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wofati front edge of roof concerns  RSS feed

 
paul wheaton
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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 ...
psp_roof_front_1.gif
[Thumbnail for psp_roof_front_1.gif]
 
paul wheaton
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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?

psp_roof_front_2.gif
[Thumbnail for psp_roof_front_2.gif]
psp_roof_front_3.gif
[Thumbnail for psp_roof_front_3.gif]
 
Susan Monroe
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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
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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
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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
 
Steve Nicolini
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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
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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
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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
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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
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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
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Mike Oehler
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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.
 
Steve Nicolini
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Mike, do any PSP structures you know of have gutters?
 
paul wheaton
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I think if it had gutters it would, by definition, not be PSP.  All PSP roof stuff flows down to soil. 

 
Nicholas Covey
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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
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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
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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
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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.
 
Davin Hoyt
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Please find this to be the latest design details Paul has communicated with me.
Fascia_Section01.jpg
[Thumbnail for Fascia_Section01.jpg]
Wofati Fascia Section
 
Davin Hoyt
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Please find this to be a supplemental drawing.
Roof_Section01.jpg
[Thumbnail for Roof_Section01.jpg]
Wofati Roof Section
 
Davin Hoyt
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I have updated these drawings...
FACIA_section02.jpg
[Thumbnail for FACIA_section02.jpg]
Fascia Section without Exterior Wall
FACIA_section03.jpg
[Thumbnail for FACIA_section03.jpg]
Fascia Section with Exterior Wall
ROOF_section02.jpg
[Thumbnail for ROOF_section02.jpg]
Typical Wofati Roof Section
 
chad duncan
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paul wheaton wrote: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 built a doghouse last spring to try out this style of construction. I built it similarily to your picture "psp_roof_front_2.gif " but I ran the plastic and the covering board down to the bottom of the facia. The 'cap' over the plastic on my doghouse is made of cedar picket fence boards and it is built a little more like a 'U' shape. The cedar on the roof side is in dirt and will eventually rot but it is cheap and it's easier to replace that than the plastic sheet. On the side of the 'U' that is exposed, I expect that to last forever. The 'U' shape allows me to put the wood securely in place without having to perforate the poly. I'm just coming up on one year now and there are no leaks and so far no visible rot on the boards.

If you have horses near you, you can use that manure for the dirt on top and you will have grass covering it in just a few weeks. Grass keeps the dirt in place, dirt protects the poly, the poly keeps the roof dry, dry roof keeps the walls from getting wet and rotting, this eventually leads to a hole in a bucket somehow but I just can't remember how the song goes.
 
Fred Tyler
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Davin, looking at your most recent drawings that you posted in January, i believe that you switched the duff and subsoil layers. My understanding is that the dry earth layer (which you have labeled subsoil) will act as the heat storage for the wofati. So, we need to insulate the dry earth from the more conductive wet earth layer (which you have labeled topsoil), not from the wofati interior.
 
Fred Tyler
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Paul,
How many inches of dry earth and wet earth are you imagining right at the very top edge? I'm wondering what the dimensions and orientation of the shoring would be there, so that it is strong enough to hold back all that earth (and the weight of the facade) while only attached to the end grain of the roof poles.
 
Davin Hoyt
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Fred Tyler wrote:Davin, looking at your most recent drawings that you posted in January, i believe that you switched the duff and subsoil layers. My understanding is that the dry earth layer (which you have labeled subsoil) will act as the heat storage for the wofati. So, we need to insulate the dry earth from the more conductive wet earth layer (which you have labeled topsoil), not from the wofati interior.


Fred, (HI!)

I don't believe the two layers are contiguous. (sub soil here on roof versus sub soil thermal exchange below hugging sides)
I could be wrong. Maybe refer to Ant Wofati Progression model I made earlier in the year. I will revisit soon, lots happening in Texas right now
 
Davin Hoyt
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Davin Hoyt wrote:
Fred Tyler wrote:Davin, looking at your most recent drawings that you posted in January, i believe that you switched the duff and subsoil layers. My understanding is that the dry earth layer (which you have labeled subsoil) will act as the heat storage for the wofati. So, we need to insulate the dry earth from the more conductive wet earth layer (which you have labeled topsoil), not from the wofati interior.


Fred, (HI!)

I don't believe the two layers are contiguous. (sub soil here on roof versus sub soil thermal exchange below hugging sides)
I could be wrong. Maybe refer to Ant Wofati Progression model I made earlier in the year. I will revisit soon, lots happening in Texas right now


Fred,

I see what you're saying. You are correct. The two sets of documents disagree.
This subject is hard to explain/communicate to people because there is an outside patio-like area and an inside living area which "require" different insulation constructions.
Furthermore, the wofatis at wheaton labs (from which Paul bases his instruction and my details here) have different facias than those in my January model (my design within Ant Wofati Progression thread).
With all this said, I believe in the following process:
1) Wrap outdoor patio area (wing walls and outer roof) with insulation layer (duff). 2) Wrap the living area with thermal mass soil. Make certain that thermal mass soil is not reaching exterior walls/structures. Instead duff from step 1 should buffer. 3) Wrap the thermal mass soil layer with insulation layer (duff). This continues to buffer the thermal mass soil from any exterior walls/structures. 4) Place top soil layer to weigh down layers and plant/seed for stabilization of top soil layer.
 
 
Janet Branson
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Dave Boehnlein wrote: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


Oehler talks about the same thing regarding the umbrella. He recommends leaving plenty of wrinkles to allow for settling.
 
Janet Branson
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I'll be using a variation of this method on my own sod roof this week. Thank goodness for sunshine! Do have a couple of questions/concerns before I start cutting the lumber.

First, with the pitch of my roof, about .27, boards attached to the ends of my ceiling/rooft platform would lay at an angle if the ends are not cut on an angle. How important is it that the drip edge be perpendicular to the ground as shown in the diagram? Two similar roofs in the ant village have their edge on this angle. Will it cause us problems later? Is is important to make those extra cuts to make the drip edge straight up like this?

Also, the board covering the plastic on the top edge...before seeing this thread I had a similar idea, but was concerned it would be visible from space, against ant village code. Thoughts?
Roof-construction-Drip-Edge-concerns.png
[Thumbnail for Roof-construction-Drip-Edge-concerns.png]
 
Glenn Herbert
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Considering that Paul talked about making the top cap, I would think that it would be acceptable for use there. If gardens and paths and roof-edge shadows at some time of the day don't make the area conspicuous, I doubt that one board will do it. You could even camouflage it with a pole or two laid or fastened on top, or if you can get a custom sawmill cutting, make the top cap from a half-round log.
 
Davin Hoyt
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I forgot to mention the need for insulation layers (duff) below patio/porch areas. Very important! Ran across it in a model today...
 
Davin Hoyt
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Janet Branson wrote:I'll be using a variation of this method on my own sod roof this week. Thank goodness for sunshine! Do have a couple of questions/concerns before I start cutting the lumber.

First, with the pitch of my roof, about .27, boards attached to the ends of my ceiling/rooft platform would lay at an angle if the ends are not cut on an angle. How important is it that the drip edge be perpendicular to the ground as shown in the diagram? Two similar roofs in the ant village have their edge on this angle. Will it cause us problems later? Is is important to make those extra cuts to make the drip edge straight up like this?

Also, the board covering the plastic on the top edge...before seeing this thread I had a similar idea, but was concerned it would be visible from space, against ant village code. Thoughts?


I believe...
Wood materials will degrade quicker, but this (orientation) is not a problem. Sun and water will work on it. Gravity will allow the water to run back into the fascia. I would attempt to place drip edges (strip of wood along edge) to promote/guide controlled dripping. Maybe think about this last.

Also, I think this fascia capping board (and the backward tilted orientation, and the shadows cast) all fit within the satellite rule.
 
Glenn Herbert
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With the fascia and top cap aligned with the roof pitch instead of plumb and level, you would actually get rain draining positively from the top surface back into the roof sod, so it might be more durable than the original sketch.
 
Janet Branson
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Davin Hoyt wrote:I forgot to mention the need for insulation layers (duff) below patio/porch areas. Very important! Ran across it in a model today...


Thanks Davin, I'm not sure what this means though. Below the patio/porch areas? Does that mean under the eave above the patio area?
 
Davin Hoyt
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Janet Branson wrote:
Davin Hoyt wrote:I forgot to mention the need for insulation layers (duff) below patio/porch areas. Very important! Ran across it in a model today...


Thanks Davin, I'm not sure what this means though. Below the patio/porch areas? Does that mean under the eave above the patio area?


No. I was listing things to pay attention to per Fred's conversation... And I had forgotten that the porch, and/or patios of wofatis need insulation below the floor/ground/deck. So this means: insulate the ground right outside of your doors because it is a part of your thermal mass.
 
Travis Johnson
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The only thing I would add is this; if using polyethylene sheeting anyway, why not use ice and water shield to protect the front of the vertical facade? It would not have to cover the whole roof, just cover the front of the facade, go over the top then drape down over umbrella layer of polyethylene. I would use this material only because it self-seals holes like nails and screws. I would then apply a galvanized drip edge and then cover the facade with cedar shingles.

My experience with trim boards has not been good. They crack, twist, and warp with time and weather, where as cedar shingles can be easily fitted so that their multiply layers can really fill in tight spaces. It is also natural, has a earth tone to it, and last a LONG time.

Not taking away from any ones idea here, just trying to suggest a better product.

By the way...
After enduring a blizzard on this hill last night where 50 mile an hour winds shook the house and I literally watched windows flexing from the gusts, I am convinced on this hill I would be much safer underground in a WOFATI!
 
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