I have a 24×32 cabin in upstate NH that sits on 6×6 pilings in the dirt. I would like to build a concrete knee walls 4 ‘ high and 8″ thick around the perimeter of the cabin to properly support it. Probably would use a 3000 lb mix. I would also like to build a new a garage adjacent to the house with perimeter knee walls/footings as well.
I have a back hoe and plenty of time and would be able to excavate underneath my cabin a side at a time with the house properly reinforced and jacked/cross braced from underneath (a safe distance away from the edge being excavated). The walls would be on concrete footings set on 4″ of gravel/crushed rock. Everything would have rebar.
My question is this:
On the adjacent wall where the cabin meets the garage (both gable ends), should I double the thickness of the concrete foundation from 8″ to 16″ and also double the footing size and double the 2×6 wall as well? This would be to accommodate both the end of the cabin and the end of the garage.
Or should i just utilize the gable end wall of the existing cabin and make that the back wall of my garage and just use the single foundation wall (8″) underneath. I want to make sure I am safe and obviously, only want to do this once. I may have already answered my own question but will ask anyway in case I have missed something.
As usual, constructive advice is always appreciated.
Thanks in advance for your help.
Mick
Replies
Mick,
First, I would suggest that you talk to your local batch plant engineer about what 'crete to uses. I don't think he will reccommend plain 3000# mix.
Now, as for the garage, using the cabin wall/foundation as the back wall is what I would do, however. . .
The garage foundation should only be supporting the framing and not the vehicle parking slab. The slab should be on well compacted engineered fill and should NOT rest on any wall foundations.
The foundations are supporting a relatively fixed load that only slightly changes seasonally. The slab will be supporting a load that changes twice daily from zero to maybe 6,000 to 8,000 pounds. The wall foundations and the slab will be settling at different rates and any connection between them will be broken, (cracks.)
SamT
Anyone who doesn't take truth seriously in small matters cannot be trusted in large ones either. [Einstein] Tks, BossHogg.
Thanks for the reply. I will be checking with my concrete guy to determine which type of concrete I need . I do agree the floor of the garage will float separately. But my main focus is under the cabin for now. I need to secure that all the way around before I do anything about the garage Probably, that will be done next summer but wanted to make sure I planned accordingly to avoid 2 ton mistakes!
As I will be doing my cabin foundation in small increments,( a footing , then a wall on top, another footing, then another wall, until all four walls are done,) is it easier to get the concrete delivery for only something as small as 2+ cubic yards of crete? The footing is 2'x1'by 28'. Are delivery costs for 2 yds cost prohibitive? Should I even think of mixing that much myself? I am not that astute to know what the recipe for concrete mix should be for 3000# or 4000# or whatever. Maybe renting a mixer?
What do you think?
Thank you.
Mick
Buy the mixer and sell it when you're done. You're going to use it at least 8 times.
One way to get the concrete in the wall forms when you aren't lifting the house is to leave them 9" short.
Set your anchors in the house walls before the pour, but use anchors long enough to penetrate the new concrete, ie. +9".
After you've stripped the forms, wedge 8" block up tight to the mudsill and drypack under them. After the drypack has cured enough, remove the wedges and drypack those holes.SamT
Anyone who doesn't take truth seriously in small matters cannot be trusted in large ones either. [Einstein] Tks, BossHogg.
excellent suggestion Sam. Any idea what a good mix would be for the walls? The cabin is small (1 floor 28X30) . It would only go down 5 feet (1 ft for the footing and 4' for the walls, but it needs to be below frost line in northern NH. It will be about 10" thick. Any recomendations for the type of cement mixer or any recipes for a good strong concrete mix? I wouldn't need anything like fibers in the mix or ash. Just aggregate and sand and such. Thanks for the suggestion, it has some merit and I will consider it. I may have to still jack it up as it is only about 9" off the dirt now.
Mick
In all the concrete work I've ever done, I've only ever hand blended for plaster and grout. Here's some internet recipes.
A basic concrete recipe is 1 part Portland cement, 2½ parts sand, 2½ parts gravel and ½ parts water. The amount of water may vary, but it's important to add a little at a time.
Also see here.
Mix proportions by volume
Applications
Sunlite Cement
Stone orGravel
Sand
High Strength & Watertight
1
3
1.5
General Use: Paths, Floors, etc.
1
4
2.5
I would also keep a 5 gal bucket with dry mix ready for when you accidently use too much water. You can quickly add some dry mix and know it's still in the right ratio.SamT
There are three kinds of people: Predaters, Prey, and Paladins. For the life of me, I can't see why Prey feels safer from predators by disarming and emasculating Paladins.
I am curious to know what the basic diff is betweeen 3000 psi and 4000 psi in terms of recipe mixing. I understand it is a stronger blend, I just didn't know what makes it that way.
Thanks for everyone's input. It is always appreciated.
Mick
betweeen 3000 psi and 4000 psi
4000 has more cement.SamT
There are three kinds of people: Predaters, Prey, and Paladins. For the life of me, I can't see why Prey feels safer from predators by disarming and emasculating Paladins.
ash is good, ash is cheap. try for a 3000 pea gravel mix
A 4,000 psi mix should be more than adequate for everything that you plan on doing. For a couple of bucks per yard it's well worth it.
McMike
have you considered using ICF's instead?
three advantages that I can think of. first you save the price of forms. second they go together like big foam leggos third they save on the amount of concrete you'll need.
" They go together like big foam leggo's".
Sign me up...
Can we wear Zootsuits and pretend we're building an ice castle?
Edited 3/24/2007 1:25 am by 1muff2muff
1muff2muff
Have you ever used ICF's?
I have and I'm ordering more..
There are massive benefits with them and they aren't hard to use. In fact shortly after I started with them I came back from a road trip with a bad back that had me bedridden for a month {Bad seats on the car}.
MY sister-in-law with zero experiance (well, she did paint amd wallpaper her bedroom once) finished them for me. I gave her about a 20 minute instruction (I think it was 20 minutes I was pretty well zonked on pain pills) and she went ahead and finished everything for me.. All I had was the first layer done and she finished the rest of it.. it took her all afternoon. She left smiling and happy..