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Discussion Starter · #1 ·
I am looking to convert half my garage into living space but im not sure how to precede with installation of the floor joists. The joists will need to span 20 feet. Can i just install leaderboards and use joist hangers or do i need to build knee walls to set the joist on around the edge and possible across the middle. The total size of the room os 20×24
 

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retired framer
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the top of floor needs to be at 25 inches to be even with the existing structure.
It is chancy to support anything off the garage slab because it can move You could look at TGI floor joist that might span the 20 ft then you could figure out how to support that where there is a foundation. Assuming there is a foundation around the outside?
 

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Probably easier and more economical to do the knee walls on each side and one in the middle, then you can use smaller joists and rim boards, which you don't have to worry about attaching adequately to the existing walls. According to these span tables, even select structural 2x10's at 12" spacing won't quite get you to a 20' span. However, grade #2 doug fir 2x8s (which are readily available and far less expensive) at 16" spacing (or even 24") will span 10'.


If you don't want to build the knee walls, a 16" TJI joist gets you very close to your desired height with the 2x8 joists (24.25" with 3/4" subfloor).
 

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retired framer
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Probably easier and more economical to do the knee walls on each side and one in the middle, then you can use smaller joists and rim boards, which you don't have to worry about attaching adequately to the existing walls. According to these span tables, even select structural 2x10's at 12" spacing won't quite get you to a 20' span. However, grade #2 doug fir 2x8s (which are readily available and far less expensive) at 16" spacing (or even 24") will span 10'.


If you don't want to build the knee walls, a 16" TJI joist gets you very close to your desired height with the 2x8 joists (24.25" with 3/4" subfloor).
16 ft is pushing you luck with 2x10s
So you would put the whole floor on a garage floor?
 

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16 ft is pushing you luck with 2x10s
So you would put the whole floor on a garage floor?

I was envisioning 16" high 'walls' (or TJI's) along each of the 24' long walls and another in the middle, resulting in 2 spans of 10' each. Grade #2 2x8's would supposedly work for those spans.
 

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...span 2x10s 12 feet to the center.

According to the span tables I posted, you can span over 12' with #2 Grade 2x8's at 16" spacing using any of the common species used for lumber of that size. 2x10's at 24" spacing would also work, but an 1 1/8" subfloor is typically recommended for a 24" joist spacing.
 

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retired framer
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According to the span tables I posted, you can span over 12' with #2 Grade 2x8's at 16" spacing using any of the common species used for lumber of that size. 2x10's at 24" spacing would also work, but an 1 1/8" subfloor is typically recommended for a 24" joist spacing.
Have you got any experience with 20 or 24 ft 2x10s. I do and I can tell you, not a chance in hell.
 

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Have you got any experience with 20 or 24 ft 2x10s. I do and I can tell you, not a chance in hell.
I haven't tried handling something that size, but I know I wouldn't want to. I certainly wasn't suggesting that he use them, either, if that's what you're getting at. My suggestion was to use 10' 2x8's (at 16" spacing) with blocking at the center support. The OP suggested he would rather span the other direction in the room, so I suggested (or meant to suggest) 12' 2x8's (still works at 16" spacing). Since he seems to be partial to 2x10's, I mentioned the option of using 2x10's (presumed he'd be use 12' lengths, again with blocking at the center) at up to 24" spacing.


Not to mention, attaching a rim boards to full length pieces requires joist hangers, which I'm not fond of. For something non-supporting (the joist bearing directly on the support), I prefer to just put screws through the rim board into the end of the joist and be done.
 

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A 20x24 garage I would think the overhead door is on the 20' side. First you said span 20', then you said split to 12' which means the 24' side. Are you filling in the back half of the garage or splitting a 2 car into a 1 car?

You may have some foundation stem wall available to bear on if existing 2x4 walls. You also need to be aware of which way the slab slopes (drain or to door?). If you are filling in 1/2 the door also be aware of how you finish the sill plate because driveway water. Also if there is a man door that needs raised, and if you are allowing enough room for the steps into the new 1 car stall.

A sketch and some pics might be respectful for the thought these guys are putting in.
 

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Discussion Starter · #13 ·
So here is the rough sketch of what is going to be happening. The garage is currently on a slab that has footings where it conects to the house and the rest is foam wall frost protected as i live in Wisconsin. Im just looking to do the garage remodel framing to save some money as some of the early bids push our budget way to much. However why i have framed walls in the past for garages i havnt done floors.
 

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Probably easier and more economical to do the knee walls on each side and one in the middle, then you can use smaller joists and rim boards, which you don't have to worry about attaching adequately to the existing walls. According to these span tables, even select structural 2x10's at 12" spacing won't quite get you to a 20' span. However, grade #2 doug fir 2x8s (which are readily available and far less expensive) at 16" spacing (or even 24") will span 10'.


If you don't want to build the knee walls, a 16" TJI joist gets you very close to your desired height with the 2x8 joists (24.25" with 3/4" subfloor).
nice advice
 

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retired framer
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So here is the rough sketch of what is going to be happening. The garage is currently on a slab that has footings where it conects to the house and the rest is foam wall frost protected as i live in Wisconsin. Im just looking to do the garage remodel framing to save some money as some of the early bids push our budget way to much. However why i have framed walls in the past for garages i havnt done floors.

I would sit down with the man at a lumber yard and question him on beams or floor trusses or TGI floor.



Which ever you use, you would use hangers on the house side and poke into the outside wall supported with short jack studs and a king stud.

Many of the houses we build have rooms over the garage and there most times done with two beams something like 6x14" beams. They either go below the joist or flush with the joist and the joist are hung with hangers.
 

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