Code-mandated Thermal Insulation Thicknesses Require Raising Roof Access Door and Clerestory Sill Details

PHOTO 1: The new roof has been installed at SD 73 Middle School North and it can clearly be seen that the door and louver need to be raised. On this project, there were four such conditions.

PHOTO 1: The new roof has been installed at SD 73 Middle School North and it can clearly be seen that the door and louver need to be raised. On this project, there were four such conditions.

The most common concern I hear related to increasing insulation thickness (a result of increased thermal values of tapered insulation), especially in regard to roofing removal and replacement, is, “OMG! What about the roof access door and/or clerestory?” You can also include, for those knowledgeable enough to consider it, existing through-wall flashing systems and weeps.

I’m a bit taken aback by this concern; I have been dealing with roof access doors and clerestory sills for the past 30 years and, for the most part, have had no problems. My first thought is that roof system designers are now being forced to take these conditions seriously. This is a big deal! They just have no clue.

In the next few pages, I’ll review several possible solutions to these dilemmas, provide some detailing suggestions and give you, the designer, some confidence to make these design and detailing solutions. For the purpose of this article, I will assume reroofing scenarios where the challenge is the greatest because the conditions requiring modification are existing.

THE ACCESS DOOR

For many and perhaps most contractors who sell and, dare I say, design roofs, it is the perceived “large” expense of modifying existing conditions that is most daunting. Often, these conditions are not recognized until the door sill is several inches below the new roof sur- face. Not a good predicament. Planning for and incorporating such details into the roof system design will go a long way to minimizing costs, easing coordination and bringing less tension to a project.

PHOTO 2: The sill has been raised and new hollow metal door, frame and louver have been installed at SD 73 Middle School North. Door sill and louver sill flashing are yet to be installed, as are protective rubber roof pavers.

PHOTO 2: The sill has been raised and new hollow metal door, frame and louver have been installed at SD 73 Middle School North. Door sill and louver sill flashing are yet to be installed, as are protective rubber roof pavers.

Door access to the roof is the easiest method to access a roof. These doors are typically off a stair tower or mechanical penthouse and most often less than 12 inches above the existing roof as foresight was not often provided (see photos 1, 2 and 6 through 9). With tapered insulation thickness easily exceeding 12 inches, one can see that door sills can be issues with new roof systems and need to be considered.

Designers should first assess the condition of the door and frame, typically hollow metal. Doors and frames that are heavily rusted should not be modified and reused, but discarded, and new ones should be specified. The hardware too needs to be assessed: Are the hinges free of corrosion and distortion? Is the closure still in use or detached and hanging off the door frame? The condition of door sweeps, knobs, lockset and weather stripping should also be determined. Ninety-nine percent of the time it is prudent to replace these parts.

As the roof system design develops, the designer should start to get a feel for the thickness of insulation at the door. It is very important the designer also consider the thicknesses that vapor retarders, bead and spray-foam adhesives, cover and board and protective pavers will add. These can easily be an additional 4 inches.

PHOTO 3A: The new roofing at SD 73 Elementary North was encroaching on this clerestory sill and required that it be raised. As part of this project, the steel lintel was exposed. It was prepped, primed and painted and new through-wall flashing was installed.

PHOTO 3A: The new roofing at SD 73 Elementary North was encroaching on this clerestory sill and required that it be raised. As part of this project, the steel lintel was exposed. It was prepped, primed and painted and new through-wall flashing was installed.

Once the sill height is determined, the design of the sill, door and frame can commence. If the sill height to be raised is small—1 1/2 to 3 inches—it can often be raised with wood blocking cut to fit the hollow metal frame, flashed with the roofing membrane, metal sill flashing and a new door threshold installed, and the door and frame painted. This will, of course, require the removal of the existing threshold and door which will need to be cut down to fit and then bottom-sealed with a new metal closure (see details A and B, page 3).

When the door sill needs to be raised above 3 inches, the design and door considerations increase. Let’s consider that the door and frame is set into a masonry wall of face brick with CMU backup. Although most hollow metal doors are 7 feet 2 inches to match masonry coursing, after the modification the door may be shorter. For example, if a door is 7 feet 2 inches and you must raise the sill 5 inches, the new door and frame will need to be 6 foot 9 inches.
PHOTOS & ILLUSTRATIONS: Hutchinson Design Group Ltd.

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Projects: Office

DPR Construction, Phoenix

Eighty-two Daylighting Systems were installed in the renovated 16,533-square-foot building.

Eighty-two Daylighting Systems were installed in the renovated 16,533-square-foot building.

Team

Roofing contractor: Arithane Foam, Corona, Calif.
Architect/engineer: SmithGroupJJR, Phoenix
Daylighting systems distributor: Norcon Industries, Guadalupe, Ariz.

Roof Materials

Eighty-two Daylighting Systems were installed in the renovated 16,533-square-foot building, formerly an abandoned retail boutique at the corner of 44th Street and Van Buren in Phoenix.

“The use of the Daylighting Systems was an integral part of our sustainability and lighting energy savings plans for the renovated space,” says Dave Elrod, regional manager of DPR Construction, Phoenix. “The products are a cost-efficient solution to provide lighting since they nearly eliminate the need for artificial daytime lighting.”

In addition, the roof is composed of foam with an R-25 insulation value (approximately 4-inches thick) over plywood sheathing.

Daylighting systems manufacturer: Solatube International Inc.
Foam roofing manufacturer: Quik-Shield from SWD Urethane

Roof Report

DPR Construction is a national technical builder specializing in highly complex and sustainable projects. In less than 10 months, the design-build team researched, designed, permit-ted, and built a highly efficient and modern workplace with numerous innovative sustainability features.

In addition to natural daylighting, the office features an 87-foot zinc-clad solar chimney, which releases hot air from the building while drawing cooler air in; shower towers that act as evaporative coolers to regulate building temperatures; 87 operable windows designed to open and close automatically (based on indoor/outdoor temperatures); and two “vampire” shut-off switches to keep electrical devices (radios, cell-phone chargers, microwaves) from using plug energy when no one is in the office.

Access to the building was limited during construction. Spray foam roofing, which took about seven days to complete, had to be done in small quadrants because of the tight schedule as work was progressing in the other sections. The roofing workers were challenged by the barrel-shaped roof, which created footing difficulties, and the many penetrations that had to be flashed, including all PV support legs, Solatubes, skylights and HVAC penetrations. Work was completed in the middle of winter, so additional protections and efficiencies were required.

The circa-1972 building has been officially certified as a Net-Zero Energy Building by the Seattle-based International Living Future Institute through its Living Building Challenge program. It also has received LEED-NC Platinum certification from the U.S. Green Building Council, Washington, D.C.

PHOTOS: Ted Van Der Linden, DPR Construction

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