12x16 guest cabin at remote Alaska property

[ChugiakTinkerer]

I last looked at the issue of anchoring a few years ago and settled at that time on a 48" screw anchor.  I'll do some more digging to make sure I've got an anchor of sufficient strength.  I'll anchor in accordance with what is recommended for mobile homes, with some extra anchors thrown in for good measure.



The vertical ties resist the overturning force and the diagonal ties resist the lateral displacement.  A screw such as this one has a pull-out resistance of up to 6,000 lbs: https://milspecanchors.com/screw-in-ground-anchor-3-4-x-54-w-4-8-helices-galvanized/

I think I'll plan on a 2,000 lb tie-down.  That will make sourcing hardware a bit of a challenge.  For vertical tie-downs I'm thinking a strap secured across the joist and a stud will be the most secure.  I actually like the look of this safety roof anchor, just not sure of its suitability in this application.
https://www.safetycompany.com/fall-protection/fall-protection-accessories/hardware/anchorages/miller-ra41-permanent-roof-anchors/

[Reninco]

Thanks for the quick turnaround, clarifications and build concepts
I understand the post/pier selection with your existing ground situation and this makes your foundation design a wise choice as you mentioned in the upper posts. It's nice to see thoroughness of build with no jurisdictional oversight.
As the APA was mentioned in this topic and portal frames were being discussed we should be aware that APA has a calculator for walls with "openings" – this is different in details than the portal frames/drag strut concept or the perforated wall design seen in code books. The APA testing has shown a considerable amount of "extra capacity" is available. Based on typical calculations and the small size of your cabin I feel your "upper part" of the cabin is fine and one just needs to secure it to something to prevent tipping. And that "tipping system" and the forces to prevent it should be realized in some type of connection detail in the floor plate/rim area...which with this later post you have been doing. I would take a look at the connection detail that mobile homes use, and off-the shelf wall hold-down brackets and their capacities as a start.   

[ChugiakTinkerer]

I'm working on the generator shed and need it to house a 6 kW generator that has a dry weight of 390 lbs.  The pic below shows an approximate representation of the generator.  I added the blue steel skids to show what the footprint of the unit is.  At 17 inches by 32.5 inches it is a dead load of about 100 lbs per square foot.  Adding in the weight of oil, fuel, and miscellaneous accouterments and it's more like 125 psf.

Floor details: 2x8 pressure treated joists on 16" spacing.  Sheating will be 3/4 plywood.

I'm designing a stand that will raise it to a more practical working height and will spread the load across a greater area.  2x4 framing with 1/2" sheathing all around.I have two headers, each a pair of 2x6.  I'm thinking of sistering the two joists directly under the generator.

The shed will be nominally heated in the winter and will only be housing the generator.  Any thoughts on where this falls on the spectrum from inadequate to overkill?

[Nate R]

What's the span on those 2x8s?

[ChugiakTinkerer]

What's the span on those 2x8s?

Doh!  Call it a 7' 0" span.  It's an 8x8 shed with 2x6 walls.  I have a 70 psf ground snow load, and this is for a 3:12 shed roof.

The lowest span in the 2018 IRC Table R502.3.2.1(2) is 8'8" for #3 Southern Pine.  That's for 40 psf live load and 20 psf dead load.

The tributary area of the wooden stand is 12 square feet (stand is 3' x 4' x 24" tall).  That works out to about 40 psf dead load.

[ChugiakTinkerer]

I got off my lazy butt and went to Don P's toolbox (https://forestryforum.com/board/index.php?action=toolbox) to run some calculations on a single 2x8.

A single 2x8 of #2 HemFir can withstand up to 1,050 lbs of evenly distributed load before failing.  For a point load that gets reduced to 440 lbs.  For two point loads equally spaced, the 2x8 can withstand a total of 780 lbs.

Sistering the load-bearing joists looks like it will suffice.  I'm probably overdoing the wooden generator stand, but hey, if it's worth doing it's worth overdoing!

Edit to add:  Running the calcs on my 4x8 beam supporting the joists resulted in failure.  I need to go deeper and use three 2x10 to be able to withstand the weight of a roof fully loaded with snow.

[Don_P]

I'd drop the joists down inside those girders on hangers and avoid the girder overturning potential. Fresh air intake and exhaust outside? I'd put the gennie or the box on some rubber horse mat to help quiet the vibration. A packed dirt floor and ignore frost heave might be quieter yet.

I just hooked up a new to me 6 cyl diesel to the sawmill, inside the sawshed. Even though it is open sided the fumes ran me out. I've got some old downspout hooked to it right now but am going to get a section of exhaust pipe and run it up through the roof.

[MountainDon]

I just hooked up a new to me 6 cyl diesel to the sawmill, inside the sawshed..............

That will be an improvement over the tractor I remember. 

[ChugiakTinkerer]

I'd drop the joists down inside those girders on hangers and avoid the girder overturning potential. Fresh air intake and exhaust outside? I'd put the gennie or the box on some rubber horse mat to help quiet the vibration. A packed dirt floor and ignore frost heave might be quieter yet.

I just hooked up a new to me 6 cyl diesel to the sawmill, inside the sawshed. Even though it is open sided the fumes ran me out. I've got some old downspout hooked to it right now but am going to get a section of exhaust pipe and run it up through the roof.

I wasn't a fan of the concrete deck blocks anyhow.  Much better footprint with the cribbing.  With the shorter girder span I'm able to use three 2x8.

This will be kept warm throughout the winter, so I need insulation on the floor.  I'll run an exhaust pipe out the wall, not sure if I'll have an intake pipe bringing in outside air or if I'll just have it draw from the shed interior.  I'll have to play with it a while to see what the fresh air inflow requirements are.

A separate issue is how to keep it warm without having to burn hundreds of gallons of fuel.  I might add a solar collector like Ol Jarhead put up on his cabin.



Something I just thought of while looking at the preview image - I want to keep rain off the cribbing, so need to have an ample eave and rake overhang.  I had been planning on just a 12" rake, but I think I'll bump that up to 24".

[ChugiakTinkerer]

For a little better perspective, this is the generator shed as currently designed.



I'll be spending two months out there this summer, and will have my nephew to help out for most of that.  So I am in a planning frenzy figuring out exactly what I need for all of the hoped-for work that will get done.  I've got a truck arriving with about twelve tons of lumber and gravel that I will be hauling out by snowmachine next week.  I can fine tune some of the design features as I go but I need to get the bulk of the materials out while the trail is in good shape.

And again, for anyone who missed my opening introduction this is a view of the lake from the top of our hill...

Winter:


Summer:

[Don_P]

That will be an improvement over the tractor I remember. 

Oh yeah, going from 35 hp to 135, oak and hickory should no longer be a problem 

On fresh air intake, look at your cubic inches and rpms, that volume of heated air will be exiting the exhaust per minute and replaced by outside air. The engine will be producing heat but it is basically a big air pump.

Looks like there are trees around and this can be rustic. Logs would be another good sound dampener.

Oh, I try not to suck down Jeff's bandwidth offsite, link to the calcs here;
timbertoolbox.com

[ChugiakTinkerer]

...
Oh, I try not to suck down Jeff's bandwidth offsite, link to the calcs here;
timbertoolbox.com

Good point, and thanks for the link.  I bookmarked it this time.   

[Reninco]

Tinkerer those tracks are a touch bigger than my winter blue jay footprints.
Addressing your tie-downs – an improvement would be to have them in parallel alignment, the sharp angle turn at the soil line creates two issues.
A. A bending force on the tie down 
B. Large forces at the soil line
Both can loosen the anchor when a load is applied.

HUD gives a overview with drawings of suggested wind hold-down systems. Here is a screen grab, while reading the suggestion notes they mention a "metal stabilizing device" and the device is "rotated" for instruction clarity (my words) ... this prevents bending but it seems very dubious.

Of course, the device or concrete collar is not needed if you go directly to the floor rim. You may be temped to go just to the rim but it will be better to transfer the load all the way to the rafters. Code guys call this a "continuous load path".
I suggest this type of path as the parts are readily available (no I am not a Simpson dealer just familiar with their products, Mitek would also work)
-A Simpson HDU2 at the corner stud (connected to earth anchor)
-4" oc stud nailing to spread the load to the plywood, this then can spread to the top plate.
-Connecting the top plate to the rafters with a hurricane tie such as Simpson H 2.5A or a well-placed structural screw.
If needed all of these can be installed after framing is complete...
 
HUD article: https://inspectapedia.com/Manufactured_Homes/HUD-Mobile-Home-Tie-Down-Guidance.pdf

[Blessed]

Hello CT.  I put a barel stove in my generator shed.  I've got trees.  Have you checked out fuel oil drip stoves recently  ? I'm thinking about putting one next to my cabin wood stove.  Run the stack into the wood stack.  I could get by on a drum a year when I get lazy n don't want to get up n feed the stove.  Or in summer.

[ChugiakTinkerer]

... I could get by on a drum a year when I get lazy n don't want to get up n feed the stove.  Or in summer.

Our present shelter is a "insulated" Weatherport that isn't much more than a wall tent with bubble wrap.  The wood stove heats it up nicely but it wants to be fed every three hours.  A drip stove is starting to sound like a good idea!   

[redside]

It looks like you have some solid plans for moving forward with building this summer.  I just want to comment on your anchorage/tie down.  There is a good chance that the ground will raise due to expanding soil in the winter.  Its just a suggestion, but I would keep your anchorage in the first foot or so of the soil instead of using screw anchors several feet down.  There is a chance you will get some damage if the ground raises your cabin while your anchorage is below the freezing soil....something is going to bend and/or give unless your cable stretches.  If your going to float your cabin (which I agree is best given your circumstances) you need to float everything else.  The metal stabilizing device looked pretty slick and appears to be in the upper column of soil. 

[ChugiakTinkerer]

It looks like you have some solid plans for moving forward with building this summer.  I just want to comment on your anchorage/tie down.  There is a good chance that the ground will raise due to expanding soil in the winter.  Its just a suggestion, but I would keep your anchorage in the first foot or so of the soil instead of using screw anchors several feet down.  There is a chance you will get some damage if the ground raises your cabin while your anchorage is below the freezing soil....something is going to bend and/or give unless your cable stretches.  If your going to float your cabin (which I agree is best given your circumstances) you need to float everything else.  The metal stabilizing device looked pretty slick and appears to be in the upper column of soil.

You raise a good point.  I don't really have a handle on how much the freezing soil expands, but the floating pad and cribbing is designed exactly to accommodate that.  Keeping water away from beneath the structure will reduce the amount of expansion.

I'll cogitate upon ways to have shallow anchorage.  But I think it will ultimately come down to picking which sort of damage is acceptable and mitigating that.  If I can adjust the cable/strap then that may be the best way to go.

[Blessed]

   I've got a 7 kw duel fuel genny.  Probably close to that weight.  It's a wheels.  The shed has 2x6 on 16 center. Doesn't seem to be much of a problem as far as weight is concerned. Heck that little shed gets lots of weight.  Sitting on 6ea 8x16 concrete blocks. Just my experiences