Northern BC 20x36 1.5 Story Cottage.

Started by coasttocoast, June 30, 2016, 12:48:55 PM

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coasttocoast

Hello everyone,

We are finally doing it. After a few years lurking on this site, and going over the plans and building books it is happening.

Our wee family is busy as ever as today is the day our concrete arrives.

We have modified the plans to extend the length to 36', and have added a row of piers down the centre of the building. Plus a 8'x8' boot room in the front centre of the house.

Would I be able to use 2x10s for floor joists sinice they only have to span 10'? Or should I stick with the 2x12s?

Excited to be part of the building community.

How do I post pictures from a MAC?

MFB

John Raabe

Just about any decent grade of 2x10, at 16" or 24" o/c, should give you a bounce-free solid floor.
None of us are as smart as all of us.


CabinNick

We are planning the same build next year.  Looking forward to following your project. 

coasttocoast

Hello,

Here is the first picture of our build site. We don't have internet here so I am trying this from my phone. The build is going great so far. One hiccup which I will explain later. Hope this works from my phone.

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ChugiakTinkerer

Looking forward to seeing the pic, but it isn't showing for me.  You might check the URL for the image.

MountainDon has a post with pointers on how to poist images here: http://countryplans.com/smf/index.php?topic=11663.0
My cabin build thread: Alaskan remote 16x28 1.5 story


coasttocoast

So far we have done the floor joists and laid down the subfloor. Time to start the balloon wall framing.

I am doing a full upper floor on the house and I would like to have a nice exposed beam down the center of the house to support the upper floor. What is the maximum span I can do for a 6x12? Would it span 14'? This would match up with the piers that are spaced every 7'2".

I would also like exposed floor joists at 24" OC.

Still trying to post a photo. 

coasttocoast


coasttocoast


John Raabe

Beam sizing:

I expect your 6x12 spanning 14' is in the ballpark but you should check with the lumber yard or a local engineer. The grade specs of the lumber and local snow loads are the big unknowns.
None of us are as smart as all of us.


NathanS


ChugiakTinkerer

Yep, that view is gorgeous.  If you want to use the IRC as a guide, the 2015 version is available online at http://codes.iccsafe.org/app/book/toc/2015/I-Codes/2015%20IRC%20HTML/index.html

Table R502.3.1(2) shows maximum joist span for given joist spacing and nominal size.

Table R503.1 shows minimum thickness floor sheathing for a given joist spacing.

Table R602.7(2) shows allowable girder (beam) spans for interior bearing walls.  If this beam is only holding up a floor and won't be bearing any roof load at all, you would use the One Floor Only section.  Your 6x12 should perform better than a beam built up from three 2x12, which for a 20' wide building allows 10'-2" of span.  If you have a rough-sawn beam, ie actually 6" wide and not 5.5", then you can look at the four 2x12 beam as a guide.  That table also notes in footnotes that it assumes specific grade and wood type.  You'll want to confirm that yours meets the minimum strength required.

My cabin build thread: Alaskan remote 16x28 1.5 story

ChugiakTinkerer

#11
Another way to look at beam size is to calculate the total weight the beam will be supporting and run it through a beam calculator to see how it will likely perform.

To span two piers you need a beam of 14-'4".  It will be supporting a floor 19' wide, so it has an area of ~272 square feet.  If the beam is only supporting a floor and no roof, you look at the area and multiply by the sum of dead load and live load.  Assuming 20 lbs and 40 lbs respectively per square foot, the total load of that section of floor is about 16,320 lbs.  Half of that load will be borne by the walls, so your beam needs to support 8,160 lbs.

There is a handy beam calculator at the ForestryForum site at http://www.forestryforum.com/members/donp/beamclc06b.htm

You just need to input the first six fields and click on Calculate.  I used the following numbers for the first five fields:
Total load = 8160 lbs
Dead load = 2720 lbs (one third of the total load)
Length = 172 inches
Width = 5.5 inches
Depth = 11.25 inches

Using a species of "SS Doug Fir B+S" the beam passes.  If we drop down to #1 grade it fails.  So a beam of this span will be right on the edge of suitability depending on the species and quality of your beam.  If you can go with a rough cut 6" x 12" beam rather than the nominal you bump up its strength pretty significantly.  Using Width=6 and Depth=12 the beam passes with #1 Doug fir.

You can tweak the calculations where you have more precise numbers.  I was also using some conservative numbers for live and dead load.  For a sleeping area the live load to design for is only 30 lbs per square foot rather than 40 lbs.  Also depending on floor construction your dead load could be much lighter.  So a 14' span for a 6x12 beam is in the realm of possibility.  Just know that if you push the calculations too much you'll end up with a very bouncy floor.  Also, is there no permitting authority in your area that wants to tell you how to build?

Edit: Just wanted to add a couple points.  First, a beam like you want can be accomplished with an LVL beam.  Second, my example is only for the interior beam supporting the second floor.  For foundation beams use Table R602.7(1).
My cabin build thread: Alaskan remote 16x28 1.5 story

Don_P

#12
The Forestry Forum calcs are mine as are the ones on my calc storage site timbertoolbox.com They are as good as the inputs and are used by a number of design pros but are probably not going to be accepted by a building official for a beam submission.

The WSDD (wood structural design data) manual over at awc.org does have solid beam span tables and would be respected as prescriptive by most building depts. (they are the folks who create the code span tables)

edit, here it is;
http://awc.org/codes-standards/publications/wsdd-1986_1992revisions
Notice that above it on that page is another download of the design strength numbers for different grades and species of wood, grab it as well if you go this route or if you are using my calc.

QuoteYour 6x12 should perform better than a beam built up from three 2x12
No, a built up beam has better distribution of defects than a solid sawn member. At 2 ply there is a 10% allowable increase in bending at 3 ply there is a 15% increase in Fb.

In the design value supplement download above are all the strength adjustments that are made to the "base design values" that are in the tables... aaargh, in fact it just hit me. That publication is divided into 2 categories "Dimensional lumber 2-4" thick" and those base design values, and then "Timbers 5"x5" and larger. The timber category takes a heavy strength hit. Go back to that Dougfir in #1 grade, in lumber it has these design values
Strength of the outermost fibers in bending tension (bend a popsicle stick and watch the fibers in the belly of the bend tear)1200psi, stiffness 1.8 (stiffness is most often the limiting factor, not a strength thing, it is a serviceability limit), horizontal shear strength (resistance to ripping a check down the length of the board under high load)180psi.

Now those values in a #1DF heavy timber
Fb-1350, E-1.6, Fv-170
Wow, that's odd, in Dougfir the heavy timber IS stronger, in most species I've played with it is the other way around... it is less stiff so there is probably the control, what will limit the allowable span.


.. longwinded edit, sorry should have made a new post  d*



coasttocoast

Thank you for all the great info folks. We do appreciate it.



coasttocoast


coasttocoast

Hello,

We are going with a 6x12 center beam. For ease of installation is it ok to have the beam installed in 7' sections or is it better to have one long 14' section?



Mike

Don_P

The way it was sized was for a 14' clear span... if you install it in two 7' sections it will fall on da floor  ???


coasttocoast

The 7' sections would match up with the pier foundation that run the center length of the house, which are spaced at 7'2". I was hoping to eliminate a post in the living room.

Don_P

Ah, you have several 7' spans and one 14' span? Yes you can make simple spans out of them. I'd be tempted to spline a piece of 3/4 ply or similar between beam ends to help hold alignment as they season.
Weightwise I sawed a 6x12x14' in white pine over the weekend. I slid it into the truck solo, my sweetwife helped unload and put it on top of a pile about 5' tall. This was dead green. Soo I guess by writing that, my leanings are to have as few joints as possible.

When I looked in the WFCM an 8x12 was looking better... pgs 95&96. Chugiak, rereading the above, did a better job at describing beam design, tropical brain bake here  ::). There is also a good series of beam design equations and diagrams in that manual. One to look at is on pg 41, that is the uniformly loaded simple span. The reactions at each end equal half the load, makes sense. Then look at pg 55, a continuous beam over 3 supports. Notice the reactions there. Each end post takes 3/16 of the total load and the center post takes 5/8 of the total load. The design example on pg 58 is our 14' beam... doesn't get easier than that  :D

I'm assuming there are footings under the piers. Your site has a lot of "fetch" to the wind, keep that in mind.

coasttocoast

Hello,

Well the rainy season has arrived and I'm worried about my subfloor. The build is going slower than expected, with, work, weddings, weather, but we are moving along. The exterior walls are up as well as the bathroom and kitchen walls.

We had a local fella mills is a 6"x12" beam and 2"x10" floor joists. Beautiful wood.

Does anyone know of a good method of covering a build with tarps? I have two 30'x30' heavy duty tarps. The walls ar 12' high.

I still have to raise the central beam, exterior wall sheathing, and floor joists.



John Raabe

#20
Will you be leaving it through the winter? I would think you need to get it under a temporary roof of some kind that will drain water away and also carry your snow load! It will be easy to come back in the Spring and have sagging tarps holding little lakes of ice and snow. Might be time to put a team together!

Have you used a subfloor material that can survive such exposure? Then you might just leave it and see what you have to replace when you come back.

Good luck, John
None of us are as smart as all of us.

ChugiakTinkerer

Many decades ago I was on a crew building cabins and we had a long patch of rain.  The boss's solution was to hang plastic tarps on a temporary structure that was supported by vertical braces and ropes strung in the trees.  This was just to keep rain off the foundation and crew and would not have held up to any amount of snow or wind.  John's right, the best thing would be to get a roof over the structure.  Tarps rigged for over-wintering could end up being worse than doing nothing by channeling and pooling the water.  Were I in your shoes I'd call in whatever chits I have and at least get the roof sheathed, if not with roofing applied.
My cabin build thread: Alaskan remote 16x28 1.5 story

Bridge Boy

You have a very nice build in a beautiful location.  Like John and ChugiakTinkerer suggested, I would somehow complete the roof with sheathing and even a temporary roofing material.  It would also be great to at least sheathe over all walls.   I think you are at a point where you would observe a lot of weathered material by using tarps over an extended period of time.

Wish you well,

BridgeBoy

CabinNick

Your build is looking great.  I am curious about your floor plan.  Are you going to enter through the "boot room" into the living/dinning area?  I have been planning the same but thinking of putting the mud room on the long side of the building.  Also have contemplated having the mud room enter into a hall that would replace the bedroom and hall closet in the plans (i.e short hallway between the bathroom and bedroom).

coasttocoast

#24
The tarp thing is only temporary. I have to leave for a week long shooting gig and I want to keep it protected. For now the tarp is draped over the sides and it is funnelling the water out the front and back window openings. So I do have a dry work space. Tomorrow I'll complete the wall sheathing. My wife came up with a neat way of raising the plyboard into place on the 12' walls with some staples and paracord. So far it works great.  (I'll explain that another time).

Yes I will have a roof on this season. Honestly I am a little intimidated by the thought of doing the roof.

As for CabinNicks question. Yes we will be entering through the boot room into the living room. The left wall runs the full length to the rear of the house. The bathroom is mid way down the right side and shares a wall with the kitchen in the rear right of the house. There are doors on both the left and right walls, one into kitchen and another into the dining area.

It's almost 4am and it's raining pretty good and the trap is keeping 95% of the floor dry. Looking forward to tomorrow.