A Catch 22 Product Specification

Specifications occasionally include unintended contradictions, and in some instances they are related to schedule.

Not long ago, I reviewed a specification for roofing that included a requirement for a particular "ice and water shield" product and allowed no substitutions. The application requirements for the product included a minimum ambient temperature of 40 degrees F. That looked good from a quality control perspective, but the schedule for this fast-track, multi-building project in snow country required construction during the winter, when temperatures were expected to be well below 40 degrees F, and neither the schedule nor the budget allowed for temporary tenting and heating of whole buildings. As a result, in order to meet the schedule, the contractor had to apply the product under conditions that were not recommended by the manufacturer and were not in compliance with the specification.

Roof Design Basics for Snow Country

Leaks from ponds created by ice dams can frequently be traced to roof design. Roof designs that funnel snow to narrow spaces and narrow eaves are likely to promote the development of ice dams and resulting roof leaks. Roof designs with changing slopes that drain steep roofs to flatter roofs are likely to promote the development of ice in the area where the roof slopes meet. Standing seams of metal roofing can restrict snow runoff and promote the development of ice dams near the lower ends of valleys. Roof designs that include opportunities for warm interior air to reach the underside of the roof are likely to cause roof snow to melt and allow melt-water to run down and refreeze at the eaves, forming ice dams and leak-producing ponds behind the ice dams.

Some design principles to minimize the risk of ice dams and resulting leaks include the following:

1. Keep the roof design simple. Avoid complex roof architecture that requires runoff to change direction or follow circuitous paths to get off the roof. 
2. Avoid or minimize 'waterfall' conditions where runoff dripping from a high eave can freeze on a lower roof.
3. Avoid roof configurations that include a high, steep roof intersecting a lower, flatter roof surface.
4. Make way for snow. Remember that snow cannot get through tight spaces easily passed by water. Roof designs should allow wide paths for snow movement. Avoid tight dormer spacing, tight valleys, and other roof configurations that would restrict snow movement. 
5. Avoid standing seam configurations that restrict snow movement. Snow may move down-slope easily in a direction parallel to standing seams, but standing seams in valleys and roof slope changes can act like brakes, restricting snow movement toward eaves. Snow movement around chimneys and similar items can be restricted by standing seams, so special consideration should be given to a seam layout that will promote effective snow movement.
6. Keep the roof surface cold - especially up-slope from eaves - by keeping warm interior air away from the underside of the roof. Paths for interior air to reach the underside of the roof must be effectively blocked by a complete air barrier on the warm, interior side of the insulation (or by a properly installed, complete air barrier type of insulation).
7. Include support for underlayments, flashing, and roofing membranes at intersections between roof surfaces and related construction. Do not expect watertight integrity where a design calls for a dormer eave to intersect a main roof plan at a point without special construction to support underlayments, flashing, and roofing transitions.
8. Consider roof orientation and exposure when designing a roof. Snow will generally melt sooner on a roof exposed to sunlight than on a more shaded roof. As noted in 2 above, snow melt from an exposed roof can meet colder temperatures and refreeze as ice on the more shaded roof.
9. Minimize use of skylights and roof windows. Even the most energy efficient of these will melt snow that lands on them, and the melt-water is likely to refreeze as ice as it runs down on colder roof surfaces.
10. Do not expect an underlayment product like "ice and water shield" to compensate for design features that promote ice dams.
11. Consider the need for snow removal maintenance. Designs with features that promote ice dams may require frequent snow removal to minimize leaks.

Aesthetics and structural integrity are commonly the first considerations in roof design. Roof designs for snow country should also include basic considerations and accommodation of snow behavior in order to minimize problems caused by ice dams.

Metal Roofing Specifications: "No Visible Oil Canning" equals Mission Impossible.

On my first visit to the job site after the roofing contractor had started installing standing seam metal roofing, the Clerk called me aside and said, "I think we've got oil canning."

I looked at the newly installed metal. It looked fine.

"Wait a while", he said. As the sky changed and the angle of the sunlight changed during the day, oil canning appeared, then disappeared, then reappeared differently. "The specs say 'no visible oil canning'," the Clerk accurately noted.

The spec writer's best intentions, possibly influenced by the designer's best intentions, were that from Day One and under any and all light conditions the metal roofing would exhibit no visible distortion. Seeing the situation in the field, a part of my mental faculties that were still intact suggested we had a problem that was more perceived than real. Over the next few days I visited and photographed a number of other projects with metal roofing - from afar, up close, and under different light conditions. These appeared to be carefully crafted installations with little or no distortion related to the installation. Yet under some light conditions and viewing angles, they all exhibited 'visible oil canning'. I put the findings into a little presentation for the client, who had been alerted to the oil canning condition by the Clerk. Following the presentation, the client was satisfied that the metal roofing was normal in terms of visible oil canning. The spec writer? Well, that's another story.

(Visit http://www.smacna.org for an October 2005 newsletter article on oil canning and information about how to minimize it.)

Roof Drainage Design: Foresight or Afterthought?

If we could just get it a little further away or get it to go over there, everything would be okay.

We usually locate the roof drains near the low point

We were working on the layout of the roof plan for a large, irregularly shaped building, designed with the structure gently warped to shed water to the edges. A drafter was adding roof drains to the plan, and I noticed that he was locating some of the drains about half way up the slope between the low point and the high elevation. I asked him why he was doing that, and he replied that he thought the drains at mid-slope would collect half the runoff on its way to the low point.

"Oh, I forgot to tell you," I said. "We usually locate the roof drains near the low point." He looked skeptical until I added, "It's office policy."

A notable roof warranty exclusion

Manufacturers of single ply roofing membranes offer warranties that vary in duration and conditions of coverage. The warranties typically include a lengthy list of requirements and exclusions. One of the most notable exclusions, which appears in all caps and/or boldface type on some warranties, is a statement that excludes representations or promises made by a representative of the manufacturer which differ from the provisions of the published warranty.

The 'sales rep' exclusion highlights a common dilemma. The manufacturer's sales rep typically has to please several "masters". The rep has to please the architect and project owner in order to get the manufacturer's product or system specified. Then the rep has to please the roofing contractor, the first-line customer who will actually purchase and pay the manufacturer (or distributor) for the product. And, of course, the rep has to please the manufacturer with productive sales. In construction, full payment usually follows installation, so the manufacturer's rep may be involved in site visits, inspections, and warranty processing related to project completion. In order to get paid upon project completion, the rep has to pursue the satisfaction of all these parties - the roofing contractor, the architect, the owner, the manufacturer, and maybe even a few others. That may be a tall order under circumstances where the interests of those parties are not all aligned, and one outcome may be a promise that cannot be kept. The 'sales rep' exclusion suggests that manufacturers have had experience with reps making promises that are contrary to the terms of a published warranty, and the exclusion protects the manufacturers from that problem.

Considering again the question "Who is the customer?", I recall a conversation with a manufacturer's rep several years ago. We were concerned with the quality of work that was being done by a roofing contractor, and we thought the manufacturer's rep might be able to help persuade the roofing contractor to do a better job. The rep's response to our request was very enlightening: "I can't really help you out with that," he said. "The roofing contractor is my customer."

Roof Drainage Design: Early design decisions can influence roof and wall performance

It is possible for architectural designers to rely too much on technical details, specifications, and construction quality to overcome the challenges created by a design concept. A design concept can overwhelm the intended performance of roofs and walls that are expected to manage water and keep it out of a building’s interior. Where a roof slopes down toward or against a wall, the best flashing detail may simply not be up to the task of protecting the building from leaks. A roof configuration that includes numerous dormers and valleys, changing slopes and materials, and multiple levels can make drainage paths so convoluted or restricted that ice formations and leaks in snow country are almost inevitable. Roof design complexity also challenges effective ventilation of roof framing areas, especially in and around dormer and cathedral ceiling areas.

It’s interesting that popular features like dormers that mimic historic buildings can also bring problems like ice dams and leaks.

Avant-garde designs that tilt walls and rely on the wall materials to perform like roofs also risk performance shortcomings.

The best time to consider these possibilities and minimize risks is when the design is still in a formative stage.

Roof Shingle Warranty: What's in it?

There may be a popular notion that a 30-year shingle is one that comes with a full 30-year warranty against leaks, so that if you (or, more likely, your building) experience a roof leak, say, 27 years from the date of installation, you can call the shingle manufacturer, and someone will re-roof your building at no cost to you. Wish it were so!

One widely known shingle manufacturer has produced a lengthy warranty that, based on my review, does not even include the word "leak". It warrants shingle "performance", but for that manufacturer, performance is apparently not related to the possibility of leaks.

Although there are numerous shingle manufacturer warranties and options available, the basic warranty, even for a "30-year" shingle, covers labor and materials to replace shingles that are proven to have significant manufacturing defects within a more limited period of time (like 2 to 10 years from manufacture or installation). After that the cost of labor is excluded, and the cost of shingle material is pro-rated based on the expected life of the shingle. Other exclusions are numerous. Tear off, disposal, replacement of flashing and other accessories are typically excluded, as are shingle replacement in cases where installation was not completed in accordance with the manufacturer's recommendations or where ventilation is not adequate. Under some circumstances a reduced limited warranty may be available from at least one manufacturer for shingles installed over insulated roof sheathing or vented, insulated sheathing. Perhaps the most notable of all exclusions: the warranty does not cover damage to the inside of your house and your furniture and other belongings.

Other cautions: At least one manufacturer recommends open metal valleys and will not generally provide warranty coverage for shingles installed in closed (woven or close-cut) valleys. Shingle warranties are typically transferable once from the initial owner of a roof to a subsequent owner with proper notification and paperwork and, in some cases, payment of a warranty transfer fee, all within a period of time stipulated in the warranty. Warranties against wind blow-off are also qualified to exclude circumstances where weather or temperature conditions or roof orientation have not or do not allow for the self-sealing adhesive strips to seal; and that can take months or maybe longer. And limited warranties for algae resistance are available for some shingles - you may qualify for limited financial assistance to pay for algae removal.

Still not satisfied? With some shingles you can get a lifetime warranty - that is, the shingle is warranted for the life of the original purchaser. However, that too is pro-rated after an initial period of maximum coverage. And, when you depart, it may automatically convert to a 50-year warranty for your survivors. Wow! Does that give you peace of mind?

The normal disclaimer applies: Read the fine print in your shingle warranty to see how it applies to you and your circumstances.

Finally, don't forget that the spaces around and between the shingles are not usually covered by a shingle warranty.

...in the Details

Rain diverter in Cordoba, Spain