| . 1 . 2 . >> |
| Author |
Message |
ak_flyer
Member
|
# Posted: 22 Jun 2014 19:19
Reply
Hey Guys
I was just curious is there a major structural difference between these connections of the rafter ties.
1. Rafter Tie connected to the studs just below the top plate.
2. Rafter Tie connected to the Rafter and sitting on the Top plate.
Picture to help illustrate what aim asking. Thanks in advance.
|
|
ak_flyer
Member
|
# Posted: 22 Jun 2014 19:22
Reply
Sorry my original picture was sideways
|
|
Don_P
Member
|
# Posted: 22 Jun 2014 22:38
Reply
Yes, there is a structural difference.
Attaching the tie directly to the rafter restrains the outward thrust of the rafters very effectively.
If the tie is attached to the studs the horizontal force from the rafters needs to be restrained at the rafter to plate connection, then the plate to plate connection, then the stud to plate connection, then the tie to stud connection.
|
|
Just
Member
|
# Posted: 22 Jun 2014 23:32
Reply
what if you did this??
|
|
Don_P
Member
|
# Posted: 23 Jun 2014 06:56 - Edited by: Don_P
Reply
Bingo! Watch the size of the birdsmouth, leaving plenty of "meat" over the notch.
|
|
Wilbour
Member
|
# Posted: 23 Jun 2014 11:32
Reply
I was wondering about this myself. Shaving a foot off the height on the first floor could offer valuable space in the loft. The two problems I see with lowering the rafters is all the weight on the loft floor is now supported by the fastners of the rafter to the wall studs whereas when they sit on the top plate the forces are more evenly spread. Second but less of an issue is the outward forces of the roof is better controlled by rafters fastened directly to them.
|
|
ak_flyer
Member
|
# Posted: 23 Jun 2014 16:54
Reply
I have researched this design as well.
The rafters would still sit on the top plate so that wouldn't be an issue.
The outward forces should be under control because the triangle shape is unbroken, as Don_P said watch out for the seat cut on the rafter. So that a 2x6 doesn't turn into a 2x4 for example.
The main deal breaker for me was the extra cost of running a 10' wall instead of an 8' and the longer rafters required. Not so much the cost of the lumber but the extra flights I would have to make, to get the materials to my place.
I do like the design, if you search around on here one of the other members has a nice Google sketch up of that design.
|
|
Just
Member
|
# Posted: 23 Jun 2014 22:09
Reply
When I did it I supported each loft joist with a faults 1 ft. jack stud scabbed to each stud and a 14 in. cross brace holding the joist against the stud.
|
|
|
Don_P
Member
|
# Posted: 23 Jun 2014 22:37 - Edited by: Don_P
Reply
A let in ledger is the code way of supporting a floor in a balloon framed wall. the joist is nailed to the stud but resting on the ribbon ledger. The joist could then extend on out over the ledger to grab the rafter tail like you drew above.
|
|
Just
Member
|
# Posted: 24 Jun 2014 09:44
Reply
In my cabin I used full 8 ft. studs plus single bottom and double top plate making the wall 99.5 in high.Then i lowered the ceiling in the first floor to 85.5 in. or the height of the door header. With 8 in. loft joist that left me a net gain in loft clearance of 14 in.s [thats alot at 4 AM when you sit up in bed and hit your head on a rafter] %^&*#%*!!
Good luck with your plans. just
|
|
Wilbour
Member
|
# Posted: 24 Jun 2014 10:17
Reply
Quoting: Don_P A let in ledger is the code way of supporting a floor in a balloon framed wall. the joist is nailed to the stud but resting on the ribbon ledger
So like this?
|
|
toyota_mdt_tech
Member
|
# Posted: 24 Jun 2014 10:30
Reply
Wilbour, I'm guessing the ledger board is "let it" and the rafter tie or in this case, ceiling joist would set on top of it and nailed into the side of the wall stud.
|
|
Wilbour
Member
|
# Posted: 24 Jun 2014 16:26 - Edited by: Wilbour
Reply
Yah. That's what I was trying to convey
|
|
Wilbour
Member
|
# Posted: 25 Jun 2014 09:03 - Edited by: Wilbour
Reply
Here is a shot from cabanavillage.com
What they don't have is the Ledger running across the wall
|
|
Just
Member
|
# Posted: 25 Jun 2014 10:46
Reply
they have used jack studs . the first joist has its own jack stud the second 3 rd and 4 th are sitting on a header supported by 2 jack studs and so on . it takes a little more lumber that way but you end up; without; a ledger board protruding into the room. that is why i chose to use them , except i cheeped out and only used false 1 ft. jacks.that cabin is 15 years old and still stands tall and strait ..
|
|
Wilbour
Member
|
# Posted: 25 Jun 2014 11:02
Reply
I think I better understand what "let in" means. The ledger is actually cut into the wall stud and sits flush with the wall
|
|
Just
Member
|
# Posted: 25 Jun 2014 11:30
Reply
"WELL" yes thats what it means " BUT " IF you let it in the full width of the ledger in a 2x4 stud wall , so it dose not protrude into the room, it will weaken the wall more than i care to do , hence the jack studs . i am sure a building inspector would approve cabinavilage design . I am sure'!! he would turn his nose up at mine !!!
|
|
Wilbour
Member
|
# Posted: 25 Jun 2014 12:18 - Edited by: Wilbour
Reply
I think Jack Studs may be the way for me to go. It's not that much more in cost and it gives me more space to attach sheathing
|
|
Just
Member
|
# Posted: 25 Jun 2014 12:48
Reply
if you are building a small cabin without inspection it will be fine but if you must submit plans then your building inspector will see that on the plan and give his opinion . How big a cabin are you planing ?? good luck..
|
|
Wilbour
Member
|
# Posted: 25 Jun 2014 13:50
Reply
Quoting: Just How big a cabin are you planing ??
Finishing an existing 10 x 16. It was started years ago and never finished. There is presently no loft, just a 12 12 pitch roof. Previous owner did not understand the significance of jack studs and headers over windows so I will be fixing some of his shortcuts anyways.
|
|
Don_P
Member
|
# Posted: 25 Jun 2014 21:53 - Edited by: Don_P
Reply
Go to fig R602.3(1) here;
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_6_par010.htm?bu2=undefi ned
The right side of the drawing shows a 1x4 let in ledger (inset into a notch in the studs) In both your nailed on ledger and in Just's short scabbed on blocks the joist is hanging on nails rather than being supported by wood. This can work (think about joist hangers) but is an engineered rather than a prescriptive solution. The engineering revolves around the load on the joist and the allowable shear on the nail used in the wood used, they are trying to keep it simple in the prescriptive solution to the problem.
Remember whenever you balloon frame to fireblock the studs between floors, block the stud bay in the wall to avoid creating a chimney in the wall between floors. That is the main problem with old balloon framing, wicked bad, fast moving, people eating fires. Never give fire a chance to roar between floors.
|
|
Wilbour
Member
|
# Posted: 26 Jun 2014 07:21 - Edited by: Wilbour
Reply
From the above mentioned site:
R502.6 Bearing.
The ends of each joist, beam or girder shall have not less than 1.5 inches (38 mm) of bearing on wood or metal and not less than 3 inches (76 mm) on masonry or concrete except where supported on a 1-inch by 4-inch (25.4 mm by 102 mm) ribbon strip and nailed to the adjacent stud or by the use of approved joist hangers. The bearing on masonry or concrete shall be direct, or a sill plate of 2-inch-minimum (51 mm) nominal thickness shall be provided under the joist, beam or girder. The sill plate shall provide a minimum nominal bearing area of 48 square inches (30 865 square mm).
When I get back home I will uplooad photos of a small cabin I almost purchased (long story filled with betrayal and deceit). I found the owners Flicker account which shows 10ft walls face nailed with a 2x6 and the 2x6 joist nailed back through the ribbon from the end. Trust me the photos are worth a thousand words
|
|
Wilbour
Member
|
# Posted: 26 Jun 2014 16:06
Reply
As promised here are two shots of a cabin I almost got to purchase. It was a really nice 14x12 with a full loft. As you can see the 2x6 is face nailed to the 10ft studs and the 2x6 joists are nailed through the ends.
framing_01.jpg
| 
framing_02.jpg
|  | |
|
|
Don_P
Member
|
# Posted: 26 Jun 2014 21:12
Reply
One thing the internet has demonstrated is that bad framing is in no danger of extinction 
|
|
Wilbour
Member
|
# Posted: 26 Jun 2014 22:36
Reply
The owner is a home builder by trade. Perhaps it was best the deal fell through ? It was a nice cabin.
|
|
Don_P
Member
|
# Posted: 26 Jun 2014 23:02
Reply
It wouldn't collapse but it is bad framing, as are his rafters and gable walls. Non inspected area?
|
|
toyota_mdt_tech
Member
|
# Posted: 26 Jun 2014 23:28 - Edited by: toyota_mdt_tech
Reply
I would be concerned first, the 24" centers, then the floor just nailed onto the rim joist thingy??? , which is face nailed into the studs. When the load is applied upstairs, and it gets heavy, I would think the nails could shear or pull out and the entire upstairs drop right on top of anyone downstairs. 
I cant really see the floor area but it looks like the rim joist is nailed around the outside of the post, then joist tied into them. So with weight as you build the cabin, could the floor shear from the post too?
|
|
Don_P
Member
|
# Posted: 27 Jun 2014 06:07
Reply
Quick math, if the nails have an allowable shear of 90lbs each, 2 nails per stud ledger to stud=180 lbs allowable shear. Holding up 2 feet of width x 6', one end of a 12' joist, x 30lb/sf live load +10 psf dead load=480 lbs design load.
Allowable load is not ultimate strength, we rarely see design loading, but yes he is deep into his safety and doesn't know it.
|
|
Wilbour
Member
|
# Posted: 27 Jun 2014 08:59
Reply
Quoting: Don_P It wouldn't collapse but it is bad framing, as are his rafters and gable walls. Non inspected area?
It was in an unincorporated township in another province.
I don't want to come down too hard on this builder and his little cabin since we are all guilty of saying my favourite two phrases:
"That will hold" and "That aint gonna show"
I have learned 3 things with this experiance:
1. Scary what you can find about people on the internet when you are purchasing a home/cabin from them 
2. How to properly frame a second story 
3. Don't try to purchase a home/cabin from a divocing couple 
I eventually got my deposit back and now I own a fixer-upper 2 hours drive, not 16 hours from home 
|
|
Just
Member
|
# Posted: 27 Jun 2014 11:38
Reply
Quoting: Wilbour existing 10 x 16
this is how I increased the livability of a loft with 8 ft. walls
|
|
| . 1 . 2 . >> |
