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wofati front edge of roof concerns

paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15609
Location: missoula, montana (zone 4)
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So I tried to redraw this from mike oehler's book, and then added my concern.

The dark brown is the wood. 

The black lines are the plastic (polyethelene) sheeting.

The light brown is soil.

The yellow arrows represent sun rays. 

So, the black plastic degrades with UV, right?  So isn't this exposed part gonna disintegrate?  Plus, won't it look butt ugly? 

So for my next post is my idea ...


[Thumbnail for psp_roof_front_1.gif]



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paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15609
Location: missoula, montana (zone 4)
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The first pic shows the rough idea.  The second pic shows a bit of a closeup and some more detail to the idea.

My idea is to not have the plastic wrap all the way to the bottom of this board.  In addition, add several more layers of black plastic where shown.  These would be "sacrifice" layers.  Let the sun have them.  In fact, maybe a layer (or two) of some sort of UV safe stuff (?). 

I'm thinking that all of the non-angle wood would be black locust (should last 100 years in the weather with this sort of use).  So it can take care of drip stuff and it can help shield the plastic from the sun.  It would also replace the look of the plastic with the look of wood.

In the second pic, you can see the plastic getting such a pinch!  The blue stuff represents wood deck screws. 

So ... I have to qualify all of this by saying that I have never built a PSP structure before, and that after reading Mike Oehler's $50 and up underground house book, this one issue made up about 80% of my concerns. 

Will this work?  Is there anything I'm overlooking?



[Thumbnail for psp_roof_front_2.gif]

[Thumbnail for psp_roof_front_3.gif]

Susan Monroe


Joined: Sep 30, 2008
Posts: 1093
Location: Western WA
I don't really understand what you're talking about, but can't any exposed plastic be covered with something?  Even with multiple layers, it's just going to degrade one layer at a time, and then what?

Sue
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15609
Location: missoula, montana (zone 4)
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Well, surely you can use layers of something that is UV resistant. 

I suppose one could cover it with cement.  Or, since it is sort of covered by wood, maybe a bit of cob right there would hold up for a really long time.

Dave Boehnlein


Joined: Jun 10, 2007
Posts: 291
Location: Orcas Island, WA
    
    2
I haven't seen the book, but just to check, are you sure the author didn't recommend leaving the excess plastic exposed only temporarily to allow for settling. I know with liner ponds a common mistake is that people lay down the liner & fill it up. Then they cut the excess plastic and walk away. However, with a pond it can take as much as 18 months before  the liner has fully settled. Therefore, we never cut the excess material off of our pond liners until a couple years have gone by so we don't end up cutting it wrong.

Perhaps the intent is to cut it or cover it with something later. Are there finished photos in the book? Do they show a sloppy poly edge hanging over or do they show a neat & tidy edge?

Dave


Principal - Terra Phoenix Design
http://TerraPhoenixDesign.com
Steve Nicolini


Joined: Nov 15, 2008
Posts: 224
The photos are finished.  He pinched the plastic down after wrapping it around the low side of the overhang. 

I think Paul's concern is with the soil settling on the slope of the roof, but I am not sure.

If the soil isn't cultivated, on a 1:3 slope, do y'all think it will erode at all?
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15609
Location: missoula, montana (zone 4)
    ∞
If he were to trim it later, couldn't water get in?  My impression is that he has carefully designed it this way so that water hitting the vertical surface will drip off at the bottom edge.  Apparently he once had a different design and water kept coming in the house.

Steve Nicolini


Joined: Nov 15, 2008
Posts: 224
I think it would allow water in.  Drainage drainage drainage.  Paul, what if you covered that top piece of lumber with soil as well?  Would that help prevent exposure of the roof plastic?
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15609
Location: missoula, montana (zone 4)
    ∞
Steve Nicolini wrote:
I think it would allow water in.  Drainage drainage drainage.  Paul, what if you covered that top piece of lumber with soil as well?  Would that help prevent exposure of the roof plastic?


It would help prevent exposure to the roof plastic, but it would also lead to the wood decaying.


Steve Nicolini


Joined: Nov 15, 2008
Posts: 224
True.  I think what you drew up is pretty good, and would probably work.  I wonder if soil settling would pull hard enough on the polyethylene to tear it. 
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15609
Location: missoula, montana (zone 4)
    ∞
Mike?
Mike Oehler
author


Joined: Jan 03, 2009
Posts: 60
Location: Bonners Ferry Idaho
    
    1
Valid concerns. Yes the sun will deteriorate the poly and yes it is ugly. Former clients of mine have built galvanized sheet metal caps to put over the poly. A lazy man's way (mine)is to just put a temporary sheet of poly over the thing every year. Only takes a little time.


author of:  The Fifty Dollar and Up Underground House Book and The Earth Sheltered Solar Greenhouse Book Visit Mike Oehler's Website
Steve Nicolini


Joined: Nov 15, 2008
Posts: 224
Mike, do any PSP structures you know of have gutters?
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15609
Location: missoula, montana (zone 4)
    ∞
I think if it had gutters it would, by definition, not be PSP.  All PSP roof stuff flows down to soil. 

Nicholas Covey


Joined: Oct 09, 2008
Posts: 179
Location: Missouri/Iowa border
I wonder if they make vinyl or metal facia covers that are wide enough to cover the entire shoring board.

And it wouldn't need much of a gutter, maybe a vinyl j channel since the runoff would only be what was running off the top of the board itself. It might minimize drip across a doorway or window though.
Steve Nicolini


Joined: Nov 15, 2008
Posts: 224
So if someone used Mike's design and built their home in the dirt, but decided to put up a gutter in one area on the downhill side to collect runoff water, would that be PSP? 

It seems to me that some gutters might help hide the Front edge poly and help collect rainwater too. 

How are gutters so bad?  Just using the extra material?
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15609
Location: missoula, montana (zone 4)
    ∞
It's not that gutters are "bad", it's just that if you have one inch of space where a gutter would be of use, then you don't have a PSP structure. 

That's why the design can be challenging.  That's why the video has that segment that has you do those exercises about getting light in from all four directions.  What gives PSP its super-power is this simple idea:  all water flowing downhill flows into soil.  Never anything gutter worthy.  If you can stick to this principle, you get to have all the bennies that go with PSP.  If you dodge the principle, then you lose your bennies.




Mike Oehler
author


Joined: Jan 03, 2009
Posts: 60
Location: Bonners Ferry Idaho
    
    1
Seve, I sympathise with your desire to collect rainwter off the roof of PSP but have shelved the idea as probably unworkable. We were going to try to collect roof water off the Ridge House with sand just below the down side of the roof, drain tile at the bottom and a layer of polyethylene below that to catch and contain the moisture so it would run into the drain tile. We gave it up after reading reports of the miserable amount of water earth yields as opposed to a hard surface roof. Since we are planning a pond with the Ridge House we will catch the water off the ponds glazing (it's also a greenhouse with several other functions) and off several metal roofs we are going to install over other sturctures specifically for precipitation catchment. Otherwise you might be able to catch water off a PSP roof by laying out on the roof a layer of polyethylene duting rains and snows then rollong it up again. "Gutters" as such only work off hard surface roofs.
Steve:
A gutter will never work off the drip board and as a cattchment device on the drip bards because they are at the highest pqrt of the roof. You put gutters on the losest part of the roof. Go to a shop that works with sheet metal to have them make you a cap to protect the drip board poly. Take the dimentions to several shops nd get estimates.
 
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