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Author Topic: Jack Sobon Shed on Concrete Foundation... What is a good sill plate to use?  (Read 1060 times)

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Offline sterling08

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   Hi everyone! I am a new poster on the forum, but have been intently reading the relevant material for a long time. I am building a variant of the infamous "Jack Sobon" shed. I have modified the design to change it to a 16'x26'. The reason I did this is because I had an existing concrete pad to use (the pad was a floor for a dog kennel by the previous owner). I specified everything to fit this existing pad, purchased all my materials (red and white oak) and had in mind to use 8x8 white oak for a sill plate. However, since then everyone that looks at my existing concrete pad tells me that it is not in a good location, as it is in a "low spot" that has drainage problems. (The concrete pad is very thin without any rebar).
   Anyway, long story short, I am now building a new concrete pad that will be properly excavated and built. However, now that I will have a good concrete foundation, I am no longer wanting to put the 8x8 white oak sill plate down. I am instead looking very seriously at using pressure-treated 2x8 dimension lumber for the sill plate. If I no longer use a "heavy" sill plate, what is the best method of connecting the 8x8 posts to the 2x sill plate? 
   I could place bolts in the concrete and let them protrude up through the post several inches, but I am kind of favoring the thought of bolting down the 2x material to the concrete (with proper vapor barrier, of course) and then cutting shallow mortices into the sill that only protrudes about 3/4 of the way through the sill, so it will not wick moisture. Is this reasonable, or are there better methods to do this?
   Thanks in advance. Sterling.

Offline Dave Shepard

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I'll o get a pic. Back in five. 
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Offline Dave Shepard

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I would use a 3x8 sill of a rot resistant species, white oak,  black cherry,  locust. I used 2x8 and when I cut the stub mortises, it weakened the end of the sill. You can see the 8" HeadLoks I put in the end. If you go 3" thick, and don't bore all the way through, the 3x8 will be strong enough. You went to the trouble of timber framing your shed, putting it on pt will not look good. The sills should be anchored to the slab well,  I used expanding anchors. Your siding should be nailed to the sill. This is what traditionally held the frame to the sills. With a 3x8 sill, you have plenty of of nailing purchase. 



Raisus interruptus:

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Offline flyingparks

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Why don't you want to use the 8x8s anymore. Just curious. I like Dave's method...3"...nice. You could also use pressure treated 2x on the slab and put the 8x8 on top.

Offline sterling08

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Dave,

   Thank you very much for the recommendation to not use a 2x sill plate. The photos were very helpful. I see what you mean about the stub mortise weakening the thin sill plate at the corners.

flyingparts,

   Why not use the 8x8's? Well, that is a good question. There are two factors involved. One factor (a very small factor) is that the frame almost looks better to me without the "fat" 8x8 sill. The biggest reason though is that I have gotten a local sawyer to cut a mixture of white oak and red oak timbers for me. (I already took delivery of them and have the timbers on-site). Well, I was careful to specify enough of white oak for the 8x8 sill plate, as I wanted that to be "rot resistant", but I let the sawyer choose what species of oak to use for the rest of the 8x8 material that I needed (and he chose red oak, probably because it had less value to him). The red oak is fine for the tie beams and posts, which are also 8x8, but since the ends of the top plates (in my current design) are exposed to the elements, I am liking the thought of the top plates being white oak. If I use 8x8 white oak for both the top plates and also the sill plates, I don't have enough 8x8 timbers in the white oak species and will need to procure more timbers, which is not that big a deal. However, if it was not really adding value anyway, I thought to maybe simply remove the 8x8 sill. Of course, maybe I shouldn't worry about using the red oak for the top plates. If I did that, I still have sufficient timbers available for the 8x8 sill, like I had originally planned.

   Here are two images of the current shed drawing, one with an 1.5" treated lumber sill and one with an 8x8 timber sill (I just added the 8x8 sill for a quick visual, don't get hung up on the fact that it shows the posts going all the way through the sill. I was lazy and didn't feel like doing the detail work on the 8x8 version if I'm not going to use it).



Shed with 8x8 sill plate:


 



Shed with 1.5x7.25 sill plate (2x8 pressure treated):


 

   Oh, one other small piece of information: I do plan to use board and batten for the siding.

Offline Dakota

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How about cutting your 8" white oak in half and make your sills 4" thick ?
Dave Rinker

Offline Dave Shepard

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I agree on the 8x8 not looking good in this case. There is no need for them if the sills are fully supported and you don't need to cut joist pockets. I'm glad to see you went with four bents. Jack and I had a discussion about lengthening the 3 bent frame, and there are some issues with rafter thrust breaking the post tops. Using wide, thick roof boards can help, but adding a bent is better. 
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Online mike_belben

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I suggest a row of asphalt shingle to keep the wood off the concrete.  No matter what you use.  And if you do any type of vapor wrap, do not tuck it at the bottom, be sure the bottom skirt lets moisture rivets shoot right out the bottom. 

My father made this mistake of tucking the wrap on a tripled 2x12 PT sill around 1984.  Fast forward to 2015. The windows start getting hard to close drywall keeps cracking.  Whole house had to be jacked up to replace a powder sill. 
Revelation 3:20

Offline Don P

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At a quick glance, have you checked headroom at the top of the stairs?

Offline sterling08

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Dakota,

   I could do that, but since I don't have my own band mill, this would be a real chore for me. I do have the "Alaskan" chainsaw mill, but this would be a lot of work! I have been working on this since last fall (not much over winter, as I'm doing this outdoors), and my oak timbers are starting to become seasoned (read: HARD). 


Don P,

  Thanks for the input. I have reviewed the headspace again and it appears to be OK, at least for a shed. I had removed the brace by the stairs, but otherwise the clearance is acceptable for me. (See photo below).


   I am still contemplating my sill plate options. I think that I will go with the 8x8 white oak sill plate after all. The reason for this is that this shed will house my lawn mowers, tillers, snowblowers, etc. I can see that the 8x8 sill would work a bit like a "guard rail" from potential damage from the INSIDE of the shed. (My children mow the yard. A common refrain at our house is "I didn't try it!", the implication is that since it wasn't intentional, I'm absolved of all responsibility). 

   The only question left is how much should I worry about using red oak for the top plates whose ends will be exposed to the elements? Is this a really bad idea? Here are my options for the top plates:

1. Get some more white oak 8x8 timbers.

2. Use the red oak that I already have.

3. Use red oak, but scarf white oak unto both ends where it protrudes out into the elements.


   Which of the above options would you guys recommend that I go with?

Thanks, Sterling.







 

Offline Don P

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Can you bevel the bottom of the projecting plate and tuck it behind a fascia that protects it and the barge rafter? It wouldn't hurt to borate the end grain heavily.

Another option would be to eliminate the sill, use post bases with a standoff to raise them up an inch above the concrete and let in a treated vertical 2x12. You could then stop the siding higher above the ground, similar to a post frame skirt board.


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