CMU Foundation Wall

[jrtm76]

I am a designing an 800 SF addition to an existing house and I am thinking a CMU crawl space foundation wall with I joist trusses are my best option since the grade is sloping from the rear of the house.
I am in north Georgia and wanted to get advice on what considerations I need to take on designing this wall system.
The CMU foundation wall will be carrying a 8' plate wall with pre-eng. roof trusses.
I appreciate all the help I can get from you great people!

JR

 

[PT999]

Basement walls are designed to resist both the vertical load applied and hydrostatic pressure from the adjoining soil (think of the wall as a dam resisting water pressure after heavy rain)

Poured concrete walls are always stonger than CMU walls, thus a poured concrete is a better choice, and even better if reinforced with rebar. Additionally below grade CMU walls must have their cells fully grouted, so that it becomes solid... but even so, still not as strong as poured concrete, because of the inherent weakness of the mortar joints.

So CMU walls are not a really good idea, and especially not a good idea if the adjoining earth is clay and thus has poor drainage. But if you are going to do it anyway, then add reinforcement, say #5 in every other cell, and make it thicker than the usual 8 or 10 inches.

I am speaking from experience in New York State where I have seen wall failures even in poured concrete walls.

But on the other hand if CMU walls is the way its done in your immediate local area, and nobody has had a wall blow out, then apparently soil conditions are good for drainage, and of course a CMU wall is no problem for vertical load.

Good luck, and have a Professional Engineer size and work this out for you, My comments are just general statements.

 

[jrtm76]

PT999,
Thank you so much for your comments and suggestions.

I agree with you that a continuous pour and rebar will be much stronger than a 2-system wall (footing + cmu).

The addition will only require a foundation wall that is about 32" high from existing grade plus the footing. I have seen many people in this part of the state use a concrete footing with a CMU wall, sill plate then the rest of the structure. The ground here in north Atlanta is red clay and our frost line is about 12".
The home owner wants (most of them do) whatever is cheaper to build, I am meeting with the basement company saturday to see what they suggest.

Do you know where one can find CAD details/.jpg drawings of this type of foundations?

Again, thanks for your suggesntion.

Jrtm76

 

[jrtm76]

<marquee direction=right behavior=scroll>any other suggestions?</marquee>

 

[shepherd]

jrtm76,


Contact the local building offical to determine which code you are required to follow. The code will provide prescriptive requirements for what you are looking for.

Shepherd