these conditions that I believe it should be required to procure their license.<\/p>\n
WHY THE IMPORTANCE<\/h4>\n
The interface of roof base flashing and masonry through-wall systems occurs on a majority of commercial construction projects. If this transition is not performed correctly, moisture intrusion behind the roof base flashing to the interior will occur (see Photo 2). When this occurs, besides angering owners, it befuddles the architect. Photo 1 (left) shows a nice through-wall flashing drip extended out from the wall, weeps and roofing terminated with a termination bar and sealant. What could be wrong?
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PHOTO 2: Moisture intrusion at the base of this wall was the result of water circumventing the through-wall flashing
and roof base flashing termination seen in Photo 1. A big concern with conditions, such as this, is the propensity of the materials to promote mold growth.<\/p><\/div><\/p>\n
The exposed brick above the termination bar and below the stain- less-steel drip of the through-wall flashing is susceptible to water flowing down the surface of the brick. Water passing through the brick above is supposed to be weeped out; however, at the exposed brick above the termination bar, the water moves into the wall and has nowhere to go but inward.<\/p>\n
The cost to repair these conditions can be, depending on the conditions, expensive. Repairs often require brick removal and through-wall flashing mitigation. In this particular case, be- cause there is a stainless-steel drip, my team recommended a stainless-steel counterflashing be pop-riveted to the drip and extended over the termination bar.<\/p>\n
CHALLENGES<\/h4>\n
Why is the interface of roof base flashing and masonry through-wall systems so difficult for architects and roof consultants to detail? I believe it is because they have no clue it needs to be detailed as an interface, especially because detailing of appropriate through-wall systems is so sporadic. I endeavor in this article to change at least the knowledge part.<\/p>\n
The detailing of this condition not only requires the ability to interface two building systems, but also requires considerable time to ensure specification of wall sectional details and roofing details are appropriately placed where the responsible trades will see them.<\/p>\n
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PHOTO 3: Still under construction, the stainless-steel counterflashing has
been installed. The roof base flashing will terminate below the stainless-steel counterflashing receiver. Hutch prefers brick below the through-wall flashing and above the roof deck, though the masonry mortar joints below the through-wall flashing should have been struck flush.<\/p><\/div>\n
NEW CONSTRUCTION<\/h4>\n
New construction provides us a clean slate to \u201cdo it right the first time\u201d. The first order of business is to determine the height of the base flashing. This can be tricky with tapered insulation and slope structures with saddles. Let\u2019s consider the following examples (see Detail 4, page 3):<\/p>\n
EXAMPLE 1<\/strong> Thus, the surface of the roof at the wall will be 15 inches above the roof deck.\n<\/ul>\n Because you would like to work at the masonry coursing level and given that concrete masonry units (CMU) are nominal 8 inches, you are looking at placing the through-wall flashing 24 inches above the roof deck.<\/p>\n This 24-inch dimension of where to place the through-wall flashing needs to be placed on the building section and\/or wall section because the mason, which will be onsite prior to the roofing contractor, will need to know this information.<\/p>\n This 24-inch height begs another termination question: What occurs at the roof edge with this height? Hold that thought for now. Terminations at intersections will be discussed in future articles. PHOTO 4: Instead of the construction in Photo 3, here, concrete masonry units were installed below the counterflashing receiver. If ever exposed, CMU will readily take on water. CMU walls also can excessively absorb adhesives and two applications are recommended.<\/p><\/div>EXAMPLE 2<\/strong> \u00bb The roof deck will drop 6 inches from the roof edge to the low point. The through-wall flashing should be at \u00b119 inches (11 inches of insulation plus 8 inches for roof base flashing) above the low point of the roof deck. The exact dimension needs to be worked out in the wall section.<\/p>\n As noted with the previous example, the location and height of the through-wall flashing should be placed on the building section and\/or wall section because the mason, which will be on- site prior to the roofing contractor, will need to know this information. PHOTO 5: Twenty years ago, Hutch had to be creative when the through-wall flashing could not be raised and the roof surface rose above the wall flashing. In this photo, an interior gutter (with roof drains) was designed at the base of the wall below the through-wall flashing. It has performed well for decades.<\/p><\/div><\/p>\n With the required height for the through-wall flashing, based on the roof insulation, one can begin to detail the roof to masonry wall. For our discussion, we will assume the roofing is a single-ply membrane. The first challenge is to draft the condition correctly: roof deck location, support structure, angle at the wall, wall components, appropriate cavity spaces, wall insulation (should run down below the roof deck).<\/p>\n Thinking about how the wall and roof will be constructed, the sequencing is helpful. If you are not familiar with the construction of buildings, get yourself out in the field, watch and learn.<\/p>\n Following are key components of the detail to be shown:<\/p>\n Draft the detail at a minimum of 3 inches equal to 1 foot. Anything smaller will not allow for the appropriate level of detail to be shown.<\/p>\n \u00bb In the sheet-metal and flashing section, specify the fabrication of the counterflashing receiver and provide it to the masonry contractor for installation. PHOTO 6: Four inches of additional insulation are going to be added to this existing roof, which Hutch designed 25 years ago. The new insulation will require raising the interface of roof base flashing and masonry through-wall systems.<\/p><\/div><\/p>\n \u00bb I suggest that not only should the specification call for priming of the substrate, but also that this be noted on the detail.<\/p>\n PHOTO 7: Demolition in progress to add more insulation to the existing roof seen in Photo 6.<\/p><\/div>The roof termination at the wall now can be detailed. Draw in each layer of insulation, noting its attachment method. Do not show a single thickness. Drawing all the components helps the draftsman understand the components, will help achieve a more accurate detail and conveys to the contractors you know what the hell you are doing. It is amazing how poorly drafted 95 percent of new construction roof-related detailing is.<\/p>\n PHOTO 8: The masonry contractor segmented the demolition so the brick above could be supported.<\/p><\/div>\n When completed, this detail has provided an appropriate interface be- tween two very important building envelope systems (see Detail 3). Photos 3 and 4 show a recent project.<\/p>\n With the advent of increased required thermal insulation and the emphasis on tapered insulation to remove water from the roof as quickly as possible, designers are often presented with new insulation heights well above existing through-wall flashing conditions. Two design options are available to correct the condition that exists:<\/p>\n Option 1 is certainly the more often accomplished detail. I designed option 2 a couple decades ago and it still is working (see Photo 5). I mention it so you have this solution in your design repertoire.<\/p>\n PHOTO 9: The through-wall flashing has been raised to a new height to accommodate the additional insulation.<\/p><\/div>As with all reroofing work, test cuts of the existing roof system should be taken to determine not only the existing roof\u2019s composition and roof deck type, but also to determine the depth of the existing roof(s), so the required height of the new through-wall flashing can be determined.<\/p>\n The same exercise shown in the examples in the \u201cNew Construction\u201d subhead, page 1, needs to be undertaken so that you have a handle on the roof insulation heights. Photos 6 through 9 are from a recent project and show how this work is undertaken.<\/p>\n Prior to detailing, the exterior wall components should be determined. As with the roofing, this is best done through an exploratory opening.<\/p>\n The final detail will look much like the one for new construction but with many components labeled as \u201cexisting\u201d. A demolition detail should be prepared showing the extent of brick removal (see Detail 1). Although this can be done in a building elevation, we find photos with notes work well. The drafted detail should express new materials versus existing. This is most often done by ghost outlining existing materials with new materials being dark lined with As with new construction, coordination is critical because now the interior of the building needs to be dry. With our reroofing projects, the roofing contractor typically assumes the role of the \u201cprime\u201d contractor and, thus, has supervisory control over his subcontractors. So roofing contractors are not searching \u201cAngie\u2019s List\u201d for masons, we often have this work under an allowance and assign the mason to the roofing contractor after the contract is awarded. This prevents non-qualified contractors from being involved and raises the quality of workmanship.<\/p>\n \u201cDo it right the first time\u201d is the perfect mantra for design and construction of the interface of roof base flashing and masonry through-wall systems. When not detailed and left to the contractor\u2019s whims, the resulting moisture intrusion is difficult to determine, correct, expensive and leaves owners questioning your abilities. But thinking of the interface of roofing and masonry walls holistically, one can perhaps see the concerns, design for them and delineate them so that the crews in the field can accomplish them.<\/p>\n Happy consulting.
\nWe are dealing with a flat roof, tapered insulation, cover board and bead-foam insulation in ASHRAE Climate Zone 5, which has an R-30 minimum.<\/p>\n\n
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\nThis time, we\u2019re dealing with a structurally sloped roof deck at 1\/4 inch per foot toward centrally located roof drains. The roof width is 48 feet. Tapered insulation saddles between roof drains set 24 feet off the masonry wall. The roof is composed of cover board and bead-foam insulation. This is ASHRAE Climate Zone 5, which has an R-30 minimum.<\/p>\n\n
\n\u00bb The height of the flat and tapered-insulation saddle at the wall is 10 5\/8 inches; we\u2019ll say 11 inches, which will be approximately level with the roof edge with its 5 inches of insulation.\n<\/ul>\n![\"PHOTO](\"\/wp-content\/uploads\/2016\/11\/Screen-Shot-2016-11-17-at-10.26.21-AM-300x222.png\")
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\n\u00bb In the masonry section, specify that the mason is to install the counterflashing receiver provided by others.
\n\tNote that the mason is to provide needed dimensions, especially if the receiver is covering a cavity.![\"PHOTO](\"\/wp-content\/uploads\/2016\/11\/Screen-Shot-2016-11-17-at-10.26.31-AM-227x300.png\")
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ROOFING REMOVAL AND REPLACEMENT CONSTRUCTION<\/h4>\n
\n1. Raise the through-wall flashing.
\n2. Design an interior gutter and allow the existing through-wall flashing to remain.\n<\/ul>\n![\"PHOTO](\"\/wp-content\/uploads\/2016\/11\/Screen-Shot-2016-11-17-at-10.26.54-AM-300x217.png\")
\nmaterial poche (see Detail 2).<\/p>\nTHE DEVIL IS IN THE DETAILS<\/h4>\n
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