Balloon vs platform?
mikeolder
| Posted in General Questions on
I’m considering installing a let-in ribbon board half way up a 18′ tall 2×8 wall for second story floor joists above a garage. Long story, but I cant use platform style on this one 26′ long wall. No inspections or code enforcement in my county in zone 5 Iowa.
But I noticed this style would be more energy efficient with less thermal bridging compared to the platform style, as long as you had a good fire block..?
If I decided to build balloon style with joists resting on a notched in ribbon board, what what be a good material and method for the fire block? I’m thinking insulating the spaces with rockwool might be enough..
Thanks
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Replies
Do you have any pics or a drawing showing what you’re trying to do and where you’re trying to do it? A few scary thugs jump out at me like “notching” joists and “no inspection or code enforcement”. Just because you aren’t getting inspected doesn’t mesh you should build to code. Most of the stuff in the code books is there FOR YOUR SAFETY. This is especially true for the structural stuff. It is VERY dangerous to skimp on the structure, and notching in long spans is one of the worst things you can do.
IF your existing beam can safely carry the extra load, joist hangers might be your best option to hang joists. Without at least a drawing it’s really hard to know what you’re trying to achieve here.
Mineral wool is often used as a fireblock material, but it has to be a tight fit to work and it’s not always the best material to use depending on the application.
Bill
Most 2 story four square farm houses in the midwest are built using balloon framing, so there's no doubt in this inspectors mind the method is acceptable. You don't notch floor joists. You notch the 2x8 wall studs.
Surprised this method isn't used to reduce thermal bridging..
I'm guessing its the fire hazard why its not used, not the strength.
https://i.servimg.com/u/f59/14/97/22/52/1a1a1h10.jpg
Deleted
Mike, Balloon framed 2 story with notched ledger board to carry 2nd floor joists is a regularly noted design variant in double stud walls, as you stated for eliminating the thermal bridging. Outside frame carries roof load, inside frame everything else, with both minimally connected and well designed (shear). I can't see a load carrying problem with a 2x8 balloon framed stud wall with let in ledgers, unless you are planning a dance floor for elephants on the roof terrace.
Fire blocking is one consideration, another is vapor isolation and active ventilation to prevent hazardous gas intrusion (car exhaust, stored materials VOC's) into the (presumed) living space above? I would consider also Airtight drywall method for the garage interior, sealing all framing penetrations just in case, and a small continuous vent fan.
Again assuming living space above, you'll need insulation. Dense pack cellulose works to block fire as well I've read, you just need a sufficiently tight blocking at the garage ceiling level to hold it up?
Mike, You may want to take a look at Greg La Vardera's site about Swedish Platform Framing for some ideas.
http://blog.lamidesign.com/p/swedish-platform-framing-info.html
Malcolm: thanks, that's nice! Benefits of a double stud without the complexity. Like!
Darren,
There are a few details that might need altering. Some alternate way of maintaining lateral stability for the floor joists in the absence of rim-joists, and it needs a very thick foundation wall - but its an interesting starting point.
Thanks everyone.
I'm building a tall garage for a car lift and I'll install the ribbon board for the next owner. The ribbon board and fireblock will be under the drywall allowing the next owner to easily add 30% more living space, as he wont need my 18' ceiling in the garage and the existing living space is directly adjacent.
The Swedish platform frame isn't really a variant of balloon framing because the studs do not cover two stories uninterrupted, but both walls reduce thermal bridging compared to western platform. Hard to believe the swedish second stories floor joists are held up by ribbon boards lag bolted to the studs though. But its ingenious how the second story floor deck extends all the way to the outside edge of the building, locking the joist in. But I'd have to notch or "let in" the ribbon regardless if the studs covered a single story or two.
https://www.youtube.com/watch?v=LUthssuOYks&t=252s
Mike,
Adding the let-in ledger is a great idea to future-proof the space as it were. Here if the stud bays are filled with any of the common types of insulation it isn't necessary to add fire-blocking, but solid lumber blocking is required on all walls over ten ft for structural reasons. Might be worth checking your local code.
You will need to subscribe to read it but as I recall this article was very interesting.
https://www.finehomebuilding.com/2017/07/24/balloon-framed-walls
Walta
Only nails holding the second story floor joist ledger on?
It does seem counter-intuitive, but a typical joist hanger with the same loading, like the Simpson LUS ZMAX, is held up by nails.
After looking at the prices for 20' 2x8's, I can see why the swedes don't use a continuous piece of lumber.. I can live with building one level at a time, but will notch the ribbon ledger into the studs. Main thing is there is no rim joist but only single plates which you need to nail your sheathing to anyway..
What I don't like is that the floor joist is not attached to the wall stud, only resting on the ribbon ledger..