Open rafter ceiling on a "Shed Roof" sunroom?

[mpildis]

I recently began building an enclosed porch/sunroom off of the side of my house. There was originally a screened in porch on a concrete slab there but I tore it down as it was in bad shape and not big enough for the jacuzzi I want to put inside. After seeing how poorly that thing was put up (and it stood for 50 years), it gives me a warm feeling about what I'm doing, however I have some concerns now and want to make sure I'm doing it properly and don't have any issues down the road (drywall/stucco cracking)or have the damn thing collapse. I extended the concrete slab and put in a proper footer 36" deep around the perimeter. The outside dimensions of the new room are 18'-8" Long by 9'-8" Deep. It is standard 2x4 wall framing. It has a "shed" roof style, 5/8 OSB, asphalt shingles. The new room top plate is standard 8' high, and top of the ridge where the roof connects to the house is about 11' high, so it is just about a 4:12 pitch. I used 2x6 rafters (which all of the tables I looked at said this was sufficient for my span - 9'8", calculated for 10psf dead load and 50psf snow load with a 240 deflection which puts me right at the limit for the 2x6's - I'm in Southeast PA so snow load is more like 25-30psf). Rafters are 16" OC and are joist hangered into a 2x8 PT header board which is lagged into the house studs & house brick every 16" or so. I used 1/2 x 5-1/2" galvanized lags. At the sunroom wall the rafters have birdsmouth's cut, are toenailed into the top plate and I also used a Simpson H-1 Hurricane tie on each rafter. Now for my question: Originally I was going to run ceiling joists from my top plate of the new wall to the house however I REALLY screwed up. There are 3 windows on the house wall which will now be inside the sunroom and they are slightly higher than 8', so if I were to run ceiling joists they would go right into the glass if you get what I'm saying. I am wondering if It is OK to have an open ceiling and just drywall over the rafters. Do I need ceiling joists for structural purposes since this is a shed roof and not a gable? I am worried about the extra stress of not having ceiling joists and extra dead load of the drywall on the rafters and am wondering if I undersized the rafters for this application? The other thing I was thinking about doing was putting collar ties about 2/3 the way up the rafters and attach them to the house with joist hangers. That way I would have a sloped and then flat area on the ceiling. I was planning on using 2x4's for this as it's only a 3' span. I don't know if this would help structurally or not, and then there's the downside of adding the extra dead load of the 2x4's onto the rafters (although I know it would be minimal). The only other solution I have is to tear out the 3 windows and lower them so that I can run the ceiling joists, although I'd really like that tall ceiling. I think I covered all of the info you might need. Any help would be greatly appreciated as I'm at a dead hault until I figure out what to do.

Thanks!

[Don_P]

I hit a dead halt when you said brick... is the ledger at the top of the rafters lagged through brick veneer and into studs behind it?

[mpildis]

I hit a dead halt when you said brick... is the ledger at the top of the rafters lagged through brick veneer and into studs behind it?

No, let me elaborate. The ledger spans across the original house and an addition. The original house is solid brick (it's about a 5 foot span in which I used lag sleeves). The other 13 feet of the ledger connects to the addition which is wood framing. Curious though what would of been the issue if it was through brick veneer?

[Don_P]

We are not allowed to bear on brick veneer or hang a lag through it to get to the structural framing behind it (Since the lag would bend and be bearing on the non structural veneer).

So anyway assuming that connection's good, the question was whether the 2x6 rafters can support dry wall directly applied to them in 50psf snow load area with a 9'8" horizontally measured span. Checking the codebook table 802.5.1(6) Rafter Spans, ceiling attached to rafters;
16" oc...#2 SPF-9'9", #2 SYP-10'2", #2 Hemfir-9'7", #2 DF-L-9'9". Check the stamp on the lumber and measure inside of bearing to inside of bearing (clear span) but I'm guessing you squeeked by.

[mpildis]

We are not allowed to bear on brick veneer or hang a lag through it to get to the structural framing behind it (Since the lag would bend and be bearing on the non structural veneer).

So anyway assuming that connection's good, the question was whether the 2x6 rafters can support dry wall directly applied to them in 50psf snow load area with a 9'8" horizontally measured span. Checking the codebook table 802.5.1(6) Rafter Spans, ceiling attached to rafters;
16" oc...#2 SPF-9'9", #2 SYP-10'2", #2 Hemfir-9'7", #2 DF-L-9'9". Check the stamp on the lumber and measure inside of bearing to inside of bearing (clear span) but I'm guessing you squeeked by.

Yea, by my calculations I did just squeak by. Actual bearing-to-bearing span is 9'-4", it's SPF #2. After a little more research actual live load for snow here is 30psf, so that gives me some breathing room (I never like being at the threshold). Guess I really should have did more research and calculations before I started, but I'm relieved it's ok. This might be grounds for a new thread but I'll bring it up here anyways since it's related. I'm going to go ahead and put the collar ties about 2/3 of the way up the rafters so it will help tie them in more and give me a flat section on the ceiling. Wondering how I should ties those into the house though? Planning on using 2/4's for the collars since it's only a 3 foot span and joist hangering them off of a 2x6. Question is though if I need to lag that 2x6 into the house studs of if just nailing it in will suffice. I'm re-studding the house wall so it would actually be sitting on the top of those new wall studs and supported underneath. I was also going to stick some cripple studs between my collar ledger and the rafter ledger so that physically has something underneath it as well (The force needed to sheer all my lags is enormous but I'd still feel better if it physically had something underneath it. Also, since the collar tie ledger will be spanning across the original house section and the addition, some of it will be resting against brick. This is now inside the room though so is it necessary to make that section pressure treated?

[Don_P]

Not necessary but I would at least slide some tarpaper or some type of break between them.

The force needed to shear the lag connection is not enormous it is quantifiable and should be safely greater than the load. The AWC connections calculator can figure it for you, awc.org

Nailing the ceiling joist ledger in for that span is ok.

[mpildis]

Not necessary but I would at least slide some tarpaper or some type of break between them.

The force needed to shear the lag connection is not enormous it is quantifiable and should be safely greater than the load. The AWC connections calculator can figure it for you, awc.org

Nailing the ceiling joist ledger in for that span is ok.

Don, thanks for all your help. Good thinking on the tar paper, I have plenty left from the roof. You have me paranoid now though regarding the fasteners. If I calculate the area of the roof (10x18) and multiply by the load of 40psf (10 dead + 30 snow load) it gives me 7200 lb's of roof...woof! I went and took a look at the calculator. At the moment there are qty 16, 1/2 x 5-1/2 Lags holding the ledger into the house studs. According to that calculator the shear strength of each lag ia 347lb's?? That seems awefully low to me but if that is the case that would give me 5552lb's of lag strength. You obviously know more than me but I would think that's a problem. Granted the weight of the roof isn't solely on the lags and is distributed to the walls as well, but still I'd like to see that number higher than my roof weight. On top of that each Rafter (13 total) is attached to the ledger with a Simpson sloped joist hanger. There are qty 8, 10D nails per hanger into the ledger. Again, according to the calculator, shear strength of each nail is 77lb. So 8 x 13 x 77 gives me 8008. Any case for alarm there? The end rafters are not joist hangered (toenailed and angle bracket into the ledger) and are bearing above the side walls (gable studs between them and top plate), so there is weight distribution there and oviously not all of the weight of the roof is directly on the nails/lags, and neither are the nails/lags in direct shear for that matter so I don't know if there's any cause for alarm. You'd know more than me. Any thoughts?

Footnote:

What boggles me is how the old porch stood for 50 years. They used a 1x6 for the ledger and is was nailed in with literally about 10 nails. Rafters were all toenailed in with 2-3 nails. It was a bit smaller than my room, was 8 deep x 16 long.

[Don_P]

Yup there's the difference between what we do now vs what they did in the old days. will it fail? probably not, is it up to what they would like to see? not quite. We are designing around an event that might come around once every 50 years and then with roughly a 2:1 safety margin to allow for material and installation variability. I can't confirm your work though, you'll need to satisfy yourself that you've done due diligence :)

[mpildis]

Yup there's the difference between what we do now vs what they did in the old days. will it fail? probably not, is it up to what they would like to see? not quite. We are designing around an event that might come around once every 50 years and then with roughly a 2:1 safety margin to allow for material and installation variability. I can't confirm your work though, you'll need to satisfy yourself that you've done due diligence :)

So what would be a safe shear value for both the ledger lags and joist hanger nails? 2:1? I don't think those joist hangers could even provide that. At the moment, the joist hanger nails total shear is slightly over the roof weight. As I mentioned in my previous post, the leger lags are not. Here are some pictures of what I was planning on doing with the wall studs to try to get piece of mind. Doesn't seem like there's much difference between option 1 and option 2, but option 3 would give me solid member support below the rafters as well (but I'd lose an extra 1.5" of interior room). A fouth option would be to lay the wall studs flat like in pic 1, but turn the cripple studs sideways and cut the rafter angle in them so that they would sit under the rafters. Half of each cripple stud would be sitting on the collars ties then though and the other half would be resting on the new wall , don't know if that's a no-no.

Option 1
i629.photobucket.com/albums/uu14/mpildis/ledgersupport-1.jpg

Option 2
629.photobucket.com/albums/uu14/mpildis/ledgersupport-2.jpg

Option 3
i629.photobucket.com/albums/uu14/mpildis/ledgersupport-3.jpg

It won't let me post links so I had to get rid of the http :// in the beginning of each link so be sure to add that.

[Don_P]

Sorry to be slow to respond. The safety factor is already built into the allowable values you looked up, the ultimate yield will be around twice the values they gave.

Any of your pics looked fine to me. It would be easier to nail the new studs onto the old flaways though.

You should be able to post pics and links now.

[mpildis]

Sorry to be slow to respond. The safety factor is already built into the allowable values you looked up, the ultimate yield will be around twice the values they gave.

Any of your pics looked fine to me. It would be easier to nail the new studs onto the old flaways though.

You should be able to post pics and links now.

Don, thanks so much for your help. I don't want to be a nuciance, but I have 3 more questions and then I think I'm good.

1) I'm going to put the collar ties onto the rafters so I have a flat section on the ceiling. The roof is only a 4:12 pitch. and I'm wondering how long the collar ties should extend against the rafters. Please see this pic:

http: //i629.photobucket.com/albums/uu14/mpildis/collartie.jpg

I was thinking about making them 48" long so I get 2 of them out of an 8' 2x4. That would give me a 16" against the rafter from the first point of intersection. If I make them 52" long, they would stop right where they hit the roof plywood. Making them longer than that and having to cut the roof angle on them would be a real pain and seems excessively long to me. Does 3 10D nails staggered per collar ties sound sufficient?

2) Should I place little studs between each rafter at the half-way point to keep them from twisting since it's going to be an open rafter ceiling?

3) The rafters are toenailed into the top plate and have simpson h2 hurricane ties on the outside wall. Since it is going to be an open rafter ceiling, should I place hurricane ties on the inside wall as well or is this overkill?

Thanks!

-Mike

PS. still won't let me post an image or url. Had to put a space after http: for it to let me post.

[Don_P]

http://i629.photobucket.com/albums/uu14/mpildis/collartie.jpg

It's really a non structural nailer although it does provide a triangular backup to the structural framing, which is a good thing. 4' and 3 nails sounds fine.

Blocking between rafters won't hurt anything, is a good thing, but is not required by code.

Hurricane ties on the outside face should be sufficient.

The panel I have for your user info has you listed as a full member which should allow you to post pics and links... I understand the inner workings of a skillsaw much better than these things though.