Garage Conversion Framing

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Old 11-11-18, 02:01 PM
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Garage Conversion Framing

Hello all,

I am new to the forums and kind of the whole DIY process. Anyway, I am in the preparation of converting a garage into a living space. It is a one car, 'open gable roof' type garage with a total rafter span of 10ft (width) and length of 20 ft. It is about 7" step down from the house and built on a concrete slab. The wall framing comprises 2x4 studs and the cathedral ceiling comprises 2x6 rafters. The roof does not have eaves so there is no soffit ventilation for the rafters. I am planning to keep the cathedral ceiling so I have to have closed cell foam insulation plus the permeable insulation in the ceiling (R=49 total), however, to accommodate that, I have to bulk up the rafters from 2x6 to 2x12s. The same thing is valid for the walls: I have to bulk them up from 2x4s to 2x6s to accomodate the minimum R=20 requirement for the area. I have two questions:

1. Do I attach the 2x10 rafters and 2x6 studs next to the existing ones to build them up? Doesn't this cause too much heat loss since I would end up with 3" thick rafters and studs?

2. How do I build up the ridge plate to accommodate for the rafter width increase? Do I just add whatever is required underneath?

Thank you!
 
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Old 11-12-18, 09:03 AM
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I for one, am not a fan of cathedral ceilings for several reasons, some main one's being there a bear to heat and cool properly, not fun to paint, lighting can be a challenge.
How tall are the walls in this garage?
How is lowering the rafters by that much going to effect all your window and door openings?
If I had to do this job I'd be drilling and counterboring the lumber and using 3" long bugle head decking screws every 2 ft. and adding onto what's there not just attaching to the sides.
Another challenge is on the outside, keeping water from coming in from under walls.
 
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Old 11-12-18, 09:15 AM
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Add a 2x6 ledger horizontally onto the top plate of both walls. Add a new ridge beam directly under the existing one and support it with a few temporary posts. Simpson strap ties can be used on both sides of the ridge to tie the new and old together, or use 8" long ledgerlok lags every 32" or so. Then add new rafters directly below the old ones... fit them between the new ridge and ledger that you put up. Be sure you get the angles right and make sure they fit tightly.

On the walls, just get some 2x6 and a table saw... rip the 2x6s down to 2"... shoot them to the bottom plate and on top of the existing studs with a framing gun and 3 1/2" long nails.
 
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Old 11-12-18, 01:14 PM
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Hello XSleeper, thank you very much. Your post has been very helpful. So adding 'on' instead of 'next to' is a better idea. OK, that is what I thought but I wasn't sure if ripping 2" pieces on a table saw would be easy. I just bought a table saw and I never used it before. Is it relatively easy to cut narrow pieces?

Also, how do I attach the new rafters to the old ones? Again with the straps or ledgerlok? Thanks!
 
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Old 11-12-18, 01:17 PM
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Thank you very much joecaption! The walls are 8.5' tall and making the rafters wider does not affect the window and door openings.

Can you elaborate on 'keeping water from coming in'? Thank you!
 
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Old 11-12-18, 01:28 PM
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You don't really need to attach the new rafters to the old ones, but you can if you want to. You are building a roof under a roof. Each rafter would be nailed to the ridge and the ledger.

I can't comment on your ability to use a table saw. Ripping boards is basic stuff.
 
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