Conflicting Specs

[mark2457]

Hi All

 

Designing a new garage for the the house I'm buying (tear down 1-car and build 2.5 car). Going pretty well, but stuck on framing:

 

Wall construction

1. Treated bottom plate bolted to foundation maximum 6' apart, must be within 12" inches of all comers. Bolt
2. size 1/2" x 10"
3. Double top plate required
4. 2x4 maximum 24" o.c. rafters to line up with stud below.
5. Install 1/2" plywood or notched 1x4 wind bracing at comers in 2 directions from top diagonally outward a distance of 72 inches measured from each comer at sill plate.
6. Short walls to be braced per current adopted !RC.
7. Garage door headers, double 2x12 with 1/2" plywood flitch plate opening to 8ft.
8. Headers up to 16 ft require a minimum 1/8" x 11" steel flitch plate with double 2x12 or equivalent.
9. Large headers are to be sized for loads imposed.

 

Roof construction

1. Rafter minimum 2x6 up to 24' span.
2. Ridge board 1 size larger than rafter.
3. Minimum 2x6 ceiling ties maximum 48" on center
4. 1/2" plywood or OSB roof sheathing rated for span

Aren't Wall Construction No 4 and Roof Construction No 3 conflicting? I've never heard of a ceiling tie. I assume it's a rafter tie. If it's not a conflict, does it mean every other rafter tie has to be 2x6 vs 2x4?

 

A few other points: I'm using 2 x single garage doors (probably 8 feet), so I assume I can just get away with 2x12 with 1/2 ply flitch plate. regardless whether I need the steel or the ply flitch plate, I'm gonna have to use 2x6 studs to support these aren't I?

 

If I use auto framing can i just edit the suds under the headers to be 2x6 and will it retain this if I rebuild the framing?

 

Can I build my own header material with the flitch plate?

 

thanks

 

Mark

[DRAWZILLA]

Just change your ceiling spacing to what you need using the "Joists direction tool.

This sounds more like a plan check correction, if so just give them what they want or get an Engineer to do it.

[Kbird1]

I think what they are calling a ceiling tie is actually the Ceiling Joist , and in a garage one every second Rafter is probably fine since loads are low , however having seen your other post , with the vaulted Ceiling etc the minimum may not be sufficient since you are "weakening" the system by having the Ceiling at 10' on 8' high walls.

 

2x4 walls are fine , your beam is 2x   1 1/2 material and a layer of 1/2 ply   ie  3/12 inches , stiffer the beam the better though for garage door motors pulling on it ,and I usually use double Cripples and Double studs to stiffen the door frame and give plenty  of room for the garage door installer to attach his brackets.

 

PS keep the concrete curb ( if you have one) back from the door opening so the installer can install his brackets properly.

 

M.

[mark2457]

Thanks Guys

[Jay_on_Cape]

What kind of siding do you have?  If it's vinyl you may want to up the wall sheathing thickness.  It's a garage so you probably won't mind a few ripples if it's your own.

 

 Check your roof sheathing.  The stuff we use around here can't span 24"  with just 1/2".  We use 5/8" (or 19/32") with plywood clips. 

 

 You probably don't need flitch plates for your header if it's just an 8' span with 12' of tributary load unless you have a high snow load there or a floor above?

[WendyatArtform]

RE: tieing the roof, semi-vaulting, etc:

 

Myth - you can tie if you are 1/3 from the top of the rafters.  So if your 10 ft ceiling on 8 ft walls works depends on your roof pitch.

Truth - to tie the roof you have to be 1/3 from the bottom of the rafters, or lower.  And, you are allowed less rafter length.  Crack the code book and look for the slope adjustment factor.  Or better yet, buy yourself about 2 hours of an engineer's time and make sure your spanky new garage doesn't sag on you! 

[Richard_Morrison]

You are WAY over your head structurally. (2x6 rafter for up to 24' span? I don't think so. Sizing the ridge board to be one size larger than the rafters doesn't work without intermediate supports, which you don't have.)

 

Collar ties are unnecessary if you have ceiling joists (nailed properly to rafters), and as Wendy says, don't do anything unless they are in the lower third of the rafter. If you are using them just to tie the rafters together to keep from separating at the ridge, then straps are easier. Consult a structural engineer, as Wendy suggests.

[builtright3]

I haven't heard mention of what your roof pitch is but it looks like you are definitely under designed structurally. I couldn't imagine the rafters working for snow load (on your post heading it says you are in Chicago). If you don't go to an engineer you may be able to get some minimum standard framing details, rafter spans and ceiling joist spans (or rafter ties) from your local building department.

[Kbird1]

I agree , 16" max centres  and you may need a structural RidgeBoard ,15x3 or perhaps deeper, since you want to raise the Ceiling off the plates   , Engineered trusses might get you there too and of course the Truss engineer will do the engineering for you.

[WendyatArtform]

You are WAY over your head structurally. (2x6 rafter for up to 24' span? I don't think so. Sizing the ridge board to be one size larger than the rafters doesn't work without intermediate supports, which you don't have.)

 

Collar ties are unnecessary if you have ceiling joists (nailed properly to rafters), and as Wendy says, don't do anything unless they are in the lower third of the rafter. If you are using them just to tie the rafters together to keep from separating at the ridge, then straps are easier. Consult a structural engineer, as Wendy suggests.

 

Oh baby - I didn't see that (the 2x6 rafters).

 

Yes.  If your code officer doesn't flunk you, mother nature will! 

[Gawdzira]

Why do so many people shun engineers? Engineers are your friend. Engineers know lot's of stuff about engineering, gravity and making sure people in and near buildings stay not dead.

[builtright3]

Why do so many people shun engineers? Engineers are your friend. Engineers know lot's of stuff about engineering, gravity and making sure people in and near buildings stay not dead.

 

Did I miss something here? I didn't see a post where anyone shunned engineers? Or is this just a general comment?

[lbuttery]

I think collar ties is the concept here

 

BTW: my architect spec'd a very large/heavy ridge beam for my addition

just before I  bought all the material my partner Joe pointed out that the collar ties should be sufficient

 

went back to architect and WHOOPS she had missed them on the plan

 

I bought Joe a nice crab dinner at Red Lobster

 

Lew

[mark2457]

What kind of siding do you have?  If it's vinyl you may want to up the wall sheathing thickness.  It's a garage so you probably won't mind a few ripples if it's your own.

 

 Check your roof sheathing.  The stuff we use around here can't span 24"  with just 1/2".  We use 5/8" (or 19/32") with plywood clips. 

 

 You probably don't need flitch plates for your header if it's just an 8' span with 12' of tributary load unless you have a high snow load there or a floor above?

 

I was thinking of using called SmartPanel (they sell at Menards). Like harde board from what I can tell, but comes in 8x4 sheets. Uses some on an outdoor kitchen island once. Worked great

 

Thanks for tip on sheathing

 

I agree on the flitch plate, but village requires it. Seems way overkill.

[mark2457]

RE: tieing the roof, semi-vaulting, etc:

 

Myth - you can tie if you are 1/3 from the top of the rafters.  So if your 10 ft ceiling on 8 ft walls works depends on your roof pitch.

Truth - to tie the roof you have to be 1/3 from the bottom of the rafters, or lower.  And, you are allowed less rafter length.  Crack the code book and look for the slope adjustment factor.  Or better yet, buy yourself about 2 hours of an engineer's time and make sure your spanky new garage doesn't sag on you! 

 

Thanks. Got a buddy who's an architect. He'll do the calc's for me (but not plans: doesn't do residential)

[mark2457]

You are WAY over your head structurally. (2x6 rafter for up to 24' span? I don't think so. Sizing the ridge board to be one size larger than the rafters doesn't work without intermediate supports, which you don't have.)

 

Collar ties are unnecessary if you have ceiling joists (nailed properly to rafters), and as Wendy says, don't do anything unless they are in the lower third of the rafter. If you are using them just to tie the rafters together to keep from separating at the ridge, then straps are easier. Consult a structural engineer, as Wendy suggests.

 

Thanks Richard

 

i have a buddy who's an architect (having dinner with him this week). He'll do all the calcs for me, but not drawing. Right now I'm just trying to visualize a design and then update the structural stuff based on his calcs. I'm also want to price out cost of raw materials if I buy them vs. buying one of the available kits from Menards/Lumber84, etc. 

 

Ultimately will need to decide whether to have plans professionally drawn (what would it cost?) or just buy some off the shelf plans if I can find something close to what I want.

 

Main thing I want that's out of the ordinary is 9ft walls (so I can handle an 8x4 sheetgoods and 8' 2x's easily). Village limits me to 15' ridge height. Based on this and my dodgy calculations, I came up with out 5" rise for each 12"

 

Thanks for the heads up. 

 

Regards

mark

[Kbird1]

if you want to keep cost down and still have head height , just go with a Truss roof , flat ceiling and use  9' or even 10' high walls , perhaps 10 if a Workshop for the extra storage /ducting etc.

 

Might want to consider 8' high doors too instead of the usual 7'

 

M.

[mark2457]

Thanks for tip

 

Was just pricing out trusses for 24'x24' at Menards. Came out:

 

2 x End truss @ $76.49

10 x Common truss @ $51.49

Total - $663.47

[Kbird1]

At those prices I'd put them on 16" OC ( 2 extra?)  to help eliminate ripples etc especially in the drywall (if you have it) and put a stud under each one even with the double top plate , this will also allow for straighter walls , if going with Fiber cement Panels as you suggested I usually use a double stud at each sheet joint too to give better nailing at the edges. (sheets Vertical)

 

M.

[mark2457]

Thanks Mick

 

Priced it out with hand cut rafters and was about 40% more (in raw materials). Was thinking about going with 16" OC as I'll have a lot of wall storage and shelves.

 

Good idea on double studs at sheet joints

[Gawdzira]

If you are on a tight budget look into O.V.E. framing. Optimum Value Engineering. It will save about 30% of the framing material budget. Also, with 9' plate you can get plywood in 4'x9' or 4'x10' sheets at a lumber yard.

[mark2457]

If you are on a tight budget look into O.V.E. framing. Optimum Value Engineering. It will save about 30% of the framing material budget. Also, with 9' plate you can get plywood in 4'x9' or 4'x10' sheets at a lumber yard.

 

Thanks for suggestions Alan

 

I priced out lumber for hand cut rafters and roof trusses. Trusses were 40% cheaper, so re-did plan (attached) with them.

 

 

Slab still looks like I'll need a monster truck to get in. 

Garage Slab and Trusses - pitch 4-12.plan