Okanogan 14x24 by a lurker :)

[ChugiakTinkerer]

For unsupported spans for rafters, you just look at the horizontal distance, not the roof pitch distance.  Is your deck 10' deep?  If so, then the unsupported span will be 10' less the thickness of the ledger and less the depth of the beam on top of the log posts.

I'm slowly getting a handle on your design concerns.  Give me long enough and it starts to sink in.  The beam calculators at FF have been really helpful for me in figuring out some of my girder spans.  As I understand it you'll attach a ledger to the cabin and run your rafters off of that.  The one corner of the house is going to be taking more load than it probably was designed for, so you might consider a post or other support on the corner, supporting the ledger board.

That corner for the hip rafter looks to be roughly 10' by 8'.  There's some artful way to figure out exactly how much area of the roof the hip will be supporting; all I know is it will be something south of 40 square feet.  If you use 40 s.f. as an upper bound, then you can put a number on the load to use in the beam calculations.  The more I look at this, the more I wonder if a doubled rafter will be sufficient.  What happens when your main roof sheds some snow onto the porch?  Is double the ground snow load a realistic number?

Edit: OK, probably the snow shed from the cabin roof won't put a load on the hip rafter, but it will on the straight rafters.  You'll want to make sure they are beefy enough to withstand that.

[ChugiakTinkerer]

The diagram here ( http://www.beamchek.com/loadbook/img165.gif ) shows what I mean about figuring out what area of the roof will be bearing on the hip rafter.  That diamond shown is 50 s.f.  I think for your situation it will be slightly less, but I'm no structural engineer so don't hang too much on my guesswork.  Also because of the shape of the load, it won't actually be evenly applied along the length of the hip rafter.  More weight will be focused on the center portion.  I leave that derivation for the diligent student to figure out.   

if you've got a 50 lb per s.f. snow load, the total live load will be 2500 lbs on that hip.  It will also be supporting the dead load of itself and the roof area, but half the weight of the jack rafters as well.  For a simple beam calculation, I'd consider using 3,000 lbs for an evenly distributed load and figure that will put you in the right ballpark.  Scale up or down if your snow load is different.

Edit: Using 3,000 lbs and a span of 168", it looks like three 2x12 is what it takes to support that load.  That seems like overkill, and maybe I'm way wrong in my head-scratching. 

[OlJarhead]

The deck is 10 feet deep and 8 feet past the wall of the cabin.  Beam is 6" supported every 6 feet by 6+" posts (many are 8").  So the span will be 10 feet minus the 6" beam and the 1 3/4" ledger so ~9'4 1/4"

The 12:12 pitch will slough the snow off onto the porch but primarily only in the section below the roof and maybe a little past it so that will be carried entirely (unless I'm missing something) by the rafters from the corner back along the face of the cabin.  This is also the southern face.

So, looking at that I need rafters to support the snow load there.  I know many using 4-6" logs as well as 2x6's and having no trouble with current snow loads but I'm certain if we got snow like there was in the 70's and 80's things would be different for them

Closest snow load I can find is Republic which is 54 but it's a lot wetter there.  Tonasket is 25 but it's lower in elevation though closer in climate.

[OlJarhead]

On the cabin framing, the foundation under that corner is a concrete footing with a surface bonded cement block wall and 2x6 wood framed wall on top of that.  Should be pretty strong for the corner but I could put a post under the hip rafter by cutting out the corner of the post and setting it against the wall and then using timber lock or ledger lock screws to secure it.  That ought to support the hip pretty well.  It  will span just shy of 13'6".

[OlJarhead]

http://www.seaw.org/assets/docs/WhitePapers/WABO-SEAW%20Snow%20Load%20White%20Paper.pdf
For those in WA State this helps.

Of course it doesn't account for the differences inside some of our larger counties like Okanogan where snow loading could be as high as 100 in places (or perhaps more) and very low in others.

[MountainDon]

Member medeek has interactive maps available for many states. Washington state is located here.   It offers more precision than data in tables.

[ChugiakTinkerer]

Member medeek has interactive maps available for many states. Washington state is located here.   It offers more precision than data in tables.

Medeek's stuff is just amazing.  After looking at that WA snow load page I am even more impressed.

[Gary O]

OJ, yer place looks marvelous.

Lotsa work


...and it shows

keep a fire

[OlJarhead]

Thanks Don.  His site shows this:
Normalized Ground Snow Load = 0.0170 psf/ft.
Pg = 0.0170 x 3101 = 52.8 psf

As close as I can get it to my place anyway (if I could zoom in more I could get closer but this is close enough I think).

[OlJarhead]

OJ, yer place looks marvelous.

Lotsa work


...and it shows

keep a fire

Thanks Gary   It is a lot of work but I enjoy it   Keeps me young as they say (though I don't know who they are and the aches and pains don't seem to agree either)

[OlJarhead]

Your rafter looks to be pretty close to a 2x10 in performance.  You can check a general beam calculator and plug in the dimensions of your rafter here:

http://www.forestryforum.com/members/donp/beamclc06b.htm

Picking some arbitrary numbers, I did a few calcs to see how your rafter compares.  For a Doug fir #2 with a 12' span, 300 lbs live load and 100 lbs dead load, the deflection calculation is as follows:

2x8 nominal deflects 0.1637"
1.75 x 8 actual deflects 0.1044"
2x10 nominal deflects 0.0788"
Double 2x8 deflects 0.08184"
Double 1.75 x 8 deflects 0.0522"
Double 2x10 deflects 0.0394"

You could actually run your porch dimensions through this calculator and see how your rafter will hold up to the snow load as a single or as a double.  Using the Doug fir again and a span of 156", your rafter in single mode can withstand 850 lbs before it fails.  Assuming 24" rafter spacing that means a rafter in the middle is supporting 26 square feet of roof.  850 divided by 26 isn't much, only 32 lbs a square foot.  Your snow load probably exceeds that.

If you double up your rafters like you mention, then running a 3.5 x 8 beam through the calculator allows up to 1710 lbs, which allows you to double your total load on the roof to 64 lbs.  If you need more support you should consider a different rafter or a spacing of 16".  Also, that's based on the physical properties of Doug fir #2.  Your wood may be better (or worse) and should be taken into account.

Edit: I reread your comments above and realize you're just looking at whether to double the hip rafter.  Given the calcs above I would definitely double it.  Oops, also realized my all calcs were using 144" span.

The more I run the numbers the more it looks like a true 3.5" x 8" beam is darn close to a 2x12.  Perhaps that will be more than enough for a ~13' span.

[OlJarhead]

After much reading and research I decided to just use a ledger and when I got to the cabin did some math, used some online calcs and set the ledger to give me a 3.3:12 pitch.  Couldn't quite get to 3.5 but am close enough that the difference is negligible when it comes to cutting the angle on the rafter


With the temp ledger setup I was able to make my 'template' rafter and then set about making 4 more.  Marked the template 'do not use' and put it back on the top of the lumber pile (under cover) so it will be there when I get a chance to make more


Checked the seat and saw that my outer wall was either set originally a little out or had moved slightly when I installed the side.  But I couldn't move it by hand so I nudged it with the tractor bucket (yes I did! lol).


After playing a little with the rafter seats and the wall I was able to nail them in place and call it a day


I think with this angle the 12:12 roof will slough the snow right off to the ground actually   I could be wrong but if I am than these rafter should hold it.  They are Ponderosa and I mill them to shrink 1/8
to 1 3/4 (max) but found they have not shrunk at all really and measure 1 7/8".....either that or I forgot and milled them at 2" because I swear I intended to make them smaller but they are not so who knows.  They are lighter (by a LOT) and have been drying a while so should be close to 20-22% which is typical for air drying so perhaps I did mill them at 2".  Anyway, they are beefy and should take the load.


Until the cows come home

I just need to get the hip made now but my plan is to run both ledgers right to the corner (one over the other) and set the hip on top of them (like the rafters).  I may set a post under the ledger, just not sure yet but I am using 'Ledger Lock' screws so it ought to take the weight.  I plan to miter the end of the hip at 45 degrees / 84ish degrees to fit right on the corner but I'm not sure how well it will anchor if I do that.


Meanwhile.....yes it's July folks....yes we've never seen weather this cold in July....can't really complain but am totally amazed.  It's been a VERY cool spring and summer so far.

[Redoverfarm]

Eric at least you got the pitch at 3/12 or a little above so it is applicable with metal roof.  Manufacturer requires it to be at least 3/12.  If not some other roofing should be used.   

Yes the 12/12 will shove the snow on the 3/12.  At least mine did.  But it all depends on the surface area of the 12/12 above the 3/12+.  The only problem area will be the "hip" portion.

TWT (tweak with tractor) is more common than you think.  I recall using mine several times when person power was not quite enough.

[OlJarhead]

Ya, I figured the 3.3:12 pitch would give me just that little extra downward slope that the big 12:12 will push it off.  The hip is not under the big roof so won't benefit from any of it's 'push' but on the other hand won't get snow from it anyway.  It will only carry what is dumped on it by nature   But with a 4"x8" hip I think it will be able to take the punishment since that's actually stronger than a 2x12 (I'm fairly certain since a 3.5"x8" beam/hip is almost the same).

My only figuring now is whether or not to bevel the top of the hip for each slope.  Easy rafters shows two angles, one for the 3.3:12 pitch and the other for the 4.5:12 pitch on the end wall.  Never considered this before but it makes sense to me at the moment.  I'm guessing it just gives a flat surface to nail to on each side.

I am hoping to get the hip built on my next trip and maybe some jacks installed.

On a side note, since I had to come in from the corner a little to allow room for the hip and the rafter tail above, the rafter to the right of the hip will be a little closer to the next than my normal 19.2" centers and I can set the first jack closer to that one which should help bear a little more of the snow load.....somethign to ponder anyway.

[ChugiakTinkerer]

...  Marked the template 'do not use' and put it back on the top of the lumber pile (under cover) so it will be there when I get a chance to make more

I should try that trick on my next project.  I have the bad habit of setting a board aside for a specific use, and then 10 minutes later picking it up and using it for something else.  Making notes on the lumber would save a lot of grief and do-overs.

As far as that hip rafter goes, it looks like you're good with the doubled 1.75x8.  My seat of the pants estimate is that the tributary load area on the hip rafter is 36.4 square feet.  At 50 lbs snow load and 6 lbs dead load, that's a total load of 2040, dead load 218 lbs.  For a 3.5x8 beam spanning 156", it passes the beam calc with select P Pine and just fails with #1 P pine.  So pick your prettiest rafters and use those.  On that calculator the deflection fails for a floor (1/360) but passes for a roof (1/240).

You may not want to cut anything off the hip rafter to get the bevel, as it's just beefy enough doubled up.  You could cut some beveled shims on the table or band saw to get the angle you need.

[OlJarhead]

Good point on the hip.  I just grabbed stuff I'd milled for the rafters and realized some of it wouldn't pass muster   Gotta pay better attention next time!  And need to watch that when milling.

Sometimes it's hard to get the knots into the center of the board, or impossible, with knotty wood and really it should be milled into panelling and not construction lumber but it's a cabin and if it doesn't appear to hold up I'll replace those rafters if need be or add more but I don't think it will be an issue really.

[OlJarhead]

One thing I've been debating is whether or not I should bevel the top of the hip.  Seems most don't do it but with a 3.3:12 pitch running into a 4.5:12 pitch I wonder if it might be better so the sheathing can land flat against the hip.  Maybe I'm overthinking it?

[bac4uw]

"Meanwhile.....yes it's July folks....yes we've never seen weather this cold in July....can't really complain but am totally amazed.  It's been a VERY cool spring and summer so far."

No doubt! The usual PNW July 5th magical 'summer time' switch is a bit late this year. I'm fine with it while I'm working / building, but it's unusual.

Your place is looking great! I love that part of the state. I think we're going for a red metal roof as well.

[ChugiakTinkerer]

Hey. Don_P blessed me with a link to the AWC Wood Frame Construction Manual, and it has a section on hip and valley beams.  Not sure if you've looked at it, but here's the link: http://www.awc.org/pdf/codes-standards/publications/wfcm/AWC-WFCM2015-ViewOnly-1510.pdf

Page 301 of that document spells out what is recommended for a hip beam.

[OlJarhead]

Thanks -- I'll check it out!  I've been milling (two weekends in a row plus a couple days) and am back at the cabin Thursday but once again to run the sawmill so unlikely to get any cabin work done.


I was set up in Wellpinit this weekend and milled up 30 logs for a customer

[OlJarhead]

Get to be back at the cabin Thursday through Tuesday   Maybe the Cherries will be ripe (and not overripe or eaten by bears or birds) and I can pick them

I'm milling all weekend through so no time for cabin work   Soon though!  I swear it!

[OlJarhead]

Ordered a new chainsaw today

Got the Husky 576XPW with 32" B&C

Will buy a 24" or 28" B&C for it also but decided to go with the big bar for some large logs I need to buck up right now   And that will give me some extra bar for a BIG pine I need to fall (yes I know a 24" bar will work for falling a 48" tree but I like a bar that bites deeper than 50% of the tree -- maybe because I don't fall for a living

Anyway, excited to add this new saw to my stable of tools   The 455 Rancher I have is a great saw and the 576 should be a good 'big' brother to it and it's a pro grade saw so expecting good things from it

[JavaMan]

Awesome! I brokedown and saved a few dollars and got the 455 like the one you have with the 24" bar (I think it is).  Used it today for the first time. Awsome!

Up at my place probably the rest of the week. I will have big machines here tomorrow ( I am hoping it will only be a 10 hour +/- job). Going to get the road to the top of my his done and the hole dug. I am stoked! And pumped!   

It is downright cold for this time of year!

If you were closer i'd invite you over...

[nailit69]

Awesome! I brokedown and saved a few dollars and got the 455 like the one you have with the 24" bar (I think it is).  Used it today for the first time. Awsome!

Up at my place probably the rest of the week. I will have big machines here tomorrow ( I am hoping it will only be a 10 hour +/- job). Going to get the road to the top of my his done and the hole dug. I am stoked! And pumped!   

It is downright cold for this time of year!

If you were closer i'd invite you over...

Javaman...  Glad to see you're back at your place and making some forward progress... it seems your project stalled out for quite some time and I was starting to get a little bummed thinking you'd sort of given up on it. 

IIRC, you mentioned in a post that you live up near Brownsville or Keyport? We're sort of neighbors at both places... I live in Olalla and my cabin is up near Palmer Lake.

[OlJarhead]

Jeff I'll give you a call when I head up (tomorrow is the plan) for a short stint.  Would be a good time to visit your place

Glad you like the 455   I love mine!  It is my sawmill saw now for the most part but I have used it a ton in the last 5- years