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Skylight framing- cutting one rafter

Aunty Lulu

Registered User
Joined
Oct 12, 2020
Messages
11
Location
Denver, CO 80209, US
Hi -I am framing a skylight and can not find a framing detail in the code except one for metal rafters. Figure R804.3.5(1)
My rafters are 2" x 6" on 20" centers with a 16' span with a 12:12 pitch. I will be removing one rafter and putting in a 30" wide x 39" tall skylight.
Can anyone steer me to the proper code for this? I am in the Denver CO area.

I would appreciate any input.

Thanks, Aunty Lulu
 
I believe he is looking for wood detail. I would except if 2 x 6 joist hangers used in same place on the wood as is in the metal detail.
 
Don’t the rafters that carry the headers need to be doubled? If you look at the metal detail carefully, they have nested the second member into the first ... its not obvious.
 
Hi -I am framing a skylight and can not find a framing detail in the code except one for metal rafters. Figure R804.3.5(1)
My rafters are 2" x 6" on 20" centers with a 16' span with a 12:12 pitch. I will be removing one rafter and putting in a 30" wide x 39" tall skylight.
Can anyone steer me to the proper code for this? I am in the Denver CO area.

I would appreciate any input.

Thanks, Aunty Lulu
See IRC Section R802.9 as follows:

R802.9 Framing of Openings
Openings in roof and ceiling framing shall be framed with header and trimmer joists. Where the header joist span does not exceed 4 feet (1219 mm), the header joist shall be permitted to be a single member the same size as the ceiling joist or rafter. Single trimmer joists shall be permitted to be used to carry a single header joist that is located within 3 feet (914 mm) of the trimmer joist bearing. Where the header joist span exceeds 4 feet (1219 mm), the trimmer joists and the header joist shall be doubled and of sufficient cross section to support the ceiling joists or rafter framing into the header. Approved hangers shall be used for the header joist to trimmer joist connections where the header joist span exceeds 6 feet (1829 mm). Tail joists over 12 feet (3658 mm) long shall be supported at the header by framing anchors or on ledger strips not less than 2 inches by 2 inches (51 mm by 51 mm).
 
See IRC Section R802.9 as follows:

R802.9 Framing of Openings
Openings in roof and ceiling framing shall be framed with header and trimmer joists. Where the header joist span does not exceed 4 feet (1219 mm), the header joist shall be permitted to be a single member the same size as the ceiling joist or rafter. Single trimmer joists shall be permitted to be used to carry a single header joist that is located within 3 feet (914 mm) of the trimmer joist bearing. Where the header joist span exceeds 4 feet (1219 mm), the trimmer joists and the header joist shall be doubled and of sufficient cross section to support the ceiling joists or rafter framing into the header. Approved hangers shall be used for the header joist to trimmer joist connections where the header joist span exceeds 6 feet (1829 mm). Tail joists over 12 feet (3658 mm) long shall be supported at the header by framing anchors or on ledger strips not less than 2 inches by 2 inches (51 mm by 51 mm).
And that folks is the bare minimum.
 
My rafters are 2" x 6" on 20" centers with a 16' span with a 12:12 pitch.
Another 8" and you would be required to double the trimmers. Knowing that the rafters are over-spanned already....code is the minimum allowed ....what does that tell you?
 
Don’t the rafters that carry the headers need to be doubled? If you look at the metal detail carefully, they have nested the second member into the first ... its not obvious.
I did see that. I assumed it was a track to be able to screw the clips on the open side.
 
If the rafter span (horizontal distance from exterior wall to the ridge board) is 16 ft, the roof is seriously under structured. Perhaps 16 ft is the width of the building and the span is 8 ft.
If that's the case, the location in CO is important but to be safe I recommend doubling the rafters unless there're rafter ties just above the skylight.
You really need more information to design a roof in CO regardless of what the code says.
 
If the rafter span (horizontal distance from exterior wall to the ridge board) is 16 ft, the roof is seriously under structured. Perhaps 16 ft is the width of the building and the span is 8 ft.
If that's the case, the location in CO is important but to be safe I recommend doubling the rafters unless there're rafter ties just above the skylight.
You really need more information to design a roof in CO regardless of what the code says.
Thanks- The rafters are indeed 16' from floor to ridge board (what I can measure with the room finished). The house is 115 years old so it must be working- back then they did what they did. The roof is 12:12 so maybe that helps. I did see on one place in the building code that one species is ok for that span but not the spacing. So, I will double the rafters and put in some beefy headers above and below the skylight to be safe. Thanks for your input.
 
See IRC Section R802.9 as follows:

R802.9 Framing of Openings
Openings in roof and ceiling framing shall be framed with header and trimmer joists. Where the header joist span does not exceed 4 feet (1219 mm), the header joist shall be permitted to be a single member the same size as the ceiling joist or rafter. Single trimmer joists shall be permitted to be used to carry a single header joist that is located within 3 feet (914 mm) of the trimmer joist bearing. Where the header joist span exceeds 4 feet (1219 mm), the trimmer joists and the header joist shall be doubled and of sufficient cross section to support the ceiling joists or rafter framing into the header. Approved hangers shall be used for the header joist to trimmer joist connections where the header joist span exceeds 6 feet (1829 mm). Tail joists over 12 feet (3658 mm) long shall be supported at the header by framing anchors or on ledger strips not less than 2 inches by 2 inches (51 mm by 51 mm).
Thank you for such detail classicT
My roof window will start 7' from the bearing point of the rafter, roughly in the middle of the 16' span (I am not at the house so can't measure for sure), so does that knock me out of:

Single trimmer joists shall be permitted to be used to carry a single header joist that is located within 3 feet (914 mm) of the trimmer joist bearing.

My plan is to double the trimmer joists but not the one joist that I cut out. Do you think that will work?

Sorry, in previous posts, I wasn't using the right name for the trimmer joists.

ALu
 
Doesn't matter its a graphic, DOES THIS MAKE IT ALL BETTER
use LTP or A35 at all side

View attachment 7050

Thank you for the info on the ties and yes, a diagram does "make it all better".
So, this summer at our museum we had an exceptional wind event and lost a roof (with all the trusses). I overheard the contractors that came (to revel in the fact that THEY hadn't built it), say that the builder was supposed to use nails not screws for those strong ties. Is that correct? I would MUCH rather use screws if it is ok (i'm really not enthusiastic about having 115 years worth of dust and mouse crap raining down on me with all that hammering- I'll get enough with an impactor). I did see in the code book that they reference nails and how many (when not using ties) but nothing about screws.

Thanks, and please don't get mad at what might be to you a stupid question... up here on a ranch Wyoming, we kind of just use common sense because there are no inspectors to speak of- but that house is in Denver...
 
Simpson does make screws that can be used with their connectors:

Do NOT use cabinet screws, drywall screws, decking screws, or other stock screws from big-box stores, because many of them are brittle and will snap with repeated bending under cyclical load.
 
"16' from floor to ridge board" is not the dimension of the rafter span. If this is a simple gable roof, what is the total width of the house?
 
If the 2x6 rafters slope 12 in 12 and are 16-0 long measured along the rafters, then the horizontal span is about 11-2 and the width of the house would be about 22-4.
 
Simpson does make screws that can be used with their connectors:

Do NOT use cabinet screws, drywall screws, decking screws, or other stock screws from big-box stores, because many of them are brittle and will snap with repeated bending under cyclical load.
Thank you- I found the strong tie site and found the right screws: Strong-Drive® SD CONNECTOR Screw SD 9 1.5"
Deck screws are exactly what the contractor used on the building that lost it's roof.
 
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