New Construction Basement/Porch Foundation

741 Views 21 Replies 4 Participants Last post by Nealtw, 6 mo ago

detroiit

Discussion Starter · 6 mo ago

4

Hello Everyone,

Was wondering when pouring the foundation walls/porch for a new construction residential how come with the smaller porch design (plan1 and plan1.1 jpg) does the foundation wall extend all the way down to basement and is closed off and then just filled with dirt for the slab to rest on.. is it more efficient this way or is it because it is a 2 story entrance? The other plan2 and plan2.2 has a bigger porch but is UNexcavated and looks calls for cmu or poured stem wall but is not a two story or is that because it is inefficient (waste of concrete/expense) this route so they would backfill as normal up to the main foundation wall then trench out?

Thank You

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Nealtw

· #2 · 6 mo ago

Is one at ground level and the other in need of stairs off the porch?

detroiit

Discussion Starter · #3 · 6 mo ago

Nealtw said:
Is one at ground level and the other in need of stairs off the porch?

They both require a step onto porch.

Reactions: 1

Nealtw

· #4 · 6 mo ago

detroiit said:
They both require a step onto porch.

I don't understand what he wants it for.

detroiit

Discussion Starter · #5 · 6 mo ago

Nealtw said:
I don't understand what he wants it for.

The question is about the foundation wall extending down to the basement and closed off vs the plan with the larger porch is unexcavated. Was wondering why the excavate all the way down and finish off the porch well below for the smaller porch.

Nealtw

· #6 · 6 mo ago

detroiit said:
The question is about the foundation wall extending down to the basement and closed off vs the plan with the larger porch is unexcavated. Was wondering why the excavate all the way down and finish off the porch well below for the smaller porch.

Is one door at the basement level?

3onthetree

· #7 · 6 mo ago

The reason is the excavation overdig.

The shallow porch is within the basement's overdig, and you can't levitate the porch foundation pour in the air, so it will be a full basement story pour. It doesn't matter structurally, it is only about methods of construction. Waiting for backfill then pouring the porch later would just settle with the backfill and extend the foundation pour project timeline.
The deeper porch is beyond the basement's overdig (that example drawing may not have a basement anyway, and the porch is shown as a trench, but for discussion it has a basement and porch footings). So the porch foundation can just go to frost depth, and the part of the porch foundation wall will be bridged into the basement wall (haven't seen it done, but it appears the "CMU Lead" is filling under the bridge with CMU).

Here is the excavation in RED for the full story basement, in BLUE just to the frost depth:

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Matt1963

· #8 · 6 mo ago

In the second picture this assumes that you don't have to over dig even farther. Soil conditions effect the over dig.

Nealtw

· #9 · 6 mo ago

detroiit said:
The question is about the foundation wall extending down to the basement and closed off vs the plan with the larger porch is unexcavated. Was wondering why the excavate all the way down and finish off the porch well below for the smaller porch.

Here, they dig the hole for the basement 5 ft bigger all around for safe working in the hole.
So the smaller porch would be in that 5 ft so they are saying add another 4 ft to the width and include that foundation in the hole
The bigger porch is outside that 5 ft hole and only needs to be down to frost depth.

detroiit

Discussion Starter · #10 · 6 mo ago

3onthetree said:
The reason is the excavation overdig.

The shallow porch is within the basement's overdig, and you can't levitate the porch foundation pour in the air, so it will be a full basement story pour. It doesn't matter structurally, it is only about methods of construction. Waiting for backfill then pouring the porch later would just settle with the backfill and extend the foundation pour project timeline.

The deeper porch is beyond the basement's overdig (that example drawing may not have a basement anyway, and the porch is shown as a trench, but for discussion it has a basement and porch footings). So the porch foundation can just go to frost depth, and the part of the porch foundation wall will be bridged into the basement wall (haven't seen it done, but it appears the "CMU Lead" is filling under the bridge with CMU).

Here is the excavation in RED for the full story basement, in BLUE just to the frost depth:
View attachment 722156

OVERDIG! That makes sense. So the main reason is efficiency and as well as the over dig area if it remains mostly undisturbed in the bigger/deeper porch allowing the soil to not have to settle then it's good and they go 42" below after the basement is backfilled for porch footings. But like @Matt1963 is saying that is assuming they do not even have to dig even further which then in turn that entire porch area would be done with the basement like the smaller porch and filled with dirt and then do the slab as usual I'm assuming since it's possible it could be in the overdig area.

Both plans do have basements and to the right are the garages.

Nealtw

· #11 · 6 mo ago

detroiit said:
OVERDIG! That makes sense. So the main reason is efficiency and as well as the over dig area if it remains mostly undisturbed in the bigger/deeper porch allowing the soil to not have to settle then it's good and they go 42" below after the basement is backfilled for porch footings. But like @Matt1963 is saying that is assuming they do not even have to dig even further which then in turn that entire porch area would be done with the basement like the smaller porch and filled with dirt and then do the slab as usual I'm assuming since it's possible it could be in the overdig area.

Both plans do have basements and to the right are the garages.

We have had builder that will not dig the whole garage to basement level and have the far corner at frost depth. With stepped footing and working up and down slopes.
It makes for a royal pain in the ass for the people doing the foundation. If it is a close call have it dug out.

Matt1963

· #12 · 6 mo ago

detroiit said:
OVERDIG! That makes sense. So the main reason is efficiency and as well as the over dig area if it remains mostly undisturbed in the bigger/deeper porch allowing the soil to not have to settle then it's good and they go 42" below after the basement is backfilled for porch footings. But like @Matt1963 is saying that is assuming they do not even have to dig even further which then in turn that entire porch area would be done with the basement like the smaller porch and filled with dirt and then do the slab as usual I'm assuming since it's possible it could be in the overdig area.

Both plans do have basements and to the right are the garages.

Because you have a 42inch min cut (Frost) then you most likely will be ok in picture two. (It's 12 inches were I am)

To be in a safe working hole, labor and industries in my state makes me be 2 ft clear at the bottom of a hole, then I can go straight up 4ft and then 1 to 1 slope from there to the upper grade.

So on an 8ft cut (basement) you would then bench cut about 4 feet up and excavate the porch from there. Footing and walls would tie in and just step to grade. One pour.

Other factors can apply.

Are you trying to figure out budgets based upon designs?

When estimating these kinds of excavations and foundations one must do an educated guess and then explain to the owner how such estimates were done.

Most builders are much more comfortable after the hole is backfilled.

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detroiit

Discussion Starter · #13 · 6 mo ago

Matt1963 said:
Because you have a 42inch min cut (Frost) then you most likely will be ok in picture two. (It's 12 inches were I am)

To be in a safe working hole, labor and industries in my state makes me be 2 ft clear at the bottom of a hole, then I can go straight up 4ft and then 1 to 1 slope from there to the upper grade.

So on an 8ft cut (basement) you would then bench cut about 4 feet up and excavate the porch from there. Footing and walls would tie in and just step to grade. One pour.

Other factors can apply.

Are you trying to figure out budgets based upon designs?

When estimating these kinds of excavations and foundations one must do an educated guess and then explain to the owner how such estimates were done.

Most builders are much more comfortable after the hole is backfilled.

Makes sense so the the bench cut area is pretty much left alone and the 2ft clear area would just be back filled and as you stated there is a 42" cut after the fact so porch can be trenched out after and either poured or cmu block. The reason behind this was to see how excavation efficiency plays a role and this can be done with budget based on design, yes.

Nealtw

· #14 · 6 mo ago

detroiit said:
Makes sense so the the bench cut area is pretty much left alone and the 2ft clear area would just be back filled and as you stated there is a 42" cut after the fact so porch can be trenched out after and either poured or cmu block. The reason behind this was to see how excavation efficiency plays a role and this can be done with budget based on design, yes.

You save a little in concrete and back fill. We sometimes get that for a deck post footing that will be some distance away from the house.

Matt1963

· #15 · 6 mo ago

detroiit said:
Makes sense so the the bench cut area is pretty much left alone and the 2ft clear area would just be back filled and as you stated there is a 42" cut after the fact so porch can be trenched out after and either poured or cmu block. The reason behind this was to see how excavation efficiency plays a role and this can be done with budget based on design, yes.

The goal is to excavate once, pour once and backfill once. That's typically the most efficient way.

Site conditions don't always allow for that.

Reactions: 2

3onthetree

· #16 · 6 mo ago

detroiit said:
then it's good and they go 42" below after the basement is backfilled for porch footings

detroiit said:
and as you stated there is a 42" cut after the fact so porch can be trenched out after and either poured or cmu block

No, and I think you are even misunderstanding what Matt1963 said. You do not backfill and then re-excavate later for the porch when you have frost footings. Everything is dug at once, porch and all. A "bench" cut, if used in excavation, has to do with the earthen walls caving in, not the foundation. If the upper tier (the "bench") happens to be at the depth of the porch frost line, so be it. Whether you do a bench cut, or the angle of repose has to do with the type of soil you are digging in.

detroiit

Discussion Starter · #17 · 6 mo ago

3onthetree said:
No, and I think you are even misunderstanding what Matt1963 said. You do not backfill and then re-excavate later for the porch when you have frost footings. Everything is dug at once, porch and all. A "bench" cut, if used in excavation, has to do with the earthen walls caving in, not the foundation. If the upper tier (the "bench") happens to be at the depth of the porch frost line, so be it. Whether you do a bench cut, or the angle of repose has to do with the type of soil you are digging in.

Okay I see what you are saying now so it's all done at once. The area up against the foundation wall say if the wall is 8' and there is a 2' setback that is completely dug out all 8' down (the area you have showing in red) but 6' back where the bench cut/porch is (area shown in blue) you take down only 42" and pour the footings just for the porch so not as deep as the foundation wall and build up the porch all in one go. The area between would be re-filled though I'm assuming (shown in purple). P.S those racoons are too damn cute lol.

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3onthetree

· #18 · 6 mo ago

2

That drawing markup is not to scale, it was just for discussion, so I don't know how far out an excavator at your site would choose to dig. I assume that is not your house anyway because both drawings of house designs are so different.

So here are a couple interweb photos that might help put this to rest (they are elusive photos googling with the word "bridge"). There is a gap in the overdig under the higher elevation footing - and this is where the "CMU Lead Wall (Typ)" comes into play, I believe they are saying to infill under the bridge with CMU after the pour has been stripped ("Typical" means it is a contractor decision on where and how many, not the designer to dictate). I haven't ever seen the CMU, usually you just load up the rebar at the bridge.

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Nealtw

· #19 · 6 mo ago

detroiit said:
Okay I see what you are saying now so it's all done at once. The area up against the foundation wall say if the wall is 8' and there is a 2' setback that is completely dug out all 8' down (the area you have showing in red) but 6' back where the bench cut/porch is (area shown in blue) you take down only 42" and pour the footings just for the porch so not as deep as the foundation wall and build up the porch all in one go. The area between would be re-filled though I'm assuming (shown in purple). P.S those racoons are too damn cute lol.

How far is it, your red line showing eight feet deep would be 5 ft from the house?
The depth of the higher footing is dictated by the distance to the raised footing.

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Nealtw

· #20 · 6 mo ago

3onthetree said:
That drawing markup is not to scale, it was just for discussion, so I don't know how far out an excavator at your site would choose to dig. I assume that is not your house anyway because both drawings of house designs are so different.

So here are a couple interweb photos that might help put this to rest (they are elusive photos googling with the word "bridge"). There is a gap in the overdig under the higher elevation footing - and this is where the "CMU Lead Wall (Typ)" comes into play, I believe they are saying to infill under the bridge with CMU after the pour has been stripped ("Typical" means it is a contractor decision on where and how many, not the designer to dictate). I haven't ever seen the CMU, usually you just load up the rebar at the bridge.
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I spent 3 hours explaining that bridge to a new engineer one day. He made 4 phone calls before he passed it and let us pour concrete. We lost a day over that.

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