Snow load calculation

[masona]

Thanks, done the rough calculations

474 OBS plywood = 14220kg
EPDM 1mm thickness roof area 1390 m² @ 1.27 kg m² = 1765kg

Therefore total weight of roofing materials approximately 15985kg

207 Solar panels total weight = 4413kg
622 concrete slabs @ 25 kg each = 15550kg.

Therefore total weight but NOT including the weight of the solar panels bars = 19963kg

Am’I right adding 15% to the total roof materials weight of 15985 therefore = 18382kg.

So in theory they have gone over the 15% weight limit?

I have checked the structural engineer reports, they have measured the building outline length at 55.000m x width 31.000m

I have checked this 4 times and I make it, length 42.700m x width 32.540m.

 

[jeds]

Dead load of around 0.26kN/m² will be less than the original design load. Add 0.75 for snow and wind and you've only got about 1kN/m². That's pretty low. My view remains that the load isn't an issue. It's the detailing and design of the roof alterations that are at fault.

 

[masona]

I make the final measurement of the building length 42.800m x width 31.700m but the structural engineer worked out the calculations on a bigger roof span (L) 55.000m x (W) 31.000m so in theory it's the wrong calculation?

I'm wondering if they done this so they can put more solar panels up because on the their first page quoted;

"Addition of Solar Panels Array to South facing roof will use up most of the residual strength of the roof and therefore the installation of hung ceilings, air conditioning etc. may be impossible without strengthening of the roof structure"

Also if the solar panels weight is more than 15% of the roof covering then building regulations apply which they didn't do.

 

[masona]

We've got our own independent Structural Engineer to check our roof, oh dear!

I know you cannot give me a proper answer, would you say it's safe under the building for the time being until it's sorted out?

Further to our recent visit to your property, we write to confirm our advices. You appointed us to advise on the issue of roof overloading due to the addition of solar panels fitted on a weighted ballast dead-bearing system to avoid penetrating the roof membrane.

We duly inspected the roof internally and externally and noted a degree of excessive deflection in the z-purlins leading to undulations in the roof surface. We have undertaken a structural calculation (to BS5950) of the most heavily loaded of these z-purlins (i.e. the ones at or near a row of ballast slabs where all the solar panel load is applied) and attach separate load calculations (for clarity of the loading build-up we have used) and the design calculation itself (based upon the maximum bending moment and shear forces obtained from the load calculations).
These show that the z-purlins are significantly overloaded and fail by a large margin in buckling, the applied major axis moment under full snow load (7.88kN) being 4.865 times greater than the purlin’s buckling resistance moment capacity. In the circumstances, we consider that some remedial action is required to rectify the situation.

 

[masona]

I have written to the Building Control Office about the Document A regards anything that's over the 15% increase of the roof covering as needing to be checked.

Their reply,

As the work has been completed over a year ago the Council are unable to take any action under the Building regulations, unless the premises were to fall into a dangerous condition, at which point the owners would be contacted to take remedial action to ensure the safety of occupants

So basically build something against building regs then you're okay after 12 months

The problem with solar panels is that they are usually installed under a competent person scheme whereby the electrician self certifies the whole installation including the electrics, the structure etc under a CPS.

So you don't have have to be in a Competent Person Scheme if you're qualified tradesman

 

[jeds]

masona, the building regs thing is correct. No enforcement after 12 months. But, in any case, the enforcement would be against you - not the solar panel people - so it would still be your responsibility to pursue them.

I'm still a bit confused about the loadings. Going on your figures and your smaller dimensions the dead load is less than 0.25kN.m², which isn't a lot in roofing terms. Your engineer is calculating nearly 8kN on the Z purlins (which I take to be total load) but that means each purlin must be bearing getting on for 35m² of roof. Does that sound about right? (35m²) And that doesn't include any live load, which is typically three times the dead load or more.

Obviously your engineer has got sight of the building so there's no suggestion he is wrong. It sounds like you've got a double whammy here; the roof was way over loaded by the solar panels but was also way under spec'd when it was built. AND, was not detailed that well either, which isn't helping.

Bottom line though is the solar panel people should have advised you not to proceed and I think you should pursue them over that. Did your engineer offer any solutions? Can the roof be strengthened or are you looking at removing the panels?

Also, I hate to say this but the roof might be in real danger if it snows heavily. So keep an eye on the weather.

 

[masona]

Thanks Jeds,

I'm still a bit confused about the loadings. Going on your figures and your smaller dimensions the dead load is less than 0.25kN.m², which isn't a lot in roofing terms. Your engineer is calculating nearly 8kN on the Z purlins (which I take to be total load) but that means each purlin must be bearing getting on for 35m² of roof. Does that sound about right? (35m²) And that doesn't include any live load, which is typically three times the dead load or more.

I'm not sure & I don't think so(?) from what I have seen is the Z purlin (150mm) are 1.5m centre, 6.5m lenght from trusses to trusses. We have 6 trusses over 42m wide plot

Also from the solar panel engineer 2nd visit report is difference, now they recommending 40mm birch plywood when we have 18mm OSB ply and this is the first time they've mention the plywood thickness.

Our engineer suggested either strengthen the roof or take the solar panels off.

IMO it's impossible to strengthen roof without taking off the solar panels, all the plywood and rip out all the membrane and start again. I can't imagine the costs alone!

I think the easiest would be to take off the solar panels off then leave the roof alone but the next problem from what I understand is the solar panels are owned by an investor company.

Gonna get messy!

 

[jeds]

Sorry, just re-read it and they do include snow load, which makes a bit more sense on the total loadings. Looking at load tables for Z150 single span purlins at 1500 centres gives you 0.81/m which over 6m span is bang on 4.86kN.

But that doesn't explain the immediate severe deflection. The engineer calculates 7.88kN but a good part of that is live load which isn't currently present. So the purlins should not actually be exceeding their design limit. Still, you can bowl on for a while without having to keep looking up.

 

[masona]

But that doesn't explain the immediate severe deflection.

Got to be because there's no noggins and extra timber joists to support the 18mm plywood

 

[masona]

I have written to the Building Control Office about the Document A regards anything that's over the 15% increase of the roof covering as needing to be checked.

Their reply,

As the work has been completed over a year ago the Council are unable to take any action under the Building regulations, unless the premises were to fall into a dangerous condition, at which point the owners would be contacted to take remedial action to ensure the safety of occupants

Right this is the situation now, Sika Technician reported that the solar panel installers used the wrong slabs protection mat which is a torch on bitumen felt sheet as this will have a chemical reaction and will disintegrate their membrane hence why we have a leaking roof.

All the solar panels and slabs will now have to come off from them to inspect for any damaged, am'I right assuming they would have to apply for the Building Control Application because of the Document A of the 15% weight increase in the roof covering?

So basically the question is, before they refit the solar panels back on they would have to apply for the Building Control Application?

Sadly because of this our membrane warranty is now void