Look at my garage wall to slab...

[DKAudio]

It seems very odd to me that the slab in my garage is level with the top of the 2X4 sill/sole plate. Is this common? The house was built in 1954 but am unsure as to when the garage slab was poured. Te plates are still solid but I am concerned with them rotting.



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[pushkins]

I've seen this done many times before, the situation is usually an older garage that was built on a concrete foundation but had a dirt floor, or a thin concrete layer, sometimes an asphalt floor was added a few years later. After some time someone decided that a concrete floor would be much better than dirt, cracked and breaking up old thin concrete or old asphalt, so they pour the concrete inside using the bottom plate as a form and level indicator.
Your right about keeping an eye out for wood rot this situation is set up for just that thing, untreated wood is not to be in contact with concrete in any way as the wood will suck any moisture from the concrete.
If the bottom plate is still much higher than the ground outside then your more than halfway from trouble just keep an eye on it.
Termites also love this situation so watch out for them as well.

[DKAudio]

The foundation is at least 4-6" higher than the sole plate all the way around. I have also never seen termites. I am currently adding joists in the garage and am going to insulate and hang 5/8" drywall. If I want to rock and insulate the walls how would I even do that?

[pushkins]

Why 5/8" drywall ? 1/2" for a detached garage would suffice just as well and offer just as much insulating properties. 5/8" is normally used for fire retardation (firewall).
As for the walls If it were me I'd look at adding blocks between the studs (treated material) to help give support for the drywall at the base. Make sure your drywall doesn't touch the concrete 1/4" to 1/2" should be enough.

[DKAudio]

I was always taught to use 5/8" for ceilings and 1/2" for walls. The reason for this is to prevent sagging...you think 1/2" on the ceiling would be fine even with 24" OC joists?

This brings up a question…
I had to add 3 2X6 joists because there were a few spots where the joist span was 48" OC. I added these 3 so I could attach drywall everywhere at 24" OC.

The joists in the garage are 2X6’s spanning the width of the garage, they are 20 footers. The roof is a hip so it is angled on all 4 sides and uses 2X4’s for the rafters. There is then a center 2X4 running the length of the garage, it rests on top of all the joists, connected to that is another 2X4 on its end running the same length (if you picture it, the two 2X4’s create an L, one laying flat and the other on its end). These 2X4s are attached in 2 spots, the front and back center rafters.

Now, I know that a hip roof bears load on the exterior walls. However, at a ¼ of the way in on both sides there are some 2X4 vertical trusses nailed to the rafters and then toe nailed to the 2X6 joists. I was adding these to my new 2X6’s and was going to use rafter ties to tie the 2X6 joists to the long 2X4’s running perpendicular to the joists in the center of the garage. I was also thinking about adding a truss or two to that 2X4. Would this be a good idea or do you not want to “pull” down the rafters in a hip roof? My reason for doing it is because I don’t want the 20 foot 2X6 joists to sag once the weight of drywall is attached (also use the space above for storage, mostly extra lumber).

I created a quick sketch since the above is probably confusing. This would be looking against the rafters, I only drew 2 rafters and 1 joist to avoid further confusion...

[pushkins]

The 2x4's running down the center simply stop the 2x6 ceiling joist from deflecting.
20' is an awful long way for a 2x6 to span especially if your going to hang drywall, it wouldn't meet code nowadays and it would without doubt sag (even more with 5/8)
The vertical 2x4's are taking some (little) load from the rafters to the 2x6 ceiling joist near the wall.
A better option would to to add collar ties 2' down on each set of rafters horizontal and bolt these to each rafter (either side) on the other side of the bolt add a 2x4 (or 6) vertically down to your 2x6 ceiling joist and bolt it to that as well. That will help with your ceiling weight.

[DKAudio]

I just took a laser level and found out that right now with no drywall the joists are sagging 1.5" in the middle! I guess I will stop what I'm doing and try to do what you said. I should probably try and jack each joist up, correct?


Also, since the roof is hipped (slopes on all 4 sides) I cannot get to the 1st and 10th joist to do that, there would be no where to attach the collar ties. The second and ninth joist the rafter is only about 3 feet out from the sides, the third and 8th only about 5 feet, the middle 4 joists I can do without an issue.

Is the below picture what you where thinking? When you say "either side" you mean I can pick a side, I don't need to double up on the collar ties and verticles, do I? Also, would drilling a hole for a bolt in a 2X4 rafter weaken it a lot? A 2X4 isn't very much material as it is, what size bolt would you use?



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[pushkins]

Yes your picture is correct, the collar tie would be one side of the rafter and the ceiling joist support would be on the other side on the same bolt. The bolt would not need to be any bigger than 3/8" make sure you use a washer.

If you have a nail gun you could simply nail the collar and the joist support into the rafter and ceiling joist, this would make the job supper quick with pretty much the same result, if you nail it move the location of the ceiling joist support so as not to be driving nails into the backs of the collar tie nails.

Another option (maybe easier) would be to install your collar ties then install the ceiling joist supports in the middle span of the collars down to the middle of the ceiling joists.
Naturally no matter what method you choose you will need to level out the ceiling joists, run a string line and with a 2x4 push up the joists till level then nail etc...

Around the internal perimeter of the ceiling area, you will probably have to nail onto the top of the wall top plates a "drywall nailer", this is simply a 2x4 laying half exposed on the top plate so you have somewhere to screw the drywall on the edges.

[DKAudio]

Thanks, should the collar ties be 2X4 or 6 or bigger?

Again, you would not worry about pulling down on the 2X4 rafters? I am just picturing them splitting and cracking.

Should I not store anything on the joists?

Finally, what about the 6 joists where I cannot really add collar ties to as described in my last post? I can take a picture later if you want.

The rafters are cut flat for a few inches level with the top plate so I have a nailer to attach the drywall already.

[pushkins]

Does this garage have a ridge beam or are the rafters directly supporting their opposing rafter ?

2x4 or 2x6 either one will do the job, if your going to hang the joist support from the middle of the collar then definitely go with the 2x6 (that's what I'd do if it were me).
I'd also be careful what you store up there weight wise, with what you have described and the 2x6 ceiling joists it's simply not sized to accommodate a great deal of load.
10' something 2x4 rafters are simply under sized on either 24" ctr. or a 16" ctr. Yes I've seen them on plenty of garages of your vintage and on some DIYer jobs BUT try and get plans approved in your local building department for a new build !
adding the collars and joist supports will increase your load limits but your also "adding" drywall
1/2" 4x8 sheet of drywall weights in at 54 lbs
5/8" 4x8 sheet of drywall weights in at 70 lbs
as you can see that is like storing between a 1 1/2 to 2 bags of concrete up there every 32 square feet.
The areas where you cannot add collars should be okay, you can still attach the joist supports by bolting them to the rafters and dropping down to the joists (OR SEE BELOW SIMPSON STRAPPING)

If you store "a lot" of weight up on those joists you might see a little sag on those rafters but if you keep in mind your situation when tossing stuff up there you should be good to go, in other words don't be trying to store a dozen 5"x11 7/8" LVL's or fill up the entire space with "I think I might need it one day" lumber.

I know you have already mentioned about installing some 2x6 ceiling joists, but here is a chart for span lengths.

Douglas fir 2x6 max. span is 10'3"
Douglas fir 2x10 max. span is 17'3" (much closer to your 20')
Douglas fir 2x12 max. span is 21'

As a foot note you could attach the joist supports with Simpson steel straps and nailed with Simpson #10 nails, this would save a heap of time and money, straps at the top joint (tie to rafter) and bottom joint wrapping under the joist and back up the other side of the support.
If you have a 2x ridge beam you could use the same straps and attach one joist support right in the middle down to the joist (with the steel strap wrapping like mentioned above)

[DKAudio]

There is a ridge board but again, just a 2X4. I guess I will take everything down and store it in the shed. I will take a picture or two and post. For the vertical pieces I already added I was using metal mending plates and 8D 1.5" nails.

[pushkins]

Even though the ridge beam is only a 2x4 you can still use the nailing plates and the #8 nails are fine too.

[DKAudio]

Here are some pics...I am starting to wonder if I should just forget the whole thing. I got a decent woodburner and temporarily install it every winter and take it down in spring. When it was 0 out I could only get the garage to 25 after hours and hours of burning. I wanted to insulate and drywall the ceiling because of this. Anyways, here are some pictures...you can see the new 2X6's that I added because of the color.



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[pushkins]

I think your on the right track, weight on the 2x4 rafters is really my main concern.
You could install a lighter material on the ceiling. You could make up any R value lost in replacing drywall with another product by upping the r value of the ceiling insulation (drywall offers only about .5 R ). Even 1/4" ply would save you 40 odd lbs / sheet
If you still want to do drywall attach your ceiling supports to the ridge beam with the metal nailing plates (be better to have the plates a little longer) it would be better to cover the entire width of the ceiling joist with the plate then run up the support 3-4", same with the nailing plate at the ridge beam.
Make sure the ceiling joists are "attached to the wall" on either side by nailing into the rafters and top plate. The reason behind this is that the roof load is pressing down on the wall in essence trying to push them outwards, the ceiling joists are there to hold the walls in, when you increase the load on the ridge it's important to ensure the joists are doing their job.

[DKAudio]

Thanks for helping out so much, I appreciate it.

I can borrow a framing nailer from my Dad so I will add some nails in the joists to top plate.

I would probably only use drywall because I still want it to look good. I will use 1/2" instead of 5/8" though.

Are you saying to use the ridge board to attach the verticals instead of adding collar ties? The ridge board is probably only about 4' long, the roof then starts to pitch on all 4 sides. I can use the ridge board for a few joists, use collar ties for a few more and then at the front and back just use metal plates and verticals attached to the rafters. Does that sound good?

Thanks again!