Timber Framers Guild Forums Tools Timberframe Design Timber design using a bent system

I have a timber framer who I like very much and is offering an affordable price for his frame. Big companies refused to use a bent system because the middle bay of the home is 20' wide. The timber framer I'm working with said it could be done by breaking up the bay at the front of the house, but leaving the gabled bump-out great room with a clear 20' span. Structurally, it seems to work. My only concern is that he is using a 5x7 ridge purlin on the gabled bump-out, and it spans 17'3". He said he could increase it to 7x7, but that the ridge sees very little load compared to the valley (and they are sized at 8x10). Does this seem sound? By the way, the entire frame is in oak.

My second concern (or point of contention) is that he is attaching the roof purlins insde a 2" pocket, but nailed with galvanized 70d nails from the top (not visible on the inside). Is there a joinery method that requires no more labor but without nails?

I have PDF copies of the design that I would be willing to email to anyone for their opinion.

Many thanks.

Two thoughts:
i would use screws instead of nails anytime.
Sounds like a classic case for an engineer analysis of the frame to determine which size timbers are required wherever.
deralte

olpjeb,

My opinion is that this is between you, your framer, and a licensed engineer who is familiar with traditionally joined timber framing.

cheers,

Gabel

From your description I would say that the rafters are restrained at the bottom end by a horizontal member (bottom chord) and are in compression at the top. In that case the ridge does little for the main structure of the roof beyond preventing deflection of the rafters at the peak.
Or..long story short, you have trusses, which are more than adequate for the span.

But, don't take my word for it, take an enginers word (and stamp) for it.

As for the fasteners, typically some type of mechanical fastener is used in this location and if our predecessors had access to the mechanically produced (read cheap) fasteners we have now, they would most likely have made use of them in this location. Spend the extra money your framer would cost here on something fun.

Re screws vs. nails: Nails actually have more shear value at the same shank size and near the end of the member either screws or nails would require pre-drilling. I doubt however that shear is an issue here and inasmuch as it’s all hidden would be inclined to leave it to the framer preference.