How to Frame on Sloping Slab

17 years ago

I would appreciate advice on a bit of framing I have to do over a slab that is presently sloped. Here's the deal.

We are in the midst of completing a 2-story, 1000 s.f. addition to our house in Austin, Texas, which we bought 18 months ago. The addition has a pier-on-footing foundation which is connected with bolts to the slab foundation of the house. Both the slab of the main house and the new piers-on-footing foundation are in great shape, well connected, and level. You can see photos of the addition with more explanation here:

http://www.johnhorse.com/ftp/addition.htm

Here's the problem: Next to the new addition is a 10'x12' office that sits on its own little slab, and this slab slopes gently away from the main house. The slope is especially noticeable now that the office butts up against the addition.

Now, what we want to do is demo the office and reframe it to 18' high, same as the addition, making an open 10'x12'x18' high space for a stairwell up to the 2nd story of the addition.

I would appreciate suggestions on how to deal, economically but sensibly, with the little sloping slab under the 10x12 office. Mudjack it? Coat it with a self-leveling top coat? Leave it and just adjust with the frames?

The total slope of the little slab is about 1 1/4" over a 10' run.

P.S. I'd also like to know what would be BAD ideas, since those are the ones I'm likely to gravitate to by nature.

Here is a link that might be useful: Photos of My Addition

Sort by:Oldest

Comments (4)

deckman22
17 years ago
Sounds like you build the office on top of a patio otherwise I don't understand why you have 1 1/4" of slope. Anyway don't try a concrete top coat, you need at least 3 1/2" of concrete for that & you only have 1 1/4". I would deal with it in the framing & leave the floor alone for the easiest fix.

Al
sierraeast
17 years ago
If the only thing hitting the existing slab will be the stairwell, then i would think you could leave the existing slab. If you are running the stairs along the house wall and up to the second story,in order to keep the stairwell level, the outside stringer will be longer at the bottom with that tread being higher than the inside. I did this on a stairwell from a balcony down to an existing sloped patio. I figured it would be a little akward coming off the last step onto the patio, but ended up being no biggie. The patio had a 1" slope/8' so close to what you have.

If you are running the stairwell from the outside of the existing slab on up to the second story, i dont think that 12' is going to be enough run for the height you have, so you might end up pouring a landing where your first step will be to get enough of a run where you wont have a tall riser and narrow tread.The landing would be poured level without having to worry about the existing slab.A fairly comfortable stairwell is typically a 7" riser with a 9" tread.The longer the run,the less riser height and greater tread width.
Related Discussions
How soon - Slab to Framing?
Q
Comments (4)
In our neighborhood it seems like only a day or two between the concrete being poured and crazy fast framing happening. I marvel at one day there's nothing and then bam, a framed house.
...See More
Stupid question about attachment of frame to slab
Q
Comments (6)
"...you will probably also need strapping or connector plates." Strapping nd connetor plates help hold the studs to the bottom plate, the top plate to the studs, and the rafters or trusses to the top plates. Nails in tension (withdrawal) have very little strength, nominally zero in many places. High speed winds do not just produce side loads but also produce lifting forces. Wind striking the side of a house turns up and down, the upward winds then produce a lifting force on any roof overhang, just wind swirling over a roof and dropping can produce lift on the roof structure similar to the lift on an airplane wing. If you think about typical house construction it relies on a few fasteners to hold position and weight to keep things down. Racking forces are accounted for, and downwards loads, but not lifting forces. By adding straps and connectors nails are loaded in shear instead of tension. The structure has more resistance to uplifting forces.
...See More
framing walls on a concrete slab with radiant heating
Q
Comments (5)
I would not be too quick to sell that liquid bonding material short. Back in the early 80's I was working maintenance for a large municipal school department and we an area where we needed to use the tubes of liquid nail, but like you, we were a bit skepticl of how well that stuff works, so we decided to give it a test. I took a 4' piece of 2x4 and cut off about 6", then I used the liquid nail to sister the cutoff piece to the side of the remaining 2x4 on one end and I put it in a vise to clamp it. I left it in the vise overnight, and the next morning I took it out and clamped the short piece in the vise and tried breaking the joint by both lifting an twisting on the longer piece of 2x4. After two of us grabbed the 2x4 and pulled on it as hard as we could causing a twisting force on the joint, the joint finally failed, but when we examined where the two pieces of wood had been joined we discovered the glue had not failed. The wood on the shorter piece of 2x4 had split amd sheared away, which accounts for why the joint finally failed, but the actual wood to wood glue joint was still intact.
...See More
How to slope/waterproof original wood window with storm window outside
Q
Comments (3)
The bottom part of your window frame is the sill, This the part you see when the window is open and runs to the exterior. When water gets by your sashes you want it drain to the exterior as it is designedto do. The interior horizonta part of your trim at the bottom that meets the lower sash would be the stool, if it has one. Idealy this is slightly tilted so it drains water to the inside and prevent water from sitting on it.The idea is to prevent as much water from entering the sill and to drain water out that does enter it. Tilting the inside sill may not be needed but it is a nice touch.
...See More
austinbirdman
Original Author
17 years ago
Thanks for the advice. I think I'll try this. The original office was built long before my time, but it's behind a former garage (now converted to a family room) on its own little slab pad. It was most recently used as a darkroom by the previous owner. Originally it must have been either a tool shed off the garage or a small addition built just to be a dark room (probably the latter, since it has its own electrical panel and lots of 5' high outlets for the developing equipment).

If I correct the slope with the framing, will my lumber be pushing out on the downward slope? Other than normal bracing, is there anything else I should do to rein in the slight downhill inclination?

The slab has been stable since we bought the house, by the way -- tipped in the same way, that is.
sierraeast
17 years ago
When landing on concrete, i generally knotch the bottom of the stringers at the front of the first step to accept a pressure treated or a redwood 2x4.This 2x will span the width of your stairs,laying flat, and allows you to anchor it to the concrete with wedge anchors drilled down into the slab. You can connect the stringers to the 2x with clips.I typically make the knotches 1-1/4" instead of 1-1/2" to keep the stringers slightly off the concrete. The treads should provide you with enough lateral support, but you can cross brace the underside if you fell you need more stability. You also might consider running a middle stringer as well. The minimum out here for width is 36", so i always use 3 stringers.

How to Frame on Sloping Slab

Comments (4)

deckman22

sierraeast

Related Discussions

austinbirdman
Original Author

sierraeast

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

How to Frame on Sloping Slab

Comments (4)

deckman22

sierraeast

Related Discussions

austinbirdmanOriginal Author

sierraeast

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

austinbirdman
Original Author