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Old 01-17-2009, 11:09 AM   #1
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supporting floor joists in basement.


I'm going to cut 3 1st floor floor joists to make room for a new staircase design and location.
My question is how to support these joists.
I was thinking I could build a short section of wall (about 2.5') in the basement using PT as the soleplate and build up from there. I would need some kind of footer for it. How big of an area do I need for a footer?
Does this seem like a reasonable approach?
My original idea was to hang a joist header off of the closest full length joist and support that corner of the joist header with a lally column. I think the wall idea may be easier to build and result in a stiffer floor.
Any thoughts are appreciated.
TIA
There is a small error in the picture, the left most joist (blue) is actually a double 7.25 LVL.
The stairs are against the outside of the house (top and left) and the center bearing girder (bottom of pic).
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Old 01-17-2009, 01:29 PM   #2
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Personally the wall idea sounds better. I think I see what you're trying to do. Starting at the top of the stairs (which is the top left corner of the drawing), the stairwell comes down a few steps, and then turns 90 degrees.

I'd do the support wall idea. As far as footing size, that has to be calculated out, unless you wing it. And winging it probably isn't going to go over too well with anybody. You might have luck asking your building code official (I love the guy in my town) when you go for the permit, but he'll probably ask for a sealed drawing. If you lived by me, I'd have a sealed drawing wrapped up with a bow on its head for you inside of 2-3 hours. I'd talk to the town first, they're a free resource.

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Old 01-17-2009, 02:38 PM   #3
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supporting floor joists in basement.


Strangely, my town didn't question the footing. I told them I was going to put a footing there. They said call when it's all framed out.
I guess this drawing is a little confusing. This drawing is actually the first to second floor. The direction of travel is counter clockwise to go up. I'm going to basically repeat it for the basement stairs which will be directly below the main staircase.
Like I said, originally I was going to just use a lally column sitting on a 2' square x 1' deep footing baut now since the plans have changed to a wall instead, the bearing surface (sole plate of the wall) on the basement floor is much larger. Also the load is basically the tributary of an 8' x 3' floor and 2 short sections of wall. At most 1500 lbs. total load.
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Old 01-17-2009, 04:49 PM   #4
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supporting floor joists in basement.


I would just go with a wall
The only time I would install a footer is in a dirt basement

My notes on what I found for code on building stairs for my addition:

STAIRS: Min Width 36
Handrails should extend no more than 4.5 into the stairway, Min 34 up from the stairs 36
They need a support bracket every 4
MAX rise 7 inches, Min tread width 10
No more then 3/8 difference on tread widths (rise?)
Min head room clearance of 6 8
Slope of riser may not exceed 30 degrees
Max nosing extension (may vary)
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Old 01-17-2009, 04:59 PM   #5
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supporting floor joists in basement.


This is a load bearing wall and will be inspected so I think I'll need a footer. Besides our basement floor is only about an inch thick.
I found the minimum specs in the Massachusetts building code. Basically, a minimum of 12" wide by 6" would be adequate to support two floors. Given that, anything I do with the footing will be overkill.

Scuba Dave, you're quoting IBC code for stairs, Massachusetts (5311.5.3.1 and 5311.5.3.2) is 9" minimum tread x 8.25" maximum rise.
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Old 01-17-2009, 05:30 PM   #6
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supporting floor joists in basement.


That's strange, I checked my notes but I didn't include a link to where I found that info. Our stairs to the 2nd floor are 9.5" step & about 8.25" rise. MIL & wife hate 'em as they are too steep & do not give enough room to step. I don't have big feet & my sneaker is 12" from toe to heel
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Old 01-17-2009, 05:49 PM   #7
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My current staircase has 8 3/4" tread with nearly an 8 1/2" rise, so the new tread and rise will be a luxury.
Staircases take up a lot of room and when you have a small house like I do, you try to squeeze every square inch out of it.
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Old 01-17-2009, 09:12 PM   #8
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If it was me I would saw cut the existing slab and install a 1' wide by 1' deep by what ever length haunch with 2 #5 rebar. that will give you the proper haunch to support the wall and floor loads. BOB
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Old 01-17-2009, 10:03 PM   #9
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supporting floor joists in basement.


All you need to do is double up the first full lenth joist on either side of your stair opening and put a double joist header across and hang whays left of your cut joist on it.
You dont need to waste your time on any footing or concrete work.
This is how you frame a stair opening. Any framer should be able to tell you this. It is framing 101.
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Old 01-18-2009, 09:18 AM   #10
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supporting floor joists in basement.


Quote:
Originally Posted by Clutchcargo View Post
This is a load bearing wall and will be inspected so I think I'll need a footer. Besides our basement floor is only about an inch thick.
I think the reason he wants a footer is the basement floor is only 1" thick. Seems like a lot of weight would crack the floor.
Anyone know if using a 2x6 or 2x8 PT bottom plate would spread the weight out enough? If the floor is 1" I'd be inclined to pour a footer too I think
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Old 01-18-2009, 09:25 AM   #11
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supporting floor joists in basement.


But there is no weight. the joist carry everthing and the foundation walls carry the joists.
If he is worried about the stairs setting on the floor thats no more that the people walking around on it now.
I would set the stringers on a piece of 2x6 plate and nail that to the concrete but nothing more. If the concrete is 1" I guess you could break out a patch and make it 6" thick. Sidewalks and driveways are typically only 4".
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Old 01-18-2009, 09:36 AM   #12
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supporting floor joists in basement.


I could be misinterpreting the drawing, but I don't think you can frame it that way. You'd hit your head on your way up the stairs. I think the way it goes is you're going up the stairs starting at the top left of the picture, then half way up there's a landing (at the bottom left of the picture) and you make a 90 degree turn to go up the rest of the steps.
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Old 01-18-2009, 09:43 AM   #13
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supporting floor joists in basement.


Aggie you're correct. There are two landings and the basement staircase will be directly below the main staircase. That's why I need a break in the floor joists one both the first and second floor with a supporting wall supporing those joists. A 3d view would have made this much clearer.

The 1st Floor layout has changed slightly from this view but the staircase is still pretty much the same. The basement door and entry to bathroom have changed from this layout.

2nd Floor plan
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Old 01-18-2009, 09:50 AM   #14
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supporting floor joists in basement.


youre right Aggie. There is a landing there.

will there be a new wall added along the stairs?
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Old 01-18-2009, 09:52 AM   #15
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supporting floor joists in basement.


The wall he wants to build is circled in red
That would be a supporting wall as the joists would be supported by the wall. There will be 2 sets of stairs - one from the 1st to 2nd floor, the one from the basement to the 1st floor
So that is the reason you can't run the joist all the way to the outside wall

Is that right?

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