20x30 single story, floor joist hangers????

[Don_P]

Hmm, not sure where to carry on this conversation, feel free to split the thread 
Thank you for having an engineer look at this John.

This is a scan from a timberframe design book, look at my deflected model above. The top pictures show a high posted cape. The bottom pictures are a computer engineering program's Finite Element analysis of the frame. The computer magnifies, exaggerates, the deflections to show the forces at work. Where they have bracing we have a notch.


If the engineer feels as I do I think there is potential in running the rafter over the kneewall and extending the floor joists out to tie to the rafter tails, another triangle. You're definitely into engineered joists by then, I don't know what the detail would be.

The codebook is set up with framing checked at 30, 50,and 70 psf snow loads after which engineering should automatically be required. Wind is checked at 90, 100, 110 mph before design is required. I think your engineer will have heavier details somewhere in there, you are selling plans nationally, it would be good to have calculations at each of those levels... on the entire frame. Lay the entire thing on his desk, piers to ridgeboard.

I have debated in the past whether to offer and also ask the community to help chip in for this. You do a lot of good here John.

[rsbhunter]

Ok, it makes sense what everyone is saying about the load forces acting on the walls as a horizontal force , instead of a vertical force.....i (not knowing) didn't know that a 2' added height to the side wall would increase the force that much...but thats why i'm not a engineer or contractor...they would be falling like leaves!!!!! Thanks for the help, i will stick with the plans as are, a separate 12x16 or 14x20 would be my best route......might look at the other plans available and have a project waiting when i finish the 20x30...I am going with the 6' spacing on piers, and i am looking at expaning the length by 6'...the protective covenants state that it has to be 600sf....and as i will either do double 2x4 walls, or 8", i want to make sure it meets either the "footprint" or living space requirements...Thanks again for all the help....rsbhunter

[John Raabe]

Thanks Don for those diagrams. They cleverly help demonstrate the forces visually.

There are so many possible loading situations that a house can be subjected to. These come not only from rare events of weather and "acts of God", but the acts of local agencies as well. All stock plans, including mine, advise builders to check with the jurisdiction and perhaps a local engineer before building. You will likely also see a similar note on custom designed plans and even ones done by a local architect.

No matter how much we work at it there is no way we can produce plans that meet all the possible loading situations a house could experience. In fact, you and I, not being licensed engineers in all 50 states in question, could be considered "impersonating a licensed professional" and thereby taking on liability by expressing opinions and suggesting solutions that don't involve the local professionals. Codes and loads are all very local and we should not try to second guess them.

For me and my plans I think I will be calling out more engineered truss roofs since they are always freshly coordinated with local conditions. That also means it is getting harder and harder to do standard framing without knowing all the local loads and code interpretations. In short, a house built using standard framing from the past may no longer be allowed in your county.

We have now probably completely confused rsbhunter who only wants to build a simple house. Sorry about that...
That is why I will now shut up. 

[rsbhunter]

No, ANY advice is welcome....i just figured that i would gain by going to 10' walls, but it would really be better to just stick with the original plans, and build a separate bldg later...Thanks for all the help...rsbhunter

[MountainDon]

That also means it is getting harder and harder to do standard framing without knowing all the local loads and code interpretations. In short, a house built using standard framing from the past may no longer be allowed in your county.

I don't know that I agree with that thought.    The vast majority of the country is within the basic 90 mph wind zone. Most of the area of the country does not need any special techniques because of seismic concerns. There are maps that show snow load for most of the country. That's all in the IRC along with the minimums materials that if assembled correctly can pass a code inspections.  Some markets, PNW, FL, Gulf Coast, CA have special requirements and those are spelled out either in IRC notes or in special state editions of the IRC. Those special cases become more difficult to negotiate but we have owner-builders who have made it through the mine fields with great success. Those areas would likely still require some special design and engineering input, but those would be the exceptions.

Perhaps a 20' wide plan with gable end walls with columns for a structural ridge beam could be drawn out and spec'd for the snow loads that are used in the IRC rafter tables? Maybe one gable end showing a straight down support to a concrete foundation and the other end showing a split multiple column support to allow the insertion of a window? 

[MountainDon]

....there is potential in running the rafter over the kneewall and extending the floor joists out to tie to the rafter tails, another triangle. You're definitely into engineered joists by then, I don't know what the detail would be.

That is a very interesting concept. 

[John Raabe]

All interesting concepts. We almost have a design team!