24x72 Greenhouse

Hello all. Recently joined the forum and have already gained a tremendous amount of knowledge. I appreciate every ones opinion, especially when they differ.

I work with a local non profit that helps build community gardens. The group was gifted a 24x72 greenhouse with ventilation, temperature control, overhead door-the whole deal. We do have some money for construction but are trying to do as much ourselves as possible. I am doing my "google due diligence".

If you have any exceptional resources, tips or tricks, it would be appreciated!

Thanks.

Nick Dee wrote:
If you have any exceptional resources, tips or tricks, it would be appreciated!

Can you be more specific? What questions do you have that you need answers to? I am sure we all have hundreds of exceptional resources, tips, and tricks, but 99% of them might be off topic for what you need.

Good point Tom. I will start with 2 specific questions.

1. What kind of floor to put it?
The greenhouse will serve 2 main functions. To grow as much edible food as possible and as a learning center. We want to use this as a tool to teach the local community members more about growing. The project leader wants to treat it like a true commercial greenhouse and pour a concrete slab throughout. I would rather see a hybrid of sorts with concrete walkways, some in soil beds, some containers and an area for seedlings.

2. Is it possible for "skilled volunteers" to erect?
We do have some money for construction but not a ton. One company gave us a bid that said it would take their crew 3 weeks and cost over $20,000. That is in addition to engineering. We are considering hiring a construction manager and then recruiting the most skilled volunteers that we have. Is this possible or are would we be in over our heads?

Nick Dee wrote:Good point Tom. I will start with 2 specific questions.

1. What kind of floor to put it?
The greenhouse will serve 2 main functions. To grow as much edible food as possible and as a learning center. We want to use this as a tool to teach the local community members more about growing. The project leader wants to treat it like a true commercial greenhouse and pour a concrete slab throughout. I would rather see a hybrid of sorts with concrete walkways, some in soil beds, some containers and an area for seedlings.

2. Is it possible for "skilled volunteers" to erect?
We do have some money for construction but not a ton. One company gave us a bid that said it would take their crew 3 weeks and cost over $20,000. That is in addition to engineering. We are considering hiring a construction manager and then recruiting the most skilled volunteers that we have. Is this possible or are would we be in over our heads?

I would recommend gravel or mulch as an alternative to concrete. You are going to have people fall down or kneel down, might not want to have them doing that on concrete. A good bit of pea gravel will keep it from getting muddy in there, look nice, and be practical. Maybe have some decorative stepping stones make a path along the middle.

As for if it is possible for skilled volunteers to erect, what is involved in the erecting? Will they need to make cuts or weld metal? If it is simply assembling precut pieces then they should be able to do it (I would recommend having someone with a strong construction background oversee it). Make sure you have the proper liability insurance because with something this big someone could get hurt.

I agree with Thomas on the gravel part. I would add that I'd put landscape fabric under the gravel to prevent the gravel from sinking down into the sub surface once it becoems muddy. Also, anywhere where you are going to be filling flats, potting, and transplanting, should have a solid surface under it. A plywood platform on top of the gravel works fine for this. But you just want something that will allow you to sweep up debris.

2. Is it possible for "skilled volunteers" to erect?
We do have some money for construction but not a ton. One company gave us a bid that said it would take their crew 3 weeks and cost over $20,000. That is in addition to engineering. We are considering hiring a construction manager and then recruiting the most skilled volunteers that we have. Is this possible or are would we be in over our heads?

I'd get a few more bids. And ask to see their project plan. It might be that you can do the "barn raising" yourself, but higher them to do the plumbing/electrical/etc.

When you say "commercial greenhouse", it sounds like you mean for hydroponic/container/flat production. That's typically what they are used for. If you're growing mostly food, unless it's all pepper or tomato, an amended soil floor is what I would use (though this is not without it's drawbacks). I'm assuming you're not going to be using injectors/dutch buckets, etc. A concrete slab for something that size is going to be really expensive, around here you'd be looking at over $12K.

Concrete is easy to clean, and has great thermal mass, but the price tag, ouch! Weed fabric with pea gravel is much cheaper, and you could built grow tables sized for whatever containers you're going to be running. If you get a better idea of the details of your production system, you can tailor the surface to meet the needs.

Without seeing the actual greenhouse, it's hard to say what skillsets you'll need, but most kits can be assembled by people with little construction background. If you plan on installing 3-phase electricity, I'd call an electrician, but I've done all my own 110v wiring, anybody can, just get one of those DIY books from your local hardware store. Ditto for plumbing. I would second the advice about insurance, and maybe add a waiver for anyone that wishes to participate.

I should have mentioned that the local concrete company will donate the concrete materials.

We have found that engineering an older (2001) greenhouse is a real challenge. It wont meet 2012 International Building Code for load capacity or wind load. That means we need to beef it up, which wont be cheap.

We have talked with a few retired construction managers, I believe we can get one of them to lead the erection of the greenhouse.

Most companies we have talked to have never built a greenhouse and they seem afraid to try it. So far only one company has been willing to even bid it.