2018 IRC Hikes Costs in Seismic and Coastal Areas

Filed in Codes and Regulations by on November 3, 2017 0 Comments

blueprintFor the first time in at least four editions, many builders working in jurisdictions that choose to adopt the 2018 International Residential Code may see a modest, if not significant, cost savings — as long as they are not building homes in areas at risk of significant earthquakes or along the Atlantic and Gulf coasts.

A new report on the Estimated Costs of the 2018 IRC Code Changes by Home Innovation Research Labs shows cost impacts for most homes ranging from a minor $100 increase to a $600 savings over the 2015 International Residential Code.

Builders in moderate- or high-seismic regions may see more significant hikes, however. New maps widen the seismic design category in several areas including New England (particularly New Hampshire), eastern Tennessee, and near Charleston, S. C.

For houses now subject to seismic wall bracing, foundation anchorage and footing reinforcing provisions, cost increases may range anywhere from $2,400 to $7,100.

Near the boundaries of higher seismic design categories, builders may want to obtain a geotechnical report, which could allow them to pursue an alternative determination of their seismic hazard. Costs for such a report can range from $500 for a study based on soils maps to $2,200 for a full-blown site study. For some homes, it’s more cost-effective than providing the additional wall bracing and foundations that would otherwise be triggered.

Builders constructing homes in coastal flood zones may also see additional costs. New provisions require exterior slabs such as parking pads and sidewalks adjacent to or under elevated buildings be constructed to break up (“frangible”) under flood conditions or be designed to resist flood loads (e.g. erosion and scour).

Costs range from a savings of $1,100, if a slab is made frangible by removing turn-down edges and wire reinforcing, to an increase of $2,100 if a slab is engineered to resist erosion and scour.

Stairways and ramps constructed below the base flood elevation in coastal flood zones must also now be constructed with open or partially-open risers and guards, be designed to break away under flood conditions, or be raised above the flood level. Depending on the option selected, costs range from a savings of $800 to an increase of $11,100.

Savings in Store

On the bright side, some new code provisions may represent significant savings where builders opt to incorporate certain practices into the construction of a home.

An option to bury ducts in ceiling insulation is estimated to save builders as much as $700 when following prescriptive energy code provisions, or as much as $4,100 when the performance path is used.

Another new option for constructing an unvented attic using air-permeable insulation (typically blown fiberglass) in warmer climate zones could save as much as $9,200.

Previous Home Innovation studies detailed significant cost increases when adopting newer codes. A study for the 2015 IRC suggested a more modest increase of around $2,000 for many homes, and a potential modest savings of around $600 for some homes versus the 2012 IRC.

More information on significant changes in the 2018 IRC and NAHB’s recommended amendments can be found in the 2018 Code Adoption Toolkit.

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