[cumak]

Last fall we had our roof redone, and we had the roofer install two skylights. He took care of the roof framing and skylight installation, and I'm going to do the interior work including framing the ceiling opening.

Today I cut open the ceiling to start planning the light shaft, and I have most of it figured out except for one thing. The collar ties (or ceiling joists, not sure what the correct terminology is) intersect the rafter in the middle of the skylight opening. On the right side the collar tie is on the "outside" of the rafter (from the perspective of the skylight opening), but on the left side the collar tie is inside the opening. Please take a look at the pictures for clarification.

So, I have to move the left collar tie to the other side of the rafter. My question is, do I have to install a new full-length 2x8 collar tie, spanning rafter-to-rafter? Or, can I install a partial-length of lumber, and bolt it to the existing collar-tie somewhere in the middle of the span?

There's not much room up there, and the back side of the roof is lower pitch. If I have to run a full span, it's going to be very difficult to get in that space to secure it to the back rafter.

I'm not a structural engineer, but my gut tells me that bolting should be fine because there is very little lateral force (just the weight of the ceiling). I doubt that it would sag from that. I know the collar ties also prevent the rafters from spreading, but the shear strength of 4 or 6 bolts will surely be better than the existing nails at the ends of the collar ties. So, in that case I don't think the bolts will be a weak point.

However, I can't go by my gut alone because I pulled a permit for this so it will need to pass inspection. So, is there a way to do this that would meet code? Are there requirements for the amount of overlap, number and size of bolts, etc?

Thanks for your help.

-Mark

 

[Ron6519]

I think you should have ordered a narrower unit.
I'm not exactly sure what the framing I'm looking at represents. What does the sheetrock change in plane represent? A ceiling transitioning into a wall?
Ron

 

[cumak]

Ron - as far as I know, Velux only makes skylights in a few widths, and if you have 16" OC rafters like me then the only one that works is the 30" unit. It's designed to fit in the space between 3 rafters (removing one). If your rafters are 24" OC then they have a 22" unit, or a 44" unit if you want to remove one rafter. But around here most roofs are built 16", and this is the size skylight that everyone uses. I think my installation is pretty typical.

To explain the sheetrock, the vertical wall is a short wall, about 6' high. Then the sheetrock follows the rafter at 45 degrees until it reaches 8'. Then it transitions to the ceiling. The section you're questioning is that 45 degree section where the sheetrock is hung on on the rafter. The skylight opening starts in this section of the rafter, and continues above the height of the ceiling.

Thanks,
Mark

 

[kwikfishron]

If you have no access to move the joist from above just cut out one more bay of rock and move it from below.

 

[tcleve4911]

From the looks of the picture, the 1/2" channel on the skylight seems to be on plane with the collar tie. That's good.
Can you slip a piece of 1/2" into the channel?
That's how Velux designed those so 1/2" stock goes into that slot to create a perfect finish.

Hopefully the roofer guy knew that and set the window with that in mind.

 

[cumak]

If you have no access to move the joist from above just cut out one more bay of rock and move it from below.

Oh man, that would be so much extra work. Plus, I would never get the new ceiling to match the existing, because it has some sort of texture. So far I've only cut away enough of the ceiling to accommodate the skylight opening, and I'd like to keep it that way.

If I really need a full-span joist, then I'll find a way to do it from above (even if it means hiring someone who can fit into tighter spaces than myself :whistling2. However, it would make life a lot easier if I could just cut away the end of the existing joist, and bolt together with a new one mid-span.

From the looks of the picture, the 1/2" channel on the skylight seems to be on plane with the collar tie. That's good.
Can you slip a piece of 1/2" into the channel?
That's how Velux designed those so 1/2" stock goes into that slot to create a perfect finish.

Hopefully the roofer guy knew that and set the window with that in mind.

Yes, that channel does accept 1/2" material. However, the inside if the 1/2" is about on the same plane as the inside of the collar tie, so there's no space left to cover it with anything. The skylight is perfectly centered between the rafters. Is it supposed to be offset away from that collar tie a bit? If that's the case, there's nothing I can do about that now.

Thanks,
Mark

 

[tcleve4911]

Mark
I think I understood your explanation.
So the face of the 1-1/2" encroaches the 1/2" channel correct?
So you can't slip 1/2" into the channel without the 1-1/2" interfering correct?

Can you cut 1/2" off the face of the collar tie?
You just need to cut it back to the point where the drywall intersects.

Hand saw, a sharp chisel.
They used to trim barn timbers that way......

 

[cumak]

Yes, you're correct. I would say the face of the joist ends up being about 1/4" "proud" of the face of the drywall that would slip into that grove. So, I'd have to take 3/4" off the thickness of the joist.

However, keep in mind that the opening in the ceiling is about 48" long, so I'd be cutting away half the thickness of the joist over a length of 48" (in order to keep the opening square). I appreciate the creative thinking, but that's a very difficult cut to make. Also, wouldn't it weaken the joist more than my other idea of just bolting another partial-length joist to the other side of that rafter?

Thanks,
Mark

 

[tcleve4911]

Part of the answer to that depends on what the collar tie is actually doing.
If it is just to tie in the outside wall from spreading, 3/4" is sufficient.
If it's carrying the ceiling and other loads, you are correct.

Thanks for the creative thinking comment......

So one more ...way out of the box.......

Move the skylight over 3/4"......:yes:

Maybe the roofer would help out if you explained what he left you with.
Offer to pay him something...or some token to help both of you.

I really think this might be the way to go.
Everything else is so complicated.

Just the fact that you're going to the building inspector......

Moving that skylight is an easy fix once you get past the hurdle of "I just had that installed"
:thumbsup:

 

[tpolk]

you have to move the skylight or the collar tie, does not appear to be room to move skylight or shim right side to match left

 

[tcleve4911]

you have to move the skylight or the collar tie, does not appear to be room to move skylight or shim right side to match left

I respectfully disagree.

There looks to be plenty of room on the right side to slide the skylight 3/4".

 

[tpolk]

I respectfully disagree.

There looks to be plenty of room on the right side to slide the skylight 3/4".

looks like bottom right corner is tight but if there is room to move and roofer wont ream then great :thumbsup::thumbsup:

 

[cumak]

looks like bottom right corner is tight but if there is room to move and roofer wont ream then great :thumbsup::thumbsup:

Looking at it closely, it's pretty close as to whether or not there would be enough space on the right to move it sufficiently. However, even if I could do, I have to say that would probably be my last option for a number of reasons. At the top of that list is the fact that skylight survived a very heavy winter and rainy spring with no leaks. The flashing works, so I'd hate to mess with it.

Seems like addressing the collar tie somehow is a better way to go.

 

[kwikfishron]

I'll find a way to do it from above (even if it means hiring someone who can fit into tighter spaces than myself :

Doesn’t matter how long you stare at it, it’s in the way just move it over.

 

[Gary in WA]

"However, I can't go by my gut alone because I pulled a permit for this so it will need to pass inspection. So, is there a way to do this that would meet code? Are there requirements for the amount of overlap, number and size of bolts, etc?" ----

Cut it back where needed, no bolts required, lap the ceiling joists, just follow the guidelines, especially footnotes "d,e,f, and g", add a vertical support to the ridge, and follow the chart for the adjustment factor after "h" of elevation where joist lap is located:

bottom two charts, watch your snow load; R802.5.1(9); http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_8_sec002_par023.htm

Gary

 

[cumak]

Thanks Gary! This is what I was looking for. I won't claim that I completely understand it, but this gets me going in the right direction.

After reading through, I see the provision for "ceiling joist to ceiling joist lap splice" and the required nailing schedule. However, I don't see where such a splice must be supported by a vertical strut. Am I missing it in the fine print somewhere, or is this just common sense/good practice?

-Mark

 

[Gary in WA]

If the collar tie/ceiling joist was cut and side spliced in the middle of a large span, it would be difficult to figure the amount of lap for your local inspector as the Code is "grey" on this. 3" lap or butt joint is acceptable with required nails --- over a bearing wall.

I would just cut out the joist at the shaft framing end tying the joist up to the rafter there. Frame the ceiling opening first, if the opening is within 3' ofcode allows up to 4' header joist with single trimmer joists (existing);
http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_8_sec002_par030.htm

Gary