How to tell if roof can handle solar panels?

[foo]

I have a roofer that will install 10 x 100 watt panels onto my roof for an off-grid/battery application.
How do I know if the roof can handle the panels?
The roofer mentioned using two beams of pressure treated wood attached to the roof so that the panels will be mounted to those beams.
Does that strengthen the roof structure enough, is that amount of panels not that heavy, should I ask more questions?

Thanks for any information.

[solar pete]

Hi Foo

You just dont attach panels using wood (you use the wood to create a structure to mount the panel rails), well we dont anyway. Those little 100watt panels are not that heavy, so if you can walk around on your roof no worries you should be fine. If you cant walk and or jump around on your roof then you probably have issues.

[J.P.M.]

I have a roofer that will install 10 x 100 watt panels onto my roof for an off-grid/battery application.
How do I know if the roof can handle the panels?
The roofer mentioned using two beams of pressure treated wood attached to the roof so that the panels will be mounted to those beams.
Does that strengthen the roof structure enough, is that amount of panels not that heavy, should I ask more questions?

Thanks for any information.

The weight's not the issue. Wind loading is probably more important; seismic and dead loads probably to a lesser degree. Depending on where you are, permitting and plan check will require you or your assigned vendor to account for such things before permits will be issued (if required).

[Sunking]

Let me guess you did not have a Structural or Electrical Engineer involved in the project?

[foo]

Hi Foo

You just dont attach panels using wood (you use the wood to create a structure to mount the panel rails), well we dont anyway. Those little 100watt panels are not that heavy, so if you can walk around on your roof no worries you should be fine. If you cant walk and or jump around on your roof then you probably have issues.

Oh yeah, I've had three guys walking around on my roof without issue. Installing vents and satellite dishes.

[inetdog]

Installing vents and satellite dishes.

Make sure that you take the shade from those objects into consideration when laying out your panels.
You do know that the cost per watt for 200-300W panels is far lower than the cost per watt with 100W panels? Is the space on the roof to small and oddly shaped for larger panels?

Make sure that you provide at least 4" clearance between panels and roof and allow for free air circulation. The idea of solid wood members does not sound good for that aspect.

[sdold]

It also sounds like something that would dam up rain water, if installed horizontally across the rafters.

Beware that wind uplift force on the array can be much more than the weight of the panels.

[foo]

I'm going to keep doing research.
I'm realizing I'm very far off from making an informed decision on what I should/can do.

Thanks for all the info.

[Mike90250]

...the roofer mentioned using two beams of pressure treated wood attached to the roof so that the panels will be mounted to those beams.....

Ha. the roofer has kids and you are going to send them to college for him! PT wood is useless on a roof, it will twist and warp. But it won't rot.

There are commercially made rail/rack systems that mount on roofs, and hold the panels. They even come with certs to meet codes.

You will need to have the roof plans certified by an engineer to both hold the weight, and the wind load. Or you may have to consider a pole mount in the yard.

But you CANNOT bolt some lumber on the roof and attach panel to it. That will fail any inspection.

[inetdog]

But you CANNOT bolt some lumber on the roof and attach panel to it. That will fail any inspection.

Or if not inspected, it will simply fail.

[russ]

Ha. the roofer has kids and you are going to send them to college for him!

Pressure treated wood is about the worst idea possible - the roofer has shown he has no idea.

[Krazy1]

Pressure treated wood is about the worst idea possible - the roofer has shown he has no idea.

^^^This^^

I'm a roofing contractor in Florida. Run from this guy because he has no clue. I'm assuming you have a shingle roof? If he bold 2'X6" directly to your roof, it will impend the flow of water causing it to back up under your shingles. This is where the real damage begins.

[foo]

Well, I came back here with what the roofer thought was a solution to the damming problem.
The roofers suggestion was to place the 2x4's on 1x2 shims that are placed underneath the 2x4's at an angle.
The thinking there would be that there would be run off.

After reading the feedback here I realize I will have to do some research on mounting brackets.
Are there mounting rails that will add to the integrity/strength of the roof?

Thanks for the added info.

[sensij]

Well, I came back here with what the roofer thought was a solution to the damming problem.
The roofers suggestion was to place the 2x4's on 1x2 shims that are placed underneath the 2x4's at an angle.
The thinking there would be that there would be run off.

After reading the feedback here I realize I will have to do some research on mounting brackets.
Are there mounting rails that will add to the integrity/strength of the roof?

Thanks for the added info.

Is there any reason you can't reinforce the roof properly, from underneath? I'm not an expert, but doubling up the rafters, or adding trusses, seem like they could be fairly inexpensive things to do.

The commercially available rails are engineered to hold the modules, assuming a good roof. If you want rails that also help the roof, you'd need some help from a structural engineer.

[foo]

There's a room right under that part of the roof.

I will have to see if opening the room's ceiling is something the roofer can do or if that will have to be contracted out.

Actually I'm considering the engineer idea. Looks like I need someone with some brains on how to best approach this.

What does it cost to hire a structural engineer for work like this?