[papercreters] Re: Reciprocal roof

Your overall plan sounds reasonable. Some details concern me.

I would encourage you to consider ventilating the roof and possibly creating some redundancy in your water protection above the papercrete. My concern is that you are sealing your papercrete above and below with layers that are not particularly good at allowing moisture to escape if ever you get the smallest leak, or condensation. The water may simply stay in the papercrete and become a perfect growth environment for mold.

Remember, adding substances such as borax to your papercrete mix to inhibit mold is a good idea, but it is always a backup plan. The best defense to avoid mold is KEEP YOUR PAPERCRETE DRY.

I suggest using saplings or old pallet wood as furring strips on top of the papercrete roof insulation running straight up the roof from the eaves all the way to the center ring. The furring strips can be made from many multiple pieces and need not necessarily be one big long strip. (This will all be hidden, so the appearance won't matter. It's all about creating an air gap and allowing air flow from the eaves to the ring.)


Then attach more saplings or pallet wood laterally across the furring strips to make enough of a lattice work to attach your roofing. As an extra layer of protection, I suggest another layer of tar paper on top of that lattice work before attaching your final petrified hessian layer.

When attaching the petrified hessian, I would suggest thinking of "shingling." Shingles are inherently redundant. Water must get past the exposed tabs of one row of shingles, then get through the upper (covered) portion of the next row of shingles below that before it can penetrate the roof. Overlapping each row of petrified hessian 50% over the next layer down assures that every part of the roof has 2 layers.

Then make sure to have standard roof vents near the top of each pie wedge roof section to allow warm moist air to escape. This venting could easily be incorporated into your cupola design, making it a functioning roof vent.

Also make sure to install vents down low at the eaves to allow cooler dry air to enter. Screen off all these vent openings, top and bottom, to keep birds, squirrels, and other critters out.

This will create an air gap above the papercrete that will allow air convection to flow. If any water ever does get inside your roof, now it will have a path to escape and dry out.

The only additional MATERIAL costs for this multiple redundant layered roof is the extra layer of tar paper, and fasteners. The saplings or pallet wood should easily be acquired for free. In my humble opinion this very small extra expense would be worth the triple redundancy to have the more reliable water protection. You will have also addressed the biggest problems that caused some early papercrete homes to be abandoned. (Crestone Colorado comes to mind.)


40' Diameter is one big span.

Does that include the overhang? Or is the overhang in addition to that?

It would be worth doing the math to be absolutely certain that your poles will support the load you will be asking them to.

That will be the largest reciprocal roof I have ever heard of being built.

How will you be attaching the roof poles DOWN to the structure, all the way down to the foundation? What will keep the roof from becoming a giant frisbee in a big wind? Cat2 Hurricane winds of 96-110mph are not chump change. Poorly attached roofs will blow completely off in such winds. You cannot depend on the weight of your roof to hold it down in that kind of wind.

I would suggest SERIOUS continuous steel strapping or steel cable looped over the poles running all the way down the walls UNDER your foundation tying the whole structure together. The metal strapping can get buried inside your wall stucco so it is not seen.

It wouldn't hurt to have extra strapping running down from the ends of the logs at the eave edges down some posts anchored in heavy stone or concrete foundation pads under that. Your big overhangs will be important to protect your walls from water, provide a wonderful porch area, and solar shading to keep the house cool in the summer, but they will also be a huge wind catch. STRAP THAT ROOF DOWN TIGHT.



--- In papercreters@yahoogroups.com, Garth & Kim Travis <gartht@...> wrote:
>
> Greetings,
>
> We are at the point of ordering our wood. Unlike most people, we are
> going to have to buy our poles, no woods on our land. Balancing the
> diameter of the poles between strength and ability to lift them into
> place is an interesting challenge. We are looking for strength tables
> for yellow pine logs, machine barked and kiln dried.
>
> We are in the process of building a 1/24 scale model of our building.
> It is teaching us a lot. And yes, I did realize that I am building a
> lever. My original design had two henge, one inside the other. Then I
> realized I would rob my roof of strength if I put the outside one in, as
> it would no longer balance the center of the roof.
>
> The building will be 16 sided, thus 16 main poles for the roof. The
> diameter is 40', with a 5' over hang. So we will be using 30' poles.
> My original estimate was for class 2, that is 8" to 10" at the top, but
> I do believe they are too big to work with, so we are going to go down
> to 6" to 8" tops. The henge and uprights are built from heavier posts,
> being a size up, as in 10" to 12" diameter at the top. Fortunately, I
> do have a front end loader that will help us get them into position.
>
> We are adding a porch on part of the building, for 3 sections, so I will
> have 4 posts at 40' to deal with. We are also looking at doing 16
> secondary rafters, that come off the mains and go to the halfway point
> between the mains, on the henge.
>
> The roof will be covered with 1"x then tar paper that will get painted.
> The painted tar paper should last long enough for us to get the
> papercrete, a mixture of paper and Portland only as 50/50 by weight, 1'
> thick, up there. It will be made into blocks, down on the ground and
> mortared into place. Then covered with petrified hessian.
>
> A central cupola will be installed over the opening in the roof to act
> as a heat chimney, a very valuable addition to a home in Texas.
>
> Our maximum wind load is a category 2 hurricane, no snow load.
>
> Does this sound reasonable?
>
> Bright Blessings,
> Garth & Kim Travis
> www.TheRoseColoredForest.com
> Bedias, Texas
>



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