Thanks for your reply and suggestions.

I believe I should have put in wording that I am asking about a commercial installation where numerous lenghy rows of inclined panels create a complicated aerodynamic system, which is rather different from a garage roof. I assumed that a picture is better than a thousand words and came out to be wrong.

Hi JohnDG,

Just a note to say you sent in what I thought was a very useful BS British Standard in post 1, which I then pasted the sites page further down this thread to try and explain to Anatoli about the need to know the loading on the roofs and wall as well as the loads on the solar panels. But he seems to have refused to view these detail.

I am writing to say there was no way I was treading on your toes, I was just trying to get the correct help to someone it seems (Anatoli) does not want or need help anyway?

Take care my friend. No need for a reply, just letting you know what was going on .

No worries .

Hi Anatol,

Is that link a link to the picture of your set up then?

If it was on a normal sloping roof, sometimes the panels replace the roofing tile or shingle. The Solar panel is not going to weigh more, in fact it is likely to be lighter than the tiles it replaced, (if the tiles were replaced). So no added stress?

It could be said that a roof with a smooth type tile, or Slate would not only be lighter but the wind pressure and stress on the roof is less than a roof with curved Spanish type tile? It is also considerably heavier using the Spanish type tile.

Take care.

Sorry to differ with you, but usually the solar PV panel Contractor does not remove existing roofing tiles, rather the panels are mounted on an aluminum or steel framework which are then anchored to the roof framing or sheathing with special mechanical attachments. That's how they'll be done on my new roof come next week when the PV Contractor decides to get here.......

Solar PV panels can weight anywhere between 5 and 10 pounds per Square Foot. That's considered a DEAD LOAD and is applied down onto your roof structure VERTICALLY.

You don't say whether you have a sloped or flat roof. If you have a flat roof with solar panels propped up like in the photo, then there is certainly a wind force to be reckoned where they'll be a vertical component of the wind force (as determined by vector analysis) directed down into roof. There are several different analysis procedures available to determine the design wind force that'd be acting on the PV panels, and hence, onto your roof framing....ANSI A58.1 and BOCA, etc.. If you're not a structural engineer and not comfortable with performing the calculations to determine whether the additional loads imposed by the solar PV panels and wind loading acting on your roof will cause a structural problem, then I suggest that you obtained the services of a licensed professional engineer (structural engineer) to help you out.

Hello CM,

I thank you for the reply post.

I can understand the weight and stresses of Panels on any roof, especially if it is at an angle on a flat roof, and in addition to fully tiled roof.

However, it depends on the structure of the building, whether it may have a concrete roof, and how and where your building/s are situated with respect to the local valleys and any expected weather and or wind. It may be that your building/s are 'sympathetically' situated with respect to any slopes for instance, and may be low single storey structures?

Perhaps these are not the ideal items to fit to anyplace where there is any possibility of 'Twister's' for instance?

I have seen buildings which have a whole roof full of these Panels but, they are built into the side of a slope or hill with the front elevation only, virtually all of the structure to be seen. Obviously, when and if possible the structure has to be built to support any and all expected load, including contents, and the load of the building itself. On a flat prestressed concrete roof which is tied into the building as a whole then I cannot see this type of structure is going to fail in any way. And just local to me and on a couple of threads here on CR4 a single storey flat roofed structure has been added to with one or more floors.

Of course all this talk is a complete waste of time because any structure, part of or, added too, any building has to have been designed into the overall structure and necessary strength.

I wish you luck, and I will look for details and help from an organisation I am a member of who design and advice about exactly what your post mentions. Homes and other structures which may not be part of the main part, to utilise Solar and other designs to complete a design which suits its locality and each building has included any and all Insulation to help keep it safe and cosy.

This organisation is in the UK but the type of advice they give is relevant to any Country hot or cold. Unfortunately I cannot recall the name at this moment. If you are truly interested please say so to remind me and I will have another look around my place.

Take care

Hello Babybear,

Thanks or the input. I have to agree with you that determination of the Design Wind Load depends on a whole host of factors, including but not limited to, exposure, height of point of interest above ground surface, other buildings and/or vegetation, type of roof configuration, shape and configuration of the surface on which the wind acts, etc etc. That's where the codes such as ANSI A58.1, BOCA, and the like come in and take into account numerous factors used to make an APPROXIMENTATION of the Design Wind Force. Of course there are local and state building codes that still use an Empirical methodology where the designer shall apply a certain wind force (in pound per square foot) acting normal to a vertical surface. Of course, this wind load has to be adjusted to take into account sloped surfaces like the solar PV panels that are a part of this blog.

We don't know what type of structure is in the roof of the commercial building that Anatoli is concerned about. He hasn't mentioned it, nor has he described what type of commercial building and where he is located. I presume he's in Europe somewhere? Anyhow, not enough information has been provided to ascertain whether or not the existing roof structure can safely support any additional dead and wind loads. My experience here as a Structural Engineer in the NE part of the USA is that the original design engineer (if there was one at all) of a building usually picks out the structural members for a roof that have very little reserve capacity remaining in regards to Design Total Load (here in New York State outside of NYC that usually means Empirically Applied Minimum Design Snow Load incl. ice + Design Dead Load). Usually, for a flat roof such as the case for most commercial buildings, a Design Wind Load doesn't usually govern in the overall design choice of a structural member and that includes Design Wind Uplift, which is minimal at best.....UNLESS there is something "propped" up such as solar panels, HVAC equipment, etc, then a Design Wind Force must be used in the design comps that are used for choosing a structural member. Usually in this part of the USA, it is quite normal to have structural steel framed roofs in commercial buildings, and rarely are concrete frames and suspended flat slabs used unless the client has money to burn or has an Architect that thinks he's as gifted as Frank Lloyd Wright or thinks he's another Rembrant, etc, and he has bent the client's ear enough.....you get the picture, right???? Ego's play an important part.

The type of roof framing all depends on what the economies are for the client having the building constructed. It may be quite different there in Europe where concrete is used more in building construction.

IMHO, no matter how the building is constructed and where it's located, my opinion is that Anatoli should have a qualified Licensed Structural Engineer determine if the building roof and superstructure can safely support the addition of a Solar PV system. It's cheap insurance for him to know that his huge investment in the panels won't be a waste of money in case the building roof fails. Too many times I personally have found that the addition of any new equipment (such as solar PV, radio equipment, HVAC, Cellular telephone equipment) placed on an existing commercial building, be it steel or concrete framing, usually requires that the existing roof framing to be beefed in order to safely support the additional equipment.

Then again, he can roll the dice and see what happens' to his building roof sometime in the future.......

Hi Anatoli,

Please check out these sites which may give you the stress/loading factor you require.

It would have been a great help if you had given more details of the structure, concrete, metal roof, wall load carrying etc?

This is the search field:

http://www.google.co.uk/search?q=chart+for+load+stress+with+solar+panels+on+a+factory+roof&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-GB:official&client=firefox-a

1. Articles | Creating the Vision | ReliabilityWeb.com: A Culture of ...10 Sep 2009 ... Factory Ventilation (HSE). With conventional north light roof ... With stand-alone units, we could never load the machines fully. .... Delivery of the solar panels would take 6–8 months, so we phased the project into the second year. ... The charts showed that after installing the air receivers, ...
   www.reliabilityweb.com/index.php/.../creating_the_vision/
2. [DOC] DIVISION 13 - SPECIAL CONSTRUCTION File Format
   Single source factory fabricated and installed aluminum clear span ... Performance Organic Coatings on Architectural Extrusions and Panels. .... Where permitted by code, a 1/3 increase in allowable stress for wind or seismic load shall be ... Owner's choice from standard color chart. Motorized roof sash, including ...
   www.wisconsinsolardesign.com/manuals/Solarium%20specs.doc
3. Plugged In - JSOnline A Madison utility will install solar panels on the roof of the State Capitol ... glass for use in photovoltaic solar panels. The factory employs 54 people. ...
   www.jsonline.com/blogs/business/pluggedin.html?tag=solar
4. [PDF] high-performance building with energy-efficient File Format: PDF/Adobe Acrobat
   10-foot by 40-foot solar electric roof panels, each with 12 flexible photovoltaic modules factory laminated to the surface of a vinyl carrier mem- ...
   www.vinylroofs.org/downloads/news/vinyl_roofs0407.pdf

Take care and please get back to me when necessary.

Thank you for all answers.

The roof in question is flat. Its construction is really beyond the question. What I am looking for is a tool/method to estimate (!) an additional load on the roof created by a solar PV system. I do not need engineering level calculation I only need a tool to pre-qualify roofs for a PV installation at a feasibility study level.

I certainly understand that an actual project shall require detailed analysis performed by a licenced structural engineer. At the same time, I hope that wind load can be estimated at a much lower cost. I suppose geometry of panels and historical wind data should be sufficient to estimate an additional load with +/- 20% precision.

Any practical suggestions?

Hello Anatoli,

You make no mention of one of my previous posts which lists a search page plus several other sites which may be of use.

You may well get some information if you send the geometry of the roof and panels to the local Weather Station.

You also say the roof construction in "beyond the question"? Well please allow me to differ. Any pressure on the roof by and including its own design, the panels, and the wind and weather (snow for instance) is completely to do with any design of the roof and factors I have mentioned.

You flat roof may not be much more the some 7" x 4" (~175 x 100 mm), or it may be a 6" (150 mm) concrete slab, which is or is not bound to the walls in some way.

To say I find your 'throw away' remark that the "construction" has no bearing on the design of anything subsequently fitted to the roof and building, completely unbelievable.

Our searches may find a completely separate software package for say, plastic as apposed to concrete roofs so it is very much part of the equation when searching for such software............

I will continue to search for the software requested but you really should, out of courtesy, give details of the roof and any supporting beams. And in all honesty, the structure of the buildings walls and foundations should also be part of your design outlines, as should the position of your building in your local terrain and compared to any other local structures.

Take care and no offence intended.

Dear Babybear,

I appreciate your comments and I did look at all your links. None of them comes even close to my question.

I'll try to explain my need again. I want to have a tool (preferably Excel sheet) that would allow me to pre-qualify a commercial scale (min 1000 m2) roof for a potential PV system installation. I really think I not need to go into details of roof construction as I do not want to find out if the roof is capable of carrying my system. Instead I assume that I know how much load a roof can tolerate and want to project that capacity to the design of PV system. I hope I have made myself clear and you will be more comfortable to agree that in my case roof design does not really matter. It will definitely come into play if/when the actual system is designed, for now - I do not have care. imho.

My business case is based on two contradicting demands: (1) my optimal pitch is 30 degrees; if I go lower I "underpoduce" electricity, (2) higher pitch causes higher load. As well, lower pitch allows to put rows closer and squeeze more panel on the same roof.

Hello Anatoli,

Thank you for the extra detail you thought and deemed necessary, but no thank you for your limited discussion about the apparently important detail you saw fit to keep from me.

You say in part you do not care, however, I do care and will point out what should have been obvious to you, had you read the posts on this thread.

NOTE: The post #1 of JohnDG gives the details you require. If can find time and courtesy to check this out below you will see in has a BS (British Standard) on this subject which explains how to work it out.

There are other sites on the JohnDG post #1 which may be of help.

I suggest you post and thank JohnDG for this information. It is the very least you can do, when you obviously took no notice whatever (apparently) on what appears to be a very useful site and sites listed by JohnDG

ORGANISATIONS Homepage Benefits Save CO2 CO2 Calculator Save Money Carbon Solutions Consultancy Accreditation Energy Training Partners

Home > Organisations > Active Roofs > Wind Loading Active Roofs Issues around Wind Loading Wind loading on solar panels depends on three basic elements: the wind speed, the height of the panel above the roof, and the relative location of the panel on the roof. The EurActive Roofer project undertook numerous wind tunnel tests using scale models of roofs with panels, as well as testing theoretical calculations that can, in time, form the basis of a European standard. Although the findings are complex they can be summarised as follows. Wind Speed, Pressure and Loading Map courtesy of BRE. The Shetland Islands are in Zone VThe wind loading needs to consider the maximum recurring wind speed and not, as is used for micro wind turbines, average speeds. The map above shows UK maximum speeds in metres per second and, in broad terms, no normal solar panel properly fitted is likely to add an unsafe wind loading to a typical UK roof in zones I to III so a simplified calculation method can be used. Special attention needs to be paid in Zones IV and V, principally North and West Scotland and the Northern and Western Isles. Where more detailed calculations are required, BS6399: Part 2 (Code of practice for wind loading on building structures) should be used, or - when available, the Europan standard on wind loading EN1991-1. The calculation process has six steps: Determine Site wind speed Vs Determine Effective wind speed Ve Determine Dynamic pressure qs = 0.613 Ve2 Determine external surface pressure pe Determine internal surface pressure pi Determine net load on the PV module P = (pe - pi) A This web page will not attempt to show all the factors brought in, but the information required includes the building height, altitude, distance from the sea, the distance from edge of town, site altitude, topography, distance to and height of surrounding buildings and other factors for all 12 wind directions. BRE Digest 436 gives more information on this process and there is a BRE program BREVe. BS6399-2 gives external pressure coefficients for a wide range of roof shapes including flat roofs, monopitch roofs, traditionally pitched roofs and hip roofs, but does not specifically address PV or other solar panels. The diagram above shows a schematic plan of a pitched roof with wind coming from two directions (West and South if North is the top of diagram), showing the various wind pressure zones on the roof for which calculations may need to be undertaken. In zones I to III it is often possible to use a simplified formula for the wind force F = q sCpnetCaA Where: qs is the dynamic wind pressure Cpnet is the net pressure coefficient Ca is a size effect factor that reduces to a value of 1 for an array under 5m diagonally across, and A is the loaded area of the PV module. In this case the dynamic wind pressure (qs) can be found from reference tables that consider just the building height, altitude, zone and whether local topography is significant or not. There are two values needed for the net pressure coefficient - one for potential uplift and the other for the downward force. Panel Height and Design The project had earlier identified five basic arrangements of panels. In essence, for traditionally mounted panels on the surface of a roof, Cpnet can also be found from tables, with the values varying on whether or not they are within 300mm of the roof edge - so this becomes an important design feature. The type of fixing is also crucial for traditional stand-off panels. Hook fixings must not be so flexible that they significantly lift the surrounding roof tiles. The maximum gap between tiles with a hook installed should be less than 6mm and it is recommended that maximum deflection of the hook should be less than 70mm at the design wind load. This can be checked by applying the design wind load to a hook or dummy roof using weights and a pulley system and measuring the residual deflection. Integrated designs that are nominally airtight can be treated like any other roof cladding in accordance with BS6399-2 (providing they do not protrude from the roof by more than 100mm). Air permeable roof tiles or slates also use a variant on the simplified calculation method, with some allowance for whether or not they fit onto the main roof battens directly. The situation for PV modules on flat roofs is a little more complex, depending partly on whether they are mechanically fixed or free standing. Both will need to resist wind uplift but freestanding modules will also need to resist sliding. Wind loads will depend on the location of the module on the roof, whether the roof has a parapet and whether the PV support structure is open (above left) or fully clad (above right). Calculations will also need to consider where the modules are on the roof, with different net pressure coefficients applied for those near the edge, in corners or at the centre of the roof. On flat roofs, a key calculation can be to determine whether there is a risk of overturning; for this the mass of the unit and ballast must exceed the wind force (moment), which is turn affected by the angle of inclination of the panel. NEF would like to thank BRE and the other partners in the EurActive Roofer project for their assistance with this page. The information given is for guidance only and should not be used in place of proper engineering calculations in accordance with the relevant British Standards.

Hi Anatoli,

You may find your answer here. It also included

http://www.greenroofs.com/archives/sustainable_editor.htm

Take care

Dear advisers,

Thank you for the time you took writing your comments. I have read each post attempting to answer my question and checked every link. Pity that some of you have invested so much time answering questions I did not ask. I feel sorry for the well intended but wasted effort.

John, moon, thank you for no bs suggestions.

Capt, baby, you are adorable! Forgive me, but I skipped all your behavioural opinions; got no time for that.

Enjoy!

Anatoli,

Babybear's #11 posting said it all in regards to your actions herein. Enough said about that.

As far as my comments, well let's just say that I tell it the way it is and I don't pull punches, ever. In response to your childish outburst: I would not describe my comments "babyish" in any way.....I'd say that they were pretty much "SPOT ON" in regards to your behavior in this forum, especially when it comes to withholding vital information from CR4 members trying to help you, nor were you too clear about exactly what information that you wanted from the get go buddy. I truly don't mind helping people when it comes to engineering concerns, but when those same people disregard mine and others advice then I have a big problem with that. If you had been one of my clients and acted the way you did so here, then I dear say that I'd discharge you and would not further represent you in any way. That is something I've never done before with a client in 32 years as a Professional Engineer, but I'll grant you this in that you'd be the first. Congrats Anatoli!

If you want free advice I suggest that you go and seek elsewhere, lest you become a real pest around here.... because what you seek here and what you'll get from us from now is a BIG FAT ZIP, plus a big wave bye bye as I and others here kick your arse out the door!

That's all I will say about this from here on in about this blog. I have better things to do than get "played"......

"What we've got here is failure to communicate"

PERFECT!!!!!

****LMAO**** @ Guest's comment!!!!!!!!!!!!!!

Not at all. I happened to have a productiove communication with people capable to share knowledge.

For those interested in content I'm willing to share my findings:

http://web.dcp.ufl.edu/chini/courses/bcn5584/pp/3.ppt#1

http://cr4.globalspec.com/thread/24760#newcomments

windloadcalc.com automates the process of calculation

Authors, both experienced engineers, explain how to calculate wind loads based on two slightly different standards. As expected and I tried to explain, there is nothing about roof structure there, it's all about wind load.

Have fun educating yourself ;)