Author Topic: 18x20 1/2 story cabin in NY  (Read 624 times)

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Offline carlsonNY

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18x20 1/2 story cabin in NY
« on: September 02, 2018, 04:43:17 AM »
Hi everyone,

I 've been gathering tons of valuable information from this board and am excited to hereby begin my own project thread.

We will be building in the Hudson Valley in semi-upstate New York using predominantly balloon framing techniques at 24" OC, 2x6 stud walls as shown in my uploaded screenshots and SketchUp file.

I digitally framed the building as best as I could and am looking for some opinions/advice on my job as I am sure there is room for improvement so please feel free to download the sketch up and have a look around. The second story will be solely for sleeping purposes and won't involve any utilities or appliances. I am looking to frame the house using douglas fir-larch #2 lumber from the local lumbar yard. The structure will be placed directly on an insulated slab with radiant heat tubing inside. We are also planning to wrap the whole house in insulated sheathing.

I am particularly interested in opinions/advice on the following points:

  • It seems builders are split on the topic of using let-in ledgers vs jack studs. I have opted into nudging my studs and placing a 1x6 ledger to hold my floor joists. Are there any particular concerns on this per my design?
  • The 2x10 joists are spanning 14' 1" max; the code allows for 14' 3" so I am right on the edge. However does my method of fastening them to the studs on top of the ledgers vs. hanging them improve stability here? 
  • The roof rafter are shifted 1 1/2 per side to allow for fastening them to each other at the ridge. I am not sure how conventional this is but I thought it would make for a very stable connection... should I revise this?

A few notes:

The Ridge Beam is a 11 1/2", 3 1/2" LVL.
I have not yet framed for windows and exterior doors as I wanted to get some feedback from you guys first/while I am working on those designs.
The local code asks for fireblocking which I have yet to add to my drawings.
The spiral staircase is a placeholder; we have a particular model in mind that will fit.

I believe this is it for now, thank you for reading and I am looking forward to any replies!







Link to SketchUp file:


https://drive.google.com/open?id=14DSndTNz13AAabo48CAjPJoYLIyfVERg



UPDATE:

I realized I forgot to add a header to the upper level storage area access. Here is a quick screenshot of my fix (using 3 2x6s):




Offline ChugiakTinkerer

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Re: 18x20 1/2 story cabin in NY
« Reply #1 on: September 02, 2018, 06:08:38 AM »
Welcome to the forum!

Your design looks to have a few differences from code that will get an inspector's attention.  Do you have a county building inspector to contend with?

I just helped my sister build a shed with loft using jack studs.  On my cabin I went with a let-in ledger.  Either one works, but you need to consider a 2x for the ledger rather than a 1x.  There needs to be enough area supporting the end of the joist so that the load is distributed enough to not crush the wood fibers.  From an engineering standpoint that varies with the load, but from a code standpoint that means a minimum of 1.5" of support on either end of the joist.  It is covered in the IRC in section R502.6.

I concur with your reading of the joist span table.  You are just at the threshold of long enough, but that might result in more bounce than you want.  I'd consider going with a 16" spacing or moving up to a 2x12.  Or drop down to 2x8 on a 12" spacing.  That allows you to stay on the 24" rafter spacing and would increase head room by 2 inches.

It looks like you've designed a structural ridge.  I'm a little weak on what's required for a birdsmouth connection but the bearing at the top end of the rafters looks small to me.  Also is that ridge beam adequate for the load you'll be putting on it?  Offsetting the rafters is not unusual, it's actually a good way to tie them together to prevent uplift.

My cabin build thread: Alaskan remote 16x28 1.5 story

Offline carlsonNY

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Re: 18x20 1/2 story cabin in NY
« Reply #2 on: September 02, 2018, 08:20:06 AM »
Thanks Chugiak for your reply!

Yes, the LVL is sized according to the manufacturers specs.

Great question on the birdmouths, I thought I had looked it up somewhere to conclude that the notch is adequately sized, but maybe someone else can chime in on that + I will look into it again.

I stayed away from a 2x for the ledger because it would cause a notch bigger than 25% of the stud depth which wouldn’t be up to code but agree, a 1x seems tiny for such a job.. definitely something I have been confused about.

Love your idea of going with 2x8s spaced 12“ OC for the joists: would I then use blocking between them and the studs to fasten them?


Offline akwoodchuck

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Re: 18x20 1/2 story cabin in NY
« Reply #3 on: September 02, 2018, 09:30:14 AM »
Here's a roof frame I'm working on now....I like to put a plywood gusset on each side of the rafter pairs, then block in between em over the structural ridge....super stout, good rafter connection, keeps everything in line....


Offline ChugiakTinkerer

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Re: 18x20 1/2 story cabin in NY
« Reply #4 on: September 02, 2018, 01:18:30 PM »
Love your idea of going with 2x8s spaced 12“ OC for the joists: would I then use blocking between them and the studs to fasten them?

I don't have a code authority so I just wing it!  d*

You'll probably have bird blocking at the eaves?  I would shorten the joists enough that you can put in blocking that runs from rafter to rafter, flush with the outside edge of the wall.  Then drop in the joists and use the bird blocking as a sort of rim joist.
My cabin build thread: Alaskan remote 16x28 1.5 story

Offline MountainDon

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Re: 18x20 1/2 story cabin in NY
« Reply #5 on: September 03, 2018, 09:37:20 AM »
Re the let in 1x as a support for the floor joists.  ChugiakTinkerer is half right on what IRC 502.6 states. carlsonNY is correct on the allowed depth of notching into a wall stud.  IMO, using jack studs to support joists is a waste of resources as well as being more costly, and makes it harder to insulate the wall as the stud bays size is decreased. Unless you blow cellulose or spray foam, that is. Even then the extra stud decreases the effective insulation R-value.

The bearing surface for a floor joist must be 1-1/2 inches BUT there is an exception when using a let in 1x4 (note code states a 1x4 is okay) AND the joists are nailed to the adjacent stud. However, that requires each floor joist to have a wall stud so the joist can be nailed to the stud. If the joist ends are supported by a top plate (1-1/2 inches or greater) that does not need to have the joist nailed to a stud.   The nailing schedule is in IRC 602.3(1).

IRC version, state by state is over here.



I was wondering how you were planning on getting the roof insulated?  The energy code calls for R-38 or R-49 for NT state, depending on where you are.  The is a REScheck program that allows some horsetrading when one area can get extra insulation to make up for another that has less than the code rules. Some places mandate it to be used, others make it an option. I was able to install larger windows by insulating the north wall more. Even using a 2x12 as a rafter you can't get that much insulation in the rafter bays without going spray foam. Depending on the foam you can hit R-38 filling the entire 2x12 bay but I don't think you can hit the R-49.

Just because something has been done and has not failed, doesn’t mean it is good design.

Offline MountainDon

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Re: 18x20 1/2 story cabin in NY
« Reply #6 on: September 03, 2018, 09:38:39 AM »
I would think the ridge beam manufacturer would have recommended methods for securing the rafters to the LVL.

What size mattresses would you be planning on for the upper level?  My experience is that king size is very difficult to move up/down winding staircases; spiral would be worse, I think.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline ChugiakTinkerer

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Re: 18x20 1/2 story cabin in NY
« Reply #7 on: September 04, 2018, 06:45:03 AM »
Thanks MountainDon for the correction.

Regarding the spiral stair, if you happen to be a big person like me you should find one to try out in real life.  They are cramped, and it's hard to get a feel for it from Sketchup.

Edit: Oh, a thought on the ledger... is there any value in using a 2x6 that is let into a 1" deep notch?  It would be 1/2" proud of the wall framing but could be flushed up with the interior wall covering such as drywall.
My cabin build thread: Alaskan remote 16x28 1.5 story

Offline SouthernTier

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Re: 18x20 1/2 story cabin in NY
« Reply #8 on: September 04, 2018, 10:22:23 AM »

I was wondering how you were planning on getting the roof insulated?  The energy code calls for R-38 or R-49 for NT state, depending on where you are.  The is a REScheck program that allows some horsetrading when one area can get extra insulation to make up for another that has less than the code rules. Some places mandate it to be used, others make it an option. I was able to install larger windows by insulating the north wall more. Even using a 2x12 as a rafter you can't get that much insulation in the rafter bays without going spray foam. Depending on the foam you can hit R-38 filling the entire 2x12 bay but I don't think you can hit the R-49.

I went with the 2x12 rafters in mine for the insulation.  You can easily get the prescriptive R-49 with closed cell foam (using a 6.5 per inch rule of thumb).  However, prescriptive also says fiberglass in the wall plus 1" of exterior foam, which leads to condensation (http://www.greenbuildingadvisor.com/blogs/dept/musings/2012-code-encourages-risky-wall-strategies).  By going with more exterior foam on two walls (to move the due point into the exterior foam), I was able to eliminate (through Rescheck) exterior foam on the back gable (front gable I will use rock wool in a 2x8 wall) and reduce the ceiling requirement a little bit.  But yeah, with a cathedral ceiling (as opposed to an attic) there really is no choice but spray foam, unless you want to put rigid foam on the roof deck as well.

Offline carlsonNY

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Re: 18x20 1/2 story cabin in NY
« Reply #9 on: September 04, 2018, 01:06:29 PM »
...I like to put a plywood gusset on each side of the rafter pairs

Thanks for sharing; I think I do prefer everything to be in line so I am updating to use this method.

The bearing surface for a floor joist must be 1-1/2 inches BUT there is an exception when using a let in 1x4 (note code states a 1x4 is okay) AND the joists are nailed to the adjacent stud. However, that requires each floor joist to have a wall stud so the joist can be nailed to the stud. If the joist ends are supported by a top plate (1-1/2 inches or greater) that does not need to have the joist nailed to a stud.   The nailing schedule is in IRC 602.3(1).

Thanks for evaluating and referencing me to the right sections in the code. To comply, I will update my ledger board to be 1x4 and my floor joists to 2x12's spaced 24"OC to be able to fasten to my wall studs.


I was wondering how you were planning on getting the roof insulated?


I am in Climate Zone 5 & 4 Marine, Ceiling R-value:38, Wood Frame Wall R-value: 20 or 13+5h. .

After some research (thanks SouthernTier for the article!) my plan was to install 2 layers of 2" rigid foam around the entire structure to block condensation and make R-20 (in accordance with Table R806.5 climate zone 5). I would also fill the cavities of my 2x12 rafters with 2x12 fiber glass batts (=R-38) and my 2x6 walls with 2x6 fiber glass batts (=R-19) which are air-permeable and thus allow drying of the walls to the interior. That should give me ~R-58 in the ceiling and ~R-39 in the walls.

Referenced Table:


Basic design:


I would think the ridge beam manufacturer would have recommended methods for securing the rafters to the LVL.

I am planning to use a Microllam-lvl https://www.weyerhaeuser.com/woodproducts/engineered-lumber/microllam-lvl/ and haven't been able to find any diagram or written explanation on this from the manufacturer but I will keep looking.

As to the spiral stairs issues: I 've lived with spiral stairs and am aware of the dimensional restrictions. I am currently thinking of centering the staircase in the width of the room which would permit some extra space to the side of the staircase for possible transportation of things to the second level. We will be using a flexible mattress (brand:Casper) which I am sure we can somehow get up there.

I will soon be sharing all the updates via another round of screenshots and sketch file. Thanks everyone for helping out!


Offline Don_P

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Re: 18x20 1/2 story cabin in NY
« Reply #10 on: September 04, 2018, 05:41:38 PM »
Try this, I was starting to write something and googled an image, and this popped up  :D
Notice the beveled plate on top of the beam, we call it a cant strip.
https://countryplans.com/smf/index.php?topic=13815.0




Offline SouthernTier

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Re: 18x20 1/2 story cabin in NY
« Reply #11 on: September 05, 2018, 04:17:25 AM »
Interesting reading through the thread you just posted the link to, Don.  Just spent all day Sunday building this (the lookouts and barge rafters):



That wasn't easy.  I know lots of details show double rafters where the lookouts attach, but I have really beefy rafters (2x12, #1 doug fir) and the lookouts aren't that long.

I attached the rafters to the ridge beam (a double 1.75" x 14" LVL pair) using these:



I will install collar ties below the beam as well.  Always more to do.
« Last Edit: September 05, 2018, 06:03:07 AM by SouthernTier »

Offline carlsonNY

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Re: 18x20 1/2 story cabin in NY
« Reply #12 on: September 05, 2018, 06:18:28 AM »
Try this, I was starting to write something and googled an image, and this popped up  :D
Notice the beveled plate on top of the beam, we call it a cant strip.
https://countryplans.com/smf/index.php?topic=13815.0

Thanks Don. This seems like a good method; I ll use a cant strip + the aforementioned plywood gussets to secure.


 

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