Perka: Getting Equal Bids

Return to Perka Library Getting Equal Bids POINTS TO COMPARE • WIND LOAD. Have the builder specify this value in lbs./square feet. As a good benchmark, use 12 lbs./square feet. A building should handle this pressure acting on the total building area facing the wind. Be careful about wind loads expressed in miles-per-hour, because engineers must make a number of assumptions to convert wind speed to actual wall pressure. • ROOF SNOW LOAD. Ask what each company’s engineers uses for a roof (not ground) snow load, which can vary greatly based on geography. All companies calculate roof snow load – perhaps differently – based on ground snow load maps developed by the American Society of Civil Engineers (ASCE). For example, assuming a standard 3/12 roof slope, an absolute minimum roof snow load in snowy areas is 20 lbs./square feet. Regionally, roof snow loads range from 5 to 10 lbs./square feet in lower Midwest. You should also discuss the topography of the building site with each company, as well as surrounding structures because they can have an impact on snow drifting on the roof. • COMPONENT DEFLECTION. By definition, is the amount of component movement when under load. Excessive deflection can be cosmetically unpleasing, such as roof sagging, or it can impede building use making it difficult to open doors and windows. Excessive deflection generally isn’t a concern as long as proper wind and snow loads have been prescribed. The major exception being when exterior walls and rafters are to be covered with drywall, because excessive deflection can cause seams to open up. Normally, engineers try to limit deflection to the unsupported length of a member divided by 180. This means, for example, that the deflection of a 90-in. long member would be limited to ½ inch movement. For all walls and ceilings with attached drywall or plaster, and for all floors, limit component deflection to the unsupported length of the member divided by 360. • WOOD TREATMENT. For major structural components exposed to the ground or the outside elements, find out whether the waterborne preservation treatments (ACA, ACZA or CCA) have the value of 0.40 or 0.60 lbs./cu.feet. This can be highly variable, depending on the treatment process used and the type of wood used, since every board or column won’t absorb these copper and arsenic preservatives equally. The 0.40 treated wood is adequate for most applications, but a minimum treatment level of 0.60 is required for any structural member embedded in the ground. • WARRANTIES. Always dig into the specific fine print of warranties and other component details to make sure you’re comparing apples to apples. Check exterior siding details (base metal thickness and tensile strength, how much zinc used) and finishes (types of paint, rust protection). When soliciting bids, make sure you hold the builders to the specifications you desire. Don’t just jump at the lowest bid without examining every aspect of all bids, from builder reputation and warranty to quality components and construction timeliness. (Source: May/June Issue of FIN)