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Gold Rock
10-21-2011, 08:49 PM
What's the minimum rafter spacing for using the ubiquitous white/blue heat shrink plastic? Same as conventional sheathing? Links to any info sources? I'm putting a roof over my 30 footer. Does anyone have any informed input/experience on snowloads? Here in the Pac. NW snowloads can be monumental. Though short lived, snow accumulation of several inches or more is almost an annual occurence in my area and is often followed by a heavy rain meaning very heavy relative loads. Thanks in advance gents.

dredbob
10-21-2011, 10:35 PM
I can't say anything about the shrink wrap plastic, but having several had several boats covered by various tarp shelters framed with PVC pipe, I can say that for resisting heavy snow loads, nothing beats a steeply sloped roof with a sharp peak, as opposed to a more rounded one. With a steep pitch, the snow will mostly slide off.

Bob

Gold Rock
10-21-2011, 11:22 PM
Quite true. Adding pitch is one counter to roof loads. I've been trying to recall the various structures I've seen at the yard and I will say that I don't think 16" centers are particularly common. Then again, most are steeply pitched, not, most certainly, flat or shallow pitched shed roofs.

thud
10-22-2011, 12:47 AM
Go look into this place; http://she-kon.blogspot.com/
He's building a huge boat under that big blue tarp.
(KnottyBuoys)

Gold Rock
10-22-2011, 01:06 AM
Yeah, those are some pretty interesting pics. Looks like he may have tucked some bat insulation between the frames forming the shelter. Good idea. It also appears that there's considerably more than 16" between those frames. Hmm.

BBSebens
10-22-2011, 08:36 AM
Rick (KnottyBouyz) is a regular poster here on the forum. PM him about his shed, im sure he'd be happy to help.

BTW, use the white plastic unless you want a blue tinted build. Until he turned on the lights inside, all of Rick's work was blue. kind of amusing to us anyway.

thud
10-22-2011, 03:13 PM
In Alaska I built several of those "Blue Tarp" sheds over the years.
Nothing as elaborate as Rick's though.

The important thing I learned was the Blue Tarps are not water proof but will stand up to the rigors of winter winds and freezing Temps for at least the whole winter. They leak water and melted show. That's not good.
So....
The first layer is 6 mill Visqueen. Water proof, but will not do well right out in the elements.

So the Water proof Visqueen is the first layer, and the Blue Tarp covers that, and you have a good work shop for winter or all weather.

You have to keep air flowing if it's cold outside and heated inside. You'll get Rain from Condensation if you don't.

I used Jugs half full of water as 'tie down' weights. That would allow some Flexibility to the Blue Tarp.

Ricks Turquoise Palace is a lot more elaborate than mine.

On snow load, the normal roof truss gap in snow country is 24". But with Visqueen if you inflate your tent once in awhile you can get away with 48". Just keep the snow from sticking.

MN Dave
11-01-2011, 08:13 PM
There is a pretty elaborate plastic shed in this thread. http://forum.woodenboat.com/showthread.php?80153-Just-fore-the-fun-of-it-)

thud
11-01-2011, 08:56 PM
Yes it was! A marvelous job. I've lived in worse!

P.L.Lenihan
11-02-2011, 03:46 AM
If you go the bowshed route, here are a few things I found to be most helpful in making it last:

1)Lay strips of carpeting along the bows to keep chafe to a minimum.

2)If you expect condensation issues,line the inside of the roof with the same material as the outside.This will also give you a small insulating advantage.

3)Lay intermediate bindings/straps on the outside over the poly between the bows or ribs of your roof.This will keep the poly snug and prevent it from flapping itself to an early death.

I used clear vapour barrier poly, 6ml., for my shed and it lasted for near eight years with only the bowed part getting a second sheathing after the first 5 years or so. It handled,snow,freezing rain and big winds without a single failure.

The oddest thing of the whole affair was the written warning stamped on the poly vapour barrier;"NOT FOR EXTERIOR USE".

The shrink wrap approach is also a good one but may be more expensive and it does not come in clear, which is a real boost anytime it is not summer.Think green house. -12C on a sunny day meant +12C inside the bowshed!

It was a cheap and effective temporary shelter for my boat project.

Good Luck!


Cheers!

Peter

Gold Rock
11-04-2011, 01:43 AM
Thanks all, for the replies. I have much food for thought.