Archive through January 28, 2008

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Author Message Wayne Yancey Senior Member Username: wyancey Post Number: 166 Registered: 05-2005 Posted on Wednesday, August 23, 2006 - 07:15 pm:    How do any of you spec glass thickness if at all? 1. Delegate design of monolithic glass or IGU pane thicknesses to the manufacturer based on clear and concise performance requirements? 2. Spec minimum 6 mm (1/4") unless othrwise required to meet neg./pos. wind loads? Seems like delegated design. 3. Other specifying methods. I am in a mild pissing match with a GC over this issue. No questions please. Just the facts as you see them. Thanks George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 215 Registered: 11-2004 Posted on Wednesday, August 23, 2006 - 08:38 pm:    Answer 4: 1 and 2 above. (Referenced standard ASTM E 1300) Wayne Yancey Senior Member Username: wyancey Post Number: 167 Registered: 05-2005 Posted on Thursday, August 24, 2006 - 11:08 am:    George, Thanks for the prompt reply. The GC in question here seems to think the design professional should engineer and specify the eventual glass pane thicknesses for each lite to resist loads created by wind and snow. I have never encountered this issuue before. I have always designated this to the manufacturer and referenced ASTM E 1300 along with performance criteria. Usual Part 1 paragraph under perforamance requirements article would read: "Glass thickness designations indicated are minimums and are for detailing only. Confirm glass thicknesses by analyzing Project loads and in-service conditions. Provide glass lites in the thickness designations indicated for various size openings, but not less than thicknesses and in strengths (annealed or heat treated) required to meet or exceed the following criteria:" At most I would specify minimum 1/4" (6 mm) with 1/2" air space which conforms to most IGU manufactures standard offering up to a maximum size. I have never calculated longhand (with aid of E 1300) or by the software created by the Standards Design Group. Have I been lucky these past 33 years? Thanks Wayne Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 385 Registered: 07-2002 Posted on Thursday, August 24, 2006 - 02:30 pm:    Wayne: I'm with you. we specify 6 mm typical unless we want a thicker glass for some reason -- like a handrail or acoustical reasons and then have that language in the spec that references the ASTM and requires the manufacturer/fabricator to provide thicker lites where required for loading reasons. never had a problem with this that I am aware of. I think suppliers are just getting fussier and trying to pass of liability to anyone else they can find on the jobsite. Wayne Yancey Senior Member Username: wyancey Post Number: 169 Registered: 05-2005 Posted on Thursday, August 24, 2006 - 02:54 pm:    Thanks Anne. I hate to be alone. Anonymous   Posted on Thursday, August 24, 2006 - 02:36 pm:    If you are using AIA A201 as the general conditions, refer the contractor to the language that requires design by GC for portions of the work when required by the Contract Documents. Gets them every time... If you do not have A201 in your Project Manual, so sorry... Wayne Yancey Senior Member Username: wyancey Post Number: 170 Registered: 05-2005 Posted on Thursday, August 24, 2006 - 04:16 pm:    Dear anonymous, I did just that. Quoted Article 3.12.10. Thanks Wayne Bill Coady CSI, CCPR Junior Member Username: billcoady Post Number: 2 Registered: 06-2006 Posted on Saturday, August 26, 2006 - 12:24 am:    I like Waynes idea #1. Idea #2 has some pitfalls. Consider these ideas: A)Curtainwall and storefront glass is typically 6mm or thicker to meet windload, snowload, impact, blast or sound attenuation requirements. B) The use of windows or window walls in the design many times dictates that <6mm glass be used because of weight or dimensional limitations on the sash frame members or hardware systems. This thinner glass may well meet the performance requirements. C) Wayne's wording about thickness designation being for detailing only is good. I suggest a caution when stating that a specific thickness is the "minimum" unless you have done the calcs for the project and the specific system selected. If you default to 6mm as the minimum you may experience issues as discussed in my point "B" above and cause the owner to either pay more than necessary, create unnecessary confusion for you and the GC during submittal time, or end up with manufacturers that supply thinner glass without announcing it to the world. It happens more often than you would imagine with window systems. Marc C Chavez Senior Member Username: mchavez Post Number: 277 Registered: 07-2002 Posted on Friday, January 25, 2008 - 04:23 pm:    A new twist on this subject: We are using the delegated design paragraphs in Masterspec and it talks about criteria “sufficient to perform services” The spec has criteria for glass, deflection etc. etc. and the architect guessed 1/2 inch for the thickness. The calculations (by contractor engineer say 5/8 inch) So who pays? The general question is what is the designer's responsibility when the "design" is delegated. This leads to a question: Where in the "contract documents" do we discuss the fact that the A/E "construction documents" arn't? They are "design intent" drawings or contract drawings. You can't build from them. You need shops and coordination drawings and other contractor created work EVEN without delegated design you still need these things. signed, Delegated in Seattle Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 25 Registered: 10-2007 Posted on Saturday, January 26, 2008 - 12:53 am:    I would appreciate clarification as to what is meant by "design intent". I have operated on the premis that our CD's need to define the the work product or we need to assign the Contractor the responsibility to provide the detailed design based on criteria we define. In the absence of delegated design the shop drawings are a mechanism for the Contractor to communicate how he has interpreted all of our, hopefully consistent, criteria. At times it almost seems as if designers have used the term "design intent" as an excuse for not providing the needed information. Marc C Chavez Senior Member Username: mchavez Post Number: 279 Registered: 07-2002 Posted on Monday, January 28, 2008 - 12:47 pm:    It is certainly true that designers can use delegated design as a cop-out. I don't have the drawings but in this case I believe we drew the "glass wall" or something similar with 1/2 inch glass. These walls are very specialized and require a lot of structural design that neither the architect or SE have regular access too. You have to draw something to show the hole being filled by some product, but you don't have the knowledge to design it. What do you do show, a giant blank? I'm not taking sides here, If the architect should have said "1/2 inch min." or "thickness subject to delegated designer's calcs" or whatever and did not, then the Owner owes the contractor more money. If the contractor should have realized that the design needed to be done by his/her engineers, they should have been asked for their educated guess and then they are held to the result of their bid. Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 707 Registered: 07-2002 Posted on Monday, January 28, 2008 - 01:13 pm:    Marc- we use "delegated design" all the time, particularly for glazing and exterior systems, and I've often used it for interior light gage steel. it has not (that I am aware of) been a bidding or cost issue. first, obviously, it has to be clearly stated in the specs that the system is contractor (delegated) design. then this is one instance where there needs to be reference on the drawings to the spec section and the thickness or dimension should not be on the drawings unless it is designated "1/2" minimum" or a reference to the glazing schedule which would have that same information. we also designate that portion of the drawings as "diagrammatic only subject to verification" or some words like that. obviously the designated design portion will be a little iffy in the bidding, but they can certainly figure out the costs to engineer the system and that preliminary guessing gets into the bids. I'm not certain how well this would work in a public bid condition, but certainly in negotiated work, it happens all the time. I would express also that in some cases, the designer is not able to provide the needed information and isn't qualified to do so. (like... many of the glazing conditions we have on our projects). preselection of subcontractors is a big part of it, and continual refinement of the design and conditions as part of ongoing development of the designs is part of it also. We also rely a great deal on testing and mockups. Anonymous   Posted on Monday, January 28, 2008 - 01:54 pm:    another thing...glass of same tint color should be same thickness through-out...unless one desires varying degree of transmittance...and appearance. Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 708 Registered: 07-2002 Posted on Monday, January 28, 2008 - 02:59 pm:    regarding tint: I've been able to ask glass suppliers to "adjust the tint" so that all the glass appears the same. In that case, when I know that we're going to use multiple thicknesses of the same glass, the language I use is "adjust the tint so that visual appearances of all lites is the same as 1/4" clear, or "1" insulating unit"... or whatever your standard for color is.