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inverted roof on a cob house  RSS feed

 
paul wheaton
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Location: missoula, montana (zone 4)
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I received the following question via PM:

I have questions regarding the upturned sticks supporting the roof on the building in the first video.  They extend out in an upward direction, and it seems they would lead rain water into the house.  Maybe not a problem if sealed in cob.


And this is in regard to the video I uploaded here: 

http://www.youtube.com/watch?v=7qzX1jUWa_s

I think it has to do with the house that is called "bedrock".  My impression is that that house channels water to the center of the roof and then runs it off of one edge.  It has a pond liner.

Does that answer the question?

 
Glenn Kangiser
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No, Paul.  The pond liner is fine if it extended to the total extent of the roof with a facia of some sort providing a drip edge at the bottom as in mike oehler's instructions for the high edge of the house in the uphill patio area.  The problem is that the roof support sticks are extended out into the rain past the edge of the pond liner roof.

The way I see it, soince they slope downhill, rain will hit them outside of the roof and adhere to them, following them under the roof and into the house.



It could be possible to put a drip stop under the bottom of the support member that would intercept the drip at the bottom of the member to make it drip to the ground there before getting all of the way into the house.  One would be required on each down sloping member.
 
paul wheaton
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An excellent point!

I think one could put a notch in each stick a few inches in.

 
Glenn Kangiser
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I did that on one horizontal pole beam I had extending out.  A chainsaw cut is about wide enough. It requires about 3/8 inch wide to prevent the water from getting across it.  Multiple grooves on the bottom may help.
 
Jim Argeropoulos
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When doing an asphalt shingle roof you extend the first course of shingles 1/4 past the drip edge because water drips off the shingle better than it will the painted aluminum.
Would it make sense to use a layer of asphalt shingle starter strip under the pond liner and extending past the wood? Maybe violates your goals, but it is an idea.
 
Glenn Kangiser
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If angled up at the edge, the water would still run down the underside of the shingle and onto the sheathing - possibly into the house, as it will the extended sticks. This is a problem Mike Oehler discovered on the high side of his underground cabin in the uphill patio area and wrote about.

If angled down as on a conventional roof the shingles will act as a drip edge as you mention.
 
Kathleen Sanderson
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Yes, there are *reasons* for most of the traditional building forms, LOL!  A roof, in general, needs to force water to flow down and away from the building; any other form is going to require a lot of thought and attention to detail or you'll have a leaky roof.  A high price to pay, IMO, for 'breaking the mold' and defying tradition.

I think the exposed roof support members may have trouble with rot eventually, too.

Kathleen
 
Glenn Kangiser
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Yup - the cool factor is there but with new designs come new problems.  This one could be cured by putting the outer circle of branch supports on the bottom and bringing the membrane of the extended sticks - at the very end and extending the liner at least over the side of the last support allowing water to drop off at the outside edge.  Another branch whose only function is trim could be added if desired. 

I do weird unconventional stuff too, but often have to work out or live with the problems.
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