Shed foundation, spanning 8' question

[tomsmith]

Hello,

I'm building a 12x24 shed this summer and am creating the plans to help me figure out how it will look and go together.

I've decided to build it on a pier foundation with 12 piers altogether - 3 rows of 4.

I'll be using PT 2x6 as the foundation frame with joists 16" OC and each joist attached to Simpsons strong ties with 16d galvanized nails. I'll also be attaching blocking between each joist to stop them bowing inwards/outwards.

For the foundation though, the 2x6 joists will be 8' in length so the 2 center piers will have 2 2x6's resting on one off the 'saddles'. I'm worried that this might causing bowing as 2x6 won't be 'continuous'.

I've drawn it up in Paint to illustrate:

Where the 2x6's meet in the middle saddle, how can I stop the joists from lifting up under a heavy weight?

 

[awonderfulworld]

Why not just use 12' pieces of wood? They're easy to get (or on the rare occasion, special order). 12' lengths are common for decks.

Make sure you use pressure treated.

 

[tomsmith]

Even if I use 12' pieces of wood, I still have the problem of the join in the middle for a 24' span?.

 

[srmofo]

Just scab a board across the joint. You can hide it on the inside and cut those joists shorter since you are using strong ties.

Use carriage bolts and glue when sistering and you'll never have a problem.

The other option is to build smaller sections and then join them together but that will require more materials

 

[billp603]

Not sure if I follow your plan? To have a run of 24' with 16" o.c. you'll need 19 joists, so your footing plan will look like the attached picture, with a footing every 6th joist. 2x6's will work for the joist on the footings, but the intermediate ones will now only be supported by the rim joints spanning the full 12'. You'll need at least a 2x8 to span 12'. I would use 2x8 for everything with double 2x8 beam joists over the footings to to transfer the load to the rim, and a double rim joist as well. All of the hangers can use 10d nails, 16d is way overkill and will split 1.5" thick wood more than it will hold in it. There are a number of online deck joist span tables and framing charts.

 

[theoldwizard1]

Hello,
I'll be using PT 2x6 as the foundation frame with joists 16" OC and each joist attached to Simpsons strong ties with 16d galvanized nails.

First, depending on you load, I think 2x6 even 16" OC are kind of "light". What kind are you going to be storing in there ? Personally, I would spend the extra money and go 2x8 or possibly 2x10 24" OC (less foundation piers !)

Second, there are a zillion different Simpson brackets ! Which one are you looking at ? Most base brackets are for 4x4, 4x6 or 6x6 posts. What you really want is something long (8-12") with at least 16 attachment holes (8 on each side) evenly spaced from the center of the bracket.

I am a big fan of the Simpson screws where allowed. Not cheap, but with a cordless impact they are actually fun to install !

For the foundation though, the 2x6 joists will be 8' in length so the 2 center piers will have 2 2x6's resting on one off the 'saddles'. I'm worried that this might causing bowing as 2x6 won't be 'continuous'.

Which is why you want a long bracket.

Where the 2x6's meet in the middle saddle, how can I stop the joists from lifting up under a heavy weight?

The best solution is continuous lumber.

The joint will "lift" because it is saging in the center. 2x8s will minimizes this

You could use Smpson MSTA12 straps on the top across the tightly butted joint. A tight **** (did I just really write that ?) will transfer that load along the bottom edge to the next piece of lumber. This likely would not pass "code".

 

[tomsmith]

Hi

Thanks for all the great responses! The joist types I was planning on using are:

http://www.homedepot.ca/product/joist-hanger-zmax-2-inch-x-6-inch/935252

I don't mind springing a bit extra for the 2x8's and it look like that's the way to go. I plan on storing:

lawnmower - 22" cutting path so regular size
Snow thrower - gas powered but not a very large one
Kids and our bikes
A couple of tools that take up too much room in the garage (e.g. small table saw)

The reason I want it bigger is that in the future I might turn it into a workshop. If I do, I'll put up a wall between the workshop side and the storage side so I don't end up with dust all over the bikes and mower etc.

Billp603, I see what you're saying about the 12' span for unsupported joists being too much. I had thought blocking the joists would have prevented that but I think that was just wishful thinking on my part.

If I use 2x8's, it sounds like the 12' span should be OK.

I'll have to check the price difference between switching to 2x10's and using less piers. Each pier is going to cost around $35 so I'm guessing multiple piers is cheaper than using 2x10s.

 

[theoldwizard1]

If I use 2x8's, it sounds like the 12' span should be OK.

The table says 11'4" for #2 Spruce/Pine/Fir 16" O.C. with blocking. I would not worry about an extra 8" unless you have a picky inspector.

I'll have to check the price difference between switching to 2x10's and using less piers. Each pier is going to cost around $35 so I'm guessing multiple piers is cheaper than using 2x10s.

2x10 #2 Spruce/Pine/Fir 16" O.C. is good for up to 14' span.

Make sure your joist hangers are galvanized (most are) or plated for rust resistance. An impact with the proper screws is the fastest way to install the hangers and joists.

 

[Beemer533]

I did a plan for a friend of mine who wanted to minimize piers and couldn't do a slab for various reasons...
His was 12x12, but I adjusted it up for 12x24 here.

This allowed for only 6 piers (9 in the 12x24 plan here) and the floor joist could be 2x6 as the span is only 5 1/2'.

It isn't in the plan here, but the pier spacing for the main beams is 11' 8". Overkill, but it should be really solid.



Here is an "exploded" view of the 3 main beams; they are composed of tripled up 2x8.


just another thought....

 

[theoldwizard1]

This allowed for only 6 piers (9 in the 12x24 plan here) and the floor joist could be 2x6 as the span is only 5 1/2'.

That's good !

Here is an "exploded" view of the 3 main beams; they are composed of tripled up 2x8.

Tripled 2x8s for the center and outer beams ! WOW !