Design Loads
All residential, commercial, and accessory structures shall be designed and/or constructed to resist standard loading from wind and seismic loads, as well as standard live loads and dead loads per the current building code, to provide the minimum requirements to safeguard the public safety, health and general welfare.
Design of the structure may be prescriptive per the Building Code, or if out side of the prescriptive requirements, shall be designed by a design professional and they shall provide design criteria, calculations, and professional stamp and signature on calculations and plans where applicable.
Types of Design Loads
Snow loads for Whatcom County are determined by the study produced by the Structural Engineers Association of Washington (SEAW) as revised in January of 1997.
Load Requirements & Determination
The snow loads that are given are ground snow loads and for the design of the structure may be reduced by calculation per the current adopted codes by a design professional.
A design professional shall take into account exposure, slope, snow drift, unbalanced snow, sliding snow, roof valleys, adjacent roofs, lower roofs, and all other load cases as required per the current code requirements.
Calculation of Loads
Snow load is determined by multiplying the site elevation and the given isoline under which it falls as set by SEAW.
The Snow Load Revision Chart shows general locations by elevation and the given snow load for those areas.
For accurate snow load information for your site call the Whatcom County Planning and Development Services Office at 360-778-5900 with your parcel number and have a Plans Examiner look it up for you.
Zones
Every structure shall be designed to resist loads from an earthquake or seismic event for its given seismic zone.
Whatcom County is located in seismic zone D-1 in the west half of the county and D-0 in the east half.
Codes
Design of the structure may be prescriptive per the Building Code, or if outside of the prescriptive requirements it shall be designed by a design professional and they shall provide the design criteria, calculations, and professional stamp and signature on the calculations packet and plans where applicable.
Hazards Information
For additional information regarding design maps on earthquake hazards you may go to the United States Geological Survey’s (USGS) website.
Bearing Capacity
Allowable Soil Bearing Capacity for Whatcom County is 1,500 pounds per square foot. For most residential and commercial projects this soil bearing capacity is satisfactory. If your structure requires more than 1,500 pounds per square foot you will be required to provide a Geotechnical Report from an engineer.
Special Structures
Larger structures such as Cell Towers, Industrial Manufacturing Equipment, structures over 3 stories in height, and like structures require an engineer's soils report.
Questionable Soil Areas
There are also small areas of the county where questionable soils exist, like expansive soils, high ground water tables, or areas that were over excavated or where soil waste and debris has been deposited. These areas would also require an engineer's soils report. These areas are not common and you would be notified at the time of permit submittal if the building official is going to require an engineer's soils report.
Whatcom County lies entirely within the 85 MPH 3-second gust wind zone, per table 6-1 of the American Society of Civil Engineers (ASCE) / Structural Engineering Institute (SEI) engineering design manual.
Wind Exposure Zones
Depending on your location, the wind exposure (openness) would be B or C and because Washington has areas categorized as special wind zones, and if you are within 600 feet of an open body of water, it could be exposure D.
Up-Speeding
There are also a few areas that can fall under the area of wind up-speeding. This is where the mile per hour measurement of the wind is actually increased if your site is located on a steep slope, mountain areas, or bluff areas. For definitions of exposure refer to current codes or consult your local jurisdiction.
Designing Structures
It is possible to design your structure prescriptively in zones B and C, but if your site is located in an exposure D zone or if the effects of up-speeding are present you will need to have your structure analyzed by an engineer to handle the wind loads that could affect your structure.
Other loads that may need to be considered are traffic loads or parking loads adjacent to your building that may create surcharge on your footings or basement walls. There are many different loads that can affect the performance of your structure. In all cases it is best to think about these early in your design process so that they can be figured out prior to starting your project. Be sure that your designer knows about these items prior to design of your structure.
Flood Zones
When building in flood zones or flood ways special designs for foundations or provisions for flood vents are required.
Adding Additional Loads
There are also cases that can add additional loads to your structure, such as cranes or hoists, sprinkler systems, solar panels, hydronic heating systems, roof mounted equipment, etc.
In most cases when these types of loads come in to play an engineer will be required to provide analysis and direction for construction.