Cameron Miller

Marty Mac wrote:My short answer is no. :) 

Is this a permanent residence or an occasional use cabin? What kind of weather are you building for? Snow load? I'm not sure from your post if you are asking about the overhang on just the gable ends or the whole building. If your thinking about a plywood overhang all the way around will you want to collect rainwater? Were will you attach rain gutters? If you don't plan on having rain gutters do you have some other plan to get the run off away from your foundation? Critters are also something to consider. Where I am wasps ants mice ETC ETC will move into any and all cracks gaps or holes they can find and they seem to be able to find them all.


My opinion is build at a minimum to code and I tend to build above code.

Permanent residence. Lots of rain. Gutters and non gable overhangs are already planned for - my only concern currently is the structural integrity of overhanging 5/8 plywood on the gable ends of the house shown in the diagram

16 x 16 cabin. 45 degree roof pitch. 5/8 plywood roof sheathing, tar paper then horizontal 1" x 4" x 8' boards 16" OC, then metal roofing screwed on top. The 1 x 4" boards will overhang 11", and the metal roofing exactly 1" beyond this (acting as a drop edge) - so total overhang is 1ft.

Im mostly using the 1 x 4 boards to simplify the overhang, without creating a complicated fascia board / ladder overhang with me awkwardly laying 16' in the air hanging over the roof edge.

Instead im considering just scrapping the 1" x 4 boards and just overhanging the plywood 11".

Would this work? Or would it be too flappy? Considering it would be an entire plywood section im assuming it would be stronger then 1 x 4 boards 16" OC. Actual 1 x 4 boards are 3/4" thick.

I originally got the 1 x 4 overhang idea from this video: https://www.youtube.com/watch?v=RexXz8JVGnA

Thoughts?

Traditional houses used diagonal hardwood boards for sheathing walls, from my understanding it used to be 1x boards. I too want to sheath a small cabin in the same pattern - however it appears 1x boards at (HD / Lowes) are whitewood (soft) and are appearance boards. 2x boards such as 2 x 8 are actually cheaper then 1x boards and plywood.

The wall studs will be 2 x 6 which I believe should be strong enough to hold the extra weight of 2 x 8 sheathing. Having 2 x 8 walls would also be 3x as thick as a typical plywood wall, be more rot/mold resistance, stronger, permeable/breathable, sound absorption, etc.

Any unforseen issues you may see if I sheathed a cabin with 2 x 8's? Could have an issue with the boards being warped. These also wont be T&G. One option I could do is staple strips of wool between the boards when nailing them to the wall. Thoughts?


EDIT: fudged the math. 2 x 8 boards are about 22% more expensive then 23/32 plywood.

Excellent ideas! I like light straw idea a lot. Im hoping the property I decide to get has clay on it, or I guess clay is always present if you dig deep enough, right?

Now for the rafter insulation not sure how I would do that, more of a brainstorm in progress, with it hanging from the rafters. Ill have to use plywood or stick supports between the rafters, or I could just use plain straw and no clay for this portion.

Ill be using 2 x 6 wall studs 16" on center, exterior wall will be 1/2" plywood, interior wall will be either plywood, wood tongue and groove planks, or just plain planks. No vapor barrier or moisture barrier. Will be in the Tennessee (Sub-Tropical, but still has winter weather with below freezing). There wont be any wiring in the walls (its an offgrid cabin) and wont be any AC.

I want to use a natural and cheap insulation material, I do not want to use modern insulation (fiberglass). Id like to use sawdust (mixed with lime or borax "anti mold/insect") which I could pack in to the wall cavities as I build up the wall. This will get tricky when I get to the "fire blocks" in the stud framing. If I am using plywood for the interior wall, I would nail in the plywood, pour in the sawdust mix, pack it down until its level, and so on. I will be packing it down otherwise it will eventually settle leaving air gaps. However, sawdust can cause headaches later on if I wanted to get in the wall or inspect or modify, etc, especially if the wall is a 4 x 8' plywood, taking that piece off the wall will make a giant mountain of sawdust inside your house. I considered using some sort of cardboard bag like a leaf bag and fill that up with sawdust, tape the top, then pack it in to the wall cavities, but I am unsure on the practicality of this - not to mention insulating the ceiling rafters (45 degree angle).

Another consideration is tightly packing straw in the wall cavities, this has the benefit of not pouring out like sand as sawdust would. I powder the straw with lime/borax, build a portion of the wall, then pack the straw in to the cavity, and so fourth.

A last consideration is some sort of clay/straw "wattle & daub" type mix which will harden or some sort of "dustctrete"  which is sawdust mixed with concrete. It will have to be lime mortar and not portland cement, portland does not breathe, retains moisture and will rot wood its in contact with (the wall studs).

Any suggestions on a good natural insulation for walls? Im currently leaning towards straw. Other suggestions like wool will be too costly and prohibitive.

Proper attic ventilation is important to prevent rot / mold. Most diagrams/designs show an attic that is not actually habitable, it has blown in insulation on the floor and some sort of soffit vents on the eaves for air intake with a ridge vent for outtake or some sort of gable vents on each side of the attic for ventilation.

The house I am brainstorming is going to be 20 x 24' with a 45 degree roof, the attic will be a loft / living space accessible likely by a ladder. Exterior sheathing will be plywood for the roof and walls. Tar paper will be nailed over the plywood for the walls and roof. The roof will be made of metal on top of the tarpaper. Downstairs walls will have sawdust insulation with borax, havent decided what I want for interior walls yet, but it may too be plywood, the attic I may not even make an interior wall or insulation and will have the rafters / exterior plywood exposed, I feel this is something I will decide how I want to modify it over time as I live in and experience house the house feels. I plan to have 2 windows in the attic area. I have no intention of using membranes or moisture barriers (expect the tar paper).

Heat will be RMH or a metal wood burning stove or in emergency propane camper heater. Likely wont have any AC (will only have solar) and for cooling down its back to the olden days of cracking windows to make a draft.

Come to think of it, "venting" may not even be required, the two windows in the attic can be cracked during the day to create a draft which would act like gable vents. However, this wont be possible during the winter.

What is permies thoughts on attic venting, in particular like the house I am describing with a livable attic / loft area.

House location: Tennessee. TN is sub-tropical with humidity but still has four seasons still with freezing during winter months.

Considering through I may sheath the roof with wood planks (2 x 10 x 12) or similar dimensional lumber diagonally with tar paper on top then a metal roof. This gives strength strength, more breathability (even if the tar paper kinda defeats this) and greater resistance to moisture / rot and the nails for the tar paper wont literally go through the dimensional lumber like it would for plywood.

For breathability I want moisture to be able to escape through the walls, I dont want moisture barriers like plastic barriers choking breathability. I have inspiration from older houses before the invention of tyvek / vapor / moisture barriers. Older houses were generally thick wall studs (Balloon frame), diagonal boards (for strength) on the exterior for sheathing, tar paper was made in the 1800's so tar paper may have been used on the exterior (or nothing at all), then lath and plaster for interior walls (or more wooded boards). Wall cavities were generally filled with what ever was available, sawdust was common.

Some sort of 1" x 10" x 12' or similar boards would be acceptable for exterior sheathing. Ironically enough 1" thick boards are more expensive then 2" boards, there doesnt seem to be a lot of options for 1", most appearing to be "premium" for appearance. In the above example a  1 in. x 10 in. x 10 ft. (premium) is: $17.21. While a 2 in. x 10 in. x 10 ft. is: $12.72. ($1.5 / sq ft) .... now if you look at plywood its 15/32 in. x 4 ft. x 8 ft @ $21.45 ($0.67 / sq ft) ... so you're looking at roughly a little over double in cost to sheath the house in dimensional lumber vs plywood. What do you use the sheath your house? You mention you use "heavily-overlapped, durable timber planks". Sheathing with boards would be preferable but keeping costs low is important to me so Ill side with plywood / tarpaper. I could eventually further sheath the exterior with greenwood board + batten after construction if lumber is available on the property or I will have to find something different.

Really my concern was coming down to breathability of plywood, but if im using tar paper on the outside (which isnt very breathable) so I suppose the plywood vs planks doesnt make a difference. I plan to use sawdust for all wall and floor cavities for insulation.

I want to make a breathable house with sawdust as the insulation. Im deciding on the interior and exterior sheathing to use. Im currently leaning towards plywood internally and externally, then tar paper over the external plywood sheathing, then roughsawn board over top of that (board and batten probably).

Is plywood breathable? Its wood sheets glued together, not sure what glue is used, maybe some sort of epoxy? Would this make the house not very breathable? I wont have any house wrap / moisture barriers (besides the tar paper). I want to make sure the house can breathe and the wall cavities can expel moisture to prevent mold and the sawdust to remain dry.

Logs are going to be like 8 x 8. I suppose dovetail would work for all joinery and I believe the simplest. Any other joinery better? Would a male / female connector joinery with pegs be superior?

The picture is a birdseyeview of a 20' x 24' foundation (stone pillars) and the woodenbeams which will be joined together with joinery. The beams will be acting as a sill plate for the joists.