# 28x40 Cabin Beams on Sonotubes



## Bronson77 (Apr 6, 2020)

Hi everyone,

I have a few questions about building a ~28x40 off-grid cabin. I've been studying foundation options and we want to go the sonotube pier and beam route.

- Does it make more sense to get the floor level by raising the sonotube concrete footings to achieve level or to attach a 6x6 or 8x8 in a bracket on the sonotube to achieve level for the beam/floor work?

Is there a certain number of sonotube piers I should be using for 28x40 dimensions?

In either of those situations, I'm not sure what to do once the concrete is established, especially on the corners of the foundation.

Let's assume the sonotubes dictate a level starting point, would I put brackets to hold (2) 2x6s for a beam? Is that strong enough or what is the standard? I would assume putting one beam at 0ft, 14ft, and 28ft would be the best option? Then nail single 2x6 boards at the ends tying the beams together?

Thanks for your help in advance.


----------



## rjniles (Feb 5, 2007)

You need an engineer to design a foundation plan based on soil conditions and frost depths. This is not something you can wing


Sent from my Moto E (4) Plus using Tapatalk


----------



## Bondo (Dec 8, 2007)

> - Does it make more sense to get the floor level by raising the sonotube concrete footings to achieve level or to attach a 6x6 or 8x8 in a bracket on the sonotube to achieve level for the beam/floor work?


Ayuh,.... Level is established before ya dig,..... 

That's why corner frames are put up, 'n string-lines are run, to measure off from,....

If necessary, different length tubes can be used to maintain level,....



> Is there a certain number of sonotube piers I should be using for 28x40 dimensions?


A sonotube every 8' in every direction,.....


----------



## Bronson77 (Apr 6, 2020)

I mean building level, where the beam work starts. Not actual level level.

For instance, the first picture shows the sonotubes being level...

http://jjbventuresllc.com/images/0.jpg

The second picture shows the 6x6 posts being level, but not the sonotubes.

http://jjbventuresllc.com/images/1.jpg

Didn't know if it was better to use one method over the other?


----------



## Nealtw (Jun 22, 2017)

With a foundation you my get away without and engineer, often just cheaper to over build. 

When you go to post and beam you get into all kinds of stuff that is more critical than a foundation. Size of footing and steel required, size of tube and steel required.. Cross brasing and span of beams considereing live and dead loads of the building and other loads like snow and wind. 

Then when you have all that figured out you have to consider wind under the structure as well as criters, are you back trying to figure out how to skirt the house with gound contact material and the chance that that could cause frost lift.


----------



## Bronson77 (Apr 6, 2020)

Nealtw said:


> Then when you have all that figured out you have to consider wind under the structure as well as criters, are you back trying to figure out how to skirt the house with gound contact material and the chance that that could cause frost lift.


Yeah I was wondering how that is handled in colder climates. I'm sure insulating / heat tape pipes is required as well as using pex for incoming water since they are less likely to bust when freezing. I would also box the flooring with insulation and make sure it's tight to combat critters.


----------



## de-nagorg (Feb 23, 2014)

I built a few off-grid cabins, in days gone by.

What we did was to use a transit, and sight everything to a level height, then build the floor on that. 

You will need to be precise with your tube height, to insure that the floor is level, before the pour, and adding a strong-tie bracket in the fresh concrete, is the best way to anchor the cabin on it's piers. 

And I would space the piers closer together than you proposed. 

More like 5 rows of 4 piers each, to have them 7' apart in the 28' direction, and 8' apart in the 40' direction. 

Using a double rim joist all the way around, a center double joist, and the cross ones as singles at 8' .


ED


----------



## Bronson77 (Apr 6, 2020)

de-nagorg said:


> I built a few off-grid cabins, in days gone by.
> 
> What we did was to use a transit, and sight everything to a level height, then build the floor on that.
> 
> ...


ED - thank you! That's what I was looking for. 

Any special treatment you need to consider for this type of foundation for cold weather like you have in Wyoming? 

We'll be at 8000ft in Colorado. I mentioned earlier that I would box in the floor with insulation and heat tape/insulate pipes.


----------



## Nealtw (Jun 22, 2017)

de-nagorg said:


> I built a few off-grid cabins, in days gone by.
> 
> What we did was to use a transit, and sight everything to a level height, then build the floor on that.
> 
> ...


 Ed, when have we ever disagreed?
Support in the center of the house is directly related to bearing walls above and there is nothing wrong with 2x10s 14 ft long and 2x12 16 ft long which also allows more insulation. Cost is easily off set with a the cost and labour of more piers. I do agree with smaller beams and shorter spans and slight variance in pier height and be spaced up to make level during construction. :biggrin2:


----------



## de-nagorg (Feb 23, 2014)

We get nearly the same weather as northern Colorado, So, here Goes.

Set your piers back from the rim edge about 2 " to be able to use T1-11 siding as your skirt, around the perimeter to the ground, this will keep the wildlife out from under your cabin.

You will need to paint the T 1-11 every few years to keep it looking good.

Use 1/2" CDX plywood, as the underside of the joists to hold the insulation, and insulate the $#!^, out of the floor, then use standard T&G flooring as the floor.

Then you can build your cabin right on top of the floor. 

We used a log kit, that had uniform 8" diameter logs, that stacked like "Lincoln Logs". using a 2" wide by 1/4" thick strip of foam insulation between each log, all the way up to the ridge beam.

Get all plumbing in before insulating and enclosing the floor, because tearing up your work later to plumb is wasteful.


ED


----------



## Nealtw (Jun 22, 2017)

Beam on concrete pier.


----------



## Bronson77 (Apr 6, 2020)

de-nagorg said:


> We get nearly the same weather as northern Colorado, So, here Goes.
> 
> Set your piers back from the rim edge about 2 " to be able to use T1-11 siding as your skirt, around the perimeter to the ground, this will keep the wildlife out from under your cabin.
> 
> ...



Ed, that's very helpful. When you say set back the pier from the edge, I'm not sure how to do that. I know why you say it, because you need the T1-11 to be flush against the outside edge of the board, but i'm unsure of how to get the pier underneath the outside boards unless the pier itself is a smaller diameter or the bracket is off center?

See the image below:


----------



## Bronson77 (Apr 6, 2020)

Nealtw said:


> Beam on concrete pier.


Nice! Yeah that definitely helps me visualize what is going on. Thank you! As I mentioned to Ed in my last post, I'm not sure how to keep the pier from protruding the outside edge of the boards as to use T1-11 for siding without it hitting the pier. Any ideas?


----------



## Nealtw (Jun 22, 2017)

Build your floor above the beams or hung from the beams. Build the exterior wall with 2x6s and bump them out an inch or two just like they do when the insulate the outside of a foundation.


----------



## Bronson77 (Apr 6, 2020)

Nealtw said:


> Build your floor above the beams or hung from the beams. Build the exterior wall with 2x6s and bump them out an inch or two just like they do when the insulate the outside of a foundation.


Got it! I'm an idiot haha. I'm a newbie. Thanks for clarifying.


----------



## Bronson77 (Apr 6, 2020)

Would this be a good example of what you were explaining to me about building above the beams?


----------



## Nealtw (Jun 22, 2017)

Bronson77 said:


> Would this be a good example of what you were explaining to me about building above the beams?


 That is normal with decks where we keep them back a foot or two but with out an engineer there are better ways to cheat. 

You can straight side a sono tub by adding a piece of plywood down to ground level 

You build the floor with the rim on the edge of the beam and add another rim to the outside. Then if you kick the wall out a bit, you can get there.


----------



## Bronson77 (Apr 6, 2020)

What size diameter tube should I go with?


----------



## Nealtw (Jun 22, 2017)

Bronson77 said:


> What size diameter tube should I go with?


the 64,000$ question and what size footing? :biggrin2:


----------



## Bronson77 (Apr 6, 2020)

I'm gonna draw up your recommendations in Sketchup and I'll post an image later so you can see. I really appreciate the help. You guys are an awesome resource.


----------



## Bronson77 (Apr 6, 2020)

Ok, so here's what I have so far... 28x40. Looks like I needed 6 piers one way, 5 the other. 7ft between the 5, 8ft between the 6.

2x10s doubled up everywhere. 12" sonotubes










Does this look ok?


----------



## de-nagorg (Feb 23, 2014)

Looks like you overlooked the need for skirting, To seal it from wildlife, you need to alter the contact area between the concrete and the joists.

or use Neal's suggestion to flatside the pier, and hang the wall over an inch or two.

But yes that is the basic drawing for this kind of thing. 

One other suggestion, on installing the piers.

On one of my projects, we were on solid granite for one whole row of piers, and we had a power augur to bore the hole.

Well it took nearly 2 hours for a 2 man gas powered augur operated by 2
" rent-a-gorillas", myself and a buddy. Both of us over 6' tall, and over 250# each. to bore one hole.

Took a full 8 hour day to complete that row, and dang we were beat afterward.

So try to pick a spot that is more dirt than rock to build on.

ED


----------



## Nealtw (Jun 22, 2017)

Bronson77 said:


> Ok, so here's what I have so far... 28x40. Looks like I needed 6 piers one way, 5 the other. 7ft between the 5, 8ft between the 6.
> 
> 2x10s doubled up everywhere. 12" sonotubes
> 
> ...


Draw in the interior walls unless you are using trusses for the roof.


----------



## Bronson77 (Apr 6, 2020)

de-nagorg said:


> Looks like you overlooked the need for skirting, To seal it from wildlife, you need to alter the contact area between the concrete and the joists.
> 
> or use Neal's suggestion to flatside the pier, and hang the wall over an inch or two.
> 
> ...



Ed, yeah I had an idea on the skirting problem. I drew it up in the picture below. Basically blocking on another 2x10 to the outside to the edge of the sonotube. Backing off the 2x6 wall 1/2" beyond the outside board to create a place for 1/2" skirting. Does this look acceptable to you?

Being I would need sheathing + siding on the outside walls, I thought 1" over hang beyond the skirting would look ok?


----------



## Nealtw (Jun 22, 2017)

The plan on the left is the lay out of the piers under this house
It is a single story house so no real load bearing walls.
The red line represents the wall on the right in the picture It is 1 1/2" lower than the wall on he left which has a beam under it.


----------



## de-nagorg (Feb 23, 2014)

Bronson77 said:


> Ed, yeah I had an idea on the skirting problem. I drew it up in the picture below. Basically blocking on another 2x10 to the outside to the edge of the sonotube. Backing off the 2x6 wall 1/2" beyond the outside board to create a place for 1/2" skirting. Does this look acceptable to you?
> 
> Being I would need sheathing + siding on the outside walls, I thought 1" over hang beyond the skirting would look ok?


Looks great.

Now add flashing, all around to direct any rain off the skirt, to prevent premature rotting, and you are good to build the cabin.


ED


----------



## Bronson77 (Apr 6, 2020)

So with 4x8 subflooring, is it better to have 24" OC joists or 16"? Seems 16 would be a lot of trimming.


----------



## Nealtw (Jun 22, 2017)

Bronson77 said:


> So with 4x8 subflooring, is it better to have 24" OC joists or 16"? Seems 16 would be a lot of trimming.


Best you re think that. 16 is what we do. As long as you put the first joist at 15 1/4" you are good.


----------



## de-nagorg (Feb 23, 2014)

Bronson77 said:


> So with 4x8 subflooring, is it better to have 24" OC joists or 16"? Seems 16 would be a lot of trimming.


Trimming of what?

They are designed for 16" OC, or 24" OC.

Both will work, but you get a better covering with 16". 

I would get T&G flooring 2X6 as my floor though.


ED


----------



## Bronson77 (Apr 6, 2020)

Neal good thinking on the 15.25". Worked perfectly. Here's some of the flooring down over the joists. Should I block in between the joists?

Ed, why would you use T&G as opposed to 1/2" flooring? I'm curious to know the pros and cons. Thanks!


----------



## Nealtw (Jun 22, 2017)

Bronson77 said:


> Neal good thinking on the 15.25". Worked perfectly. Here's some of the flooring down over the joists. Should I block in between the joists?
> 
> Ed, why would you use T&G as opposed to 1/2" flooring? I'm curious to know the pros and cons. Thanks!


If your beams are not more than 7 ft apart you do not need bridging or blocking. 

If you are using Adventech floor sheeting where they are a full 48" wide, your picture is fine. If you are using T&G plywood it is only 47 1/2" wide so you start with a 1/2 sheet and plan for one extra row.:wink2:


----------



## de-nagorg (Feb 23, 2014)

For my time and money, T&G, is stronger, only needs one layer, no need for sub-floor, then top layer.

Nailed down correct, it adds strength to the framework.

And on one side up it is flooring, then flipped over it can be used as the roofing, leaving the exposed V grooves showing. 

Besides I'm a sucker for the looks of fine finished wood.

It can be finished with any sealer, can be refinished several times over it's lifetime. 

And it looks good too.


ED


----------



## Nealtw (Jun 22, 2017)

de-nagorg said:


> For my time and money, T&G, is stronger, only needs one layer, no need for sub-floor, then top layer.
> 
> Nailed down correct, it adds strength to the framework.
> 
> ...


My point was T&G plywood looses 1/2 to 5/8" per sheet so 7 sheets comes up 3" short of the back of the house and you need more than that to tie the rim joist securely to the floor.


----------



## de-nagorg (Feb 23, 2014)

Nealtw said:


> My point was T&G plywood looses 1/2 to 5/8" per sheet so 7 sheets comes up 3" short of the back of the house and you need more than that to tie the rim joist securely to the floor.


Yes you are correct.

I was answering his query in post #30, where he asked why I prefer to use real 5/4 T&G flooring. 

I should have been specific, and not confused you. 

ED


----------



## Nealtw (Jun 22, 2017)

de-nagorg said:


> Yes you are correct.
> 
> I was answering his query in post #30, where he asked why I prefer to use real 5/4 T&G flooring.
> 
> ...


I wasn't sure. :wink2:


----------

