Examples of Panels Weighing Too Much for House?

[J.P.M.]

Well they are required inherently because of the definition of ballast. You are adding weight and most places, particularly the ones with residential flat roofs do require them because of the fact you are adding weight.




residential often ask for it as it is low penetration and thought to leak much less but we have had very poor luck getting them approved and have as a matter of course stopped any attempts to do so in the future for residential (exceptions are possible of course).



exactly.



Well mounting systems are designed as a unit. None that I know of have a tile component There would be considerable torsional force on the mounting points which are usually simple clamps. Further it would require a pivot system particularly at the base which none of them have. You could likely cobble some pivots together along with the standoffs but I would highly doubt it would warrantied or covered by the pre-calculations that the manufacturers provide.



again you would need a pivot and standoff which the railless systems do not provide. The array would have no structural integrity at the joint (your example of two modules, the mid point between them). The railless systems have no way to hold the modules in a flat plane other than the bolts to the roof, a little twisting and the clamps would pop off.



Well they have a bit of rigidity and most have a latteral and vertical loading capability as in this example:

https://www.youtube.com/watch?v=jzLB06KY0i0

The rails are attached to the truss system. If you have an annal retentive installer (like me) that likes the array to be perfectly flat even when the roof isn't you might see what I mean. Walk on a common construction grade roof with a string pulled across from end to end. just the weight of a man and flex the roof 1/4 to 1/2 or so (worse on a poor roof). We like to align the rails with a string end to end. Once they are all tightened up, you can walk across and there will be no sag ( or greatly reduced) and the rail will be dead on to the string or laser line.

You do the same thing with railless and it will still sage as you walk across and work because they flex at the edges of the array where they are attached. Further the nature of the railless means you can't stagger the mount points, they have to be at the edges or corners of the PV modules.



I disagree. In a railless rigidity is exactly as you say, a characteristic of the mounting system and roof it is mounted too. But a railless system has its own rigidity, that is the point of the rails. in ground mount you mount the PV modules to the rails then carry the unit to the ground mount and bolt it as a unit to the ground mounts. you can do the same thing on a roof mount tilted system (same for an untitled one if you had a skinny installer

tilted systems without rails, once one mount fails the units will fly apart. in a railed system, the mounts share the load making a single mount less likely to fail but any one mount can be removed with redundancy with the rails.



yes the rails should not be relighed on to support the structure but the point is on a typical roof mount the load is now partially on the array, which in a railed system is distributing the load as well as helping to keep the truss all aligned. In both railed and railless you have to add lag bolts which weaken the truss. The railed system the lags are staggered, with a railless they are in line every other truss only. Thus the weight is now born by HALF the truss or rafters.

For my part, While I believe I understand what you're writing, I feel discussing this further is a waste of my time. Respectfully, from what you write and how you write it, I don't believe you have the structural engineering background beyond what you've been told to understand what I'm writing about. I suggest we simply agree to disagree as this is going nowhere.

We probably lost the OP somewhere along the way anyway.

Respectfully,

J.P.M.

[ButchDeal]

Ballasted systems in and of themselves do not need a P.E. stamp on the design simply by virtue of being a ballasted design as you first sentence seems to read. Is stamping in an uncertain situation a good idea ? Probably. Required by some localities? Yup. Inherently required by the simple fact of being ballasted ? Nope.

Well they are required inherently because of the definition of ballast. You are adding weight and most places, particularly the ones with residential flat roofs do require them because of the fact you are adding weight.

All that said, I'd suggest that as a practical matter, ballasted systems ought to be the last method of mounting to be considered, if at all. IMO, the reason it's usually attempted at all is because it looks simple with most folks being clueless about the need to consider loadings imposed by a large weight, and the need to ensure that weight says put.

residential often ask for it as it is low penetration and thought to leak much less but we have had very poor luck getting them approved and have as a matter of course stopped any attempts to do so in the future for residential (exceptions are possible of course).

If stamping is done for any reason, part of any good design/review will include consideration of what the array's imposed loads will be transferred to, such as any supporting or mounting structure, and what those loads will do to that structure. I agree that such things are often difficult or impossible to check due to lack of drawings/calcs or the ability to properly inspect load bearing members. If a ballasted system is put on a structure of unknown or unverifiable construction, expect a hard time finding a P.E. willing to take a chance on it, or if you do, expect to pay a hefty premium as you seem to be saying. That also probably makes a system more costly and harder to sell.

exactly.

On rail vs. railless racking, I can't, off the top of my head, think of a reason why railless systems on flat roofs require an array to be limited to a horizontal orientation as you seem to be implying. I don't believe the railless police are out and about on that one. Maybe a tilted array using railless systems is not practical on horizontal roofs for a lot of reasons, but I could sure design one.

Well mounting systems are designed as a unit. None that I know of have a tile component There would be considerable torsional force on the mounting points which are usually simple clamps. Further it would require a pivot system particularly at the base which none of them have. You could likely cobble some pivots together along with the standoffs but I would highly doubt it would warrantied or covered by the pre-calculations that the manufacturers provide.

Think of a one or two panel tilted mount as for a solar flat plate water heater on a flat roof. I drive by several each day with tilts that are somewhere between 20 and about 45 deg. or so. Just make the supports that are farther from the equator longer. That may not be as practical for large arrays as railed systems and so they are probably not all that common for large arrays, but there is no inherent reason why railless systems need to always be in the plane of the mounting structure or roof. One reason they may not be common might have to do with marketing and maybe also because there is little demand for such support systems. Just get longer standoffs for the supports farther away from the equator, or as long as necessary to fit the application (nothing says you can't have 4 legs/panel with all 4 legs having different lengths from one another), X brace the high side for transverse moment(s), and depending on the support length(s), maybe check for Euler buckling, flutter instability for compressive wind loading and a few other things, and call it done. Not sure what it would cost, but that's different from being not

again you would need a pivot and standoff which the railless systems do not provide. The array would have no structural integrity at the joint (your example of two modules, the mid point between them). The railless systems have no way to hold the modules in a flat plane other than the bolts to the roof, a little twisting and the clamps would pop off.

As for rail systems having structural integrity on their own : A rail has little ability to resist bending moment on its own and little structural ability beyond tensile strength to resist an axial tensile load compared to a rigid 2 dimensional structure like an array. Rail systems on arrays, depending on how panels are connected, may and probably will result in greater array rigidity than railless systems due to the rigidity of the resulting railed 2 dimensional array.

Well they have a bit of rigidity and most have a latteral and vertical loading capability as in this example:

https://www.youtube.com/watch?v=jzLB06KY0i0

The rails are attached to the truss system. If you have an annal retentive installer (like me) that likes the array to be perfectly flat even when the roof isn't you might see what I mean. Walk on a common construction grade roof with a string pulled across from end to end. just the weight of a man and flex the roof 1/4 to 1/2 or so (worse on a poor roof). We like to align the rails with a string end to end. Once they are all tightened up, you can walk across and there will be no sag ( or greatly reduced) and the rail will be dead on to the string or laser line.

You do the same thing with railless and it will still sage as you walk across and work because they flex at the edges of the array where they are attached. Further the nature of the railless means you can't stagger the mount points, they have to be at the edges or corners of the PV modules.

But rigidity in and of itself is simply a characteristic of the array/mounting system and may, or may not, be beneficial or even desirable to an array's ability to stay put in a wind or seismic event. As emartain00 seems to be writing, as for whether or not an array stays put on a roof has more to do with the number of attachments to the mounting structure (the roof) than it has to do with array rigidity. As a matter of some opinion and circumstance, a rigid array may fair worse in an event, not only because it may well have fewer connections to the support structure (for example, a roof), but also because of the possibility and perhaps likelihood of the entire rigidly connected array coming to a bad end rather than one or two unconnected panels being lost. For example, a railess system that had 4 supports per panel with the panels not rigidly connected might be better able to withstand an external loading event simply by virtue of having more attachments to the structure, although I can see where such a system would have other less desirable design considerations like being able to easily hit a rafter every time and lots of other considerations.

I disagree. In a railless rigidity is exactly as you say, a characteristic of the mounting system and roof it is mounted too. But a railless system has its own rigidity, that is the point of the rails. in ground mount you mount the PV modules to the rails then carry the unit to the ground mount and bolt it as a unit to the ground mounts. you can do the same thing on a roof mount tilted system (same for an untitled one if you had a skinny installer

tilted systems without rails, once one mount fails the units will fly apart. in a railed system, the mounts share the load making a single mount less likely to fail but any one mount can be removed with redundancy with the rails.

All that aside, as for an array or it's mounting system adding strength to a support structure, it's usual to calc out/design or proof calc a support structure on its own, without consideration of any strength that may be added by what's being supported. So, conservative and usual design practice, at least as I learned and practiced it makes the idea that an array with a rail system may add structural integrity to a support structure moot.

yes the rails should not be relighed on to support the structure but the point is on a typical roof mount the load is now partially on the array, which in a railed system is distributing the load as well as helping to keep the truss all aligned. In both railed and railless you have to add lag bolts which weaken the truss. The railed system the lags are staggered, with a railless they are in line every other truss only. Thus the weight is now born by HALF the truss or rafters.

[J.P.M.]

By the way, there is now a convenient service call greenlancer.com that is providing solar engineering services in just about all states. In most cases they can provide 24hr turnaround on standard stuff. I've pretty much quit using my local PE friend that my jobs were small potatoes to...

From their website, as much as I looked I saw no mention or example or reference to what, if anything, Greenlancer does with mechanical design. Maybe it's like dating and expecting to get lucky: Some things you have to ask for.

[J.P.M.]

exactly. Ballasted systems always need a stamp (and someone to review the structure to see that it can handle the load). This is why it is difficult to put ballasted on residential. Often the structure can not be certified as it is too old of uncertain integrity. Commercial often has specs on the large buildings to easily calculate to.





It is possible to do railed systems on flat (Horizontal) as well as both railed and railless on pitched roofs.

Railless on a flat roof though possible would result in a flat array which is not desirable.



Railes have structural integrity of their own. They tie the rafters together and are considered to increase integrity more than the lag bolts would decrease the integrity, Because they tie the rafters together and spread the load and uplift force out, especially with staggered penetrations. Drilling holes into the rafters to put lag bolts in decreases integrity.
Railless on the other hand do not have any integrity of their own, they have more lag bolts and add weight but no integrity.



exactly, and why I stated tilted systems should have a stamp.



many jurisdictions do not require stamps in any of the conditions I suggested should have them but most of the larger well established do. We stopped doing ANY residential ballast system as it is too difficult to get anyone to review and stamp for the older ones and in jurisdictions that don't require it, we didn't feel comfortable either.

Ironridge has standards for revers tilt but that is for their equipment not for the structure it is bolted to.

Ballasted systems in and of themselves do not need a P.E. stamp on the design simply by virtue of being a ballasted design as you first sentence seems to read. Is stamping in an uncertain situation a good idea ? Probably. Required by some localities? Yup. Inherently required by the simple fact of being ballasted ? Nope.

All that said, I'd suggest that as a practical matter, ballasted systems ought to be the last method of mounting to be considered, if at all. IMO, the reason it's usually attempted at all is because it looks simple with most folks being clueless about the need to consider loadings imposed by a large weight, and the need to ensure that weight says put.

If stamping is done for any reason, part of any good design/review will include consideration of what the array's imposed loads will be transferred to, such as any supporting or mounting structure, and what those loads will do to that structure. I agree that such things are often difficult or impossible to check due to lack of drawings/calcs or the ability to properly inspect load bearing members. If a ballasted system is put on a structure of unknown or unverifiable construction, expect a hard time finding a P.E. willing to take a chance on it, or if you do, expect to pay a hefty premium as you seem to be saying. That also probably makes a system more costly and harder to sell.

On rail vs. railless racking, I can't, off the top of my head, think of a reason why railless systems on flat roofs require an array to be limited to a horizontal orientation as you seem to be implying. I don't believe the railless police are out and about on that one. Maybe a tilted array using railless systems is not practical on horizontal roofs for a lot of reasons, but I could sure design one.

Think of a one or two panel tilted mount as for a solar flat plate water heater on a flat roof. I drive by several each day with tilts that are somewhere between 20 and about 45 deg. or so. Just make the supports that are farther from the equator longer. That may not be as practical for large arrays as railed systems and so they are probably not all that common for large arrays, but there is no inherent reason why railless systems need to always be in the plane of the mounting structure or roof. One reason they may not be common might have to do with marketing and maybe also because there is little demand for such support systems. Just get longer standoffs for the supports farther away from the equator, or as long as necessary to fit the application (nothing says you can't have 4 legs/panel with all 4 legs having different lengths from one another), X brace the high side for transverse moment(s), and depending on the support length(s), maybe check for Euler buckling, flutter instability for compressive wind loading and a few other things, and call it done. Not sure what it would cost, but that's different from being not

As for rail systems having structural integrity on their own : A rail has little ability to resist bending moment on its own and little structural ability beyond tensile strength to resist an axial tensile load compared to a rigid 2 dimensional structure like an array. Rail systems on arrays, depending on how panels are connected, may and probably will result in greater array rigidity than railless systems due to the rigidity of the resulting railed 2 dimensional array.

But rigidity in and of itself is simply a characteristic of the array/mounting system and may, or may not, be beneficial or even desirable to an array's ability to stay put in a wind or seismic event. As emartain00 seems to be writing, as for whether or not an array stays put on a roof has more to do with the number of attachments to the mounting structure (the roof) than it has to do with array rigidity. As a matter of some opinion and circumstance, a rigid array may fair worse in an event, not only because it may well have fewer connections to the support structure (for example, a roof), but also because of the possibility and perhaps likelihood of the entire rigidly connected array coming to a bad end rather than one or two unconnected panels being lost. For example, a railess system that had 4 supports per panel with the panels not rigidly connected might be better able to withstand an external loading event simply by virtue of having more attachments to the structure, although I can see where such a system would have other less desirable design considerations like being able to easily hit a rafter every time and lots of other considerations.

All that aside, as for an array or it's mounting system adding strength to a support structure, it's usual to calc out/design or proof calc a support structure on its own, without consideration of any strength that may be added by what's being supported. So, conservative and usual design practice, at least as I learned and practiced it makes the idea that an array with a rail system may add structural integrity to a support structure moot.

BTW, structural integrity does not always mean rigidity. It has more to do with a structure's ability to withstand imposed design loads and still be as safe as required, and fit for purpose and service.

[emartin00]

There is a need to change codes and processes if they are unnecessarily preventing solar installations. I've worked with AHJs a number of times on unnecessary requirements and got them changed in the past.

The uplift requirement is not the issue here. The AHJ is worried about the actual weight on the house to the point that, in many cases, they are requiring a full engineering analysis clear down to the footings and foundation of the home. They want to know that a system isn't going to compromise the structural integrity of a home, even in an earthquake. But I'm pretty sure that a solar system isn't going to determine whether a house will collapse in an earthquake. We have engineers stamp our system designs all the time but this is a whole other level of analysis and costs.

Where are you located?

[solarix]

By the way, there is now a convenient service call greenlancer.com that is providing solar engineering services in just about all states. In most cases they can provide 24hr turnaround on standard stuff. I've pretty much quit using my local PE friend that my jobs were small potatoes to...

[J.P.M.]

There is a need to change codes and processes if they are unnecessarily preventing solar installations. I've worked with AHJs a number of times on unnecessary requirements and got them changed in the past.

The uplift requirement is not the issue here. The AHJ is worried about the actual weight on the house to the point that, in many cases, they are requiring a full engineering analysis clear down to the footings and foundation of the home. They want to know that a system isn't going to compromise the structural integrity of a home, even in an earthquake. But I'm pretty sure that a solar system isn't going to determine whether a house will collapse in an earthquake. We have engineers stamp our system designs all the time but this is a whole other level of analysis and costs.

If dead weight is the governing issue rather than uplift from wind, I'm led to think that this is a ballasted system ?

Reason I ask: While both wind and seismic loadings need to be considered (but not acting simultaneously) as well as all other external and occasional loads, for most solar arrays, wind governs over seismic. If seismic is the concern, and from what you describe of their concerns, that's what it reads like, it's not the weight of the panels that's the problem.

From what you're writing, it almost sounds like you're planning a ballasted system. If so, the AJH's requirements are probably and entirely reasonable.

[Roger57]

The short answer is no. For all practical purposes, codes in force cover roof loadings quite well. You will not get an AHJ to change them. there is no need for that.

PV panels have a mass of ~ 2.5 lbm/ft.^2. Most roofs are OK with a dead load of probably 40 lbm/ft.^2. It's hard to come up with a scenario where the added dead load from panels would present a problem even with a design snow load added. As for uplift from wind, even in what's a completely absurd situation of a wind vector of 120 MPH applied normal to the face of a panel (blowing upward and away from the surface of the roof, the uplift would still only be ~ 37 lbf/ft.^2 less the panel weight, and that'll never happen. Same for a downward force but that's already accounted for as it'll be close to the same force on the roof without the panel plus the ~ 2.5 lbm/ft.^2 dead weight of the panel.

You need someone familiar with wind loadings on structures to help you understand why you're barking up the wrong tree.

There is a need to change codes and processes if they are unnecessarily preventing solar installations. I've worked with AHJs a number of times on unnecessary requirements and got them changed in the past.

The uplift requirement is not the issue here. The AHJ is worried about the actual weight on the house to the point that, in many cases, they are requiring a full engineering analysis clear down to the footings and foundation of the home. They want to know that a system isn't going to compromise the structural integrity of a home, even in an earthquake. But I'm pretty sure that a solar system isn't going to determine whether a house will collapse in an earthquake. We have engineers stamp our system designs all the time but this is a whole other level of analysis and costs.

[ButchDeal]

1.) As a general precept, ballasted systems ought not to be used on horizontal roofs, or any roof for that matter, where the roof has not been specifically designed to carry such a load and associated external loads whatever such loads may be. Extra care is necessary in the checking of existing roofs or other structural elements of any orientation with respect to external loadings where such loadings may not have and probably weren't part of the original design considerations.

exactly. Ballasted systems always need a stamp (and someone to review the structure to see that it can handle the load). This is why it is difficult to put ballasted on residential. Often the structure can not be certified as it is too old of uncertain integrity. Commercial often has specs on the large buildings to easily calculate to.

2.) While there is no way to ensure that any roof penetration, or any penetration for that matter will not leak, a little extra care in the design of penetrations to isolate/reduce the area of potential leaks such as the use of small, raised plinths - sometimes known rather indelicately as puss pockets when used for equipment supports - can go a long way, with one design consideration being a requirement for access and visual inspection and service of the penetration. An often unconsidered result of ballasted systems, particularly on flat roofs, is the induced strain (deformation) on the roof caused by the extra weight. That can be thought of as a ticking bomb. As the ballast strains the roof, the roof will sag. The low spot thus created will collect water. Enough said.

2.) I suppose it's possible to have railed and railless systems on a horizontal roof as well as a non horizontal (pitched) roof.

It is possible to do railed systems on flat (Horizontal) as well as both railed and railless on pitched roofs.

Railless on a flat roof though possible would result in a flat array which is not desirable.

3.) I'm not sure that railed systems increase the structural integrity of a roof, or that railless systems decrease the structural integrity of a roof. I could make a case that the likely added number of attachments using a railless system might have some advantage of decreasing the point loadings at the roof penetrations. Also, and hard to say beyond speculation, depending on how it's done, if each panel is independent of its neighbors as might be the case with a railless system, a damaging wind event may have a slightly lower probability of taking/damaging the whole array, or at least maybe a smaller part of it.

Railes have structural integrity of their own. They tie the rafters together and are considered to increase integrity more than the lag bolts would decrease the integrity, Because they tie the rafters together and spread the load and uplift force out, especially with staggered penetrations. Drilling holes into the rafters to put lag bolts in decreases integrity.
Railless on the other hand do not have any integrity of their own, they have more lag bolts and add weight but no integrity.

4.) Depending on wind vector, systems that are non parallel to a (probably but not necessarily flat, and probably but not necessarily horizontal) roof will probably see larger tensile forces in the supports (uplift on the roof) than systems parallel to a roof. Systems that are non parallel to a roof will also see more compressive forces in the supporting members (that will exert downward forces on the roof) than systems parallel to a roof. There are also shear forces from wind as well, but those are usually small compared to the other loadings.

exactly, and why I stated tilted systems should have a stamp.

5.) Any system, should be properly designed, parallel to the mounting surface or not. Non parallel systems present different external loadings and so the mechanical design has different and probably additional considerations than systems parallel to the mounting surface. All of that doesn't necessarily require a P.E. to figure out. Follow ASCE - , etc. and plug and chug. A building code or dept. may require a P.E. to do or review the calcs. and drawings, but those can actually be done by anyone who's versed in the fundamentals. It might not be acceptable to authority having jurisdiction, but in a way that's only adding some assurance that the required calculations were done to the required standards.

many jurisdictions do not require stamps in any of the conditions I suggested should have them but most of the larger well established do. We stopped doing ANY residential ballast system as it is too difficult to get anyone to review and stamp for the older ones and in jurisdictions that don't require it, we didn't feel comfortable either.

Ironridge has standards for revers tilt but that is for their equipment not for the structure it is bolted to.

[J.P.M.]

Sure the main problem is ballasted on flat roofs. These should ALWAYS require a stamp.

Then you have pitched roofs and these you have two different mounting techniques: railless and railed systems.
The railless systems reduce structural integrity and should be looked at closely
Railed systems when installed correctly increase structural integrity and should not need a stamp.

any tilted system has greatly added uplift forces and should include a stamp.

1.) As a general precept, ballasted systems ought not to be used on horizontal roofs, or any roof for that matter, where the roof has not been specifically designed to carry such a load and associated external loads whatever such loads may be. Extra care is necessary in the checking of existing roofs or other structural elements of any orientation with respect to external loadings where such loadings may not have and probably weren't part of the original design considerations.

2.) While there is no way to ensure that any roof penetration, or any penetration for that matter will not leak, a little extra care in the design of penetrations to isolate/reduce the area of potential leaks such as the use of small, raised plinths - sometimes known rather indelicately as puss pockets when used for equipment supports - can go a long way, with one design consideration being a requirement for access and visual inspection and service of the penetration. An often unconsidered result of ballasted systems, particularly on flat roofs, is the induced strain (deformation) on the roof caused by the extra weight. That can be thought of as a ticking bomb. As the ballast strains the roof, the roof will sag. The low spot thus created will collect water. Enough said.

2.) I suppose it's possible to have railed and railless systems on a horizontal roof as well as a non horizontal (pitched) roof.

3.) I'm not sure that railed systems increase the structural integrity of a roof, or that railless systems decrease the structural integrity of a roof. I could make a case that the likely added number of attachments using a railless system might have some advantage of decreasing the point loadings at the roof penetrations. Also, and hard to say beyond speculation, depending on how it's done, if each panel is independent of its neighbors as might be the case with a railless system, a damaging wind event may have a slightly lower probability of taking/damaging the whole array, or at least maybe a smaller part of it.

4.) Depending on wind vector, systems that are non parallel to a (probably but not necessarily flat, and probably but not necessarily horizontal) roof will probably see larger tensile forces in the supports (uplift on the roof) than systems parallel to a roof. Systems that are non parallel to a roof will also see more compressive forces in the supporting members (that will exert downward forces on the roof) than systems parallel to a roof. There are also shear forces from wind as well, but those are usually small compared to the other loadings.

5.) Any system, should be properly designed, parallel to the mounting surface or not. Non parallel systems present different external loadings and so the mechanical design has different and probably additional considerations than systems parallel to the mounting surface. All of that doesn't necessarily require a P.E. to figure out. Follow ASCE - , etc. and plug and chug. A building code or dept. may require a P.E. to do or review the calcs. and drawings, but those can actually be done by anyone who's versed in the fundamentals. It might not be acceptable to authority having jurisdiction, but in a way that's only adding some assurance that the required calculations were done to the required standards.

[J.P.M.]

Until recently, no one in the building industry envisioned designing roofs with the possibility of putting these solar panel arrays on them. Therefore it is scary to the building departments to allow something that was never intended by the designers. They are very risk adverse you know and subsequently you have to prove to them that the roof is strong enough. Which means some one has to dive into the ASME code SEC 7 on calculating wind loads either (which of course weren't done with solar panels in mind). They want a PE to ok the roof in order to absolve the building dept of liability. I know that there has never been a roof collapse due to a solar array, but that has nothing to do with it. I like the "can't be occupied by live loads" logic - I'm going to use that... thanks.

Not to sound like too much of an engineering prick about this, but I believe you are referring to ASCE sec 7, and probably SEC 7-16 that deals with wind loadings.

ASME Sec 7 covers recommended guidelines for power boilers. When working, I dealt with and designed to both.

As for building depts. being cavalier about such things, my limited experience with folks at the counters and others working inside of buildings is that they mostly try to do the best they can but tend to be a bit bureaucratic and once in a while more worried about covering their asses with paper than what's in front of them, but I won't paint everyone with the same brush. Besides, and as we all know, you won't win an argument with an inspector. And, I'll repeat, I've never won an argument with an inspector, except for one who worked for the Hartford Steam Boiler Inspection Service (the folks who are in effect the AHJ for the ASME Boiler and Pressure Vessel Code compliance) who showed up drunk. I had to physically remove him from the shop before he hurt himself or others.

I agree with you that a building dept. brushing off requirements is pretty scary but it does happen - and never acceptable.

But I do wonder just how a building gets to be occupied by a live load. And if it can't be an occupant, how does one remove it. Maybe a live load exorcism is required.

Because it is a standard that deals with minimum design loads for buildings and other structures, ASCE - 7 does not specifically reference PV panels, but for the most part it doesn't reference specific building features or components. Like any code the designer expected to be knowledgeable enough to use the code as a tool in/for a specific application. I used it a fair amount for the design of distillation columns, power boilers and other such things. I used ASCE 7 quite a bit even though that code does not specifically reference pressure vessels.

See SEIA (the Solar Energy Industries Association). They have a lot of information on how to deal with wind loads and interpretations of hjow to use/comply with ASCE 7 with respect to PV systems and wind loadings.

[ButchDeal]

If they use enough mounting points.

In many jurisdictions, as long as you have a mounting point every 4 feet along the rail, you don't need any sign off. If you go with a stronger rail, and longer spans, you increase the point loading on the rafter. This is where you could see a failure. But when you distribute the load evenly, by using 4ft spans, and alternating rafters, you really won't see a problem with an house that doesn't have any structural deficiencies.

As I said, When installed correctly...

We like to use ironridge XR100 with 4 foot spans. It can handle longer spans but is more resistant to flexing
We do staggered in the middle and double up on the ends.

It is pretty much what you will get when you use the ironridge design tool online.

[emartin00]

Railed systems when installed correctly increase structural integrity and should not need a stamp.

If they use enough mounting points.

In many jurisdictions, as long as you have a mounting point every 4 feet along the rail, you don't need any sign off. If you go with a stronger rail, and longer spans, you increase the point loading on the rafter. This is where you could see a failure. But when you distribute the load evenly, by using 4ft spans, and alternating rafters, you really won't see a problem with an house that doesn't have any structural deficiencies.

[ButchDeal]

Has anyone come across a scenario in which a rooftop solar system actually weighed Too Much for a home? I'm working with a city to loosen up their permitting requirements and thought that we'd be more successful in drawing more appropriate lines for when an engineering analysis should be required if we actually had examples of when solar weighed too much.

Sure the main problem is ballasted on flat roofs. These should ALWAYS require a stamp.

Then you have pitched roofs and these you have two different mounting techniques: railless and railed systems.
The railless systems reduce structural integrity and should be looked at closely
Railed systems when installed correctly increase structural integrity and should not need a stamp.

any tilted system has greatly added uplift forces and should include a stamp.

[solarix]

Until recently, no one in the building industry envisioned designing roofs with the possibility of putting these solar panel arrays on them. Therefore it is scary to the building departments to allow something that was never intended by the designers. They are very risk adverse you know and subsequently you have to prove to them that the roof is strong enough. Which means some one has to dive into the ASME code SEC 7 on calculating wind loads either (which of course weren't done with solar panels in mind). They want a PE to ok the roof in order to absolve the building dept of liability. I know that there has never been a roof collapse due to a solar array, but that has nothing to do with it. I like the "can't be occupied by live loads" logic - I'm going to use that... thanks.