Rate my foundation.

[wfopete]

Arkansas. Stick built in the late 70's, single story 30'x40' home.

2"x6" floor joist, 16" o/c. Piers with supporting gridders roughly every 7' beneath the floor joist. Black poly underneath it all.

I dug down 12"-18" (maybe more) along the outside of the block and the footings are barely wider than this 5.5" wide block. Can't tell if rebar was used but there isn't any evidence of failing block or foundation problems. The block is only 3 courses high so with the HVAC in place it's pretty tight under there.

Is this considered a sound build? Where would potential problems be and what should I look for? Thx.

 

[d.mcfarland]

It was built 50 years ago and has "no evidence of problems".

What do you possibly need to know? Seems like it's fine.

 

[wfopete]

Like they say: You don't know what you don't know.

I came here from Michigan and it seemed that foundations are/were a lot more robust than this. That might have something to do with frost lines and such that doesn't apply down here.

 

[mike93lx]

Like they say: You don't know what you don't know.

I came here from Michigan and it seemed that foundations are/were a lot more robust than this. That might have something to do with frost lines and such that doesn't apply down here.

It absolutely does. 4ft+ frost VS virtually none

 

[bowtie327]

To answer your question, I say ‘Yes’ its sound. Just based off the facts of age and that you have no foundation issues. In that, I agree with d.mcfarland and would not think anymore about it.

I don’t know what the building code’s for footings were back in the 1970’s, if they even had any. But today, 12” is considered the minimum width.

Footing requirement's are based on loads and soil bearing capacity. Having piers every 7’ really spreads those single story loads out

Just curious, what size are your floor joists?

Now if you are going to add another story or a lot of weight to your existing structure (like a huge, fully stocked library), you should have an engineer evaluate it.

 

[wfopete]

To answer your question, I say ‘Yes’ its sound. Just based off the facts of age and that you have no foundation issues. In that, I agree with d.mcfarland and would not think anymore about it.

I don’t know what the building code’s for footings were back in the 1970’s, if they even had any. But today, 12” is considered the minimum width.

Footing requirement's are based on loads and soil bearing capacity. Having piers every 7’ really spreads those single story loads out

Just curious, what size are your floor joists?

Now if you are going to add another story or a lot of weight to your existing structure (like a huge, fully stocked library), you should have an engineer evaluate it.

Joist are a little wimpy (2x6 on 16" o/c) but having 2x6 gridders on piers every 7' helps. Yeah, I figured this was totally based on a single story. Throw another story on and the whole thing goes out the window.

 

[abfish]

I've done a walkthrough of an 1830's building with a structural engineer. Didn't really require the services of a engineer, but he offers his services for free to this non profit group, A lot of commonsense stuff-

-Are the floors inside the house level? Any signs of settlement? Any "bounce" to the floor system?
-Are the mortar lines on the outside of the foundation level? Any cracks in the masonry or motor? Cracks that run vertically through masonry courses are particularly concerning
-Any signs of masonry repair?
-Are the outside walls plumb?

In the crawlspace, we looked for similar issues as well as evidence of standing water, rot and termites.

In this case, an experienced engineer gave the building a good bill of health in a coupe of hours. If he had found problems, he would have recommended further investigation.

 

[PWC Repair]

I'm in Northern Central Arkansas (mountain Home area). I've been under SEVERAL older homes around here. The 5" wide block seems uncommon, mostly 8" or formed and poured around here BUT it's probably the old fashioned "heavyweight" block that doesn't seem to exist anymore. The shallow footer is also common. We only have a 12" deep frost line here and that's only once in a blue moon! I have also noticed ALL 2x6 construction of the floor with many of the older ones being somewhat weak and bouncy. Sounds like yours was as good as it ever got in this area. with the extra girder and supports.

 

[WillyBoy]

2x6 joists with a seven foot span, 16 inches on center sounds like it should be stiff enough, but if it feels "bouncy" then clearly it's not that stiff. It's probably not going to collapse and it's likely that sistering 2x8's onto the existing joists wouldn't gain enough stiffness to be worth it.
Does "supporting gridder" mean a solid vertical support holding the ends of the joists or does that mean that's the spacing between solid blocking between joists?

 

[Superbowl]

Joist are a little wimpy (2x6 on 16" o/c) but having 2x6 gridders on piers every 7' helps. Yeah, I figured this was totally based on a single story. Throw another story on and the whole thing goes out the window.

2x6 joists 16" on center are not wimpy when they only span 7 ft. That is plenty strong enough and likely have little to no bounce because the span is so short.

I am wondering if the OP dug all the way down to the bottom of the foundation on both sides to be sure what the foundation size actually is as it could be stepped. What you need depends a lot on the soil. If it is hard pan, not much foundation is needed. If soft sand or just top soil, that is a different matter.

 

[bowtie327]

Per the span chart, 2x6 16” oc @ 7’ is well within spec.

https://up.codes/viewer/general-services-administration/irc-2024/chapter/5/floors#R502.1

 

[wfopete]

2x6 joists with a seven foot span, 16 inches on center sounds like it should be stiff enough, but if it feels "bouncy" then clearly it's not that stiff. It's probably not going to collapse and it's likely that sistering 2x8's onto the existing joists wouldn't gain enough stiffness to be worth it.
Does "supporting gridder" mean a solid vertical support holding the ends of the joists or does that mean that's the spacing between solid blocking between joists?

From each end of the sill plate, every ~7' there is a 2x6 gridder running perpendicular under the floor joists. So on a 30' run the joist are supported by 2 sill plates at each end and three rows of gridders. No bouncing noted.

 

[TRWham]

I think you mean girder, which is generally understood as a horizontal member (i.e. beam) running below and (usually) perpendicular to other horizontal members (joists or other beams) that bear on the girder(s).

I have worked on older structures where their idea of a footer was a flat spot scratched into the dirt. 2x6 joists are usually a bit skimpy but that they are only spanning 7' means that is not an issue so long as those girders are not spanning too far. How are the girders supported?

 

[Paco Pena]

If it ain't broke, don't fix it. I know that run's against the Garage Journal philosophy.

Paco

 

[BombShelter]

From what I hear, the larger issue is vapor transmission from the ground up, that's why there's plastic on the ground. Looks underneath for water damaged boards.

If any of the blocks are concerning, you can drill a 3-4" diameter holes on the exterior and fill the cores with concrete (and rebar if there's room).

 

[wfopete]

I think you mean girder, which is generally understood as a horizontal member (i.e. beam) running below and (usually) perpendicular to other horizontal members (joists or other beams) that bear on the girder(s).

I have worked on older structures where their idea of a footer was a flat spot scratched into the dirt. 2x6 joists are usually a bit skimpy but that they are only spanning 7' means that is not an issue so long as those girders are not spanning too far. How are the girders supported?

Thanks, yes girders! The girders are supported by cinder block piers. I could not tell how many piers were placed lengthwise due to duct work blocking my view but I would think they would be the same 7' spacing which would workout to five for the 40' length of the house. So 3x5 would give me 15 piers total.

 

[TRWham]

Thanks, yes girders! The girders are supported by cinder block piers. I could not tell how many piers were placed lengthwise due to duct work blocking my view but I would think they would be the same 7' spacing which would workout to five for the 40' length of the house. So 3x5 would give me 15 piers total.

So at 7' I think you are good, especially if you don't feel any excess deflection (i.e. "bounciness'). It seems a strange way to frame a floor, because they could have framed it more conventionally with 2x10s and fewer piers and beams, but perhaps they had a bunch of 2x6s to use up.