Finished the 1st floor of my 24×36 garage before winter set in, then tarped it over until warmer weather. Well, now I’m thinking about getting things moving again, and need to decide on the final details. I’m figuring on using the attached detail at the kneewall, or possibly lapping the rafters instead of butting them. The kneewall will be 4′ from the outside wall, leaving 16′ between kneewalls.
comments or suggestions?
Thanx
Don
Edited 2/25/2006 6:06 pm ET by DonNH
Replies
Greetings Don,
This post, in response to your question, will bump the thread through the 'recent discussion' listing again.
Perhaps it will catch someones attention that can help you with advice.
Cheers
'Nemo me impune lacesset'
No one will provoke me with impunity
I don't understand your question as the illustration I see that you offered shows rafters butted at ends and laying on what appears to be a nailer, is it a top plate? Maybe I'm the dumb one here?
Where is your support for your kneewalls against bowing? You have no ceiling joists to tie the walls together? Do you have collar ties at least?
Butting such major joints in framing in my mind is a bad idea.
Here are some examples of framing a gambrel knee wall that I've included, granted there is a second floor, but the nailing is meat against meat -- that is the joists are laid against the kneewall rafters to form a wide span for nailing. IF you are in an area prone to high winds or other catastrophes, I'd suggest using Simpson Ties as well.
'Nemo me impune lacesset'No one will provoke me with impunity
Edited 2/26/2006 8:23 pm ET by razzman
I left out the rest of the details, thinking that would focus people's attention on the joint where the upper and lower rafters meet, but I see how people would be nervous about giving advice, not knowing what the rest of the structure will be.
I'm looking at going with rafter ties at the lower 1/3 of the upper roof pitch rather than ceiling joists right at the top of the kneewall, in order to get the desired headroom while maintaining a lower overall building height. This thing is already going to somewhat dwarf my small ranch house.
Looks like you notch out the top of the lower rafter to hook it over the top plate of the kneewall. I'll probably do that, and lap the upper rafter to it, to get the stronger connection as you mention. Rafter ties above that, collar ties right below the ridge board, and hopefully I'll be all set. I'll add steel ties where appropriate.
Probably worth stopping in for another chat with the BI (he's also a working builder, and very helpful) for a chat before I finalize details.
Mostly what I'm looking for right now is to get enough detail to be able to tell my dad what length rafters I'm going to need. He'll be cutting trees & hauling them to the mill as soon as I give him the word.
Thanx
Don
Edited 2/26/2006 9:16 pm ET by DonNH
Yes, getting the most nailing possible is your goal and use ties when you can. Building with green wood? Wow. I guess its done but you would have to allow for shrinkage wouldn't you?
Don: We built a house w/ a Gambrel second deck. You have to be careful that the triangle described by the floor joist/knee wall/lower roof rafter is truly sturdy. That is what gives you any stiffness you get. The center section, essentially being a pentagon like a baseball homeplate has zero stiffness. I cannot get into the space behind my kneewall to see how we did it nearly 7 yrs ago, so I cannot be more specific. You also want to be sure that the triangle defined by the two upper roof rafters & the ceiling joist is very sturdy. IIRC, we solved the problem by building w/ 2X6's. The kneewall has the sillplate atop it. The lower roof rafter butts up against the kneewall stud & has a fairly long bearing surface that has been strengthened w/ the appropriate Simpson plate along the side. The kneewall is reinforced to the sillplate w/ another appropriate Simpson clip. The bottom of the lower rafter is strengthened w/ a long Simpson strap that ties it to the floor deck so it cannot kick out. In short, we built a darned strong triangle that cannot rotate off the floor deck under near hurricane winds. My job was to put on all the reinforcing hardware. Simpson made a bundle off us. My DIY labor was charged out at $.10 per hour, while my real framing carp was charged just a wee bit higher.
The rationale for that construction approach is that you cannot transmit much bending moment through the crappy joint at the top of the kneewall, so we built it as a pair of triangles for the lower roof, topped by another triangle for the attic/upper roof. That way we minimized the requirement for strength at the obtuse angle where the roof s come together.
Hope this makes sense.
Don
The Glass Masterworks
"If it scratches, I etch it!"