Backflow preventer in sprinkler system... or check valve?

I've worked on sprinkler systems but just small things. I'm in the process of replacing the valves and moving them to another side of the house. The current valves are anti-siphon as are the replacement. I figured the anti-siphon was all that was needed, as there is no backflow preventer or check valve on the current system. I wasn't aware of them until I started researching the project, but now realize I need to add an additional mechanism, especially since there will be a line without a sprinkler valve, just a ball valve for a greenhouse.

I initially thought I could us an in-line pvc check valve, however as I look into it further it appears I need/should install a backflow preventer, which is different than the check valve. And a LOT more expensive. Crickey! The least expensive BFP I could find is $100, and they won't survive even one night of freezing temps. A freeze compatible version is about double that.

Is this a must do, or will the anti-siphon and check valve suffice?

 

A back flow preventer is a good idea if you are using your home’s potable water line to run your irrigation. The preventer keeps potentially contaminated water sitting in your irrigation system from being pulled into the house system. It should be installed where you pull the water off your inlet to feed your irrigation. Is the BFP brass?
Lots of systems don’t use BFPs, but it’s a better practice to have it. If you sell your home, the inspector may ding it.
I run one because I pull water off my line before the regulator and regulate it to a much higher pressure than the house side of the system. I run both irrigation valves and spigots on this system and there is a good chance of water being pulled back into the house lines especially with the spigots.

 

It's this one. As far as I know, there isn't a regulator for incoming water anywhere either. House was built in 1961 and was a 1 owner house when I got it. Not a lot of updating happened before then. On the fence about just using the check valve I have, or biting the bullet and do the BFP. I guess $100 is not bad insurance against bad water. FFS, the greenhouse build project has become Scope Creep palooza! Lol. Can't wait until I start running power out there...

 

I would bet you are okay with a check valve, but the BFP might be good insurance, even if you have to wait a bit on it. If it were me, I would regulate the pressure going to the house side of the system. It should be 55 lbs. a lot of the valves and accessories in the house don’t tolerate pressure spikes well. I know it’s not what you want to hear, but a popped valve while you are out will be a mess.
I get the creep on a greenhouse project. My Dad is on his fourth greenhouse we have built in my lifetime. This one is 30 by 40. My Dad grows orchids.

 

Nice. Ours is going to be much smaller. Mainly to house tropical outdoor plants in the winter. I'm already thinking about scaling it back just a bit, depth wise. The width has been decided based on the windows and door we have. The side windows were laid out and came out to about 5 1/2 feet and I had the original depth at 7 feet. I'll probably reduce it to 6 feet. Less space to try and fill

 

Very nice. I’ve thought about building a small one myself. It seems, at some point in one’s life, you begin to turn into your parents.

My Dad spends most of his day outside. My parents have a fairly large lot for a suburban, So Cal home. They have .75 acre with the greenhouse, a small fruit tree orchard, a garden, a pretty large koi pond, and entertainment areas. My Dad is 82 and he will never be pried out of that home. We’ll probably find him passed away in the greenhouse or garden, which is how he would like it. Not a bad way to spend retirement.

You should post up your build as it comes along. What part of the country do you live in?

 

Your parents property sounds like a dream. I feel fortunate to have a 1/4 acre but would love to have more space. I'll post some pics once there's something to see. Right now I'm dealing with the sprinklers. Not just moving the valves, but recommissioning an old disconnected sprinkler line that runs under where the GH is going. That's how I'm able to plumb water in it.

I'm up in Sac now. For a time back in the early 90's I lived around your area in Upland. Do not miss the traffic!

 

Yeah, growing up my sister and I wanted a pool and horses. We got a koi pond and a green house I guess we did get a really big spa though. Also, my Dad and I built just about everything on the property and did all the upgrades to the house which was a really good learning experience. They bought the house new in 1978 and there was nothing, not even walls, once you got to the back yard. When I think about all the work that has gone into it over the years, it makes my head spin a little, but I wouldn’t trade it for anything. I still have some PTSD from all the tree trimming and trench digging though.

The traffic has gotten worse. When I was in HS ( early 80s), I could take my dog for a walk and not ever see a car. The city has become too interested in building. Same story with all the foothills communities along the San Gabriels. They live up the hill from us, right against the San Gabriels in what I guess you would call old Alta Loma (We’ll never call it Rancho Cucamonga).

Okay, so we have similar climates. The biggest challenge with my Dad’s stuff has been regulating temp and humidity in the summer. Orchids are pretty sensitive to variations here. I don’t know if you will have any of the same issues, but if you do, I’ve already been through the learning curve here.

 

Not so much with humidity, but the heat... yikes. We're on a week of triple digit highs, 101, 103, etc. Good thing about the location of the GH is it's shielded from full sun from noon to about 5pm by a large maple tree. In the winter the leave will be gone so it will get full sun then. I'm looking at these automatic window openers for the transom windows along the front. No power needed, opens when temps hit 75 or so. We're also planning on installing landscape shade cloth across the interior ceiling on pulleys, like roman shades, to block sun as necessary.

 

I think my Dad’s setup is similar. He uses a set of similar windows on the roof and has a screen door at the entry. The solid door stays open when it’s hot, air flows in and out the roof while picking up moisture. He also has shade cloth on the roof to moderate the solar radiation. He also uses a swamp cooler and misters to keep the humidity correct. There are roof level misters which sort of create an artificial rain periodically and others at the bench level which keep the gravel floor wet. It keeps the humidity in the right range for his orchids. There is also a reverse osmosis system to keep the water soft. This is largely to keep hard water deposits off the leaves because he shows his plants.

The greenhouse sits below grade. The two built, at this residence, prior to this one were at grade. The Santa Ana winds had damage them as there is little protection at the back of the property. One looked like it had been hit by a car. Over the years, the city has cut down many of the Eucalyptus used as wind breaks when this was all citrus and grapes. The horse trails in back of the houses were all lined with them, but most are gone now.

This one was built in 1999 when my Dad retired. He decided on the concept, and I designed the structure. There was an existing pad for the old footprint. We had a guy come in and cut a larger, lower pad, then excavate the footprint out to the length and width dimensions and four and a half feet deep. We built a footing, and retaining wall all around. Cut holes for utilities, and back filled the exterior space with gravel. The property has some terracing because it’s against the foothills.

After that we framed the walls and built the roof trusses. It’s clad with hollow core lexan sheets used for greenhouses. We built the benches, I welded together a steel structure for the exterior shade cloth. I also did the water and gas plumbing, and electrical. The floor is weed barrier at the bottom, then sand and gravel. It hold the moisture for evaporation/humidity and keeps the soil and gravel from becoming mixed.
The below grade design was primarily for wind protection, but it also made the environment easier to control, so it was a win/win.

My Dad thought about an aluminum one for a while, but in the end he really wanted a stick built structure with the architecture he likes I guess it looks like a nod to the Craftsman style architecture you see a lot in So Cal.

Because my parents are getting older, we have had to have some conversations about what to do when they are gone. The orchid collection is going to the Huntington and the Arboretum. We’ve talked to them about it and they are interested as my Dad has some rare plants. He also has some cacti and succulents which are rare and protected and will also go if the house is sold. It would be a shame for someone to destroy them to dig a pool or something.

I’m thinking of moving out of state when I retire and have thought about building something similar to what you have in mind. I’m looking forward to seeing your build for some ideas.