garage ceiling issue

[bigbob302]

Hey folks, I have been trying to decide the best plan of attack for a while here. I am insulting and finishing a 20x20 ish detached garage. there are a few things i am struggling with.

First problem is that the garage has rafter ties on 4' centers. the rear most 8' of the garage has them set right on top of the sill plate. they are sagging about 3 inches low because of all the **** the previous owner had stored up there for years. walls are 7'5 tall. in the front half of the garage the rafter ties jump u about a foot to make room for the garage door, but there are only two of them (and they are an inch off level with each other). they are every other rafter beam and no rafter tie at the very front of the garage. I hope this makes sense. Here are a few pictures.

how would you finish this ceiling? the options I have played with are:

1) install new ties a foot higher than the original ones, and on 16'' centers.
this would allow me to drywall it no problem, i know it would be nice and level, but at probably 30$ a pop plus the pain of transporting and handling 20'' 2xs it won't be cheep and it will be a lot of work.

2) put a 2x4 perpendicular to the rafter ties and flush with them on 4' or 8' centers and put some osb or metal roofing up there and hope they will hold the weight of insulation without sagging.

3) run furring strips under and perpendicular to the ties at 16'' or 24" centers and put whatever i want up there, rock, metal, osb. I still have not decided. Id like to drywall the whole thing but if i can save work with a different material Ill go that route. the issue with the furring strips is I'm gonna have to shim the hell out of them to make up for the sag in the center. will you be able to see 2 inch drop in the center?

option 2 and 3 still leave me with no solution over the garage door. pull the ties and sheet the rafters? I just don't know what to do. I don't want to make a career out of this, I don't expect a perfect tv worthy garage just a place to work on my projects.

next problem i have is gonna be venting. i don't know all the proper terms so bear with me. the garage was a ridge vent, a gable vent in the rear ( its small and u can see it in the top pic) and on the front soffit pictured below its all perf. vinyl. and is closed off from the rest of the garage, i don't know how the front exhausts. and there are no soffit vents on the sides of the garage. I know i will need to add some but its a tiny soffit.

any suggestions on all this would be super helpful. I just can't make up my mind on what to do. thanks a bunch in advance everyone.

 

[2drx4]

Where are you? Snow loading is a factor... You can't move your rafter ties to be higher than the bottom third of the height of the roof.

New rafter ties on a tighter spacing would probably not be a bad idea either way, as the structure looks flimsy. And IMHO there should be collar ties (upper third of the roof) if your rafter ties are anything but level with the bottom of the roof. They could just be 2x4s. I'm aware code may not require them and that they do not stop spreading, hence I said "IMHO".

How are you planning to insulate it? That affects venting... If you move the rafter ties up, be aware that you will need a sufficient air gap from the eaves to allow for venting, which can leave very little room for insulation. Venting also varies by climate. My instinct is that I would punch large gable vents into both sides and call it good, as I'm not a fan of roof protrusions. However, this may not be adequate for you.

 

[bigbob302]

thanks for the reply. there are collar ties, they happen to be perfectly behind the rafter ties in the pic so you can't see them. I do have to worry about snow. I live in michigan. I only have about a foot to move the rafter ties up and keep them in the lower third. It really is the last thing i want to do because of the labor and cost involved but with the walls as short as they are and al the other problems i might not have much of a choice. as far as insulation, I was gonna stick with fiberglas batts in the walls and ceiling. if the rafter ties get moved install some baffles to keep air circulation under the roof sheeting. Also gonna put up some poly on walls and ceiling before the rock or osb goes up.

 

[2drx4]

I think it will work out fine. Might be a lot of labour, but it's probably less than any of the other options to get a higher ceiling.

 

[bigbob302]

Did a bit of
Math and 2x4x18 can be had for 7$ each. I think that is the route I'm gunna take. It would raise the existing ties by a foot. Anyone have any comment about how many fasteners are going to be required? I'm thinking if I put each one up with 4 screws per side to hold it up and the. Come back with a few carriage bolts in each it should do the job. As far as venting. A few big gable vents would probably take care of it. Would it be sufficient to pull air out of the soffit area though? Seems the flow path would tend to be gable vent right out ridge vent. Thanks guys

 

[Hornman]

Ridge vents work best with soffit vent. I'm guessing that the building originally had gable vents (for flow through ventilation) and the ridge vent was installed during a reroof. If you install soffit vents, the heat in the attic will use the chimney effect to pull air out of the ridge vent. You can retrofit soffit vents using the perforated strips or the round pushins. Both are easy to install. Is it was my building, I would close off the gable vents to prevent short circuiting the air flow. The nice thing about soffit/ridge venting is that the airflow sweeps the underside of the roof, cooling it and extending the life of the roofing materials.

 

[bigbob302]

Thanks for the help guys! What do you call "soffit" that overhangs the front of the garage? Is that acting like a soffit vent that I should leave or a gable vent that I should block?

 

[2drx4]

I'm sorry, I didn't look at the pictures you posted initially as well as I could have, since I mostly liked at the framing rather than thinking about the venting.

I missed the part where you said the building was (past tense) a ridge vent. Did you mean it had a long continuous vent along the ridge of the roof? Google search will provide you an image. If it had that, or you intend to do that, then you should block the gable vent. Having the perforated soffit material in the gable rake/overhang (the underside of the roof that extends past the ends of the building) is not necessary in either case, but is standard practice in new construction.

If there is no ridge vents, and you have no intention of installing them, then I will affirm that I'd just put gable vents of a suitable size in both ends of the building, and not consider messing with the roof to install a ridge vent or whirlybirds or any other thing like that. However, there does not appear to be any perforated soffit material under the eaves on the sides of the building, and that would need to be done or something that produced a similar effect (making a pile of holes with a holesaw and putting screen over it is a valid/easy solution).

I'm sorry if I'm unclear, I might have to start over if you have trouble following me.

 

[bigbob302]

U are clear thank you very much for ur time. The garage has a small gable vent in the rear, perf vinyl under the front overhang, and it also has a continuous ridge vent at the roof peak that appears, as hornman says, to have been done at the last reroof job. No holes in the soffit at the top of the walls. And I only have about 3" to work. Rip a circular saw slot the hole length and put in a continuous vent? Hole saw and pop-ins? Guess it doesn't matter as long as their is enough air eh?

 

[2drx4]

Also, hoping to not cause any more confusion... To calculate ballpark adequate roof ventilation, take the square footage of your roof and divide it by 300 (minimum, I don't recommend this) or 150 (better).

So, say you have 450sqft of roof, then you want 3 square feet, or 432 square inches of ventilation for it. Which isn't a lot, to say the least. Then you want to divide that by a roughly 60/40 ration between intake and exhaust venting. Which means about 260 square inches of intake, and 172 of exhaust.

So, you could make that work by punching about 40 2" holes under each eave, and having a 10x16 gable vent in each end of the building (note I have oversized the gable vents... They rarely flow very well due to construction). Edit: Disregard the gable vents, I did not see your reply before I typed this.

Not saying that would be the best way to do it, but it's probably something like how I would fix it. And if somebody questioned me on it, I'd probably say something like "Well, it's not going to the moon."

 

[2drx4]

U are clear thank you very much for ur time. The garage has a small gable vent in the rear, perf vinyl under the front overhang, and it also has a continuous ridge vent at the roof peak that appears, as hornman says, to have been done at the last reroof job. No holes in the soffit at the top of the walls. And I only have about 3" to work. Rip a circular saw slot the hole length and put in a continuous vent? Hole saw and pop-ins? Guess it doesn't matter as long as their is enough air eh?

Yup, you got 'er. Rip under the eaves or punch a bunch of holes. Ditch the gable vents since you have the ridge vent, it will provide plenty of ventilation. The post I made about the math was being typed while you replied.

 

[bigbob302]

Awesome. Thanks guys sounds like I got a plan

 

[bazzateer]

Hey folks, I have been trying to decide the best plan of attack for a while here. I am insulting and finishing a 20x20 ish detached garage. there are a few things i am struggling with.

More detail required on how you go about insulting your garage?

"Call yourself a garage?! You're no better than a pumped up garden shed!"

 

[bigbob302]

Fiberglass batts and poly vapor barrier

 

[Onewolf]

More detail required on how you go about insulting your garage?

"Call yourself a garage?! You're no better than a pumped up garden shed!"

LOL. That's what I was thinking as well.