Friday, July 26, 2019

Determining a Roof Design for the Wattle & Daub Cob Cabin: A-frame supports for Lime waterproofing

I like this A-frame roof support inside this primitive cabin - vid

I've spent the day studying how to build a roof - for a shed....

So mainly it's the gable design requiring rafters or trusses with gussets - these are all terms that I jokingly put in my "Man-talk" category.

There things that I don't "want" to know about and I definitely don't want to DO - along with "squaring" and "leveling" - basic "civilization" stuff.

So that A-frame design will go well in the front of my Willow Palace - as I previously posted the photos of the initial beam design or posts.

My plan is to not do any precise measurements for this "build" - just eyeball stuff. Even the primitive builders in that link above - they use a tape measure.

So that's six feet by 12 feet - for their primitive cabin. What I plan is seven feet by 9 feet - but the exterior of the wall is 10 feet by 12 feet.

Back in the old days, all homes were built with traditional rafters (see picture above).  You know, where you use dimensional lumber (i.e. 2×8’s or 2×10’s) to support the roof.  The board at the peak that the rafters tie into  is called the ridge board.  The horizontal members about half way down are called collar ties.  These collar ties work to hold the rafters and roof planes together.
So the "rafter" design is just easier to build - rather than trusses with gussets.

http://blog.armchairbuilder.com/5528/rafters-versus-trusses-which-is-best/

 One of the major benefits for using rafters today is the open space they create.  If you plan on creating a vaulted space, rafters will help you maximize the open area.
 So for such a small shed-cabin design, trusses just are not needed.

When a job is small, rafters are many times the only way to go. 
I'm actually surprised just how much effort people put into just building a SHED!!!!! I had no idea it was such a sophisticated build....

So in that vid I linked above - at 5:15 - they show a "removable gable end" - for air. That is nice - but in northern Minnesota you want to emphasize staying warm - not some removable part with leaks. But - you can see the A-frame supports for their ridge-beam!!

 So then at 7:20 they get into the A-frame structure description.

So then at 7:50 - you can see how the Ridge Pole locks in between the two A-frames....

So as he says - the structure is very solid.

As for the actual roof design - they have a kind of plastic water-proofing and then a green roof on top of that.

I don't have moss - so I will probably try doing lime so that the white reflects the heat in the summer.

The lime will be water proof compared to just clay.

So I'll do a wattle-daub roof with straw and manure just as with the walls - and use a lime plaster for water proofing...

So here they say you NEED to mix fat into the lime to really make it waterproof

I guess that only works for QUICK lime and not hydrated lime. There is no "quick lime" in the US - that I know of. ..

 First quicklime is obtained from the heating of limestone at 1600° F (versus 2700° F for Portland cement). At that stage, quicklime (calcium oxide) may be converted into calcium hydroxide (hydrated lime) by adding a controlled amount of water to adjust the chemical affinity. This process disintegrates the lumps, pebbles, and granules found in quicklime to obtain a fine white powder ready to be mixed with the appropriate aggregates and mineral admixtures. As the lime plaster is applied onto the wall it cures and hardens slowly reabsorbing and sequestering carbon dioxide. In the process the calcium hydroxide is converted back into calcium carbonate (limestone), producing an durable, protective mineral crust.
So I'll be using hydrated lime. I was very happy with the results when I tried it out for my entrance road....

Nearly all old roofs were lime torched.  Whether slate, clay tile or stone flags, lime was used to bed the tile, or beneath them to prevent undue wind, and hold condensation.  Lime acts as a sponge to hold water, and release it as conditions change. 
https://www.heritage-consulting.org/lime-torching

 Lime is applied to the underside of the tiles, with a good mix of hair to make it flexible.
So horse manure, clay-dirt - and lime.... and straw-hay....

fascinating - the need for flexible materials as the wood dries BBC on lime-hair

So people actually tried using CEMENT instead of the old Lime - and Cement doesn't breath or dry out - so builds up fungus - and also doesn't flex.. so cracks. oops!!

OK so if I get BARN LIME (as I did before) - that is "chalk" - and then the HYdrated Lime - is the actual "lime" - and then mix those in also with the "hair" (manure - straw-hay) - and clay....



So here is an ancient wattle and daub ROOF - they're trying fern bracken with thatch on top - BBC vid

How to build a mini Rafter roof for a shed - vid

The only thing I really care about - in this vid - is that he uses Hurricane Ties - since they are EASIER to attach the walls to the rafters...





So I have screws already - I can just pre-drill holes into the logs - instead of the nails used in the primitive cabin vid linked above at 7:40 ... then I should not need to buy any hurricane ties.



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