lining up rafters and studs

[MarkAndDebbie]

Do the rafters need to be centered over studs? I am doing 24" oc studs. I talked to a guy (professional carpenter - seems to know what he's doing) that may help with my roof. He said he didn't recommend 24" oc, even with H-clips and 5/8th sheathing. He recommended 19-6 (which I had not heard of - but I see the diamond on my tape. It looks like one more rafter in 8'.) He said it was up to me, but he would do 19-6.

I don't have a problem with adding 4 rafters. I'll need to check my cotton batting to make sure it comes that size (I don't want to cut for every bay). Can we dispense with the H-clips at 19-6 (that would be reason enough for me - they are a pain)? I'd even do 16 oc if I had problems with the batting and could get rid of the h-clips (would I then use 1/2"?)

I'm under IRC. 12/12 pitch. Metal roof. 2x12 rafters. No dormers. No snow load. Anything else you need to know?

Main question - do they have to line up.

Thanks!

[Don_P]

If you use a double top plate they do not have to line up. The gobbledeygook is on the first page of the wall chapter under "Top Plate", read the exceptions.  I've never used 19.6 on anything but a floor but it would certainly work. There are fewer break patterns than with 16 oc so also look into the plywood cost as part of the equation. I use clips on every spacing and prefer 5/8 at any spacing but that is getting into personal preference. IIRC (check the chart) I believe you an get away with no clips and 1/2" at any spacing, code is minimum, not necessarily good though. And yup, they are a pain, I prefer the steel ones to aluminum.

[n74tg]

If you think about it most trusses or rafters are usually set on 24" centers with wall studs set on 16" centers.  When done that way it is pretty much impossible for every rafter/truss to sit on top of a wall stud.  That is one of the main reasons these applications use a double top plate; so it can function as a header, spreading out the point loads from the rafter/trusses that don't line up with studs.

Now, if you use stack framing where every rafter/truss sits directly over a wall stud, then of course rafter/truss spacing has to be the same as your wall stud spacing.  If you use stack framing for your trusses and wall studs, then it helps a lot to use the same spacing on your floor joists, so your wall studs can line up exactly with the floor joists.  You can probably find in somewhere in the code that you can use 16, 19.2 (you said 19-6)or 24 inch spacing legally.  I can't personally vouch for 19.2 spacing but I know it's legal to build with 16 or 24 inch wall stud spacing. 

My house that I am building uses 2x6 wall studs on 24" spacing and because my trusses sit directly over these wall studs I can (by code) get away using a single top plate.  Why would I want to use a single top plate?  Because everywhere you have wood you DON'T have insulation, and walls that have lots of wood framing members (many of them unnecessary from a structural point of view) seriously degrade the overall insulation R value for that wall.  I've read about R-value decreases of 25% for conventionally framed walls, so the wall that you thought was R-19 is now really somewhere around R-14 and that is before you further decrease it by installing windows.

The most common reason I've heard against using 24" stud spacing is that it makes getting the sheetrock to lie really flat a little harder.  Some say it's real difficult if you use 1/2" thick sheetrock on 24" stud centers.  I haven't sheetrocked my walls yet, so it's too early for me to be able to answer personally.  I'm considering using 5/8" sheetrock anyway, so that might help smooth out the walls.

Like you, I used 5/8" sheathing (OSB).

I discuss all this in my housebuilding blog, address below, if you're interested.

Good luck with whatever you choose. 

 

[MountainDon]

If you think about it most trusses or rafters are usually set on 24" centers with wall studs set on 16" centers. 

Our cabin is the opposite. 2x6 wall studs on 24" centers with 2x6 rafters on 16" centers.

Three our of four walls are sheetrocked inside with 5/8" drywall. The other is 1x T&G. No waves in the 5/8" rock.

The roof was built on 16" to meet the snow load I wanted and be ab;e to use 2x6 rafters.


There's not one single best way to build a cabin.

[NM_Shooter]

There's not one single best way to build a cabin.

Quite possibly the best thing to keep in mind!

[Hi Road]

A couple of thoughts:

I think the 19.2" spacing has it's origins with TJIs.  If you spec TJIs the supplier may give you a 19.2 layout option. 

Also, if you plan to use rafters at 24" oc (or trusses) and will be using 7/16" OSB roof sheeting and are in a heavy snow l load area you may wish to use "H" clips mid-span between the rafters along horizontal the OSB edges.  This hardware will increase the the ability of the sheeting to resist deflection. Check with the manufactures recommendations too.

My two cent worth.

Merry Christmas to all.

[MountainDon]

   hi road

Note: Installing 7/16" OSB or plywood roof sheathing panels on top of the trusses and/or rafters spaced at 24" on center without H-clips is allowed by code and by the performance standard on the grade stamp on the sheathing; however, the roof sheathing may be springy or feel "soft." If we place the H-clip at the halfway point (12") between the trusses and/or rafters, the adjoining sheathing panel stiffens considerably. As a result, the fastening of the roof shingles will be easier and the roof will remain flatter and more "in plane" over time (i.e., no sags and/or bowing due to accumulated load).

H-clips also provide the recommended spacing between two adjoining panel edges, allowing room for panel expansion if the panels get wet during construction

[Jens]

almost every roof I have ever seen or built is 24" oc.  H clips help with thinner sheathing, plywood is nicer than OSB here IMO, because it carries a better point load.  In other words, I can easily punch a hole in OSB with a hammer, not so with plywood.  I framed a house with walls on 24's once, this is what I learned...

if you are going with single wall siding, use plywood not OSB.  If OSB stuff, it will warp quickly. 
if I did it again, I would apply 1x3 strapping across the studs on 16" centers, and attach the drywall to that, then you don't need 5/8 rock
         your back will thank you.
just spend a few more bucks on a few more 2x's, and you get your insulation for a fraction of the cost of 22.5" batts.

I will probably not build on 24's again, unless I use spray foam or natural (like slipstraw) insulation.  It is a decent savings on lumber to go with 24's, but insulation, sheetrock, and siding can be more expensive.

[MarkAndDebbie]

however, the roof sheathing may be springy or feel "soft."

On a 12x12 roof I won't notice the springyness (spralled flat gripping for dear life )

FYI for everybody. We ended up deciding on 24" centers with 5/8ths plywood with h clips.

One reason for the walls being 24" oc is actually that it reduces my labor (framing, insulating, drilling electrical, etc). And I'm already slow and expensive. It also makes certain things easier with bigger bays - like drilling.

Thanks.

[Jens]

fyi, I think that clips are not required on 5/8 plywood.  Still nice, but they can be a pain in the but sometimes.