Wind load calcs on roof ventilators & fans

Mechanical Plans call for the mechanical contractor to submit wind calculations on curbs,fans and gravity hoods and to attach to roof deck based on wind calcs. Mechanical engineer also list specific manufacturer and size of these same components on plans. My questions are, why is the engineer of record not responsible in detrmining how these components should be fastened to roof deck? Shouldn't the Engineer of record provide these details? Why should another engineer need to get involved coming up with these calcs? This applies in Miami-Dade County Fl.

 

[ChasBean1]

hammerhedz, I certainly agree with you. Project specifications (written by the architect and design engineer) are currently designed to devoid these parties from any future lawsuits. Engineering firms' bread and butter are their specs, which tend to grow as they learn from past mishaps.

Their original intent is good - to be the brains behind a good plan on paper to be constructed by trades familiar in the construction processes. As time passes and engineering firms grow (and requirements grow as parents become vocal about losing their children in mishaps, e.g., Coconut Grove in Boston), old, often smaller projects come back to bite them because suddenly building occupants get sick or die and design flaws are discovered.

Lately, project engineering has transformed into CAD draftsmanship. Inexperienced end users drive the requirements for the build-out. With all the complexities involved, the specifications have turned into a package of manufacturer-issued garbage, such that very little actual engineered thought can be traced to the engineer, but moreso to manufacturers, distributors, and installers.

You (the contractor) and I have to work to refine the specifications to the original intent. This involves changing the industry from the way it currently stands. This is no easy task as it is driven by lawyers, but even you must agree that contractor standards should be similar enough to satisfy a common need.

"The Contractor Shall" statements were originally based on owners getting screwed with shoddy workmanship. The "shalls" have now grown into releasing liability from the designers and deferring all liability to the contractor. The cycle must stop before no more contractors remain, and any work actually delivered is shoddy due to the contractors being extended beyond their means due to short selection of people working for contracting firms.

Trades are so valuable here in the U.S., and we need to figure out a way to keep from squashing them by designers deflecting liability.

This whole issue is bigger than your specific question and should include thorough review, meetings, discussion, and resolution by the whole building and construction industry.

-CB

 

[TBP]

I know of mechanical engineering outfits that have spec's that have got to be 50 years old. They often include material that's no longer commercially available, and hasn't been for decades.

One particular "engineering" firm became quite defensive when I suggested that they out of their field, and in over their heads on a combined-cycle cogen project, and were basically billing us engineering time for photocopying. (These were HVAC/building services guys - and not much good at that - who were "designing" a 500 PSIG/650*F plant without a copy of B31.1.) They puffed their chests out, and said they billed the way they did, because "they were assuming the responsibility". I asked them why their specification "boilerplate" included statements such as (I'm paraphrasing) "contractor to be responsible for compliance with all acts, codes and regulations, even ones botched or overlooked entirely by the engineer"? If they were assuming so much responsibility, why did they need to have wording like that? Why did I have to be the one walking around telling the idiot, low-bid plumbing (yes, plumbing) contractor (never mind any sort of qualifications or expertise, "low bid" strikes again) that 300# malleable unions were, in fact, NOT the same as the 3,000# forged steel ones that were spec'd, and neither were the HVAC vibration isolators he'd installed on the on the steam turbine piping "spring hangers" according B31.1. There was a big fight over that one. Guess who got tarred as the "bad guy"? Me, the chief stationary engineer/maintenance boss. How could I have been so thoughtless regarding the project budget? It was just a few pipe fittings and some springs, what did it really matter?

One big factor in a lot of these situations is that nobody does any commissioning anymore. That gets left to maintenance. "We're out of money on this project - you'll have to catch some of the deficiencies." Translation: we've botched the design, material selection, and contractor selection/construction. We don't want to look bad, so we're going to frame YOU for any cost overruns, Mr. Maintenance Guy. BOHICA. "Bend Over Here It Comes Again".

The root of the problem is the end user. He wants cheap-cheaper-cheapest, low-lower-lowest bid. Everything from design, to material, to the contractor. There absolutely needs to be accounting input. Somebody has to be looking after the money. But accounting/MBA types should NOT be the only ones calling the engineering/construction/maintenance shots. They have been for a number of years now.

End of rant - thanks for your time.

 

[buildingconsultants]

hello all!

It has been quite some time that I have signed in but I thought this was a great thread to have a little input myself. I couldn't agree with you more ChasBean1! I hate to say it, but it almost seems as though the HVAC consulting industry is stepping into a "finger pointing" direction rather that the true "honest engineering practices" that we have all been sworn in to. It has become a vicous cirle of cover your butt and loose sight of what we are really trying to do here.

As a "junior" HVAC consultant, I see plenty of 'BS' on many a project, and continually shake my head. You are right TBP, there are projects that are "over our heads". But as "Engineers", there seems to be too much pride and not enouph thought. Sure we may be able to verse ourselves in a combined-cycle cogen project, but we are fooling ourselves if we try to relate it to common HVAC principles. I too have a long rant about this as it is clearly getting out of hand. I get the impression for all of you the you are from the United States, well the same crap happens here in Canada.

It seems like a bigger feat to even begin to solve these in-complete practices. There is too much bad-mouthing in the industry, and not enouph working together. As a "junior" HVAC consultant aka PEON, I see it too much and it is indeed frustrating. There is a lack of respect for the Practice of Engineering, Consulting, Trades, Owners, and Architects when specifications are allowed to be written as they are. The contractor has somehow become the brunt of a projects failure, maybey then you people should start writing specifications. The "Engineer" on your fan calc project might as well have said, "I don't know a dam thing about this, but I will get paid just the same to put it onto the contractor, so screw it, you just do it and I will take the credit. Doesn't that sound great!" Where is the pride in the people, you tell me.

 

[buildingconsultants]

It's me again,

Just a meager attempt to actually solve your actuall issue, here are my thoughts. I had a similar problem this winter where I had a propellor fan driven roof ventilator with a hinged type hood, (ACME Skymaster fan). Anyways, I never would have thought in a million years that a low profile fan such as this would create any problems for me, ie sucking in the elements. However such a fate came true just for me, and I got a call from a very, very upset client. The distribution tube had partially filled with snow! Isn't that great, it did that just for me. So with all my my calls and research, we would need to get an Environmental study on the wind patterns for that roof! And of course the Owner does not want to pay for that. Once in a life time event, as the storm did wipe out the city. No excuse though, we ended up building a curb around the fan location, " the little tin fence". Not really and exact science, just a junior PEON HVAC consultant and a contractor on a roof, thinking together to make it work. This is not brain surgery, it's a fan. Don't take yorself so serioulsy all the time and you would be amazed at the progress that can take place. No blaming, no pointing, and two very cold beers afterwards! And the client ... lived happily ever after.

 

To start with I'd like to say that I as a small General contractor have the upmost respect for most of the engineers I've worked with. That said, from your answers I guess I figured right and it's just a way to pass the buck and the engineer not be liable. I understand there are no perfect plans. It just seems to me that every day more and more design details and coordination between the diffrent design disciplines are not being looked at until problems arise out on the jobsite or the contractors bombard the Arch with RFI's. Archtects & Engineer's are the brains behind a project and we the contractors are the brawn. Yet when things don't work out right due to design errors or ommisions, the blame/cost is usually placed on the contractor.
To make that point I'll ask buildingconsultants who paid for the "little tin fence" and who paid for the beers?

 

[buildingconsultants]

hammerhedz

blame = me, somewhat un-predictable circumstances problems
client yelling = at me
me yelling = at me
little tin fence = owner = more yelling at me, he's fine now
beers = me

As it had been said before, the most complex situation often is solved at the simplest of solutions. This may be a shocker but, I do not know everything, and would give just about anything to meet someone who does. I enjoy working with the trades for the most part, much more than clients, Architects, and owners. I can see where problems are typically drawn towards, and it is clearly out of hand. I clearly made the error. That is the whole point I guess, stepping up to the plate when things go wrong. When it is somewhat blatant, I am not sure why things are left a mystery. I do not like or belive in blaming anyone for my problems, it clouds the ability for a person to take responsibilty for the situation they are in.

Cheers!

 

[ChasBean1]

hammerhedz - for now, drive a couple extra screws through the base frame into the fan support structure... If it's a mushroom-type fan, don't forget to gasket between the fan base and the rim of the support structure. Many cfm can be lost there! We can worry about these bigger problems as they continue to surface!... CB

 

[ChasBean1]

Buildingconsultants - cheers to you for stepping up to the plate! This is SO important and SO neglected in engineering. Just showing your face, showing concern, and offering ideas at a follow-up meeting after something's gone awry will speak wonders for your firm and prevent the irate owner from considering you for blame.

Those engineering firms that "puff their chest" and act indignant immediately go off my recommendation list to clients and find themselves without repeat business in this area.

Good job. Don't let the higher-ups in your company kill your drive to serve a common good and do what's right. I find it's usually the company brass submitting to Friedmanism - "the purpose of a corporation is to make a profit." They may understand more about business due to age and/or experience, but repeat business due to honesty and trust developed with the client still seems to be a mystery to many of them.

I'm not going to advertise my firm here, but we (as a group) have always bellied-up-to-the-bar if stuff happens later. This has always helped us maintain a good client base.