My 14 x 26 NM cabin

[MountainDon]

My 14 x 26 cabin is evolved from the little house basic plan.  But I don't like stairs or lofts other then to admire how nicely some of them have been built/finished. So one mod is to go with less roof pitch. Less roof pitch also makes me feel better about being up there to install the steel rib roofing sheets. I even looked into trusses, but the factory made ones are too much for me to justify their use. Therefore 2 x 6 rafters are in the plans. 2 x 8 ceiling joists will span the 14 ft width. No cathedral ceiling; insulation just above the ceiling, either fiberglass batts or dry blown cellulose.

One thing that has been bothering me is that the low pitch roof doesn't allow much space between the finished ceiling and the roof sheathing for insulation and air space out at the walls. Plans call for R30 ceiling to help meet energy conservation codes, and because that seems like a good minimum amount. The trusses I considered had extra members engineered in to raise the roof deck. Increasing the rafter depth to 10 inch or so would give room, but I'd rather not go that direction.

Then an idea hit me. Why not borrow from balloon framing and mount the ceiling joists lower down the wall framing? It would be a little like the world's shortest knee wall.  
Figure ONE



The interior ceiling height has been planned at about 7'6" all along instead of the norm of 8' for a variety of personal reasons.

Thoughts on why this is no good? good? problems? What have I missed?   :-/

[PEG688]

 The ceiling is a lil low but do able , our converted two car garage to master bedroom ceiling in 7 ' 4 1/2" and it's not  problem for me , I'm 6' 1" , so 7'6" shouldn't be a issue , except at point of resale and thats only IF the buyer see's it as one.

You may have  a problem with the joist as drawn you'd have to knotch each one to fit under your top plates , so you'd be 7 1/4" - 3" = 4 1/4" that would be the number/ size joist  that you'd be spanning with so you'd have a 1 1/2" x 4 1/4"  "net"  ceiling joist.  That would be a / the problem .

It appears your seat cut is to deep as well , your rafter tail will be whimpy if your seat cut is 3" deep , that only leaves 2 1/2" of rafter left at your birds mouth cut.

 

 You could sit the joist on the top of wall use a box sill then place your rafters right over the top of the joist with a 1 1/2" deep seat cut and add a plywood gusset on each side of the joist up and connected / nailed to the rafters , add pressure / anti-rotation / bird blocks between each pair in a continous line / row and you may have something the building dept. will sign off on .

I'd extend the wall sheathing right on up onto the box sill , which may require using 9' sheets of OSB for the wall sheathing, you'd avoid a row / line of solid blocking that way and tie the box sill to the wall very well that way.

The REJecter opps / inspector may require some type of Simpson clip / flat nail plate along with the plywood gussets for anti uplift . It would be stupid    but , well,  I guess ,  that's why I think he'd want a clip    

[MountainDon]

Thanks PEG, I'll digest that' make a better scale drawing of the top corner where everything meets up.  As for height we have no worry; it's still got more headroom than the RV.  

[John Raabe]

If you are going to blow the attic with insulation you can use 4" foam blocks (2 layers of 2") for air baffles at the wall line. Fit between the rafters and bring them up high enough to poke above the finished blown-in insulation depth. That would give you the 1" airspace and an R-20 or better at the wall/ceiling joint; R-30 when you get away from the wall.

[MountainDon]

Thanks for the insul tip, John.

Here are two new detail drawings, the first a more careful expansion of my first post, the second what I think you meant, PEG, by a box sill.
Figure TWO

This shows wall studs 24"O.C.  I share your feelings on them; however the interior wall plan is for 1x6 T&G pine so I don't think there should be a wavy problem.   :-/  And the exterior calls for Hardi-Plank over sheathing.

Figure THREE

Is this what was meant? Or did I misinterpret?

Thanks all.
Don

[PEG688]

You misinterperted, no plate on top  , a box sill like normal , with the rafter right over the top of the joist.  Then gussets up the sides as tie points . Your firsts cleaned up detail looks ok as drawn. I was just tring to get you more head room.

John's idea is OK  as well that's what's normally done , stilted up truss's are becoming common , they are a PITA due to the big step a guy has to make over the top of them and the odd (read wide) blocking they require .  

[John Raabe]

Here's my contribution for a well insulated roof with an exposed joist ceiling.



This has a standard platform framed ceiling (like a 2nd floor) on top of Dbl. plates. Use exposed blocking with a 3/4" reveal at the interior to give a nice trimmed out look with the 3/4" interior wood. Put down the attic flooring (or get it started) and then spring the rafters from a plate. For uplift and wind protection you would want a strap to tie the rafter, attic and wall together.

[MountainDon]

Okay, thanks, PEG. Here goes again...   :-/
Figure FIVE


Thanks again John. You've got a lot more detail there than I did.  

[John Raabe]

What happened to the exposed joists in the ceiling? You have a truss there and the ceiling finish would be nailed to the bottom of that. If you go this route, you would probably save money and/or time by having engineered trusses delivered as they would be able to use smaller lighter members.

[MountainDon]

1. I started off just wanting to be able to get more insulation, closer to R30, above a normal ceiling, but the 4/12 pitch doesn't allow for much near the walls...
2. I did consider trusses, but the truss co. won't deliver them up my mountainous road. The lumber companies won't deliver lumber and sheet goods up there either. So I'm left to transporting it all myself and trusses that size would probably take too much of a beating on my own, too short, trailer. 16' lumber will be enough of a PITA, but doable with proper loading, tieing, etc.
3. My first idea was to use let-in ledgers, sit the ceiling joists on top of them with the top of the ceil joist level with the top end of the wall joists... double upper plates nailed across the studs/joists. Then the rafters sitting on the top plates as per usual. Better shown in Figure TWO.
4. If I had drawn in the insulation in Figure TWO n(between joists) and also IF I'd darwn in the ceiling (under the joists) it would have been easier to follow.   [I'm not used to drawing plans for others to read/build from and in the past everything was pretty normal so the bldg dept never had a problem/question I guess]
5. John posted his well diagrammed drawing while I was working on my Figure FIVE. That looked a lot my my Figure THREE, except John detailed the insulation and put the ceiling above the joists for a more country look than my ceiling under the joists.
6. I posted my Figure FIVE mostly just to make sure I understood PEG's idea. As I drew it out I had decided I didn't like it because of all the plywood gussets I'd have to cut.  [years ago I made some 20' wide trusses from 2x4's and plywood plates and it was much more work than I enjoyed. They did work tho', still standing]

So, I think I'm back to either {A} building a normal 2x6  4/12 pitch rafter roof and using more foam near the walls to get an increase in R-value in that vertically challenged area, OR {B} using the plan as pictured in this modified Figure TWO (now Figure SIX)

Figure SIX


OR {C} using John's idea... I had thought of the exposed 2x8's but wondered if I'd find enough 2x8's that I liked the looks of to use them exposed in the ceiling.   :-/

Sometimes I can turn the simple into the complex.   Sorry guys  

[PEG688]

 Sometimes I can turn the simple into the complex.  

Jeesh,  ya think And Mtn D,  why do you think they call it WORK !!! >  Re your cut plywood gusset comment<    Hoy Vey

[MountainDon]

touché

[glenn kangiser]

I got tired just watching you guys kick it back and forth. :-?

[PEG688]

That dbl 2x8 with the foam in it reminds me of how Lindal cedar homes does / has done/   their headers , they add a 2x6 on the flat , like a top plate so the headers are a wood " U " filled with foam , they run that continously around the building so windows and door of less than 6' ,maybe 7' wide can pretty much be placed anywhere the client wants . They use a dbl 2 x10 IIRC at least on the Lindal we assemble 3 or 4 years ago.  

Ridged foams R value is generally pretty low in comparision to batts , and other more common insulation.  But it's a interesting way to build , not a cheap way , as Lindal's  shacks are never "cheap". They're plenty proud of what they sell , if ya get my drift    

[MountainDon]

I've always admired their appearance, and choked on the prices

[John Raabe]

The double rim as a header is a powerful and underused technique. It is the basis of the high transom detail I did for the PlanHelp.com site.



In a closed ceiling it need not have foam and you can use less expensive batts. For what MountainDon (initially) was trying to do the foam is in keeping with his desired higher insulation levels.