Looking for opinions on the following situation:
I’d like to build a partition wall in my basement that will support the floor above but it would have to sit on a 4″ slab only with no footing below. It would be problematic to install a beam above because it would have to be snaked through many mechanicals that I would like to not remove. Slab is reinforced with 6x6x7 ga mesh. Joists above are just less than 8 ft simple span. and wall length would be 10 ft. Further, even if I put a beam above, I need to frame a wall below it anyway.
Tell me if I have the right thought process here: taking the 80sf above and dividing it in half for simple span gives 40sf. Multiplied by loading (50 lb live load plus 15 lb dead) gives a total weight of 2600 lbs max that the wall would carry. 2600 lbs spread over the sleeper on the floor (2×4= 3 1/2″ wide x 10 ft long= area of 2.92 sf) therefore load on the concrete slab is 890psf. If the concrete is conservatively 3000 psi compression strength the concrete alone is strong enough BUT without any real reinforcement it shouldn’t be acting as a footing.
The soil below is compacted well and I made the assumption that the sleeper on the floor is sufficient to distribute the load evenly. I could double it up if necessary too.
Any thoughts? Thanks in advance.
GregT
Replies
That would be PLF. Any roof load, second floor load? Was the stone beneath the slab compacted? You could also increase the size of the bottom plate, 2x6, 2x8 or larger. IMO it should be fine, but i'm no engineer.
no second floor or roof load. I thought too about increasing the size of the plate to 2 x 6 or 2 x 8.
Thanks for your response.
Generally speaking, the proper way to support any significant load on a slab is to 'haunch' the slab to 8" thickness for 14"-18" width under the wall and with rebar.
Jeff
It wouldn't be load bearing if you didn't cut any of the joists. The joists should already be bearing on both ends.
Basement walls are built all the time that bear no weight.
If you are cutting joists, double up the new rim. Hanger all the old joists. Then build your wall underneath.
Woods favorite carpenter
Edited 1/15/2008 2:43 pm ET by MattSwanger
Hi Matt:thanks for the response. I asked generically but your answer told me that I wasn't real clear. Your right, the existing joists bear on both ends now but would be shortened to bear on this proposed wall to allow a stair to come down in that space. The 10 ft of the existing bearing wall is going away therefore necessitating a need for new support.
One thing is for sure, if I bite the bullet and put a proper size beam (or new rim as you say) in place, I don't have to worry about it in the future. I do have support on both ends to do this, just not for the 10 ft span underneath.
I was in your hometown today. Hope your work has picked up and you have settled your employee problems.
GregT
Thats the way I would do it, header off the opening. Hanger all perpendicular josts. That way you are safe.
Your situation sounds like you would only dead load on the floor as well. No roof loading or second floor right? So you would only need to figure 10lbs x your sq ft.
>>I was in your hometown today. Hope your work has picked up and you have settled your employee problems<<
Work never slowed down. Been quite busy. Just the employee issue is still lingering. What were you doing in BC?
Woods favorite carpenter
Whats the damage if you guess wrong?
Sometimes the prevention is worse than the fix.
Bob's next test date: 12/10/07
So you had to go and throw that one in there. I was resolved to just do it right but in this case you may have a point.
""I was resolved to just do it right but in this case you may have a point."" Must be a little while since you spent all day redoing something and kicking your own azz for not having done it correctly from the start. How quickly we forget.
They can't get your Goat if you don't tell them where it is hidden.
My thoughts exactly.
Cracked slab comes to mind, giving Radon one more spot to infiltrate the home.
A few dollars in joists and hangers to header off the opening is the best fix, he is already saving all the labor money. Woods favorite carpenter
"Must be a little while since you spent all day redoing something and kicking your own azz for not having done it correctly from the start."
"How quickly we forget."
Yes my memory was suffering. July 21, 2007 comes to mind. Thanks for the reminder.
GregT
What is it really carrying? Joist only? Joist and ceiling joist? Roof? Will a gas line get severed if something sinks 1/4"?I've seen houses where the beam fell away from the floor system and the floor was just riding in thin air. The fix was to shim the beam back up tight. Every situation is different. I've seen a house built with internal bearing points that sunk. I spent a week in the basement shoring and jacking and pushing huge concrete pads out of site. It was a disaster. Bob's next test date: 12/10/07