Cabin Ceiling Joists- Can I have fewer?

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Small Cabin Forum / Cabin Construction / Cabin Ceiling Joists- Can I have fewer?

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# Posted: 25 Apr 2012 09:12
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I plan a 12x17 cabin with a 45deg roof and a half-loft (a loft over maybe 7 of the 17 feet of length) inside. Ideally I want the rest of the cabin to have a "cathedral" ceiling feel. Can I eliminate some (or all) of the ceiling joists in the open area? What are my options for creating an open, high ceiling feel in the non loft section of the cabin? I am open to stronger beams or cables to serve as joists.

Thanks very much!

Rifraf
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# Posted: 25 Apr 2012 09:57 - Edited by: Rifraf
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chuck,

I'm sure some of the engineering folks here will have a good answer for you. In the meantime I can say that my shell cabin was 12x32 and I could have ordered it with the lofts any size I wanted.. even none at all and that would have meant very very few joists. As it is, the middle 10 feet has zero joists. And these shell cabin truss supports are only held to each other with the roof sheathing and small metal clips. No cross bracing beams.

MtnDon
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# Posted: 25 Apr 2012 10:57
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Sounds like the roof is a fairly normal 12/12 pitch with a ridge board running parallel to the long side walls; the roof rafters resting on the long walls and meeting at the peak with a ridge board between pairs. In that case ceiling joists are more than just ceiling joists. Ceiling joists are also part pf the rafter assembly and prevent the wall top from being pushed outwards by the roof loads.

To have a strong structure you really need the rafter ties. Steel rods across the width of an open area can be substituted with connecting bolts that penetrate the walls and have large bearing washers to spread the point loads into the framing structure. Such things are engineered solutions, not off the shelf or from a "cook book".

rafter ties = ceiling joists

soundandfurycabin
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# Posted: 25 Apr 2012 12:36
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Building codes typically require rafter ties no more than 4' on center. I'm planning a 14'x24' with no loft at all, and my rafter ties will consist of 5/8" rod every 4'. The rods will be threaded at the ends and secured to the rafters with a Simpson DTT2Z hold down at each end. The DTT2Z costs about $15 each and is rated for 1800 lbs of allowed tension load.

MtnDon
Member

# Posted: 25 Apr 2012 14:20
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Quoting: soundandfurycabin

5/8" rod every 4'

Sounds good

IIRC, the DTT2 have a hole for 1/2" rod
You don't really need the Z if there's no PT wood involved, but sometimes that is all that is carried.

1/2 even with the threading reducing the effective diameter still has more strength than the connector limit.

soundandfurycabin
Member

# Posted: 25 Apr 2012 18:42
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You're probably right on the rod size; I'll check my plans when I get home. I think the DTT2 is only available in Z or stainless versions because it is primarily designed to be an exterior deck tie rather than an anchor hold down.

I've also seen the rod to rafter connection done using pipe hangers over a section of pipe spanning between neighboring rafters, as well as various custom made clevis connectors. However the DTT2 came with Simpson's engineering and load testing, so it was accepted without question by my building dept plan checker. I suspect I'd have needed an engineer's stamp for the alternatives.

MtnDon
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# Posted: 25 Apr 2012 19:24
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The good thing about Simpson products is they come with a pedigree that carries some weight.