How to install solar panels over plumbing vents
To install solar panels on your house, you need a clear section of roof. Unfortunately, obstructions like plumbing vents can get in the way. You can give up the space, but there are solutions.
That’s my house in the photo above. As you can see, it’s got a nice, neat array of solar panels except for one spot where a pipe is sticking out. Darn it!
My array doesn’t cover all of my electricity needs, so having one more panel would have been nice. Plus, it would simply look better if there wasn’t a gap in the array.
I wasn’t a solar nerd back when I had my solar installed, and I’ve learned a few things that might help you if you’re facing a similar situation.
Roof vents, plumbing stacks, skylights, and other impediments to installing solar panels
A house has a lot of working components: heating, cooling, plumbing, and ventilation, for example. Many of these things use space on your roof for ventilation. For example, an unfinished attic requires ventilation to remove moisture. Plumbing requires air to allow water to move freely into drain pipes. Kitchen fans, bathroom fans, and furnaces might vent their exhaust gases through a pipe in the roof too.
Along with skylights, you might encounter some or all of these components on your roof. An otherwise uninterrupted surface for solar panels might be dotted with several protrusions, reducing the number of panels you can fit on your roof.
There isn’t a solution for all cases, but when it comes to roof vents and plumbing stacks, you do have some options.
Installing solar panels on top of plumbing vents
A plumbing vent is a small pipe that allows air to enter drain pipes or sewer gases to escape. They are small, usually between 1-1/4 to 4 inches in diameter.
Local plumbing codes will dictate how high above the roof surface the vent must rise. A common requirement is that the pipe must rise six inches above the roof. For example, California Plumbing Code section 906.1 states that “Each vent pipe or stack shall extend through its flashing and shall terminate vertically not less than 6 inches (152 mm) above the roof”.
In snowy climates, it’s common for the requirement to be six inches higher - that is, a full foot above the roof.
If you happen to live in a municipality without any such code, it may be possible to install solar panels right on top of your plumbing vent. A rack of solar panels sits about 5 inches above the roof surface. Where permitted, the vent pipe can be cut down to just a few inches above the roof surface so that it can sit in the space underneath the panels.
That doesn’t mean it’s a good idea. The International Association of Plumbing and Mechanical Officials (IAPMO) works to bring uniform guidelines to plumbing in the US and internationally, and it’s this guidance that California and other codes are based on.
Diverting vent pipes: exceptions to the 6-inch rule
IAPMO does make an exception to the 6-inch rule for vent pipes that are 1-1/2 or 2-inches in diameter. For these smaller pipes, it’s permissible to divert the pipes around solar panels.
If a pipe that’s giving you trouble is of a smaller diameter, you can use a product called the Solar Roof Jack to divert it so that it terminates either in the gap between two solar panels or at the edge of the array. The installed product looks like this:
A single Solar Roof Jack currently lists for $65 on their website, so it’s not a very expensive solution. The Jack includes flashing to ensure that the installation remains watertight.
Per IAPMO guidelines, this type of diversion is allowed only for pipes 2 inches in diameter and smaller.
If your solar installer isn’t aware of the guidelines allowing these pipes to be diverted, you can point them at IAPMO IGC 339‐2016.
You can’t install solar panels over exhaust vents
When it comes to exhaust vents, such as those for bathrooms and kitchens, you unfortunately can’t install solar panels over them. Condensation would be detrimental on the rear of the panels, where wiring and electronics like microinverters and power optimizers are mounted.
If you have exhaust vents, unfortunately your only options are to install your solar panels around them, or pay to have the vents moved.
The cost of relocating a roof vent
According to homeadvisor.com, the average cost of installing a roof vent is between $300 and $550.
If you’re relocating an existing vent, there are additional costs because the old vent hole must be patched and make waterproof.
If you’re redoing your roof, consider a ridge vent
The best time to install solar panels is when your roof is new. If you’re thinking of having your roof redone, you should talk with your roofer about how to minimize the number of obstructions on the roof. One method is to use a ridge vent instead of box vents.
A ridge vent is installed along the peak of a roof, where it won’t interfere with solar panels. These can take the place of bulkier box vents. Check with your roofer to ensure that this type of vent is appropriate for your attic.