Roof perforations

[CSFTN]

Hey - lurker in this division TMC. I just bought a new to me house, which I thought would be very good for solar+battery. I'm in a non-Tesla geographic area; I have had a decent amount of communications with a well regarded installer HQ'd in Nashville but do some work in my area, 210 miles to the West. Now that I am in the beginning stages of planning for install in the spring, I find some of the devil's details.

One of these is roof perforations. Attached is a picture of roof, facing SSW. As you can see, this is a pretty good area for panels, except there's a lot of perforations.

The roofing is new but very low quality (placed by previous owner to sell it) so it's going as part of the solar install. I'm planning for traditional asphalt shingles + traditional panels rather than solar glass, for several reasons. First of all, almost no one has solar around here, and I don't want to freak my new neighbors out. Second, is the ROI. Electricity is super cheap around here so any solar install has no ROI, and solarglass = more costly.

So here's the question. Forgetting for the moment about local code, anyone know the details about consolidating my perforations? About 1/2 of them around bathroom plumbing vents, almost 1/2 are furnaces and HwH, and then theres a large attic fan. The fan will be replaced by ridge vents. 2 of the HVAC units will be consolidated into one larger unit, so 1 of those exhaust pipes will be going away. I plan on that being the one smack dab in the middle and keeping the one almost hidden by the chimney.

Thoughts or comments?

PS - immediately in front is a porch + behind it a sunroof, share one almost flat roof without perforations and with a brand new standing-seam metal roof. It is plan A for panels, the main roof is for additional panels as needed for my electric load which has yet to be calculated.

 

[Vines]

Hey - lurker in this division TMC. I just bought a new to me house, which I thought would be very good for solar+battery. I'm in a non-Tesla geographic area; I have had a decent amount of communications with a well regarded installer HQ'd in Nashville but do some work in my area, 210 miles to the West. Now that I am in the beginning stages of planning for install in the spring, I find some of the devil's details.

One of these is roof perforations. Attached is a picture of roof, facing SSW. As you can see, this is a pretty good area for panels, except there's a lot of perforations.
View attachment 599757

The roofing is new but very low quality (placed by previous owner to sell it) so it's going as part of the solar install. I'm planning for traditional asphalt shingles + traditional panels rather than solar glass, for several reasons. First of all, almost no one has solar around here, and I don't want to freak my new neighbors out. Second, is the ROI. Electricity is super cheap around here so any solar install has no ROI, and solarglass = more costly.

So here's the question. Forgetting for the moment about local code, anyone know the details about consolidating my perforations? About 1/2 of them around bathroom plumbing vents, almost 1/2 are furnaces and HwH, and then theres a large attic fan. The fan will be replaced by ridge vents. 2 of the HVAC units will be consolidated into one larger unit, so 1 of those exhaust pipes will be going away. I plan on that being the one smack dab in the middle and keeping the one almost hidden by the chimney.

Thoughts or comments?

PS - immediately in front is a porch + behind it a sunroof, share one almost flat roof without perforations and with a brand new standing-seam metal roof. It is plan A for panels, the main roof is for additional panels as needed for my electric load which has yet to be calculated.

Here's a good link that explains the code around this.

Rules for Rooftop Solar - Fine Homebuilding

Here's the gist of it.

The code now recognizes that plumbing vents may be in the way, but they can actually share the space with solar panels. A complete rewrite of IRC section P3103.1 regarding rooftop DWV terminations now specifically allows solar panels to be placed over the top of plumbing vents. Of course, there are limitations, but they speak directly to the issue—air getting in and out of the vent. The vent, when protected from snow closure by the panel design, can be cut down from the minimum height of 6 in. to a height of only 2 in. above the roof.

The vent opening must communicate with outside air over an area no less than the area of the vent pipe, measured on the inside. For a 2-in. pipe (1-in. radius), that area is 3.14 sq. in. Assuming the pipe is clear around all sides, a panel could be as close as 1/2 in. above the vent and still provide the minimum 3.14 sq. in. of communication with the outside air.

The spaces under PV panels, however, create a cozy place for birds and rodents to nest. Such nesting now has a higher likelihood of blocking a vent, and since it would be concealed under the panel, it wouldn’t be obvious to the occupants, who might realize their drains aren’t working right but wouldn’t know why. To address this, the new provisions require vent terminations under solar panels and solar collectors be protected using a “method” that prevents birds and rodents from entering or blocking the vent-pipe opening.

These new provisions speak to the issues of air movement, snow, and nuisance animals, but don’t specify exactly how to design for them. Installing a screen over the vent is probably not a good idea, as that may create a foundation to encourage nest-building or other debris to settle in place. More commonly, the entire perimeter of the array is screened. A nonspecific code provision allows for freedom of design, but it can also allow more varied interpretation among building authorities.

 

[jboy210]

Here's a good link that explains the code around this.

Rules for Rooftop Solar - Fine Homebuilding

Here's the gist of it.

The code now recognizes that plumbing vents may be in the way, but they can actually share the space with solar panels. A complete rewrite of IRC section P3103.1 regarding rooftop DWV terminations now specifically allows solar panels to be placed over the top of plumbing vents. Of course, there are limitations, but they speak directly to the issue—air getting in and out of the vent. The vent, when protected from snow closure by the panel design, can be cut down from the minimum height of 6 in. to a height of only 2 in. above the roof.

The vent opening must communicate with outside air over an area no less than the area of the vent pipe, measured on the inside. For a 2-in. pipe (1-in. radius), that area is 3.14 sq. in. Assuming the pipe is clear around all sides, a panel could be as close as 1/2 in. above the vent and still provide the minimum 3.14 sq. in. of communication with the outside air.

The spaces under PV panels, however, create a cozy place for birds and rodents to nest. Such nesting now has a higher likelihood of blocking a vent, and since it would be concealed under the panel, it wouldn’t be obvious to the occupants, who might realize their drains aren’t working right but wouldn’t know why. To address this, the new provisions require vent terminations under solar panels and solar collectors be protected using a “method” that prevents birds and rodents from entering or blocking the vent-pipe opening.

These new provisions speak to the issues of air movement, snow, and nuisance animals, but don’t specify exactly how to design for them. Installing a screen over the vent is probably not a good idea, as that may create a foundation to encourage nest-building or other debris to settle in place. More commonly, the entire perimeter of the array is screened. A nonspecific code provision allows for freedom of design, but it can also allow more varied interpretation among building authorities.

Does putting vent stacks under solar panels create any issues with solar panel life due to condensation?

We often see considerable condensation from hot water running down the shower or bath drains coming out of the vent pipes on cold mornings. I am sure this moisture is coming out these vents more often, but only visible when it is cold. Does this moisture have any ill effects on the wiring or electronics on the underside of a cover PV panel?

 

[charlesj]

I would think you could combine vent pipes in the attic and have a larger vent going through where more convenient.
Pipe area is what matters. I have done that on my roof to limit number of penetrations, not for solar reason.
Ask the code people or a plumber on upgrade sizes.

 

[SMAlset]

I could swear I read somewhere and thought it was on our plans but not seeing it when I checked so no idea where I read it now, that the panels shouldn't be placed above heat generating? vents. I know it's not supposed to be by AC units either.

We have Eagle Roofing concrete tiles that use O'Hagin Vents (flat to surface) in a few places and the panels were able to go over these. Looks like these are made for tile, shingle, slate or shake roofs. Made for different weather situations as well.

Products - O'Hagin

 

[bemyax]

@CSFTN In my neighborhood up here in Iowa, any homes replacing a natural gas furnace use at least a moderately efficient unit. These appliances have a closed system that draws combustion air in and exhausts out through PVC pipes at the side of the home. In casual observation I have seen one home with the system exiting up, but there are length restrictions, so I'm not sure how they got away with it.

 

[jsmay311]

Reviving an old thread…

I’m wondering if anyone has gotten a rooftop solar installation done in the last few years that took advantage of the change to the IRC P3103.1 code that allows for DWV vent pipes to be reduced in height as low as 2 inches above a roof so that solar panels can be installed over the tops of them?

If so, I’m curious what “methods” were used to satisfy the language in the code requiring something to be done to “prevent birds and rodents from entering or blocking the vent pipe opening”. I haven’t been able to find any discussions online of any specific approaches that people have used.

For reference, the relevant section of code is here: IRC P3103.1.3

 

[Vines]

I wish California would adopt the IPC, but so far IAPMO is holding strong with the Uniform plumbing Code (UPC)

To answer your question, I have heard of AHJ satisfaction through either perimeter screen the array with pest barrier, or building a small wire cover for the plumbing vent, that still provides code clearances. The idea being that nothing can nest on it because the solar panels are right there.