|
| Author |
Message |
Tonerboy
Member
|
# Posted: 7 Aug 2025 12:27pm
Reply
Ok, here's my thinking I'm going to make the base frame (beams) out of 3-2x8 so I want a post that supports all 3 boards. A treated 8x8 post runs $40-50ft depending on length. 24 5ft posts will be $950-1,200. a built-up 8x8 post of 2x8 runs about $15, so 24 would be $360 which is a HUGH savings.
Let's talk about why I shouldn't do this. Posts will be set 36in deep in an 8in hole
This is for a 16x24 "stoney type" small house
|
|
MtnDon
Member
|
# Posted: 7 Aug 2025 05:39pm - Edited by: MtnDon
Reply
When beams are built up, they are positioned 'upright', resting on the edge of the 2x. So a beam made of three 2x8 is 4.5" wide and 7-1/4 inches tall.
No need for 8x8 piers, unless I don't understand your plan.
|
|
gcrank1
Member
|
# Posted: 7 Aug 2025 06:36pm - Edited by: gcrank1
Reply
I strongly recommend Not doing wood piers to avoid problems in the future. A structure of 16x24 is very heavy. Trying to fix problems beneath later is not something to take lightly, we've had more than a few inquiries here on how to fix failed piers to save a cabin.
Remember that you build from the bottom up and just adequate is not as good as overkill down there. If you dont get it right down there the rest up top is kind of a waste of time and money.
|
|
DRP
Member
|
# Posted: 7 Aug 2025 06:38pm - Edited by: DRP
Reply
Whoops, I see others have chimed in, well, more grist for the mill,
Why an 8x8 if it is only supporting 4.5" of beam width?
Engineering wise, for the code ref info go to awc.org>standards> NDS and NDS commentary, Built up columns is 15.3 and after. Basic columns are in chapter 3. Can you do it, yes, nails on 6" spacing or closer, probably at least 2 rows.
Your foundation idea is, uhh politely, needing help. Design wise, with napkin numbers there's probably about 20 tons on top of those spindly legs, how are you bracing that?
|
|
Grizzlyman
Member
|
# Posted: 7 Aug 2025 07:42pm
Reply
I would imagine it’s probably fine for compressive force only but that’s not the reality. for any rotational or shear forces the smalller 2x8 would not transfer the load evenly between them and if the connections fail then the boards would want to slide over each other. Or could twist and individual boards could crack and then there goes all the strength.
Here’s what Google says:
……
Disadvantages:
Lower strength compared to solid posts in the strong axis: Built-up posts typically have a reduced strength compared to solid posts of the same material and dimensions.
Requires proper construction: The connections between the individual pieces of a built-up post must be carefully designed and installed to ensure adequate strength and stability.
Potential for slip: In mechanically laminated built-up posts, there can be slip between the layers under load, which can reduce strength.
Key Considerations:
Load requirements:
Solid posts are generally preferred for applications with high compressive loads.
……..
You could use 6x6s posts and not need to do 8x8 and that should lower your costs.
Solid posts seem like a relatively cheap insurance policy IMO
|
|
Brettny
Member
|
# Posted: 8 Aug 2025 09:55am
Reply
Is your frost line 36in? If so just pour sono tubes right up to the bottom of your tripple 2x8 girder. No fancy brackets needed, no wood to rot and no bracing needed later. It also dos t cost much different.
I would never do wood posts in the ground for a building I cared about. Although I have a firewood shed that uses telephone poles in the ground. It also uses no concrete around them. Just tamped the clay back in and made sure surface drainage was really good at getting water away. I bought telephone poles for $1ft. That's why I did this.
|
|
Tonerboy
Member
|
# Posted: 8 Aug 2025 03:30pm
Reply
OK
|
|
DRP
Member
|
# Posted: 8 Aug 2025 08:28pm
Reply
Quoting: Brettny and no bracing needed
What!?
|
|
|
Tonerboy
Member
|
# Posted: 9 Aug 2025 11:52am
Reply
OK, my screwup. The reason for the 5-2x8 layer post was to fit better into the 8" hole with minimul repack/fill. I appreciate all of the comments re why it's NOT a good idea and understand a "house built on firm foundation" concept
Scouting out ideas instead of holes, sonotubes, concrete, simson ties, etc. I'm in Texas so no "freeze line"
Maybe the route of spending more $$ on getting the site level and concrete pads and block will be better
|
|
Aklogcabin
Member
|
# Posted: 10 Aug 2025 07:08am
Reply
I built our 16x24 log cabin using utility poles that had been replaced. Got them from the company doing the work. Cedar, and coated will a product to reduce rot.
Drilled holes with 2 man auger down 4' and put redi mix concrete in the holes for backfill. I have not seen any issues concerning deterioration. The cement does not allow water to set next to the poles.
Only issue we had was a 7.4 earthquake that caused the slight, tilt because I didn't cross brace. But I even have trees near the cabin that did the same thing. Pretty extreme.
To set the support beams , I used 6x12 i Got from local saw mill that made the 3 sided logs, for the floor. I cut a shoulder into the top of the post and bolted it. Very solid.
A lot depends on your accessibility also. I'm very remote. And everything freighted in with snogos. But I'd suggest this type of foundation based on our experience. Because it is working great.
|
|
Brettny
Member
|
# Posted: 10 Aug 2025 07:44am
Reply
When your girders rest directly on the sono tube you done need bracing. Unlike when you go sono tube, wood post ontop then girder. I would not put posts in the sono tube for the same reason as to not have wood in the ground. Concrete is just one big sponge.
|
|
DRP
Member
|
# Posted: 10 Aug 2025 10:53am
Reply
You are eliminating one pinned joint by not putting a post on a pier but the pier is still simply pinned to the girder, unbraced. There does need to be bracing from the pier, sonotube, to the structure to prevent overturning of the pier. That is the purpose of the code prescribed perimeter foundation walls. This is the reason pier type foundations have been moved to engineer required. They go without some form of independent bracing, undersized to develop soil bracing, improperly backfilled for the soil to act as bracing, and they then tend to overturn when lateral force acts on them.
Here is the first part of chapter 4, the foundation chapter in the code;
"All exterior walls shall be supported on continuous solid or fully grouted masonry or concrete footings, crushed stone footings, wood foundations, or other approved structural systems that shall be of sufficient design to accommodate all loads"
With the foundation walls being tied to the floor diaphragm, when there is a lateral push on one side or another of the building the overturning force is resisted by a long wall line that is not going to overturn.
Another thought with the no frost info. Under this sized building a 12" deep x at least 12" wide trench at the perimeter filled with at least 6" of clean gravel and a treated "crib" of 6x6's to form foundation walls, a stack 2 high would be sufficient on level ground and a 8" gravel depth. Rim joist and joists on the 6x6 foundation, no girders or posts. Screw down mobile home anchors for uplift. I think the cost would pencil out well. A garden tiller and a few hours of shoveling could make that trench is decent soil pretty quickly.
|
|
Brettny
Member
|
# Posted: 11 Aug 2025 06:44am
Reply
Of corse you need to attach the girder to the sonotube. I'm not going to site code from the book. If someone wants to read it then can.
My foundation passed with no continuous masonry wall/footing. It dosnt even have skirting nor will it ever.
|
|
Aklogcabin
Member
|
# Posted: 11 Aug 2025 11:18am
Reply
I guess I'd have to disagree that concrete acts like a big sponge. Quite possible if you bring the cement up above the ground level n and make it so water sheds away that water would not go down next to a pole in the ground that now has dirt less compacted than the undisturbed dirt. And water doesn't get near the wood. And in my use I have 3 foot overhang. So water doesn't get to it. Notice how the snow pile doesn't get even get next to them.
I've looked at the pilings many times. Absolutely no none sign of any issues at all with the integrity of them.
Not sure why folks dump on what others have accomplished successfully.
Also the type of construction has a lot to do with access. No roads where I'm at. And had to be done in the early spring when we could still get snogos there.
|
|
Grizzlyman
Member
|
# Posted: 11 Aug 2025 12:25pm
Reply
Aklogcabin
100% agree
I can tell you with 100% certainty my build would have been different if I had road access. But i don’t- Full stop. Things like cement trucks (or even powered mixers) for that matter are out of the question.
Hauling materials is 75% of the job when you’re road inaccessible- and limits what you do. That’s why this site is so helpful. We work with what we’ve got.
|
|
Aklogcabin
Member
|
# Posted: 12 Aug 2025 09:21am
Reply
10-4 Grizz. And doing your homework. Can't forget anything. But that's what makes building remote kinda fun. But certainly harder and you have to get kinda creative.
I still don't think cement, rocks ,suck up water
|
|
MtnDon
Member
|
# Posted: 12 Aug 2025 11:00am
Reply
Concrete, while it may appear to be a solid impervious mass is not. As concrete cures pores and capillaries form. These are small, but moisture can be absorbed from the soil or humid air as well as the more obvious sources such as rain and snow melt.
Moisture in concrete can transfer to any wood that is in direct contact with the concrete. That is why a waterproof membrane may be specified under the wall sill plate. Wood in contact with concrete may also need to be pressure treated to meet code. Similarly, the porosity of concrete is why waterproof membranes or coatings are used on the exterior of a concrete basement wall. A concrete water cistern will often have waterproofing on the inside.
As a related aside, here in NM most new homes use PT exterior wall sill plates on concrete slabs. As well, the lower 24" of the sheathed exterior walls (inside and exterior surfaces) are sprayed with a borate solution against termites, etc.
|
|
gcrank1
Member
|
# Posted: 12 Aug 2025 03:55pm
Reply
When I did 4x4PT posts for our deck I used BlackJack roofing 'tar' as a coating for what sits in the concrete; and domed the cap for runoff.
30yrs on and NO signs of any rot.
|
|
spencerin
Member
|
# Posted: 15 Aug 2025 09:14pm - Edited by: spencerin
Reply
Wood posts in the ground will work fine if done right. They have to be foundation grade, and when put in plastic sleeves (or other protective coating), they will last a long, long, long time. Many pole barns are built with the foundation grade posts put straight into the ground without sleeves, and they're standing strong decades later; adding the plastic sleeves will virtually eliminate all contact with moisture and insects.
|
|
|
