Structural Reviews
Structural Reviews
(OP)
Please read this quote...
"Peoria now, for example, is requiring a structural analysis by an engineer on all homes that put solar on. That's a deal killer. If you find an engineer who is cheap, you may get by with $600, more likely $1,000, for every system. In a sense, Peoria is saying they don't want solar on their homes," Neary said. "It's generally a deal-breaker."
I provide the structural engineering for many of these. When this quote came out in a local publication the cities reversed their positions. The issue I have with this is there are many valid reasons to provide engineering for these. Why is it, that money for a structural review is governing the safety of human life? As I recall, that's why we're all doing what we do.
I'm currently putting together a PowerPoint presentation to my local MAG committee. If anybody has any opinions, ideas, feedback whatever - I welcome it.
If you would like to see the rest of this article:
http: //utsolar. org/index. php/news/a rticle/ren ewable_ene rgy_bills_ piling_up/
Regards,
Ray
"Peoria now, for example, is requiring a structural analysis by an engineer on all homes that put solar on. That's a deal killer. If you find an engineer who is cheap, you may get by with $600, more likely $1,000, for every system. In a sense, Peoria is saying they don't want solar on their homes," Neary said. "It's generally a deal-breaker."
I provide the structural engineering for many of these. When this quote came out in a local publication the cities reversed their positions. The issue I have with this is there are many valid reasons to provide engineering for these. Why is it, that money for a structural review is governing the safety of human life? As I recall, that's why we're all doing what we do.
I'm currently putting together a PowerPoint presentation to my local MAG committee. If anybody has any opinions, ideas, feedback whatever - I welcome it.
If you would like to see the rest of this article:
http:
Regards,
Ray






RE: Structural Reviews
Are these new or existng trusses, or, new or existing stick framing, that the article was referring to?
Mike McCann
MMC Engineering
RE: Structural Reviews
Regards,
Ray
RE: Structural Reviews
Mike McCann
MMC Engineering
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Our populist government in Australia is giving $8000 rebates for installation of solar panels. As far as I know, no individual structural assessment of the roof is required.
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It's not just gravity that causes issues, its wind. The added dead + wind tend to fail in combined stress on the top or bottom chords (tension / compression + bending). The other wind issues are where these systems are on a flat roof and on a tilted mounting system sloping +/-30 degrees. I've now got a sail to worry about with positive and negative pressure (rotation) on the same member. Longer truss spans (esp. scissors / vaults) tend to fail in gravity loads. Most solar applications perform fine on the structure, 5% or so need recommendations.
Most importantly, who is liable at this point? There is no engineering, the city say it's ok, there is no solar warrantee & the only way a homeowners insurance policy will pick this up is with engineering. I would have to imagine that people purchasing solar panels and placing them on their property would be asking this question.
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If framing were done the same perhaps I could take comfort in that a case study could be made. Every home is usually framed by a different contractor with many crews who purchased lumber & trusses from one of many suppliers.
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Of course, your load duration factor is more severe for dead than roof live, but at least that's a reasonable way of looking at it, in my opinion.
BTW- I'm not familiar with the IRC. Are the roof live load requirements the same as in the IBC? (That's where I got the 12 psf- this is "worst case" in the sense that I'm assuming the members were originally designed for the lowest value allowed in the IBC)
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Once these structures are modified, do they get brought up to existing building codes (the modified supporting members)? UBC vs 2006 IRC / IBC poses new wind issues that can cause components to fail by that change alone. How would one go about checking an existing member, following the original building code and NDS values?
How many of us have seen this condition (see photo). A typical framer might just pass this on because it is often their doing. In a framers world this can be considered normal practice. They need working access to fit an FAU and make it happen. What are the chances that a solar installer would even know to be looking for this? After all, their concern is above not below.
As far as the 2006 IRC vs the IBC, yeah there are some differences. With the IRC typically the live load use is 20 PSF for slopes less than 18.43 degrees and 16 PSF if they are equal to or greater.
By the way, thank you for everybody's input so far. I've been challenged with these very issues and only want to do what is correct. Solar is a wonderful product and there are many advantages offered for it on both state and federal levels right now. I disagree with those that on one hand claim that solar is for the preservation of human health, and on the other hand claim that having to review it structurally is a deal breaker. It's not that 95% of these projects work fine, it's the potential for one of the 5% to go terrible wrong.
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-Kermit the Frog
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As far as engineering is concerned for houses, this is exactly the point. Whether your home is manufactured with dimensional lumber / rafters / beams OR trusses / wall panels, the idea of knowing what happens when we apply something new is important. This is not only because of it being responsible, but because it's an opportunity to validate the actual existing conditions.
Field Issues:
• Poor quality or incorrect material is used.
• Handling of material causing damage to members prior to installation.
• Components installed backwards & or upside down. I've worked on repairs for a house (just outside of Las Vegas, NV) where a contractor installed floor trusses upside down, backwards & cut the "extra length" off. (there was no extra length – trusses were used @ incorrect locations)
• No bracing installed (temporary or permanent).
• Removal of sections of top chord, bottom chord or webs. I'm working on a house now where the homeowner cut top chords & webs from multiple trusses to lay (2) layers of plywood for larger storage & walking area in their attic.
Let me pose another question:
Shouldn't a building & safety department require empirical data before it takes makes such a decision of not requiring an engineering review for solar installation? It seems that the burden of proof should be in the form of data, not some swagger words from a lobbyist.
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I think City has no business to make the call, as it is not a explicit public safety issue. Rather, it sould be settled between the house owner, and his/her insurance company. Why we want the government tell what we can do or not? Unless you believe the society we are in has more dummies than people have common sense.
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Yes. Isn't that all this society about - free choice at your own risk, which is to be balanced by who pays the bill when things fail (the insurance), and those to representing all involved in court (layers). Let the system works its own way out without politics. Too messy already.
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With that being said, I should be allowed to build my own home, with my own money, no permits, no engineering that I could sell to someone else later on down the road?
How would it make you feel knowing that your 2 year old daughter could be sleeping in a room, under a roof that is supporting 35psf and is composed of DF 2x10 @ 24" O.C. with a clear span of 24'-0"? It looks good, does that make it valid? There is a reason society has developed CBC, IRC, SBC & IBC and they are not relying on common sense to save cents.
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Many things has potential to kill use - a gas range, a boiler, bath tub...Do you want everything to be reviewed by a professional engineer? Oh, the baby cradle kills too (more often than roof).
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It's not about how you feel, it's about the laws that have been made based on past experiences. I'm not concerned with how courageous you are as a risk taker, I'm concerned about being a professional and providing a service that should be mandated as necessary. Read the code yourself:
• IRC 2006 Section R502.11.3
• IBC 2006 Section 2303.4.1.7
• Truss members and components shall not be cut, notched, drilled, spliced or otherwise altered in any way without the approval of a registered design professional.
You have the choice to choose whoever you want to in selecting engineering services. Nobody is making claim that you have to choose anyone particular, just that you should have specific conditions reviewed.
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Here's what I would suggest. Find as many good examples (with pictures) of roof failures for residential construction as I can. They don't have to be specifically related to solar panels. But, they should be the types of failures that you are concerned about with the panels.
Any presentation you give should involve a liberal of this pictures and the cost to the homeowner and such of these damages.... After all, a picture is worth a thousand words.
If you can't find good examples of this sort of failure, then I don't think your presentation will be very convincing... except to the technical minded like us engi-nerds.
Josh
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Contractor to Owner: Your engineer is screwing you by driving up the cost with these ridiculous moment frames around the garage opening. I've been doing this type of construction for 30 years. Trust me, this engineer doesn't know what he's doing....
Engineer to Owner: Well, it's certainly true that people have been doing it his way for 30 years. Then there were a bunch of failures and even some fatalities during the Northridge earthquake because of it. That's why we do it differently now.... I can show you the post-disaster investigation pictures if you like. I've got a buch of reports on the subject in my office, come by anytime to take a look.
Those sorts of pictures give us the ability to "prove" to the owner (or architect) that we're not just overly conservative academics who don't understand the real world of construction. Because we know that is how we'll be painted by contractors.... at least those who've never seen their structures go through a design level e-quake, or hurricane.
Josh
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It is hard to explain to a home owner how the "Building Inspector" didn't see this defect.
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a roof that was built to code in the last (30 years?) should be able to handle a typical solar panel roof load... after review by a professional for obvious shortcomings. i think this subject could easily turn into ..."must analyze the entire house because of increased dead load..." that would also technically be a valid statement as well...
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California adopted the 2007 CBC, which is based on the 2006 International Building Code (IBC) with ammendments, the specific reference to modifications is as follows:
IBC 2006 2303.4.1.7 – Alterations to trusses. Truss members and components shall not be notched, drilled, spliced or otherwise altered in any way without written concurrence and approval of a registered design professional. Alterations resulting in the addition of loads to any member (e.g., HVAC equipment, water heater) shall not be permitted without verification that the truss is capable of supporting such additional loading.
As far as other areas of review, if the building codes state it then one should follow it.
There is more supporting evidence in requiring a structural review than there is otherwise. To my knowledge, there is no testing or data that qualifies all homes built will provide the necessary support of 4PSF dead load. In almost every discussion about this topic the areas avoided are wind, seismic & snow. Just for the record, it is not ok to use live load for dead load. Live load is a short term loading scenario and in all the calculations performed take advantage of it.
In my research I've found that the state of Oregon is a big supporter of green technology and the state building code reflects very specific guidelines for when a review is necessary and when one is not. I believe that this state has it together.
I spoke to Ravi Mahajan (P.E., C.B.O. Structural Engineer) from Clackamas County Oregon and they have posted the following:
http://www.co.clackamas.or.us/docs/dtd/solar.pdf
Ravi also was a contributing member of the OBC.
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What I mean is that 2005 NDS allows the CD (duration of load) to bending, tension and compression checks by 1.25 (7 day) for live construction verse the 1.0 (10 years) for dead loads. So therefore the allowable bending, tension or compression is higher when evaluating a 7 day load (short term) verse a 10 year (long term).
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I don't have my NDS in front of me, but I'm certain DL only Cd is 0.9. Floor Live Load is 1.0.
hokie- the 7 days is cumulative. All Cd factors are based on cumulative time the member is exposed to load pulses exceeding some value.
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Correct, table 2.3.2 defines it as a permanent load (.9) – thank you for the clearification.
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I'd say $600 - $1000 is insignificant based on that.
There is good reason that requirements like that are put in place. Contractors who either don't know better or are irresponsible do things to potentially make buildings unsafe.
We had that go around here when "ballasted" roofing systems became all the rage many years ago and many buildings were loaded up without regard for design loads..
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With the older roof top solar water heaters, there was a much larger dead load imposed in a small concentrated area. If these are the systems you're using then you should be getting engineering. Typically, these units are only affecting one truss type and the cost on this form of service is more like $400 (from our company) unlike the solar arrays. If your company uses an engineer and you have a consistent volume your price could even be lower. Most likely your using a newer systems that lay flat over the plane of the roof surface and run a constant stream of water through the roof top and into a tank mounted somewhere on the ground. This type of system is much lighter & uniform which does not have to deal with uplift. But, I would say that you're still penetrating into the roof with places you into a grey area that nobody addresses (which I'm sure is fine anyhow).
The point is that if you're paying $1000 for this type of review then I would suggest shopping around.
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