Roof Skin and Upgrade

Title: Roof Skin and Upgrade

Award Category: Roofing

Project Address/Location

Manchester Building B
26 Ave SE
Calgary, Alberta T2G 0E1
Canada

Submitted By: Stephen Epp

Company Info

RJC Engineers

1816 Crowchild Tr. NW, Suite 200

Calgary, AB T2M 3Y7
Canada

4033385891

[email protected]

Project Description and Background: Client requested re-roofing of a conventionally insulated 23 year old 2 ply SBS mod bit system that was in reasonable condition but was set for lifecycle replacement. Client had specific thermal performance targets, sloping to-drain targets, wind uplift requirements, and drain/rain level requirement which needed a formal design. Roof consultant was required to provide an assembly that best suited this specific building and the client needs. An exterior set of concrete stairs was also included in the project that required concrete restoration and application of a pedestrian deck coating. Consultant design services were required to specify repair materials as well as the coating material applied.

Scope: Consultant was required to consult on various design aspects. A "Design Brief" letter was completed outlining various client options for consideration of both the roof and stair waterproofing. This included membrane types, cover board types, insulation thicknesses, tapered insulation approaches, impacts of raising the curb heights, fall protection, existing drain sizing, impacts to mechanical equipment by increasing insulation levels, wearcourse levels for coatings, coating types, and colours. Diagnostic testing included exploratory openings on the roof to confirm the existing roof assembly along with moisture scanning using a Tramex. Existing Assembly: - Two ply SBS - 1/2" fibreboard - 2.5" polyisocyanurate - felts and asphalt mopped vapour barrier - 1/2" gypsum underlay - steel decking sloped at 0.5% and open web steel joists Existing polyiso was in good condition at exploratory opening locations. Fibreboard was wet in isolated locations but relatively minor (less than 1%). Isolated blistering was occurring as well. Due to the good condition of polyisocyanurate, we presented a skinning approach to limit amount of landfill waste and reducing costs to replace dry insulation. Existing asphalt vapour barrier was sprinkle mopped and peeled off relatively easily so it would not conform to current wind uplift requirements. To leave the polyiso, asphalt vapour barrier, and underlay gypsum in place would require a mechanically fastened approach to meet wind uplift requirements. Interior occupancy was an open concept style office with computer workstations, a relatively low humidity environment so a high quality air/vapour barrier was not required (as opposed to a pool, gym, kitchen, etc.) Alternative to skinning was full a replacement down to the steel deck and do a fully adhered system. Client wanted to achieve R-41 and a 2% slope was targeted. They also wanted to achieve drain sizing that would accommodate future/projected rainfall levels.

Solution: For cost savings and project speed the client elected a skinning approach with the following assembly: - Torch applied SBS cap sheet - Combination board SBS base sheet and high density polyisocyanurate cover board (fully adhered with low rise foam) - 1% tapered insulation package plus crickets (fully adhered with low rise foam) - 1" polyisocyanurate (mechanically fastened screws and plates) - Existing SBS and fiberboard was removed leaving the existing polyisocyanurate - Existing asphalt vapour barrier - Existing gypsum - Existing steel deck sloped at 0.5% Resulted in a 1.5% sloped roof with an average of R-37. The additional slope could not be achieved due to existing mechanical unit curb heights. We increased slope and thermal performance as much as possible. Mechanically fastening down a new 1" polyiso covered any variation in the underlying polyiso, creating a smooth clean surface for adhering the remaining layers. The roofers liked this approach as the fibreboard did not come up evenly which would have created problematic conditions without the additional layer of iso. Around the perimeter of the roof and at each penetration we removed the full assembly down to steel deck in a 300mm wide strip to ensure an airtight transition from the field to the parapet/penetration to limit risk of air leakage into the roof assembly. Concrete stairs had any loose concrete removed and deteriorated reinforcing steel replaced with new. New concrete was poured and allowed to cure before a polyurethane pedestrian deck coating was applied over the full stair area. The "Extreme Duty" level of wearcourse was selected for traction on the stairs. Drain bodies were increased from 3" diameter to 4" diameter. Client has projected an interior stormwater pipe system replacement in the near future to upgrade interior pipe system as well. A ballasted guardrail was added around the roof hatch which is within 6ft of the parapet.

Value: Cost savings for the overall project by leaving the existing polyisocyanurate in place. Diverted approximately 900 cubic feet from the landfill. Roofing work to base sheet was done within one week using the combination of fasteners, adhesives, and combination boards. Client was happy with end result, upgrading as much as possible while working with an existing structure.

Project Images

Additional Info: We have more photos of construction if you'd like, send me a note :)

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