Glossary of Engineering Terms

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These terms are published by Engineering Express to coincide with help menus for our online tools & published articles and as they relate to the Building Component Design industry.

See also our FLOOD ENGINEERING GLOSSARY for more terms related to flood engineering.

See Also SUNROOM TERMINOLOGY for a list of Sunroom terms compliments of the National Sunroom Association


ADDITION ROOF TYPE For sunroom enclosures, roof types can be monoslope for studio, shed, or other single slope style roofs or  gable, also known as A-Frame. Roof type & slope affects the conversion from wind speed to pressure Learn More.
ATTACHED TO HOST For our column calculators,
Yes assumes pinned at top & bottom so k=1.0 and simply supported for lateral bending moment on post itself
No assumes fixed at base and pinned at top (such as for freestanding aluminum structures, k=2.0 for buckling & cantilever moment for lateral on post itself)
AHJ AHJ – Authority Having Jurisdiction. The entity with the authority to determine / enforce building code requirements. Typically the building department you submit permits to.
ASCE American Society of Civil Engineers. A professional body that provides much of the structural engineering provisions present in the Florida and International Building Codes.  Visit for more.
ASD (PRESSURES) Allowable Stress Design – where the capacity of the member in question is reduced (factored down) to an allowable factored limit as opposed to ultimate pressures where the load is factored up and compared to actual capacities.
BEAM ALLOWABLE SPAN Clear Beam Span of the panel or member in question between two supports.
BENDING STRESS The total bending stress from a transverse force in the extreme fibers of the member in question.
BUILDING ENVELOPE Simply defined, it’s the separation between the interior & exterior of a building/habitable space or air-conditioned vs. non-air-conditioned space. The ‘shell’ of a building. The building envelope is subject to ‘internal pressurization’, affecting building components that comprise the building shell.
CLASSIFICATION Screened for removable acrylic sliders, open if 3 or more sides are open, solid for glass or panels.
CLEAR SPAN The clear distance between supports of a member in question.
CLEARANCE HEIGHT Used in our mechanical rooftop equipment calculator, typically defined by this firm as the support structure clear height, or height from grade/roof level to the bottom of the unit in question. Seek confirmation from the associated unit diagram before using this definition.
CODE YEAR Select ASCE 7-16 in our online calculators only for the 2020 Florida Building Code or 2018 International Building Code (IBC).  ASCE 7-10 corresponds to ASCE 7-10 and codes before IBC 2018.
COLUMN ALLOWABLE HEIGHT The allowable clear span of a post from the slab to beam or knee brace above. If the resulting allowable height in a result is less than the allowable ceiling height, the result shall include knee walls or other supporting structures.
COLUMN SPACING For the determination of column loads, the column spacing is the average on-center spacing between columns, in decimals for our online tools (0.5= 6”).  For the determination of carry beams between columns, spacing is the clear span between two columns.  Typically column spacing is the on-center spacing of columns unless otherwise defined.
COMPRESSIVE STRESS The stress from a longitudinal force acting in compression on a member axially, typically for a column.
COMPONENTS & CLADDING The pieces and parts of a building or other structure that comprise the building envelope. Typical component & cladding items include windows, doors, door handles & hinges, exterior fascades, etc.  ASCE-7 has specific requirements for the design of building components & components of other structures.
CRITICALLY WELDED When aluminum is heated during welding, the alloys realign and weaken the member, typically within 2 inches of any heated surface.  For our calculators, if a beam or column is welded at any critical point within 2 inches of the maximum moment, select ‘yes’ which loads an alternately calculated allowable stress for the aluminum selected.  Click here for more on the topic.
DEAD LOAD (D) Dead load is the actual self-weight of an unloaded roof, floor, or similar surface.  Typically the load of sunroom roof panels, or roof trusses + underlayment + shingles or tiles, or for decks the weight of wood + connectors.
DEFLECTION The bending limit of a member – see chapter 16 of the building code, typically L/180 for glass, L/60 for screen, L/240 for plaster.  Click here for more.

Deflection is typically expressed as L/# where L = the Clear Span of the member in question. For example, a member with a 10’ long clear span that has an allowable deflection limit of L/60 would be allowed to deflect 10/60= 0.1667’ or 2”.

EFFECTIVE WIND AREA Effective wind area is the area of the building surface used to determine (GCp). This area does not necessarily correspond to the area of the building surface contributing to the force being considered.  There’s an H*H/3 rule & structural break understanding to better understand.  Click here to read more.
ELEVATION ABOVE SEA LEVEL (ELEVATION FACTOR, Ke) A variable used in wind load calculations that allows for reductions in the calculated wind load as site elevation above sea level increases. For Every 1,000 ft above sea level, atmospheric pressure and corresponding wind pressure is decreased per ASCE 7-16 (not per ASCE 7-10).  In our online tools, select 0ft above sea level if unsure or at sea level (returns 1.0 factor).
EXPOSURE CATEGORY The ASCE Exposure Category reflects the characteristics of ground surface irregularities at a site in which the building or structure is to be constructed.  The rougher the surface, the lower the multiplier that converts wind velocity to pressure. Learn More
ENCLOSURE TYPE The type of installation being installed – typically open or enclosed (screened).  Click here for more.
FBC Florida Building Code. The set of rules and regulations that constructed buildings and other structures must abide by in the State of Florida. To view the FBC, click here:
FENESTRATION Openings within a building envelope or surface such as for windows, doors, etc.  These openings require design considerations typically referred to as components & cladding design in ASCE-7.
HIGH-VELOCITY HURRICANE ZONE (HVHZ) A special wind region in Florida consisting of only Broward & Miami-Dade counties. The Florida Building Code may specify different conditions and requirements for the HVHZ than for what applies to the rest of Florida depending on the structure/application. For more information click here.
HEIGHT The total unsupported height of a member in question.
IBC International Building Code. Provides most of the wind requirements for U.S. states other than Florida.
IMPACT SHUTTER ANALYSIS If yes is selected in our online tools, the calculation for area of opening switches from Width * Height to Height * Height/3. It operates on the assumption that impact shutters are tested infinite width.

This operates on the assumption that mother nature cannot focus a maximum burst on too narrow or too wide of an area of wall or roof cladding.  Click here for more on the topic of Effective Wind Area.

LATERAL LOAD ALONG POST For column calculations, this represents a horizontal force acting on a column in question.  It could come from a membrane attached to a column of some sort or entered without an axial force for columns to analyze a column member acting as a beam.
LIVE LOAD (L) Total live load (roof and floor) such as snow or other code required loading.
LRFD (Load Resistance Factor Design) Rather than factoring down critical loads as per the ASD (allowable stress design) method, this design method requires adding the factor to the load to compare it to the actual limiting value of a component.  a 200lb force would become 400lb on a ladder that actually breaks at 400lb rather than saying a ladder that actually breaks at 400lb is reduced to 200lb to compare to the limiting load.  See our Factored Load Calculator design aid and this article for more.
MARK This is your label to help identify the answer on the accompanying layout drawings.  It has no effect on the result other than to help you coordinate your permit documents.
MEAN ROOF HEIGHT, MRH This is the average roof height from the peak to the eave. Click here to learn more.
MEMBER TYPE Member corresponds to a beam for areas such as the eave edge beam above openings or columns which are the supporting mullion posts.
MIN OVERALL BLDG DIMENSION Along with the mean roof height, this dimension helps set the end zone width to determine the length of end zone 5 (greater pressure area).  Click here to learn more.

This is the shortest building dimension.  The End zone 5 is 10% of this value, 40% of the mean roof height,  but not less than 3’  Click here to learn more about wall zones.

U.N.O. Unless Noted Otherwise. Indicates that exception(s) may exist to a specification/code requirement under certain circumstances.
OVERHANG In an enclosure or building. The overhang is the portion of the roof beyond the outer supporting wall.  It’s typically limited when roof panel spans are provided in our online calculators to limit the uplift on panels & connections as well as stresses on roof panels & beam spans.
PE Professional Engineer. Only licensed professional engineers & registered architects are able to provide signed and sealed engineering documents needed for a building permit.
PERGOLA A structure usually consisting of parallel colonnades supporting an open roof of girders and cross rafters.
POSITIVE/NEGATIVE In terms of our ASCE 7 loading conventions typically used on our online calculators or master plans, positive is the force inward into the building, negative is pushing out. Expect larger negative values due to building internal pressurization.
REACTION The force at each end of the member in consideration. Typically used to verify anchorage shear, which would be perpendicular to the member in the direction of the load.
RISK CATEGORY A classification of buildings and other structures by “importance levels” ranging from Categories I through IV. Used in determining wind speed (Vult). Category I has the lowest wind speeds, Categories III-IV have the highest. For more information, click here.

Find wind speeds for various risk categories on the ATC Wind Site.

ROOF SLOPE The angle of the roof relative to horizontal.  It’s typically measured in angles or rise over run. In some ASCE component & cladding calculations, if the roof slope is less than 10 degrees, there is a slight reduction in pressure. If complex roof or unsure, set to >= 10 degrees on our online calculators.
ROOF LIVE LOAD (Lr) The live load on a roof is the weight of any temporary objects on the roof, such as people, and equipment.  The Florida and IBC codes both require a 20psf minimum roof live load in addition to the dead load & other loads that the roof must bear.  Use our Factored Load Calculator to determine the total ASD or LRFD load for your project.
ROOF SPAN The unsupported clear roof span length between supports.
SNOW LOAD This can either be ground, roof, or drift snow, 3 very different concepts. Be sure to use the proper value for your project.
SUPPORT TYPE Four our beam calculators, ‘Simple’ follows a simply supported beam (pinned-roller) M=WL^2/8,
‘Cantilever’ assumes fixed at one end and free at the other M=WL^2/2
TOPOGRAPHY FACTOR Kzt Another multiplier when converting wind speed to wind pressure.  Use 1.0 for flat terrain. For areas on or near hills, this will need to be calculated elsewhere. Worst case is 3.0. Consult a design professional or contact us if not flat terrain for proper application of this coefficient.
TOTAL LOAD The sum of all imposing loads on a roof or wall surface measured in pounds per square foot. These loads are factored in accordance with (Chap 16) of the Florida or International Building Code or 2018 International Building Code. Consult a design professional to be sure & see our Factored Load design calculator.
TRIBUTARY WIDTH This value sets a width (ft) that’s multiplied by the uniform load (psf) to develop a load per foot (plf) on the member in question.  For considerations where you already have the load per foot on a member, select 1 foot for this option.  This value is typically half the distance to the left + half the distance to the right of the next supporting member.
ULTIMATE (PRESSURES) The factored total force acting on a member. This is where the load value is factored up rather than reducing the ultimate stress of a member in question.
UNBRACED LENGTH The factored total force acting on a member. This is where the load value is factored up rather than reducing the ultimate stress of a member in question.
UNIT DEPTH Used in our mechanical rooftop equipment calculator, Typically defined by this firm as the smaller horizontal dimension (the shorter of unit width and depth). More simply, the unit’s short side. Seek confirmation from the associated unit diagram before using this definition.
UNIT WIDTH  Used in our mechanical rooftop equipment calculator, Typically defined by this firm as the larger horizontal dimension (the longer of unit width and depth). More simply, the unit’s long side. Seek confirmation from the associated unit diagram before using this definition.
UTILIZATION Beam utilization is the sum of squares for bending & shear ((fv/Fv)^2+ (fb/Fb)^2)^0.5.
For columns is the maximum of (3) equations: sum of squares of equation above and H.1-1 (fa/Fa + fb/Fb) or H.3-2 fa/Fa + (fb/Fb)^2 + (fb/Fv)^2 of the 2015 Aluminum Design Manual
WIND DIRECTIONALITY FACTOR Kd For our components & cladding calculators, This is generally 0.85.  Change to 1.0 only if required by the building department or special use case directed by the architect/engineer.  This factor is used in the formula that converts wind speed to wind pressure & involves a reduction due to the reduced likelihood that multiple loads will occur simultaneously on a surface.  Click here to learn more.
WIND VELOCITY, Vult (Also Wind Speed) The peak 3-second gust wind speed. Consult your building department or engineer for governing codes.

Learn more by Clicking Here

Use the ATC Wind Council Site to obtain your minimum wind speed for the risk category being designed by clicking here.

WIND LOAD The total force due to wind on an object. The force can be suction or positive pressure when dealing with wall & roof pressures, or total force on a freestanding object.  Typically for Engineering Express the wind load is represented in PSF (Pounds Per Square Foot) & either ASD or LRFD (allowable stress or load resistance factor design).
WIND ZONE ASCE wind pressure location zone – Use Zone 4 for interior (non-corner) openings. Zone 5 are any corners that result in a higher wind speed to wind pressure conversion factor.  IF UNSURE, USE 5!  Click here to learn more.

Last Update: October 3, 2022  

August 19, 2020  Engineering, General  
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