Metal Roof, Uplift Issues?

[So Cal]

I have never installed on a standing seam metal roof. I know where to get the hardware and that each metal panel needs a bonding lug.
Has anyone had to prove wind uplift resistance with the metal roof? I figure the hardware is good at the PV to standing seam attachment but possibly the standing seam roof attachment down to the structure undernieth uplift resistance may not be sufficient for a retrofit pv array's increased uplift load? Anyone run into this before?

 

[GoldDigger]

I have never installed on a standing seam metal roof. I know where to get the hardware and that each metal panel needs a bonding lug.
Has anyone had to prove wind uplift resistance with the metal roof? I figure the hardware is good at the PV to standing seam attachment but possibly the standing seam roof attachment down to the structure undernieth uplift resistance may not be sufficient for a retrofit pv array's increased uplift load? Anyone run into this before?

Even for a conventional shingle roof, the attachment for the PV rails generally has to be connected to the framing under the roof, not just the plywood sheathing. The reason for this is the uplift resistance required. At a minimum, you would need to fasten to the plywood in a way which supplies pull out resistance on the far side of the plywood and then make sure that the sheathing's attachment method can carry the additional uplift forces.
The uplift of a section of a PV array can easily be twice what the uplift would be on the roof itself without the array.
If your choice of hardware attaches only to the metal roof material and does not carry the load through directly to the roof supports, chances are very good that it will not meet design requirements.

Many jurisdictions will require either a local P.E.'s signed design drawings or an engineered solution from the rack manufacturer that includes detailed attachment instructions.

 

[iwire]

We fasten to the standing seam all the time, no extra work needed.

However pretty much every roof mounted array we do gets a mechanical engineers blessing for roof loading etc.

Here is a job the company recently did, not much roof engineering on this one

 

[cowboyjwc]

We fasten to the standing seam all the time, no extra work needed.

However pretty much every roof mounted array we do gets a mechanical engineers blessing for roof loading etc.

Here is a job the company recently did, not much roof engineering on this one

When are you going to start doing some big jobs?

 

[cowboyjwc]

We require engineered calcs on every job, so the type of roof doesn't matter as much as what the roof is attached to.

 

[SolarPro]

Here's a link to an article about best practices associated with using S-5! clamps for attaching PV systems to metal roofing systems:

http://bit.ly/1gdcEW0

With existing construction, you typically need to determine the attachment method and frequency used between the metal roof to the roof deck, then work with a PE to determine whether the existing roofing system can accommodate the additional loads associated with retrofitting a PV system. If this is new construction, you can work with an engineer to specify an optimal roof gauge and attachment frequency for the array area.

 

[mgookin]

The start of any wind loading evaluation is what is the design wind speed for the zone the project is in.

So...where's the project?

 

[So Cal]

The site is Hollywood, Ca. In the hills above sunset strip. in a tree filled canyon.