5-wall thickness should be about 1.5 inches thick, right? Can you get U channel to seal the open ends to keep cold air from creeping into the cells? If you can stop cold air from channeling through the cells, I think 5 ply would be great. In Ohio I think you would see a payback in fuel savings over the life of the product. My twin wall is about 12 years old and still in decent shape. BTW, at the current cost of corn, is a corn burning heater still economical?

Isn't the insulation value more dependant on the combined airspace? So using two single panes with a 1 inch airgap would be the same as a 5 wall sheet that's 1 1/2 inches (Accounting for the multiple layers).

I know that as the airspace gets larger, there is a danger of increased heat loss due to convection currents forming, but at the small of a gap i am not sure it matters.

I'd just wonder if the expense was worth it, and also as mantioned, is the loss of winter light too great? Let's say each layer transmits 90% of available light. What's 90% of 90% of 90% of 90% of 90%? Anyone? Calculator says it's only 60%. Is that enough light for growth?

I have 3-ply on my greenhouse and if 5-ply was available and financially feasible when I built it I would have definitely used it.

Just my two cents :)

They say that hindsight produces the greatest clarity and had I known when I bought my otherwise very well made GH what I do now, it would NOT be 8 ml. double wall glazed, but much heavier and at least quad celled.

If you want to keep a heated GH in cold country and have the option to spend a bit more upfront on far more insulating glazing- do it. Then, seal the living you-know-what out of it, install a direct vent, dual combustion heater and laugh at bizzards and heating bills, WITHOUT the need for bubble wrap, pool covers and all the rest of the extras you would otherwise have to purchase then mess with, just to give you what you will already have with your super glazing.

I wouldn't worry about light either. If petunias will bloom in my GH with the light that penetrates through extra heavy bubble inside and 12 ga. solar pool cover outside, with 8 ml. doublewall in between, you will get enough too. As long as light on the roof isn't blocked with snow, you should have all of the winter light you will need for most plants and most GH owners suppliment at least some planting needs with extra lighting anyway.

If you get a lot of snow along with cold and are planning a custom design, go for a very steeply pitched roof; Alpine style. Then, you will never need to address snow removal. The steep pitch will cause it to just slide off on it's own.

Lastly, if you are going to expend the time, effort and expense of using really heavy glazing to retain heat in winter, don't forget ground insulation.

Good luck. I every your ability to custom design and build exactly the GH you really want. Most of us here have to adapt to what was available and within our budgets.

I currently have a small GH (7 x 9) with 4mm twinwall, and it is the draftiest thing you have ever seen. I am lucky that I can get away with just one 1500 watt heater for the winter. I imagine that corn may still be less expensive than gas, for corn is 5.59/bushel. It just depends how much space a corn stove would take up. I really don't need a huge GH, since I don't start seeds or anything. If I got a dual combustion direct vent heater, should I use Natural Gas or Propane? Which one is less expensive?
I grow orchids and overwinter waterlillies (Victorias), so 60% is just about right for my needs, and I also have HPS/MH lights for supplementary lighting if necessary.
I was planning to get a 16mm router bit and make channels in 4x4 wood cuts. This way they would fit in tightly and withstand the winds we sometimes have in ohio. Then I would use the silver tape for the bottom of the panels and have them routered into the base.

I would think that this would be basically a high quality 10x12 HFGH on steroids...hehe!

There would definitely be a heat savings using 5-wall vs. twin wall. The heat loss factors are 0.33 vs. 0.65, almost 50% less heat loss with 5-wall. However, "is it worth it?" takes a few more calculations. Try the greenhouse heat calculator site and type in your actual numbers: size of greenhouse, surface area, expected outside night temps. and desired inside temp. The calculator will show how many btu's are needed.

Here is a link that might be useful: greenhouse heat calculator

tigerfern: In reply to your specific question:

"If I got a dual combustion direct vent heater, should I use Natural Gas or Propane? Which one is less expensive?"

The cost for the heaters would be the same but generally, natural gas is cheaper and certainly more reliable. While LP trucks may be stuck in ditches, save only a gas line failure, which is pretty rare- neither T-storms nor raging blizzards halts the flow of nat. gas.

Insulation don't cost it pays.
How much you would save is hard to say who knows what fuel will cost in the future.
If you can afford it now is the time to do it.

In the log run it will cost less than what most of us are doing.
I have a pool cover on the out side and bubble insulation on the inside.
This stuff will need to be replaced in 4 years where you will get 3 times that out of the poly panels.
The 5 ply will cost less than replacing mine every 3 years.

gardener is echoing my own beliefs.

No amount of insulation is more expensive than that of energy to heat or cool and it's going to get even more costly in the future.

What are good sources of the 5-wall?

grhouser: Try Farmtek.com, but also- Google. It's amazing what you will come up with. Just keep good notes on which seller offers the best materials at the best total delivered cost and go from there.

BTW: A caution on cutting walled polycarb: Every time you cut it, tiny bits of materials get into the channels. It's virtually impossible to prevent it and even panels that will be used in their pre-cut state will attract bits of dust or insects. We found an air compressor the best means of making sure each channel in each panel was clear before we sealed, capped and installed it.

Hi All! Just wondering if you went with the 5 wall poly tigerfern? Mine just arrived yesterday and now im working on insullating undernieth it. I have a 4 1/2 ft trench dug under my site to install sheets of 2" maybe 3" xps board. Im trying to keep out the ground frost so that it wasnt a waste of funds to buy 5wall poly. I am also chatting with sunnyjohn regarding the possibility of using a subteranean heating and cooling system. Has anyone tried this with a 5wall?

I am not sure I understand what is meant with a 5 wall poly greenhouse. Is a greenhouse with 5 walls? could you explain? Thanks

The polycarbonate sheets have 5 walls. This could be in different configurations. It could be 5 walls all running in the same direction. Or, it could be like a triplewall with the 3 sheets running the same direction and an X in the center. By the way, 25mm is 1" overall thickness. 16mm is 5/8" overall thickness. There is also a 3 wall 25mm polycarbonate available with the polilok base and cap profile and the U to fit. Polycarbonate Sheets

I'm a future greenhouse owner commenting on cornburning stoves: Locals buy corn kernels that are deficient in some way (like mold) that can be way under the usual per bushel price. Cobs too, but they won't self-feed!