Denali 14X24

Started by redside, November 02, 2016, 09:57:52 PM

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redside

First off, a big thank you to all of the posters who's time and effort on this forum allow a novice like me to get going on the right foot.  I definitely feel like I am in the right place.

My wife and I purchased 10 acres in a remote part of Alaska.  We have finally decided on a 14x24 footprint which is a great start!  This will be a long term project due to the remoteness, but I expect to have the foundation done this spring and cabin built the following year (only able to bring materials in by snow machine).  I have "no" previous building experience.......have fun with this rookie  ???

Here is a basic idea of what I want to build.  The building is 14' X 24' with a four foot overhanging porch.  The foundation is 2 rows of 4x12 beams sitting atop sonotubes on bigfoot footings below frost line.  I would like the beams/girders to rest on top of the sonotubes (no wood post) which will be 18" above ground.  The building site has heavy snow loads and can have gust of up to 100 mph once a year in the fall.  The roof is omitted (not to great at using Sketchup) from the picture, but I have decided on a scissor truss 12/12 top chord and 10/12 bottom chord.



I have done my research, but still would love any feedback on the following questions; I know I have a lot to learn:

1. The foundation: I know I can have the floor joist cantilever the floor beams by 1' or I could hang them off the beams with joist hangers.  Both ways are accepted and the cantilever would allow me to span the 12' using smaller dimensional lumber.  Any disadvantage to setting the joist on top of the beams and utilizing the 1' cantilever?  I would think the disadvantage is stability.

2. The foundation: You can see I have a loft overhanging the porch.  The floor beams are a continuous 24' meaning that 4' will be exposed to the elements.  Would it be better to break up the floor beam into 2 sections: one section is 20' and the other, which is exposed is 4'.  I know this seems like a silly question and I am pretty confident the 24' floor beam is fine.

3. The foundation: I figure I can avoid cross bracing the sonotubes if they are only sticking up about 18" above grade.  They will be buried about 6 feet down.

4. The good old loft/vaulted ceiling bugaboo that seems to get brought up way too many times: I would like to use approximately 12' stud walls and hang the loft floor joist off a ledger/sister them in about 7 1/2 feet up from the 1st floor.  As you can see in the picture, this leaves a open cathedral/vaulted ceiling and I believe I have read that the stud walls should be no more than 10' between top and bottom plates.  I understand the wind load problem and even though I am using scissor truss, the walls could still deflect in the open cathedral ceiling area.  I will be using 2/6 studs 24" OC.  My questions are: 1) should I platform or balloon frame the gable end wall? 2)  Is the 12' stud wall acceptable?.  If I have to step down to 10' walls, I can  :-[

5. What is the point of putting in fascia and soffit on a 12/12 pitch?  I was thinking I would just use exposed rafter ties and call it good (no plumb cut or anything.  I just don't understand why people go through the trouble of putting in fascia and soffits?  I would think a 12/12 pitch would prevent the building from any moisture problems.

That is about it.  I really wanted to go with a regular ridge board ceiling, but is seems that the pressure being exerted on the top plates would be too much and a potential failure problem.  Even though this is the case, I see many homes on this forum being built without proper rafter ties......makes me wonder????  Sure is a cheaper route to go.

I abandoned the ridge beam because I wanted only two post in the open porch area.  If I used a ridge beam I would likely extend the supporting column straight down the center of the building to a footing and it just doesn't aesthetically please my eye......not to mention the extra expense and time of putting in two more sonotubes to support the columns at the gable end walls.

I really feel the scissor truss is the way to go.  The trusses will be split in half, transported to the building site via snow machine, and then reassembled on site.  The 12/12 top pitch will shed snow and the 10/12 inside pitch will provide room in the loft and a great looking vaulted ceiling.

I am open to any and all suggestions and will not be offended in any way......I am a novice to say the least.



kenhill

You could put a pipe vertically into the cement in the sonatubes and use a bracket made by Friesen's Cabins in Palmer:  http://www.friesenscustomcabins.com/photopag.htm  It is welded steel U Bracket with a large threaded nut on it so you can re-level with any frost heave or earthquakes.  I was surprised how much mine moved with the larger recent earthquakes.


ChugiakTinkerer

Yowza, welcome to the forum!  Congrats on making the leap to carving your place out of the Alaska wilderness.

Looks like you've covered everything very well.  I'm inclined to agree that the beam should be continuous including the porch.  If exposure to the elements is significant you could use pressure treated for your outside layer.  I am assuming you are planning on using built-up beams made of multiple plies of 2x, just make sure outer one is PT.

I favor resting joists on the beam rather than using hangers.  I think the difference is down to personal preference and ease of construction for one way over the other.  Your cantilever should not be any more than the depth of your joist, otherwise there is the potential for too much deflection.

I'm looking at ways to make my loft knee wall taller.  Your 3D layout looks nice but I doubt you'd really have as much usable space along the knee wall.  The 10/12 pitch ceiling will be encroaching a good deal.  It comes with the territory, I just don't want you to be surprised when you actually want to live it in it.

If you are in a borough, make sure you know what permits might be required.  Check the ASCE ground snow load for your area so you can get accurate numbers for the snow load for your roof design, although a 12/12 metal roof makes it pretty trivial.  Give some thought to whether you may someday have plumbing for summer use and take it into account when you build.  I'm looking into putting in a sand point at our property so that in the summer we can have fresh water without having to haul it from the lake.  Along that line, look into decent water filters if you are drawing from surface water.

I'll have lots of thoughts and comments down the road, I'm sure.  I am mindful about giving out too much info about my property location, so I don't name my lake in my internet posts.  Can you give us a general idea about location?  How long is your snow-machine ride to get to the property?

Welcome to the club and have a fun ride!


My cabin build thread: Alaskan remote 16x28 1.5 story

redside

#3
I appreciate the feedback...thank you.  The adjustable beam brackets Friesen uses are stout and I would really like to use them.  My concern is now I don't have any uplift protection besides the weight of the building (that said, I am sure I could devise some way to fasten the floor beams to the sonotube using some metal stapping, etc)......heck, I don't even know if wind uplift is a concern since I don't have tornadoes to deal with.  I was hoping that going 6 feet down would prevent movement and having no center beam would prevent differential settlement should there ever be any frost heaving.  To combat the frost jacking I was going to wrap the sonotube with plastic to act as a slip joint.  The soil is not the best for building.  It is a silty loam with some clay in it and there will be some expansion when it freezes.  Will sonotubes work?  I can't answer that, but it seems like my best option.

I know that room in the loft is going to be a compromise, but the cool thing about using Sketchup to help design a building is I can get a feel for the space inside.  The 10/12 pitch and a three foot knee wall will actually provide a nice sleeping area where I won't be bonking my head.  If I used a ridgebeam I could even get a little more headroom by having a 12/12 inside pitch.  Not to poach someone else's thread, but I really liked the following design http://countryplans.com/smf/index.php?topic=7672.425 .  My concern was not having rafter ties, thus, the decision was made to go with scissor truss or ridge beam.

Thanks again for the comments


Don_P

Photobucket seems to be down. Some devils advocate stuff to think about,
when you talk about a pier, then a beam on top, then joists on top of that. One point of rotation that should be thought about is the beam. As a beam becomes deeper, thinner, and longer the requirements for laterally supporting it increase.

If you extend the beam into weather make all plies treated for some distance back under the main building, water gets in more than we ever think.

If the soil heaves and moves seasonally most of the way down that 6' embedment, is it really providing bracing for that pier?

Go carefully reducing snow loads on roofs, we build for that one bad day in a century. I've had the right mix deposit freezing rain then continued snows consolidate to 3' deep on a 12/12 metal roof, stuff happens.

Balloon frame the gables unless there is a loft floor providing lateral support to the wall, then you can break it there and continue up to the laterally braced roof plane. Walls run from plane to plane, unbroken in between and WELL attached to each plane. Picture it as a floor turned on its side cause that is what it is to the wind.



redside

Don, I appreciate the feedback.  I really like the idea of platform framing the gable end wall, but understand what you are saying and agree with you regarding balloon framing it.  It still would be about a 19' wall from floor to peak and I would like to strengthen it laterally to lessen deflection during high wind.  I was thinking of adding your "plant shelf" idea which seems like an aesthetic way to solve the problem.

To be honest, the foundation has been by far the hardest aspect to make a decision about.  Many, many cabins up here use post or sonotubes with varying degrees of success.  I know it is not ideal, but it is just not logistically feasible to do a perimeter concrete footing/wall.  I suppose I could do it, but "holy moly canoly oily" it would be hard.  I narrowed it down to piers below frostline, cribbing (just have the cabin "float" on the surface), or put in a modified pressure treated wood foundation/rubble trench.

It probably will not work, so I have written off the idea of a modified wood foundation, but it essentially entailed digging a 6' trench around the outline of the building, dropping in 8' pressure treated walls sheathed with plywood/bituthene and then building off of that.  In other words, it simply replaces a concrete wall.  It would also skirt the cabin and I would have "vent holes" on the inside of the skirting to let wall cavities breathe.   This idea is good on paper since it provides a tremendous amount of weight displacement,  stability, and is below frostline.  In the real world I just know that I wouldn't be able to fully seal it from water and it would rot out. 

I figured sonotubes or post would work because the ground is flat.  I don't understand why piers would lean/topple in my situation????  Please educate me and I mean that sincerely.  In my little mind I figure it is the freezing soil that expands and pushes on the piers.  Wouldn't the soil freeze at the same rate and with the same amount of pressure around the entire prier thereby having no effect on it?

So glad I found this forum!!!!

redside

PS. Don, I agree with you on all accounts......especially building the structure for the "storm of the century".  Why not just do it right if it isn't that much extra time/money?  Up here in Alaska, I can definitely see the day a 8.0 earthquake hits while I have three feet of ice/snow stuck on that roof and the wind blowing 60 mph :-) .  There are enough forces/problems that could happen to this building......why not do whatever I can to put the odds in my favor?

Don_P

The overturning force on a foundation is usually wind or seismic. The slow leaning failures are often the result of eccentric loading and the inability of the surrounding soil to brace the pier adequately. Eccentric loading happens when the load above is not centered on the pier or the soil under the pier is not uniform in bearing capacity. The pier begins to lean. I was noticing this on a less than year old timberframe pavilion the other day. Someone oopsed the grade level footing/piers by about a foot which resulted in the posts being lined up on the inner edge of the two rows of piers, about 6" off center on each side. A surrounding slab on grade was then poured abutting the piers. Some are already tipping. As the pier begins to tip you can look at the ratio of vertical to horizontal. This ratio applied to the load on the pier represents the same ratio of vertical and horizontal reaction forces acting on the pier. As the pier leans more the horizontal component of the load increases causing the horizontal load component to increase, which causes the lean to increase... and on and on, when columns go out of plumb it can cause a self feeding problem. Think about say 5000 lbs vertical then push on the top sideways 1%, 5%, etc. A football player can push with about 80 lbs horizontal. There aren't too many fenceposts I can't wiggle over with my non football player build and there is no load overhead helping me wiggle. Park a car on top of the fencepost, let me wiggle it and I'm unstoppable. Bracing from pier to structure, in all possible directions, helps prevent that hinging.

Another way is to post frame it. Dig the pier holes, I'm fine with treated wood footings. Stand posts up that reach from footing to top plate. The walls brace the unbroken posts. Modeling this, the posts are cantilevered beams.

redside

I was originally going to use wood post for its simplicity/cost, but was concerned about longevity and putting CCA into the ground. The building site is very pristine and would hate to put any arsenic in the ground.  I guess I could use a different type treatment, but it seems the majority of people on the internet say CCA is superior and it is not as corrosive as other treatments.  I guess I could just wrap the post in grace and water shield to contain the CCA and plop the post in the ground on footing, but that just doesn't seem like it will work.  I also saw a product called "post protector" but I don't think that will work because there are uplift ribs on the sleeve that would potentially let the frost "jack" the post and it doesn't come in lengths greater than 60". 

Any insight would be helpful.....thanks.


Don_P

Toxicity is about dose, I wouldn't be too worried about that amount myself but it is not zero.
This is one sleeve without ribs and comes 66" long;
http://www.plastisleeve.com/plasti-sleeve-info/

jimvandyke

Seems like building Pole Barn Style would be your best option. Using those plastic sleeve in pole barn construction would even be better. Floor framing is still possible with pole barn construction if you can't do a slab. Use 6x6 PT Posts for the poles, I am not sure of the required spacing but for a 14 x 24 you would only need them on the perimeter. I am pretty sure you can still frame standard walls with pole barn style construction just make sure the top board of the top plate is placed correctly. I would bet you could do the posts on 4 foot centers. That would give you 2x6 walls, which allows 2 foot centers on the side walls and probably 16 inch centers on the gable ends. Your local code will tell you what you can do.

I live in a hurricane zone and there are plenty of pole barns around here framed that way. Design code here is 110 mph.

I built a 14x24 buidlers cottage (but i made it 16x24)
http://countryplans.com/smf/index.php?topic=14379.msg187938#msg187938

Just a thought.

Jim

Dave Sparks

One can always design for higher than 110 mph.  We do it all the time up in the mountains! d*
"we go where the power lines don't"

redside

Checked Jim's cottage out.  Gorgeous and built to last!  I will entertain the pole barn framing.  Would make for a strong building.

redside

So me and my wife started clearing land and we are ready to put are pilings in.  The cabin will be 16x24 with a 1/2 loft.  There will be two built up beams under the load bearing 24' walls and no center girder.  I am going to cantilever the floor joist only a few inches (4-6") over the beams.  The floor joist will be either 2x12's or 2x10s (haven't decided yet).   I have looked through plans and read the forums and it seems my plan will work with the two beams (although most people have a center beam).  Before I dig the footings, I wanted to see if anyone has any input on improvements to my plan:

1.  Due to the shape of my pier brackets, I would like to cantilever the floor joist by a few inches and inset the main beams.  I figure the beams directly under the walls would be better, but from an strengh standpoint it doesn't seem to matter since a cantilever of a few inches doesn't require any engineering.  I figured a 100lb snow load will result in a max load of 40,000 lbs on each load bearing wall.

2. I am omitting a center beam.  That said, would it be wise to place a pier in the middle of the gable end?  I figure the gable wall will weight about 3,000 lbs and I can just double or triple up the rim joist to carry the weight of the gable wall.

Getting closer!


ChugiakTinkerer

I see no harm in putting a pier under the gable wall, particularly on the loft end.  In theory the side walls are carrying the load, but you can't make a proper floor or roof diaphragm without attaching to the gable walls.  So they will be getting some load and you're wise to anticipate that and account for it.

With a non-structural ridge, the load on the rafters will want to push out the top of the side walls.  Where you have a loft that may be sufficient to withstand that outward thrust, but the open ceiling at the back of the cabin doesn't appear to have anything to counter that force.  Have you considered some exposed rafter ties in that area?
My cabin build thread: Alaskan remote 16x28 1.5 story

redside

Thanks for the suggestions. The roof will be parallel chord trusses so outward thrust is minimal in cathedral portion of cabin.

redside

Its been awhile since I posted, but I thought I would update my progress thus far.  Special thanks to all those who have gotten me this far.  This fall my wife and I were able to get the steel piers in the ground and last week I made a trip bringing in the girders.  Things are going well. Me and my wife have an arctic oven tent set up with a wood stove for the winter work and take my word, these are the best winter tents in the world, bar none.

Next trip out I am going to borrow Mt. Don's idea and build a cripple wall between the piers to provide lateral stability and give me room to store some building supplies.  The plan is to bring in materials this winter and build next summer (only two seasons in Alaska which are winter and summer).

I will likely have some questions going forward and will try to post more often.  One I have right now is whether to use i-joist or dimensional lumber for my floor joist.  Both will do my span fine and both are comparable in price.  It is tempting to use i-joist due to them being flat and less prone to warping, but I am concerned because I have a cantilever where the joist overrun my girders by 8".  It seems dimensional lumber will handle the cantilever better; the i-joist require additional support for the cantilever which seems like a pain to install.  Other worries are longevity of i-joist  vs dimensional lumber.  That said, it is difficult to find quality wood in Anchorage so engineered may be the way to go.  Your thoughts???

Some pics of work done thus far:






akwoodchuck

Thats definitely a start.... ;D ...what ya got for footers under there?
I lean towards engineered joists over sawn, soooo nice to have a flat, light, full length product to work with, especially considering the price points are so close. Two years ago I was unloading a brand new dimensional 2x10x16 off the truck and it snapped right in half....no bueno.
"The lyf so short, the craft so long to lerne."

ChugiakTinkerer

Thanks for the update.  Love the photos, especially the swans.  How on earth did you get that close?

If cost is the same for dimensional versus engineered joists I'd optimize for either performance or ease of installation.  If you have a compressed building schedule then maybe go with dimensional.  Although it's hard to find good wood.  I usually get my lumber from SBS but the quality there isn't what it used to be.  If you pick it up yourself though you can get the guys at the yard to let you pick through for the best wood.  I had a major purchase last year buying $3.5K of lumber and it took about an hour to load my trailer.  The 2x12 joists were the worst, and I had to get a second unit to find good material. Tipped the yard guy $20 for the extra effort.

I've got tent envy!  I want an Arctic Oven in the worst way. :o
My cabin build thread: Alaskan remote 16x28 1.5 story

redside

The swans must have had a nest nearby because they swam all the way across the lake to check us out.  They came within about 10 feet and were not the least bit afraid......actually they were kind of intimidating me.....those are some big birds. 

The footers are 22" diameter 1/2" steel plate welded to the sch 80 piers.  The idea is the steel plate will provide stability and prevent frost heave as well as provide a good footing.  I designed them for clay soil, but when I actually went to digging I was able to get to more or less bedrock.  In retrospect, I could have easily just dropped 6x6 post in and saved a week or so of work had I know I was sitting on bedrock.  Lesson learned is to dig some good test holes before designing the foundation.  Even though I dug a few holes with a shovel, I should have done a better job and dug a little deeper.....the rock was only a foot or so deeper than my test holes with the shovel and I had no clue I was even close. 

A 2x10 snapped in half!  I think that says it all and engineered wood seem to be the way to go.  I might give SBS one last try and see if I can pick through their stock and find something good.  I can't even hardly drag myself to the big box stores after going through their lumber and being thoroughly disappointed.  I think I will invest in a small mill once I get my small cabin built and just mill my own lumber since the commercial quality seems to be so poor these days.  I do like the idea of using lumber just because it seems easier to work with than i-joist. 


Don_P

Looking at the damp, I'd go with dimensional over I joists but you know the situation better.
With steel, can you get a generator welder in there? You could turn those posts into a rigid frame or braced frame easily.

redside

I made some custom clamps out of 2x2" square stock for the piers which I will attach a cripple wall to.  They turned out really well and the clamping force will be plenty strong without the hassle of bringing out a welder.  I did some more research and agree that dimensional lumber will handle moisture/mold issues much better.  Floor will be 5 feet above grade so this may not be much of an issue.  I like the simplicity of dimensional lumber (e.g., easier to attach hurricane ties to the girder, no special reinforcement for the cantilever, handles moisture better, etc.).  If I can hand pick through a stack at the lumber yard, I may be able to rustle up enough for the project.  I am not lying when I say the quality is terrible up here.  I am sure the floor will not be as perfectly level as i-joist, but it is a cabin.

ChugiakTinkerer

Quote from: redside on January 14, 2018, 03:19:43 PM
... but it is a cabin.

That has become my mantra!  :-[

I'm planning on using my own milled lumber for interior finish, partly because I want to and partly because the rough-sawn look will help hide some of my imperfections.  Of course, I also have a sauna to build, and a main cabin, and a workshop, and the generator shed, and a sawmill shed, and ...
My cabin build thread: Alaskan remote 16x28 1.5 story

redside

#23
Just got back from a weekend of work with my wife (couldn't do it without her).  I finally got some wood on the cabin which feels great.  The temperature was cold enough to freeze my water level full of pink RV antifreeze (not frozen solid but slushy and inoperable to say the least), but I didn't really need the level since I could mark off of my post which I cut level the trip before.  I am thinking I should fill my water level with vodka and add a little food dye.....then, if things are not going so well I can always drink in the tent!

Being a novice, I soon discovered the cold was causing the ends of the wood to split.  I soon remedied the problem by predrilling, blunting the nail ends, and hand driving the nails.  This worked pretty well, but I still ended up with a few little cracks I can live with.  The brackets I built for the post to attach the wood to worked better than expected and I could sense the increase in strength immediately. 

Next trip out is sheathing the crawl space and installing the floor.  I did wind up ordering advantech subflooring which is "full face" (i.e., makes a true 4'x8') and am excited to try it out.  I figure it will weather spring breakup. 



Beavers

Brrrrrr...that looks really cold!

So the wall is sitting on top of your steel piers?