Tag Archives: thermal factor

Who is Responsible for Verifying Design Loads?

Who is Responsible for Verifying Design Loads by Contract?

Disclaimer – this and subsequent articles on this subject are not intended to be legal advice, merely an example for discussions between you and your legal advisor.

Please keep in mind, many of these terms are applicable towards post frame building kits and would require edits for cases where a builder is providing erection services or materials and labor.

DESIGN LOADS/CONDITIONS: Plan, drafting, engineering or calculation changes needed due to Purchaser’s failure to adequately confirm criteria in this section, or Purchaser’s desire to change building dimensions or features, will result in a minimum $xxx charge.

It is solely upon Purchaser to verify with Purchaser’s Planning and/or Building Departments, or any other appropriate government, or non-governmental agencies, the ability to construct purchased building(s) at location anticipated, as well as to apply for and obtain any needed permits. All due diligence to comply with any architectural or aesthetic covenants must be done by Purchaser, and Purchaser agrees to absorb any costs associated with compliance.

Purchaser acknowledges verification/confirmation/acceptance of all Building Code, Plan and Design Criteria included on Instant Invoice. Information Purchaser has verified includes, but is not limited to: Applicable Building Code version, Occupancy Category, Ground (Pg) and Flat Roof (Pf) Snow Loads, Roof Snow Exposure Factor (Ce), Thermal Factor (Ct), Wind Speed (vult or 3 second gust) and Wind Exposure, Allowable Foundation Pressure, Seismic Zone and Maximum Frost Depth, as well as obtaining for Seller any unusual code interpretations or amendments.

Seller’s designs are all per specified Building Code and include the use of NDS Table 2.3.2 Load Duration Factors (Cd) as well as ASCE 7, Eq. 7-2 for slippery surfaces. Seller’s designs rely solely upon occupancy category and structural criteria for and at specified job site address only, which have been provided and/or verified by Purchaser. 

It is Purchaser’s and only Purchaser’s responsibility to ascertain the design loads utilized in this Agreement meet or exceed the actual dead loads imposed on the structure and the live loads imposed by the local building code or historical climactic records. Purchaser understands Seller and/or third party engineer(s) or agents will NOT be contacting anyone to confirm.

Dead loads specified on engineered roof truss drawings include the weight of the roof truss. Roof trusses are NOT designed to support ANY hanging loads or ceiling loads other than those specified as special truss loads in the Agreement. In the case of design roof truss bottom chord loads of less than five (5) psf (pounds per square foot) the bottom chord dead load may be sufficient only to cover the truss weight itself and may not allow for any additional load to be added to the bottom chord.

Roof truss top chord design loads of 5 psf (or less) are not adequate for roofing other than light gauge steel.

Seller recommends use of A1V (aluminum/single air cell/vinyl) radiant reflective barrier, an Integral Condensation Control (I.C.C. – Dripstop, Condenstop or similar), solid sheathing (with appropriate underlayment) or Purchaser applied 2″ or thicker closed cell spray foam insulation to help control roof condensation. 

In no case is Seller liable for any condensation issues. An I.C.C., when ordered, is manufacturer applied to roof steel panels only. Seller makes no representation of any R or U value for any insulation or insulation products supplied. In the event Purchaser opts to utilize snow loads, wind loads, wind exposure factors, seismic loads or ventilation of less than those recommended by Seller, or soil bearing capacities greater than those recommended by Seller, Seller and third party engineer(s) are totally absolved of any and all structural responsibility.

Any windows and/or doors provided by Seller are NOT wind-rated, unless specifically noted as such.

Any possible design responsibility for this building is null and void should any structural materials and/or construction be substituted, replaced, depart, deviate, or are otherwise altered from the Seller’s original building kit they belong to, including structural materials from suppliers not authorized in writing by Seller’s owner, or if building is constructed at an address other than as specified on plans.

Structural Engineering

I’ll take Structural Engineering for $XXX Alex

Proper Engineering in post frame construction can not be overlooked.

Alex Trebek has hosted Jeopardy!, the iconic daily syndicated game show, since 1984. With over 7,000 episodes aired, Jeopardy! has won a record 33 Daytime Emmy Awards. Some of you may even have tuned in for an episode or three.

Today’s Answer Is:

Insufficient Data to Provide an Answer

And reader PAUL from FINKSBURG has the question:

“What size header would be required for a 20′ wide overhead garage door placed on the truss bearing wall?”

Okay, enough of my being snarky. The answer to Paul’s question should be clearly indicated on the engineer sealed plans for his building, along with the required connections from truss to header and header to columns.

If somehow the engineer of record overlooked this critical element, he or she should be contacted immediately to provide the missing data. Even worse – maybe an engineer happened to not design the building, in which case CALL ONE NOW.

Whilst this may appear, on the surface to be a simple question, there are a plethora of factors which go into the determination of a structural header to carry roof loads. This would include, but are not limited to:

Pg – the Ground Snow Load

Ce – the Snow Exposure Factor (sites which are open to the wind allow snow to blow off the roof, sites which are protected from the wind keep snow on the roof)

Is – the Snow Load Importance Factor (Risk Category I buildings are a lower hazard to human life, therefore the flat-roof snow load will be reduced)

Ct – the Thermal Factor (heated buildings melt snow off, unheated buildings allow snow to build up)

Pg, Ce, Is and Ct are multiplied together along with 0.7 to determine the Flat-Roof Snow Load (Pf)

But wait, there is more…..

Pf might be further reduced depending upon the roofing material (steel roofing being slick allows snow to slide off quicker), whether or not snow retention systems are present (which hold snow on the roof), as well as the roof slope. Mix them all together and the Sloped Roof Snow Load (Ps) is created.

The dead loads imposed upon the roof also need to be added to the mix – the weights of trusses or rafters, purlins, roof sheathing, insulation supported by the roof system, roofing, truss bracing, ceilings are amongst some of the weighty culprits.

Once all of these contributing factors are combined into a psf (pounds-per-square foot) load, concentrated loads are applied to each of the truss bearing locations along the header – these are based upon ½ of the truss span (including any sidewall overhangs) multiplied by the truss spacing and the applied loads.

Not only does the header need to be verified for adequacy in load carrying capacity, but also limited in deflection. A sagging header can cause unsightly rooflines as well as preventing doors from operating correctly.

Self-engineering is not a good choice – call your engineer….now!

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