{"id":67844,"date":"2018-08-09T09:08:59","date_gmt":"2018-08-09T13:08:59","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=67844"},"modified":"2018-08-08T09:55:10","modified_gmt":"2018-08-08T13:55:10","slug":"high-rise-building-codes-for-insulated-penetrations","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/high-rise-building-codes-for-insulated-penetrations\/","title":{"rendered":"High-rise building codes for insulated penetrations"},"content":{"rendered":"
\"Photo<\/a>
Photo courtesy The Smithsonian Institution<\/span><\/em><\/figcaption><\/figure>\n

by\u00a0Jonathan Carreiro, P. Eng., and\u00a0Patrick M.B. Chan<\/strong>
\nIn the age of high-performance design and construction, thermal bridges at balconies, slab edges, canopies, parapets, and rooftop connections cause these building elements to act like cooling fins, allowing heat to flow unimpeded from the interior through these uninsulated penetrations in the building envelope to the cold exterior environment.<\/p>\n

While heating exterior penetrations wastes energy and increases carbon emissions and operating costs, chilling interior structures reduces comfort and allows condensation and mold to form on adjacent surfaces (see \u201cAirtight Vapor Barriers Worsen Thermal Bridging Problems at Structural Penetrations\u201d sidebar). Therefore, one must look for an alternative solution.<\/p>\n

Structural thermal breaks (STBs) address these thermal weaknesses in the building envelope by ensuring continuous insulation (ci), thereby improving the overall thermal performance. They are changing the design philosophy to an \u201cenvelope-first approach.\u201d<\/p>\n

How STBs insulate<\/strong>
\nAn STB is a fabricated longitudinal assembly of the same approximate width as the insulation layer of the building enclosure. It is a pre-engineered assembly containing loadbearing elements and insulation as opposed to thin insulation layers such as pads requiring additional design to make them work. It creates a structural insulated break between an exterior structural penetration (e.g.<\/em> balcony, slab edge, canopy, parapet, and rooftop support) and the interior structure supporting it, minimizing thermal conductivity between the interior and exterior structures, while providing the specified loadbearing capacity.<\/p>\n

Many building types and applications can employ STBs, with the most common being concrete cantilevered balconies. These engineered STBs contain high-strength stainless steel rebar tying in to both the interior and exterior concrete slab reinforcement. Stainless steel is approximately 70 percent less thermally conductive than regular carbon steel rebar. In addition to acting as a thermal separator in the concrete slab, the STB transfers the balcony dead and live loads back into the interior structural concrete slab. Other concrete STB applications include thermally separating concrete parapets on roofs, exposed slab edges, and architectural eyebrows.<\/p>\n

STBs are also employed in steel construction to address thermal bridging from steel beams penetrating the building enclosure to support canopies and sunshades, as well as vertical steel applications like roof snow fences and roof anchors.<\/p>\n

Lesser-known STB solutions address thermal bridging in concrete-to-steel connections (i.e.<\/em> bolt-on steel balconies to concrete slab), concrete-to-wood, and steel-to-wood applications.<\/p>\n

Compared to non-insulated connections, STBs can reduce thermal conductivity in the connection area by 90 percent for standard loadbearing scenarios, translating into average reductions in energy use and carbon footprint of up to 14 percent for the overall building per year. (For more information, click here<\/a>.)<\/p>\n

The reduction in BTUs required to heat the building also allows corresponding reductions in heating system size\/capacity, resulting in savings on capital equipment and ongoing operation and maintenance of mechanical systems.<\/p>\n

In the case of cantilevered balconies, STBs typically increase the warmth of adjacent interior floors by up to 15 C (27 F). (For more information, click here<\/a>.)<\/p>\n

\"Structural<\/a>
Structural thermal break (STB) for concrete construction contains insulation and loadbearing components with rebar that is fully cast into interior and exterior concrete structures at the penetration. <\/span>
Photo courtesy Sch\u00f6ck North America<\/span><\/em><\/figcaption><\/figure>\n

By allowing the interior side of structural penetrations to remain warm, STBs also prevent condensation, mold, and rust problems associated with today\u2019s airtight vapor barriers and elevated interior humidity.<\/p>\n

Since STBs are still a relatively new concept in North America, it is important suppliers provide local technical expertise, onsite support, and signed and sealed drawings by a professional engineer who is registered in the project\u2019s state or city. Suppliers should also be able to furnish a comparative energy performance benefit of using STBs through 3D thermal modeling.<\/p>\n

In Europe, gaping thermal penetrations through the building envelope are rare in high-rise construction because STBs are installed to simultaneously insulate and carry the loads of structural penetrations. The opposite has been true throughout North America where the adoption of STBs lags by decades. The reason for this is building codes.<\/p>\n

Unlike European codes requiring continuous envelope insulation, North American \u201cperformance\u201d codes contain loopholes of sorts allowing thermal deficiencies in one area to be offset by efficiencies in another.<\/p>\n

Since thermal insulation of structural penetrations in North America remains discretionary, the adoption of STBs has been led primarily by:<\/p>\n