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Gravity Loads
Section 606.2 of the International Existing Building Code (IEBC) states:
606.1 General. Where alteration work includes replacement of equipment that is supported by the building or where a reroofing permit is required, the provisions of this section shall apply.
606.2 Addition or replacement of roofing or replacement of equipment. Where addition or replacement of roofing or replacement of equipment results in additional dead loads, structural components supporting such reproofing or equipment shall comply with the gravity load requirements of the International Building Code. Exceptions:
- Structural elements where the additional dead load from the roofing or equipment is not increased by more than 5 percent.
- Buildings constructed in accordance with the International Residential Code or the conventional construction methods of the International Building Code and where the additional dead load from the roofing or equipment is not increased by more than 5 percent.
- Addition of a second layer of roof covering weighing 3 pounds per square foot (0.1437 kN/m2) or less over an existing, single layer of roof covering.
This section requires roof renovations and replacement of roof equipment to consider the weight of the existing roof system and framing plus live loads such as snow loading, including snow drift loads, as calculated in the 2009 IEBC. The exceptions to this requirement apply if the additional dead load applied to the roof deck and framing is not increased by more than 5%, or if a second layer of roof covering weighing less than 3 psf is added.
Section 606.2.1 of the IEBC states:
606.2.1 Wall anchors for concrete and masonry buildings. Where a permit is issued for reroofing on a building assigned to Seismic Design Category D, E or F with a structural system consisting of concrete or reinforced masonry walls with a flexible roof diaphragm or unreinforced masonry walls with any type of roof diaphragms, the work shall include installation of wall anchors at the roof line to resist the reduced International Building Code level seismic forces as specified in Section 101.5.4.2 of this code and design procedures of Section 101.5.4, unless an evaluation demonstrates compliance of existing wall anchorage.
This section requires that for buildings of a certain seismic design category or buildings with a flexible diaphragm, or any building with unreinforced masonry walls with any type of diaphragm; wall anchors must be installed at the roof line, unless an analysis indicates the existing anchorage is adequate. The roof diaphragm consists of the roof deck and its anchorage. The roof diaphragm collects lateral loads due to wind and seismic forces prescribed by the MSBC, and distributes the loads to the lateral force resisting systems such as shear walls or braced frames. To comply with these requirements, a field investigation of the existing building and roof diaphragm must be performed to determine the diaphragm construction and anchorage. Calculations may be required to determine whether the diaphragm is considered rigid or flexible. In cases where no existing design drawings are available, the field investigation survey may be expanded to perform a field measure up and destructive exploration to define “as-built” characteristics of the building.
The Massachusetts amendments to the IEBC expand this requirement to include buildings in Seismic Design Category B and C. Thus, nearly all buildings in the state would be required to comply with this section.
The level of effort for structural engineering services to comply with the MSBC 8th Edition will be highly dependent on the availability of accurate existing plans, building construction type, and age of building. To determine the seismic design category; additional design parameters such as the building’s occupancy category, importance factor, and site specific soil data will be needed to evaluate the applicability of this section.
Lateral Loads
Section 606.3.1 states:
606.3 Additional requirements for reroof permits. The work requirements of this section shall apply to alteration work requiring reroof permits.
606.3.1 Bracing for unreinforced masonry bearing wall parapets. Where a permit is issued for reroofing for more than 25 percent of the roof area of an unreinforced masonry bearing wall building assigned to Seismic Design Category D, E or F that has parapets constructed of masonry, the work shall include installation of parapet bracing to resist the reduced International Building Code seismic forces as specified in Section 101.5.4.2 of this code, unless an evaluation demonstrates compliance of such items.
The Massachusetts amendments to the IEBC expand this requirement to include buildings in Seismic Design Category Band C, but provide an exception for masonry parapets with a height to thickness ratio of 2.5 or less.
This section applies to projects that include renovation of more than 25% of the roof area with an unreinforced masonry bearing wall system, and in a certain seismic design category, to require existing parapets that are currently unbraced to be braced.
Section 606.3.2 states:
606.3.2 Roof diaphragms resisting wind loads in high-wind regions. Where roofing materials are removed from more than 50 perfect of the roof diaphragm of a building or section of a building located where the basic wind speed is greater than 90 mph or in a special wind region, as defined in Section 1609 of the International Building Code, roof diaphragms and connections that are part of the main wind-force resisting system shall be evaluated for the wind loads specified in the International Building Code, including wind uplift. If the diaphragms and connections in their current condition do not comply with those wind provisions, they shall be replaced or strengthened in accordance with the loads specified in the International Building Code.
The Massachusetts amendments expand this section to apply to buildings where the wind speed is greater than 90 mph and the occupancy category is Type III or IV, or where the wind speed is greater than 105 mph. Areas of the eastern part of the state, including Boston, have a wind speed of 105 mph. Again, this will require field evaluation of the existing systems, roof, and structural supports. The level of effort required for structural analysis and design to comply with this Code section will be dependent on the availability of original design and “as-built” drawings, construction type, visibility of existing framing and connections, and degree to which the structure currently complies with code.
This section applies to projects that include renovations to more than 50% of the roof area, in any area with basic wind speed more than 90 mph, to require the roof diaphragm and connections to be evaluated for current wind loads. |
