Double sill plate

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Old 04-21-17, 09:22 PM
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Double sill plate

Anyone done this before? P.T. sill plate like normal, and then another 2x6 or 2x8 regular lumber on top of that to gain a little more basement headroom? Anchor bolts sticking out of foundation need to be 1.5" longer than normal to accommodate, but is there any negatives?
 
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Old 04-22-17, 04:45 AM
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Never done it and don't know how 1 1/2" will make that much of a difference. Negatives will be the reach of your OSB on the exterior. It may come up a little short.
 
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Old 04-22-17, 06:16 AM
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Yup, I used a double PT 2x6 sill plate on this house. It does give a touch more headroom but if you are building it is easier to request (and pay for) walls a foot higher.

Over the years the extra lift has provided the carpenter ants frequent access, they find every crack, although I think I now have it well sealed.

Larry, doesn't the osb come up short anyway as it has to cover the rim.

I'm in the thinking stage for a new house and I would want to plan on my deck setting 2" in from the outer edge of the foundation to accommodate a thick layer of exterior insulation over 2x6 framing. That could involve using a 2x8 for the sill plate, haven't gotten that far.

Bud
 
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Old 04-22-17, 06:43 AM
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If you want more headroom in the basement, you just make your foundation walls taller. I agree 1 1/2" makes no real difference to justify the effort, unless someone screwed up and poured the walls too short..
 
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Old 04-22-17, 06:46 AM
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Why else do people do this? I see it in about 1/4 of builds I follow online or watch.

It cost a lot more to raise the basement wall a foot (because it's poured in forms). 8' forms are cheaper to rent and less concrete to pour. I can see how 1.5" is tiny, but in the grand scheme of things it's also what may make the basement feel barely too short or just the right amount of headroom when it comes to the places you baffle for beams or ductwork. I agree, the majority of the basement won't benefit. But if it prevent the illusion of a baffle being too low, it's worth it to me.

Bud - What reason besides the 1.5" extra headroom did you have?

Edit: I don't see the issue with the OSB. My walls are 8', so there's two sheets I still have to cover the rim joist and sill, and I will have raised energy heel so that automatically means no matter what I am cutting a third sheet. I do not use 4x9 sheets of OSB and run them vertical. I use 4x8 and run perpendicular to my studs.
 
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Old 04-22-17, 07:09 AM
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When built it was just overkill, but the forced hot air ducts have benefitted from the extra clearance and I have one drain line up against the sill which would have needed to be against the concrete. I'm not adding rigid insulation all the way around so it gives me room for a little more r-value on top of the foundation.

When adding up the cost to frame a house that extra layer of 2x? isn't that expensive. Switching to pine vs pt may also simplify the fasteners you use, pt needs special ones even attaching the sheathing.

Will I use a double again, yes as the extra space is convenient and I can't add it later. Somehow I think the foundation options aren't that unique as they have to deal with all sorts of height and step issues. You said rent so are you the contractor?

Bud
 
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Old 04-22-17, 07:30 AM
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I will GC my own build. My two concrete sub options 1 rents 8' forms 1 owns them. Both are offering discount if I go with 8 because at this time both are using 9 for the next couple jobs where 8 is available which means more money in their pocket by doing another job. Did some research and it appears 2 to 3 sill is very common while 4 was considered too much. I agree. It will cost me $98 more before tax to do it, and I'd be the one doing it so an extra hour or two at most. I would definitely want the anchor bolts to be the attach method versus nailing to the PT plate that is anchored. So I need to get longer than normal l/j bolts for the foundation.

Last build I did 8" thick walls and 2x8 P.T. plate. I don't see the difference between using 2x6 or 2x8 sill plates. Do you? The only difference I have found is my floor I Joists have more bearing since the rim takes 1.5" of the plate, that leaves me with either 4" or 6" of I-Joist bearing on the sill. Any input? I think 2x6 is a bit cheaper but I would be more for 2x6 because of finding straight lumber. I'd have to just compare the two at the lumber yard probably but if I remember one is typically straighter than the other.
 
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