How do you get an extra 2 inches of ceiling height? Ceiling height would be based on the length of the wall stud. So if you go with 12" joists instead of 10" your house will be two inches taller overall.

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I miss YaHey

The engineer in me always leans toward a greater safety factor. If it fits, and has negligible cost differential, go with the bigger joist.

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Remember - It's important to be comfortable in your own skin... because it turns out society frowns on wearing other people's

12 inch on 12" OC

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Just Triing
Triathlete since 9:56:39 AM EST Aug 20, 2006.
Be kind English is my 2nd language. My primary language is Dave it's a unique evolution of English.

Squeek isn't related to structure.

Deflection is. Probably the tables are based on L/120. If the numbers are the same, deflection will be the same. Makes since too 10" TJI @ 12" o.c. is a lot of wood. 12" TJI @ 16" o.c. is more common.

But in one way, yes 10" TJI will give you 2" more ceiling space. Also look at what's going between the joists. You'll have to drill 25% more joists to run plumbing. 10" ducts won't fit between the joists.

IECC requires me to have R-20 or R-13+R-5 continuous insulation. R-20 is 5.5" batts, R-5 XPS is 1".
Everything I do deals with the commercial section of the IECC, and almost always I use 6" metal studs + 5 1/2" batt AND 1" ci in a rainscreen system.

If it were my money, I'd use 6" studs @ 24" o.c. for exterior walls with an insulated panel sheathing - Zip R-sheathing or eq - and a finish (unless your building a brick house)

Ceiling height is based on floor-to-floor minus structural depth minus interstitial space minus ceiling assembly depth

We can't do 24" O.C. in exterior walls here in BC. Gotta be 16" centers.

Aside from that, I completely agree with your post.

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Long Chile was a silly place.

The wall studs are installed on top of the joists, actually it's probably joist, then subfloor, then the bottom 2x4 plate, then the wall stud. Normally wall studs are 92 5/8" to give you an 8 foot ceiling, or 104 5/8 for a 9' ceiling. So you're going to have an 8' or 9' ceiling no matter what size the joist is.

If you're talking about basement ceiling height, that's height of the concrete walls plus however many layers of base plate on top of the concrete. So again, the joist has no impact.

Am I missing something?

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I miss YaHey

Thanks for the responses,

Basically this is a 1300 sqf "modern box" addition going on the back of a 1940's post war 700 sqf house.

3 floors at 450 sqf, basement gym/open/mechanical, 2nd floor 3 beds, 3rd floor open kitchen living (we have great views up there!)

For reference in BC you need architect and structural engineered prints for any residential addition (or even a deck!) gone are the days when you could draw your plan on graph paper and get a stamp......pretty soon you will need an electrical engineer to throw around a bit of loomex.

Both floor options represent L480 deflection or above our L360 code. I will go with the beefier "T" portion for better screw purchase on sub floor. I will also use T&G sub floor....screwed, glued and all that.

If I get the 10 TJ it allows us to use dimensional 92 inch studs for a traditional 8 foot ceiling height, if I go 12 inch then finished height is around 7-10" so if I go 12 inch then tonnes of cutting studs, cutting drywall etc.

We are limited both above (code height) and below (Frost wall foundation, no rebar on existing)

For the walls we now need r-20, either 8 inch bottom plate with 2 2X4 walls (half inch air gap) on 16 OC. Or 6 inch wall with exolation. With this you can go 24" inch on the inside, but I would rather go 16 due to drywall finish.

I have priced just the raw materials for 8 inch wall and it comes in at 3.05$ CAD per wall envelope sqf (Tyvek, insulation, studs, bottom plates, VB) the foam exolation with 2X6 wall is expensive and brings that up 2$ per sqf.

Thanks for all the responses,
Maurice