# Roof Inspection by a Structural Engineer for PV System



## MikeFL (Apr 16, 2016)

Is there any history of buildings failing from the addition of solar arrays?
By the strictest interpretation of codes, the bldg dept is correct. You don't add loads without doing a calculation, just as is the case with an electric service. 
IIRC the live load (humans walking on the roof) for a roof is only 5 psf.


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## chicken steve (Mar 22, 2011)

TGGT said:


> I'm dumbfounded.


But it beats being sued for a collapse TG
:no:
~CS~


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## backstay (Feb 3, 2011)

TGGT said:


> The town I live in requires sealed letter of approval after an on-site inspection of a roof by a structural engineer.
> 
> After providing all the engineering information provided by the manufacturers a local structural engineer quoted me $2000.00 to perform this service. The array I'm planning on using is going to be about 2lbs per square foot.
> 
> I'm dumbfounded.


$500 is the norm.


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## TGGT (Oct 28, 2012)

MikeFL said:


> Is there any history of buildings failing from the addition of solar arrays?
> By the strictest interpretation of codes, the bldg dept is correct. You don't add loads without doing a calculation, just as is the case with an electric service.
> IIRC the live load (humans walking on the roof) for a roof is only 5 psf.


When I spoke to the inspections department he never mentioned known failures. His biggest concern was uplift from 3 second 90 mph wind gusts (and be bumped to 115 mph in come September). If a tornado lands on my house I'm not sure the array is going to be my highest concern.

I came across this document that encourages simplifying the permitting process for PV systems. It discusses the roof structure on page 22.

http://www.solarabcs.org/about/publications/reports/expedited-permit/pdfs/Expermitprocess.pdf


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## TGGT (Oct 28, 2012)

chicken steve said:


> But it beats being sued for a collapse TG
> :no:
> ~CS~


It's for my house.

Granted when I spoke to this person they said they never performed such an inspection, so I'm sure there's a learning curve aspect in there, or maybe they don't want to be bothered.


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## joebanana (Dec 21, 2010)

I'd get a second estimate. $2K to look at some chart's seems rather high.


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## emtnut (Mar 1, 2015)

An engineers report like that would go for $500 -$900, depending on the complexity, up here.
Don't know if it applies to your area, but we can have a civil 'technologist' stamp architectural drawings ... Cut the figure above in half for what they will do it for.


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## frenchelectrican (Mar 15, 2007)

Personally I think 2K dollars is kinda little steep for some reason but after I converted to my money and see where it stand and I know with the engineers in my area they dont charge that HIGH unless you got a very oddball or non standard construction of your building.

typically I do expect to be about 500 to 750 bucks zone for that kind of service.


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## TGGT (Oct 28, 2012)

Yeah sorry I should've made clear it's for my house. Nothing special about it, easy access to the roof and attic.

Sent from my SM-G360T using Tapatalk


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## frenchelectrican (Mar 15, 2007)

TGGT said:


> Yeah sorry I should've made clear it's for my house. Nothing special about it, easy access to the roof and attic.
> 
> Sent from my SM-G360T using Tapatalk


If common roof style it should be not a major issue but the type of trusses / rafters may change the answer on that.


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## backstay (Feb 3, 2011)

TGGT said:


> Yeah sorry I should've made clear it's for my house. Nothing special about it, easy access to the roof and attic.
> 
> Sent from my SM-G360T using Tapatalk


Who came up with this requirement? What's the population of your town? Do the people pushing this even have a clue? What is the penalty for non compliance?


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## Switched (Dec 23, 2012)

backstay said:


> Who came up with this requirement? What's the population of your town? Do the people pushing this even have a clue? What is the penalty for non compliance?


I have been looking into adding solar as a service we provide, and apparently around here all the jurisdictions require it. But... We are overreaching Cali, so that is to be expected....


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## cabletie (Feb 12, 2011)

Myself and two other coworkers put solar on our houses. We helped each other out. My town was the only one to require an architect or structural engineer to sign off on the roof structure. 

I tried to get the town to accept the drawings that I did. It showed a plan view and a cross section of the roof. It had weight per square foot and a comparison of it being less weight than a second layer of shingles. I also had the reports from the racking on wind etc. The building inspector said no exceptions, every house with solar has had, and will always have stamped drawings from an A&E. 

Calling a few A&E's on the phone, I think the prices started around a thousand and went up between three that I called. My wife called an architect on Craig's list. He looked at my e-mailed drawings, and would sign them for $300 after a site visit to verify dimensions. Done. 

I could see the town requiring it if they were trusses, but I have dimensional lumber.


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## splatz (May 23, 2015)

I think you put your finger on it, there are easy tables for things like HVAC equipment that just sits on the roof in a box, there are not easy table lookups for the wind load / lift. 

It might be that until standards are developed doing this kind of engineering could be a lot of trouble and he doesn't want to be bothered unless he can charge a bundle. 

http://www.solarabcs.org/about/publications/reports/wind-load/pdfs/Wind_Load_blanksstudyreport3.pdf


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## backstay (Feb 3, 2011)

I guess we're back to this as one solution. Or this, 
http://smartflowersolar.com/products/smartflower/ credit to Majewski for the Sunflower find.


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## splatz (May 23, 2015)

I wonder if you could make a mount so you don't have so much air flow under the panel that would prevent the wind lift and take that factor out of the engineering. 

For example if the mount sat on a 4" ventilated sheet metal skirt, maybe that gives you enough ventilation for cooling but not enough airflow that wind lift becomes a problem.


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## HackWork (Oct 2, 2009)

backstay said:


> I guess we're back to this as one solution. Or this,
> http://smartflowersolar.com/products/smartflower/ credit to Majewski for the Sunflower find.


In suburban areas there often just isn't enough space for that. And where it would fit and the homeowners don't mind looking at it, it would still probably have issues of shading from the houses (usually 3 stories) and old trees.


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## backstay (Feb 3, 2011)

HackWork said:


> In suburban areas there often just isn't enough space for that. And where it would fit and the homeowners don't mind looking at it, it would still probably have issues of shading from the houses (usually 3 stories) and old trees.


Those same issues are with my ground mounts. Which is why I stay away from cities with tall buildings.


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## Southeast Power (Jan 18, 2009)

I would think adding structural metal screwed to the trusses would count for a marked improvement of the roof.
Also, due to the design, you would maybe see some downward force.


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## Lightsmith (Oct 8, 2010)

When I lived in Pasadena a city ordinance was passed that required that with every change in tenant in a rental unit the electrical, plumbing, and HVAC had to be upgraded. It was great for the leading plumbing supply house in the city whose owner was a brother of the councilman who introduced the new regulation. 

Great for the structural engineers if all they have to do is climb a ladder and get paid $2,000 for doing so. Whatever amount the engineers paid the local officials to get this ordinance enacted was repaid very quickly at $2,000 a roof. I don't know what the going rate is where you work but in California a county supervisor can be bought for only $10,000 and so for $30,000 you can own the board. 

I wonder if they let the installation of a satellite dish slide or want a structural engineer to approve it?


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## farmantenna (Nov 22, 2012)

My Massachusetts town's building inspector said I would need structural engineer inspection, I think because my house was built before 1976.

I hope I can find one for under $500 otherwise no solar for me


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## Lightsmith (Oct 8, 2010)

Your town's inspector is evidently not aware of the actual weight of a solar panel. A residential grade panel like the Sun Power E18 230 has a total weight of 33.1 lbs. and is 61.4" x 31.4" in size. That translates into a load on the roof of 2.47 lbs. per square foot. Contrast that to someone standing on the roof who is providing a load of 150 lbs. or more per square foot. 

Placing 10 panels on the roof is going to constitute a total load of 330 lbs. spread over 134 square feet of roof area. 

There are times when it is better to go over the head of someone who is an idiot and talking instead to the city council at their next meeting.


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## MikeFL (Apr 16, 2016)

Lightsmith said:


> Your town's inspector is evidently not aware of the actual weight of a solar panel. A residential grade panel like the Sun Power E18 230 has a total weight of 33.1 lbs. and is 61.4" x 31.4" in size. That translates into a load on the roof of 2.47 lbs. per square foot. Contrast that to someone standing on the roof who is providing a load of 150 lbs. or more per square foot.
> 
> Placing 10 panels on the roof is going to constitute a total load of 330 lbs. spread over 134 square feet of roof area.
> 
> There are times when it is better to go over the head of someone who is an idiot and talking instead to the city council at their next meeting.


Someone standing on a roof is a live load of 20 psf and that can be reduced using formulas in ASCE-7. There is assumed a concentrated load of 300 lbs which can be a 250lb man with 50lb tools/ materials.

To understand loading per square foot take the horizontal projection of the member multiplied by the member spacing and that's your tributary area. Load it with the lbs and divide by the area (in sf) and that's your psf.

16' horizontal projection of the rafter on 2' centers = 32 square feet.
Put a 300 lb man standing there and you have 300lb on 32sf = 9.4psf. If your design load is 20psf you can have 2 men standing there safely.

As to those solar panels, it depends on how the connections are made and where those connections land on the roof. 

You'd never install an electric car charger in an existing house without doing a load calc on the electric service. Bldg dept says you don't add loading to a roof without doing a load calc. Do they have problems in their past or has someone lobbied for this requirement?

Down here you'd need the engineering for wind loading and at the same time the roof is going to get a load calc.


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## HackWork (Oct 2, 2009)

MikeFL said:


> Someone standing on a roof is a live load of 20 psf and that can be reduced using formulas in ASCE-7. There is assumed a concentrated load of 300 lbs which can be a 250lb man with 50lb tools/ materials.
> 
> To understand loading per square foot take the horizontal projection of the member multiplied by the member spacing and that's your tributary area. Load it with the lbs and divide by the area (in sf) and that's your psf.
> 
> ...


We install car chargers without doing a load calc all the time.


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## MTW (Aug 28, 2013)

HackWork said:


> We install car chargers without doing a load calc all the time.


We generally don't do load calcs for any residential circuit addition. Only an actual service change calls for a load calc.


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## HackWork (Oct 2, 2009)

MTW said:


> We generally don't do load calcs for any residential circuit addition. Only an actual service change calls for a load calc.


Even service changes we don't do them. Since the houses are all natural gas the inspectors know a 200A service is more than plenty. I have only been asked for a load calc on a couple standby generator jobs to make sure it was sized correctly and the load shedding was enough.


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## MTW (Aug 28, 2013)

HackWork said:


> Even service changes we don't do them. Since the houses are all natural gas the inspectors know a 200A service is more than plenty. I have only been asked for a load calc on a couple standby generator jobs to make sure it was sized correctly and the load shedding was enough.



That's true, for a 100 amp to 200 amp upgrade we never do a load calc. A 320 would call for one though.


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## MikeFL (Apr 16, 2016)

HackWork said:


> We install car chargers without doing a load calc all the time.


So if some lady has a 75A service you're going to add hot tubs, car chargers, etc. forever until when?


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## HackWork (Oct 2, 2009)

MikeFL said:


> So if some lady has a 75A service you're going to add hot tubs, car chargers, etc. forever until when?


I never said that. Don't get snippy with me.


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## MikeFL (Apr 16, 2016)

HackWork said:


> I never said that. Don't get snippy with me.


That's fair.

Why would you not do a load calc every time you add load to a service? Are you working in 1200 sf houses with gas appliances and a 200A service and you know adding 50A load is fine? What about a 3,500 sf house with electric appliances and a 200A service?


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## HackWork (Oct 2, 2009)

MikeFL said:


> That's fair.
> 
> Why would you not do a load calc every time you add load to a service? Are you working in 1200 sf houses with gas appliances and a 200A service and you know adding 50A load is fine? What about a 3,500 sf house with electric appliances and a 200A service?


I'm just telling you how it is in the real world. I don't know of any residential electrician who does a load calc when adding loads other than when the inspector requires one. Ain't no one got time fo dat.

A load calc is just a guesstimate. As experienced electrician, we can make a better guesstimate in our heads just by looking at the existing loads and comparing that to the hundreds of other houses and panels that we have seen and know what works in.

You know what uses a lot of power in the real world? Teenage daughters. They are always cold so they have space heaters in their room. They use super duty hair dryers, curling irons, straightening irons, etc. All while blasting their stereo while the TV is on. Yet load calls don't ask how many females are in the home.


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## NormousD (Nov 12, 2017)

HackWork said:


> I'm just telling you how it is in the real world. I don't know of any residential electrician who does a load calc when adding loads other than when the inspector requires one. Ain't no one got time fo dat.


I would and my guys ALWAYS would when adding a real heavy load like a hot tub or electric car charger (30A or higher). 

That's crazy to not know if it's at least close, if not over. Plus you can make more money on the service upgrade.. or if the customers are cheap and won't do it, pass the cheap job off to Craigslist hacks.


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## HackWork (Oct 2, 2009)

NormousD said:


> I would and my guys ALWAYS would when adding a real heavy load like a hot tub or electric car charger (30A or higher).
> 
> That's crazy to not know if it's at least close, if not over. Plus you can make more money on the service upgrade.. or if the customers are cheap and won't do it, pass the cheap job off to Craigslist hacks.


 I don't believe that you do load calcs. You're a known liar and thief so your words are meaningless. 

You don't need to do a load calc to recommend a service upgrade.

Residential load calls are for Mike Holt members.



> That's crazy to not know if it's at least close, if not over.


 You literally edited out the entire part of my post in which I explained how I do not do the exact thing that you just accused me of doing.


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## farmantenna (Nov 22, 2012)

TGGT said:


> The town I live in requires sealed letter of approval after an on-site inspection of a roof by a structural engineer.
> 
> After providing all the engineering information provided by the manufacturers a local structural engineer quoted me $2000.00 to perform this service. The array I'm planning on using is going to be about 2lbs per square foot.
> 
> I'm dumbfounded.


I was just was quoted $1000! I am starting to think twice about installing solar. Here in Massachusetts or my town I was told I can't install the roof feet, rails or panels myself! I need to have CSL person pull the permit and supervise the project. 

Think of it this way, you can get 30% off that amount from federal tax credit


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## TGGT (Oct 28, 2012)

farmantenna said:


> I was just was quoted $1000! I am starting to think twice about installing solar. Here in Massachusetts or my town I was told I can't install the roof feet, rails or panels myself! I need to have CSL person pull the permit and supervise the project.
> 
> Think of it this way, you can get 30% off that amount from federal tax credit


Texas only requires an electrician perform the work (not just supervise). I imagine enforcement is lax depending.

On the other hand my last inspector wanted to see my journeyman license before he would look over the job. If I didn't have it I would have to leave or my employer would be fined.

Sent from my SM-G930T using Tapatalk


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## MikeFL (Apr 16, 2016)

In Florida you can do anything you want to your own house. It has to be your primary residence and you can't offer it for sale or for lease for a period of 1 year. But if you want you can pull every permit as homeowner and do all the work yourself.


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