[Alberg30] plastic boat sheds & Don Cambell's comments
Don Campbell
dk.campbell at sympatico.ca
Mon Dec 1 10:10:37 PST 2003
Henry;
There are two things necessary with the greenhouse. The first is to have it really secure to the earth. I have 3 on the farm that are really greenhouses and have lost one when one end opened in a gale and lifted 48 - 36" pegs out of the ground. Just a few sandbags won't do if you need to close the ends. If you are on pavement, get out the Hilti and use extra long nails. It may be easier and
cheaper but cooler to add 12 or 16 feet to each end of the length so rain won't blow in and not bother closing the ends. The only thing you need worry about then is the lift off the plastic similar to lift off a sail with wind. I have used this set up for rain shelters on my wheat research and it worked well with all ground stakes 36" into soil. It is possible to use hurricane ties to eyes in
the soil to help hold the frame.
The second thing that needs to be done is really good attachment of the plastic to the walls of the frame. If you are using horticultural plastic, 6 mil is quite stiff and normally UV stable. I would have thought 4 mil sufficient for a temporary structure. Don't count on reusing the plastic, even the 6 mil material. You can reuse the structure if it is left intact, but the plastic will not
move if you relocate the frame. You can see how much they want for the normal poly lock system they sell. It is ususally expensive so you might want to use 2 x 4 and then first strap the poly over the 2 x 4 and then restrap it on the top edge with a second strap.They will show you how to use srapping to attach plastic. they have done it themselves before poly lock was invented. Avoid sags in the
plastic like the plague. Also keep the number of perlines to 3 if possible.You will find that every drip of condensation will fall from the lowest point of the sag or where the plastic hits a perline. Once it starts, the surface tension is broken and yu get a small rivulet that will flow for seconds.
Any loose attachment of the plastic sheet will allow for flapping in the wind and wear over the frame so holes will form. Most greenhouses are double poly and a fan blows air into the envelope to maintain pressure on the films so flapping is minimized..
Plastic needs to be applied on a really calm day, usually first thing in the am or last thing at night. A quick attach system really helps and uneven or local pulling of the plastic will stretch it and cause bunching and sags where you don't want them. I like to have 4 or 5 people for a sheet of plastic that is 100' x 28'. Pull it down the centre top and let it fall free to both sides. Don't
try to lift the sheet over from one side. It will stretch out of shape.
As for ventilation, the louvers you suggest will do fine for air flow for condensation reduction but not elimination, and pressure equalization, but for painting, use a fan. This means that the air inlet (Doors) at one end need to be of sufficient cross-sectional area to allow enough air in to keep the fan at its optimum air volume. You will will want to change the air once every 3 or 4
minutes at least. With plants in the greenhouse, we change air about every 1-2 minutes since temperature will rise 10 degrees for every 100 feet of length with sun on the house in 2 minutes. That is where no ends may work well - no restriction, and no fan needed. You need to look at the height the fan needs to be in the end to clear the painting area of fumes. My decks on boats in the shed are
about 8 - 10 feet off the floor, depending on whether it is on the trailer or on a cradle. There is laminar flow in a greenhouse so put the fan at painting level. A 2 speed fan motor is nice for warm days and extra air flow.
Don't paint if there is a possibility of condensation forming on new paint. Good fortune.
Don
Henry Hilliard wrote:
> I read Don Cambell's comments on plastic tenting (Vol 169, Issue 14) with interest as I am in the process of building a "greenhouse" boat shed and I plan on using a 6 mil material from a greenhouse supplier. Others in my area (Maine) have used this material with success yet cautioned me to install adequate venting - in their cases old house shutters up high at the ends to assure a flow of air.
>
> I intend to prep the deck and top sides over the winter and paint in the spring. Any advice or info from you Don others would be much appreciated.
>
> Henry Hilliard
> "Celeste" #394
>
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