To All:

At the Burlington eastern conference, during one of the many engineering discussions, it was mentioned that the TFEC needs to educate the general timber framers about when to get the engineer involved in the design process.

I would like to ask the group for their input.

When I design a frame for a client, I ask them for the following items to be provided to me, in writing. They are: room sizes and locations (a floor plan) for each floor, what type of rafter system they want, common or principal with purlins, and either wall heights or ceiling heights, doorway and window location (so they don’t interfere with braces), type of wood for the timbers they like to use and any other special info they’d like to share with me.

I then create a 3d model of the frame with my computer CAD software, including joinery decisions.

We review the frame together and work out any changes that they see or want, and any problems that I encounter while trying to fulfill their wishes.

After they have approved the design, in writing, I create dimensioned bent drawings, 3D isometric drawings, and dimensioned joinery detail drawings. These detail drawings include all of these that apply to their frame: brace detail, collar beam detail, eave detail, floor joist detail, king post detail, post detail, queen post detail, ridge detail, strut detail, tie beam detail and sill detail. Some general frame rules, such as whether or not the braces are flush with the bent’s layout face or centered. And some joinery specifications, such as whether or not the tenon is two inches off the layout face and then two inches thick, type of thing.

With these drawings they then create the frame for themselves or find a timber framer to work with them.

So, my question to the group is "When does the engineer get involved?"

What I'm trying to avoid is creating a lot of drawings and then have them checked by an engineer and finding something wrong or not strong enough and having to redraw again.
If I have to redraw something to make it right then ok, but I need to understand how to charge or not to charge the customer.
I have a client that will need his frame design stamped to comply with his building inspector.
Should I find someone now who will stamp it and ask them what or when do they want to see my drawings? And or what will they need?
And then do my best to size the timbers correctly for the loads I know?
Any and all help you can forward to me will be greatly appreciated.

I’d be interested in hearing all opinions.

Thank you very much.

Jim Rogers
Jim Rogers Timber Designs
Jim Rogers Sawmill
Georgetown, MA

Hi Jim,

I suppose that your difficulty might stem at least in part from a perceived or real need to draw demarcation lines between the various levels of services that you can legitimately provide to customers and those beyond which your current experience or level of qualification prohibit or at least advise you to proceed with caution.

As Dirty Harry says – “A man’s got to know his limitations”.

Your quandary seems in large part to lie in deciding how and where to draw the line in order to minimise design recycle and potential additional cost to clients.

Design of timber frames is not necessarily a calculation driven process. Provided there are some traditional (proven) patterns that you can copy or a design code that you can follow then an engineering review and stamping might be seen more as a legal and risk liability and responsibility compliance formality at the end of the design process rather than a hurdle which must be crossed during this process.

So what happens when there are no examples to follow or the rule book runs out ? Clearly an analytical ability or maybe even a test programme could help you to confirm or deny suppositions made during design.

Teenagers are frequently heard to complain that various parts of their anatomy are too big, small, tall, short, fat, thin, ugly, beautiful, boring, charismatic, etc. i.e. they see themselves as a collection of individual bits which either make the grade or not. Thankfully as adults we see ourselves more as a whole person better able to make allowances for a person being blessed with a hooked nose (Caesar), sticky out ears (HRH) or one leg longer than the other (Scots Haggis). Much the same is true for buildings of which a timber frame might just be seen as a skeletal component. Some animals e.g. ants and beetles have chosen to forego on having a skeleton altogether in favour of employing an external monocoque shell. This approach could be likened to the use of stress skin panels or application of weather boarding on a building which if well designed could in large part make up for all sorts of timber frame shortcomings and indeed even make the timber frame totally redundant.

The acceptance or rejectance of a design does therefore rely on the maturity and experience of the beholder together with the moral, commercial and legislative requirements that might need to be prudently demonstrated, in order to reduce personal and commercial risks associated with a particular design and most importantly the operational safety consequencies associated with same.

I shall close with a seasonal “D R ism” –

“The man, who doesn’t know, what he doesn’t know, is a very dangerous person indeed !

Regards

Ken Hume P.Eng.

In response to Mr. Hume's post, I would caution anyone from looking at the engineering as a mere formality. In many states, an engineer as a matter of law cannot simply review and stamp plans. Many do, but that doesn't change the fact that they shouldn't. Work stamped by a Professional Engineer must be work done under their direct supervision. In most cases the plans were not created under their supervision. Some states explicitly prohibit "review stamping" of plans. Too many people see the engineers stamp as the thing they are buying and not the value that a good engineer brings to the design team.

When should you bring an engineer in on the process? Well, I think that answer varies by project. In the case you described, it sounds as though at least having an engineer taking a look at the plans between your first and second visits with the owner would be a good idea. A good engineer on a moderate sized house will be able to develop a gut feel for the design without crunching any numbers in a short amount of time. This engineer may be able to provide some valuable information just in that initial look. The real design could take place a little later.

To me, the most important thing is to involve the engineer early and ask the engineer when would be a good time to really start designing.

Dear Jim: As an engineer, I often have the same question as to how far to take the drawings that I produce before handing them off to a timber framer. The answer is "it depends." When I work with a local framer that I have worked with frequently, we sit down at the begining of the project and work out the best structural approach. We each rely on our experience to guide this process. I then size members of the frame, assuming typical joint details that are commonly used by the framer. Where there are extreme demands placed on a particular joint, I will detail it. I hand this set off to the framer and he works up a set of shop drawings based on my plans. I review them and check the joinery that I had not previously detailed.
I have also worked with framing companies far removed that I would most likely never work with again. In these cases, the relationship is not there, so we both must go a little further and incur the cost of a little more give and take in the back and forth design process.
When I am asked to design the structure for a timber frame, I always encourage the architect or owner to find a timber frame company that they are comfortable with that also has a good working relationship with an engineer. It makes for a better project. If they insist that I must be their engineer, then I do the best I can to familiarize myself with the way the framer prefers to do joinery. I then try to accomodate the framer's standard and signature joinery etc. into my design. I hope this helps.
Best regards, Chris Hoppe