Roof insulation help

[weedsnager]

I have 48" Oc in my garage roof, space is roughly 20x20, I don't know if you technically call them trusses, they are 2 x 12's, 20 ft long. I want to drywall the ceiling and insulate. My question is, what type of support should I add for the drywall. Should I add perpendicular support with joist hangers? And what form of insulation?

 

[ClearSpace]

I couldn't find anything the Code Book for 48" ceiling joist spacing...24" is the maximum allowed. Personally I would nail 2x4's 16" O.C. perpendicular to the ceiling joists...2 16d nails per joist connection. 1/2" rock right over that. If there is a living space above you should use 5/8" fire code rock instead of 1/2" I might even run a few purlins from the joists to the rafters to transfer some of the load to the roof. It looks like your storing materials up there.

If you want to bring it to code add another 2x12 between each joist then strap it with 1x3 strapping and some solid bridging down the middle. Rock over that and you'll be AOK.
Price out both ways.

I've worked on 1800's homes and I've seen much much worse.

Hope this helps you out some.

-Lance

 

[RCStocker]

As a contractor and architect I will tell you that you can not hang drywall on it. You need at least 24" centers to hang dry wall and if you block it in the truss or rafters will not hold the weight. You need to put in 2x12 celling rafters to support at 2 ft. centers or build in a full truss between the existing trusses.

Your rood does not meet current code standards. It is not just a matter of holding the weight but it will not have enough screws to hold it up. A 4 x 8 sheet of drywall is about 98 pounds.

It will be very difficult to fill things in and I can not see enough in your photo to tell if your current trusses need reinforcing. From the age of the structure my bet is that the need beefing up.

You can insulate your garage but I would put in a drop down celling but they get dirty over time and will look like hell in an old garage where dust and dirt blow in. Drywall is better.

I have done it but I had to cut wholes into the roof to slip in the new rafters. Then you have a problem with support if your existing roof is not have a 3 ft. over hang. This will leave enough room above the top sill plate to support a rafter. If not you will need to install supports on the inside wall to support the new rafter. A good 2x3 nailed to the upper 2 plates should be enough support but you will need to drywall around it and block it in to cover the support. If you need a new roof that would be nice. You could strip the existing roof and cut in with ease then install the new roof.

I would not bother dry walling an old garage. I would do just the walls.

 

[weedsnager]

The house was built in 2003, not an old house.

 

[spruce]

a 4x8 sheet of drywall is no where near 98lbs

 

[weedsnager]

The 1/2 sheet I just bought for the walls said 57lbs

 

[theoldwizard1]

From what I can see in that picture, those a basically widely spaced ceiling joists. What most people don't understand is that in this type of construction, the purpose of the joist is to prevent the walls from moving outward from the load of the rafters which transfer their load down and out.

The best solution is to add additional joists half way between the existing ones. For level storage above, you should use 2x12, but that is over kill. You can probably get away with 2x8 because they aren't going to add much, if any, strength to your structure, but they will carry part of the the load of the insulation and drywall.

It is next to impossible to add a joist to an existing garage, in one piece, so use 2 pieces. If you use 2bys that are 12' long they will overlap in the center for 4'. Use construction adhesive and some through bolts. Before you secure you new joists to the top plate of the walls, take some careful measurement between them, under the existing joists. Also check to see if the wall has pushed out of plumb at the top. You may have to use a come-a-long to pull the top of the walls in.

Also, look carefully at how the existing joists are attached to the top plate and do the same.

 

[weedsnager]

I don't know if it matters or not, but it's an attached garage. I will try and get more pictures tomorrow.

 

[bczygan]

The advice to use shorter ceiling joists and connect them where they overlap is not good advice.

You need additional joists as mentioned above.

Then, 2 pounds per square foot for framing (2x12's), plus 2 pounds per square foot for 1/2" drywall, plus 2 pounds per square foot for 12" of FG insulation plus, say 1 pound per square foot for 1x2 strapping at 16"o.c., lights and misc. Total is 7 pounds dead load.

The calculator I used would only allow a minimum total load of 15 pounds/SF. And that showed a 25'-9" span for hem-fir 2x12's.

So I would try to match the existing ceiling joists.

 

[volleyball]

You guys are way over engineering this. If there will be no storage overhead, then running 2x4 perpendicular to the 2x12 spaced 24" will give you a stronger ceiling and support for the drywall.
If you cannot lose the 1 1/2" for the 2x, then screw them between. Not recommended but will work.

 

[bczygan]

The advice to use shorter ceiling joists and connect them where they overlap is not good advice.

You need additional joists as mentioned above.

Then, 2 pounds per square foot for framing (2x12's), plus 2 pounds per square foot for 1/2" drywall, plus 2 pounds per square foot for 12" of FG insulation plus, say 1 pound per square foot for 1x2 strapping at 16"o.c., lights and misc. Total is 7 pounds dead load.

The calculator I used would only allow a minimum total load of 15 pounds/SF. And that showed a 25'-9" span for hem-fir 2x12's.

So I would try to match the existing ceiling joists.

STOP

I did some more calculations, based on the fact (Above) that 2x12's (If they really are), spaced at 2' would carry way more then the needed load capacity, I looked at the OP's request directly.

Us ing beam tables I see that a 2x12 hem-fir will support 68 pounds per lineal foot at 20' span. Even a 2x10 will support 46 pounds per lineal foot.

So, using the above loads, and determining the contributing loads based on using the existing joists and adding 2x4 nailers at 16"o.c. between each joist, I get the following:
4 pounds per lineal foot of existing 2x12 ceiling joists, 5 pounds of 2x4 nailers per lineal foot of joist, 8 pounds of 12" deep FG insulation per lineal foot of joist, 8 pounds of drywall per lineal foot of joist and 4 pounds per lineal foot of joist for lights and misc.

No storage above with this depth of insulation so no live load is assumed.

That is a total of 29 pounds of load for each lineal foot of joist.

Way below the capacity of the existing joists, even if they are 2x10's.

So the OP can do just as he was asking.

Bill

 

[bczygan]

Oh......one more thing. You can use the lightweight drywall to save weight.

 

[weedsnager]

STOP

I did some more calculations, based on the fact (Above) that 2x12's (If they really are), spaced at 2' would carry way more then the needed load capacity, I looked at the OP's request directly.

Us ing beam tables I see that a 2x12 hem-fir will support 68 pounds per lineal foot at 20' span. Even a 2x10 will support 46 pounds per lineal foot.

So, using the above loads, and determining the contributing loads based on using the existing joists and adding 2x4 nailers at 16"o.c. between each joist, I get the following:
4 pounds per lineal foot of existing 2x12 ceiling joists, 5 pounds of 2x4 nailers per lineal foot of joist, 8 pounds of 12" deep FG insulation per lineal foot of joist, 8 pounds of drywall per lineal foot of joist and 4 pounds per lineal foot of joist for lights and misc.

No storage above with this depth of insulation so no live load is assumed.

That is a total of 29 pounds of load for each lineal foot of joist.

Way below the capacity of the existing joists, even if they are 2x10's.

So the OP can do just as he was asking.

Bill

Your saying use 2 X 4 nailers running parallel to the existing joists? Would it be stronger to use 2 x 12's perpendicular to the joists 16" Oc ? Or would that add to much weight?

 

[volleyball]

He is saying 2x4 perpendicular to the 2x12 like I had said.

 

[weedsnager]

Ok, I already have lumber to use, would it be better to use 2 x 12's perpendicular instead of a 2 x 4 or would it add to much weight?

 

[volleyball]

I'd use 2x4, way easier to put up. The 2x12 won't add much strength.
If you have a bunch of 2x12's that you won't use. you could run them parallel to the existing ties. I always have a better use for 2x12's than to hold up some sheetrock.

 

[weedsnager]

If I run the 2 x 12's up there perpendicular, instead of 2 x 4's I could put
Plywood or osb on top for storage

 

[volleyball]

I would put the 2x12 parallel to the existing ones. Then put the OSB on top if you want some storage.

 

[weedsnager]

The 2 x 12's I have are only 10ft long

 

[volleyball]

You can put a 2x12 from 1 old 2x12 to the next and then use hangers to put your 10' onto the 4' cross piece. I would not do this if I was going to put a lot of weight up there but I don't think you will be.

 

[weedsnager]

If I join my 2 X 12's together to make another joist it would be easier to put rolls of insulation in, but it would require a few guys to help me. If I cut them into 4ft pieces and run them perpendicular at 16" centers, I could do it myself And then blow on insulation

 

[volleyball]

You could do it that way with lots of cuts and waste plus hangers. Do it my way and you can do it yourself. Put up the 4' between two existing put hanger in middle on both sides. Put 2x12 in hangers. A 1 person job. If your 2x12 were 12' it may be worth to do your way.
You can put a 2x4 across the two existing. Put the 2x12 on top. Attach it and then remove the 2x4 and move onto the next set.
I use scraps and screws and do many jobs that most would think you need 2 people for.

 

[weedsnager]

I can't visualize what your referring to when you say put up 4 feet between two existing and what type of hanger to go in the middle?

 

[volleyball]

Think blocking. then use joist hangers like you would on a deck. so in between your existing would be the 2 10' end to end with a 4' piece going perpendicular to support the ends of the 10' where they meet.

 

[weedsnager]

Got it, thanks

 

[bczygan]

2x4's perpendicular to the existing 2x12 ceiling joists, at 16"o.c., hung with joist hangers. NOT 2x12's....they are too heavy.
You need about (40) 2x4x8's.

And you can't make a longer 2x12 beam from shorter ones without a lot of difficulty.

The method outlined above to install short 2x12's does nothing but add the loads of the new 2x12's to the existing ones. And you still need additional blocking at 16"o.c.

Save them for some other use.

As far as a lot of joist hangers goes, you have two solutions. Either use a combination of toe nailing and end nailing or a combination of joist hangers and end nailing,

And you can not use the space above for storage, period... It's insulated and you can't put down any decking. It wouldn't support the extra loads anyway.

Nailing patterns:
Single nailed:

Double nailed:

 

[bczygan]

One more thing.

If you choose to have a small area where you can have storage above, adding a couple of full length (20') 2x12's between the existing ones, and headering off an adjacent access hatch will allow some space. Best to deck it near the eaves. This will limit the insulation in this area to R38.

 

[weedsnager]

Would it even be possible to add a full 2x12 between the existing ones? Doesn't seem there would be enough space to get one up there

 

[bczygan]

Would it even be possible to add a full 2x12 between the existing ones? Doesn't seem there would be enough space to get one up there

As mentioned above, it's possible.

Do you fully understand your options from this discussion?

Did you get any better photos?

Bill

 

[weedsnager]

No better photos yet, I was in there today trying to get rid of some of the ****.....I think I understand my options.......thank you for all your help so far

 

[volleyball]

2x4's perpendicular to the existing 2x12 ceiling joists, at 16"o.c., hung with joist hangers. NOT 2x12's....they are too heavy.
You need about (40) 2x4x8's.

And you can't make a longer 2x12 beam from shorter ones without a lot of difficulty.

The method outlined above to install short 2x12's does nothing but add the loads of the new 2x12's to the existing ones. And you still need additional blocking at 16"o.c.

Save them for some other use.

As far as a lot of joist hangers goes, you have two solutions. Either use a combination of toe nailing and end nailing or a combination of joist hangers and end nailing,

And you can not use the space above for storage, period... It's insulated and you can't put down any decking. It wouldn't support the extra loads anyway.

Nailing patterns:
Single nailed:

Double nailed:

Way too much work your way. The reality it is not a load bearing floor. Never will be. 20' is too long a span for a 2x12 floor.
My take is that after the drywall is up, the insulation down, there will be some light bulky items thrown up there to get out of the way.
You want to make a regular floor out of it and it cannot be.
The OP will have to clues us in on what he has in mind. If he want a floor for heavy stuff, you have to skip the 2x12's and go to LVL's

 

[weedsnager]

The only reason for the floor up there is store things I don't use every day, your basic storage, nothing heavy

 

[bczygan]

Way too much work your way. The reality it is not a load bearing floor. Never will be. 20' is too long a span for a 2x12 floor.
My take is that after the drywall is up, the insulation down, there will be some light bulky items thrown up there to get out of the way.
You want to make a regular floor out of it and it cannot be.
The OP will have to clues us in on what he has in mind. If he want a floor for heavy stuff, you have to skip the 2x12's and go to LVL's

He needs some kind of nailer at 16"o.c. for the drywall. 2x4's are needed to span the 4' between the existing joists. That's the cheapest and lightest and easiest way.

Running members the other way would require a 20' span and 2 new members between each existing 2x12. And you still need nailers in the other direction every 4'.

And he wouldn't need LVL's to get 30 pound live and 10 pound deal loads. 2x12x20's at 16"o.c. will do it.

Bill

 

[volleyball]

Nailers at 24" OC is common today for ceiling. And my original plan to put 2x4 perpendicular would have suffice for a ceiling. The reason for some storage and having 10' 2x12 and wanting to use them led to my design. Which works well. If there are enough 2x12 10'., I would sister them to the original ties with a mending plate.

If this was my project. I would vent the soffits, put in a ridge vent, get 4x8 sheets of foam to attach to the bottom of the roof and tape the joints.

 

[bczygan]

Nailers at 24" OC is common today for ceiling. And my original plan to put 2x4 perpendicular would have suffice for a ceiling. The reason for some storage and having 10' 2x12 and wanting to use them led to my design. Which works well. If there are enough 2x12 10'., I would sister them to the original ties with a mending plate.

If this was my project. I would vent the soffits, put in a ridge vent, get 4x8 sheets of foam to attach to the bottom of the roof and tape the joints.

This is a good discussion, and you obviously have some experience to draw on. I also like the rigid foam attached to the bottom of the rafters, as a way to insulate a larger volume of space. But you need multiple layers for adequate R value. And it is more expensive than batt or blow in at the ceiling joists. Actually, my preferred insulation is foamed in place. But that isn't user friendly and is also more expensive.

Most garages have 2x6 or 2x8 ceiling joists, so if you insulate the ceiling, the insulation is above the joists and storage isn't possible. The usual R38 is 12" of depth and would be higher than the ceiling joists.

Luckily, in this case, the joists are 2x12's, so you could insulate at the ceiling and then put some ply decking on top of the joists for a storage platform. The problem here is that the decking and live load would require additional joists to cut the 4' span between joists down to 24" or 16". Which spacing would be determined by the anticipated or desired load capabilities.
Calculations would need to be made.

Adding joists between the existing ones is a way to cut the span for nailing the DW. But using 10' lengths, and then supporting them on the existing 20' joists, at the middle of their span adds the dead load of these additional joists as a point load. It would also have to be calculated, to see what is what.

For the DW nailing pattern, I prefer 16" spacing for nailing and even double nailing. In fact, I prefer screwing DW. But it's up to the OP.

 

[weedsnager]

After reading a few recent threads on metal ceilings, right now I'm leaning toward the dura-panel that menards sells..weighs less....no painting....muddin...etc.. Now, I still need to figure out what type of additional joints and insulation I'm going to use..

 

[volleyball]

There are different ways that will suffice. So hashing it out gives options.
The joists are not 2x12, they are collar ties to keep the walls from spreading.
Not designed to be a joist. I know that I'd throw stuff up there if it was mine. If you sheetrock the ceiling and fiberglass it, it will insulate but you won't have storage. If you put in an access, you lose a lot of the insulation value.
I know I can get used 4" roofing foam sheets cheap. This is more than adequate for insulation. If you have the budget for spray foam, that would be ideal. 4" on the roof deck bottom will insulate as well as stiffen the structure. But at $2k, pricey.

 

[theoldwizard1]

The advice to use shorter ceiling joists and connect them where they overlap is not good advice.

Okay, WHY ? Remember, this structure already passed inspection and was deemed good, sound construction as is.

So I would try to match the existing ceiling joists.

As I stated. in most cases it is impossible to insert full length, full sized joist without making a hole to the outside.

 

[weedsnager]

Okay, WHY ? Remember, this structure already passed inspection and was deemed good, sound construction as is.



As I stated. in most cases it is impossible to insert full length, full sized joist without making a hole to the outside.

This is what I'd prefer to do now that I've decided to put up a metal ceiling. The metal ceiling will be fine with 24" centers. I'd like to add additional joists, 2, 2x12x24's and sister them together, as most people have stated, I think it would be impossible to add a full 24' joist without cutting a hole in the roof.

 

[bczygan]

Read post #35! It answers why.

And wrong terms. sistering is slapping a joist alongside an existing one, to strengthen it, not joining end to end