How do I place a post footer in a basement crawlspace? Unusual situation
I have a project going on that has me scratching my head. Just a bit of background first. I’m coming from a background in carpentry and interior remodeling but have little structural or new construction experience.
The main load bearing beam had previously been supported by a stone wall that was in turn, sitting on clay soil in a partial crawl space/basement. Somebody had come along and tried to excavate some of that earth but did not shore things up and the stone wall under the beam partially collapsed. I’m not certain how long the house sat this way.
Here’s where I come into the picture. Over the last several months I’ve brought an engineer in, excavated the soil down to the level of a concrete slab floor (in the finished portion of the basement), and now I’ve started to dig new post footings that will support the beam.
This is the tricky part that has me scratching my head. The last footer at the rear of the house is placed so close to the exterior foundation wall (old stone as well) I’m uncertain how to dig it safely and follow local code (Western PA).
Footer details are as follows: 24″x 24″ x 12″ center point placed 14″ from the exterior foundation wall only leaving me 2″ between the footer and foundation.
The caveat is that the exterior foundation wall does not extend to a depth below the intended finished floor. It stops about 2′ short since this was only a crawl space to begin with. With that in mind, you should know that I stopped my excavation 6-7′ away. I plan to eventually build a retaining to house the remainder of the crawl space. I was originally planning to place this footer as close to the original grade as possible. Am I on the right track here? In the area specified for the footer the soil is running unevenly down hill making placement of forms difficult. Am I able to dig this and smoothe it flat? How deep can I go? I estimate the bottom of the foundation is only 3′-4′ below the top of where I need to dig the footer. Should I just smoothe is flat and place it on grade? There are specifications about undisturbed soil I don’t understand. I’m really grinding my teeth on this one.
Replies
What does the engineer say regarding your question? If not already spec’d, seems incomplete on his end.
And, any stamped plan would be compromised with our input I would think.
Sounds like your engineer only looked at support of the beam, not at digging out the rest of the space to a depth lower than the existing crawl space wall. Did he give you plans? What do they say about the depth of the new footings?
how to treat the original crawl space wall to allow deeper basement close by is another engineering task. the details such as soil structure and nature of the wall, footing, and what is above would impact the specifics.
If you plan on a retaining wall and digging out the space in the future, you would not want to complicate this task by putting the beam support footing too shallow.
undisturbed soil means just that. on a scale of tens of years. In general, you dig a footing so that the dirt at the bottom of the hole is dug to the desired level, if you dig a little deeper, clean it out and make the footing thicker, not fill the bottom of the hole with dirt to get the elevation right.
Undisturbed soil does not mean place on whatever is on the surface when you show up.
A slab which does not act as a foundation can be laid on top of gravel, or even insulation boards.
He did give me plans. I believe he only considered the construction of the beam.
It does specify in the notes that “all exterior footings and foundation system shall extend below the frost line. in no case the bottom of the footings should be less than 12 inches below I disturbed grade” This is a bit confusing since these are interior footings.
The point of the excavation is to remove the collapsed soil and stone wall and provide clearance for new posts and footings not to lower the floor.
That close to the outside wall, I would understand the footing has to be located below the frost depth. (measured outside the building)
You would have to dig the hole close to the stone crawl space wall, being careful not to undermine the wall. If it turns out that you run out of wall next to you before you get below the frost depth, you will want to be careful digging to not dig under the wall.
You really don't have to form up the footing if the soil is stable enough to let you dig the hole and not have the sides fall in. It also should be ok if the hole ends up a little wider than you want. just will take a little more concrete.
Since you do not plan to dig out and use the space, you may want to backfill around this last post and up to the inside of the wall to help keep the old stone wall in place. This will depend on the details of your supporting column.
Compliance with local codes is best referred to the local building inspection department. If you have a permit for this work, they should be able to answer specific questions, and may want to look at the holes before you set the concrete.