Exposed beam question

[RIjake]

With my project waiting for the thaw I'm home working out all the details in my head.  

I really like the look of the exposed beams like those here http://www.countryplans.com/vc.html. I'm wondering if the beams in this project are attached to a ledger board just like you would if using standard 2 bys or are they held up by a jack stud arrangement of sistered 2 bys?  I see the steel brackets in the photos, are they just lagged into a ledger?

Am I correct in assuming that this detail is not shown in the plans for the 20x30 1  1/2 or VC plans?

Now if there's one thing I've got on my land it's trees so I'm hoping that I can use them as the beams for the loft.  I've done quite a bit of research on the web regarding using green beams and letting them dry in place.  I've seen conflicting opinions on this.  I won't be using a traditional mortise and tenon but an angle steel hanger.  Checking isn't a concern for me but with time a factor I can't afford to put off the project while I wait for the beams to dry outside.  Other options are kiln drying my lumber, which involves extra cost and down time or using beams purchased from a local mill.  I'm having a hard time with the latter.  I don't want to pay for something that I can get for free on my own land!

Any thoughts?

[Don_P]

Structurally there is probably not an issue with the beams themselves being green when installed and drying in place. I've built with plenty of material that had birds in it the week before. It's certainly not ideal but as long as you know what to expect. Green timbers have roughly half the strength of dry but normally you are not into design loading during construction... just bear in mind, don't stack a pile of materials in midspan. They will check and possibly twist, this is more of a serviceability issue than a structural one, the floor above may squeek and not be flat in the end.
The connections to green timbers that subsequently dry can lose as much as 70% of their strength so that needs some thought.

[RIjake]

Anyone else?  How about the ledger board question? 

[John Raabe]

In the Victoria plan the main roof beams have dedicated support posts with solid bearing all the way down to the foundation. These are built-up posts. The spaced loft beams are supported either off a ledger let into the studs or by brackets off an exposed beam. At the wall, this support is similar to the loft rafter supports on the balloon framed walls of the 20' wide 1-1/2 story plan.

There are details for these connections shown in each plan set.

[RIjake]

Thanks John,  It's looking like I'm going to go with the 1 1/2 story plans and just use built up posts running right down to the piers of the foundation.  I want to have a second floor the full length of the house.  I'm thinking spaced timbers across the width of the house with 2" hardwood exposed below for the decking.

Depending on how the lumber market is this year will dictate if I buy timbers already dry.  Between my neighbor and me we've got a decent job for a logger so there could be a barter opportunity there.

[John Raabe]

That will be very solid. A beam and deck ceiling is very handsome. Be sure to think about any plumbing issues at a loft level bathroom (ie: consider a wall hung toilet). P-traps poking through the decking kinda spoil the look.  Also be fussy about the decking materials. Straight and dry is what you want and then install it with a good set of clamps. I've seen projects where the shrinkage was enough that the kids would drop dimes down through the cracks in the decking when they were bored.

[Don_P]

If your talking about waiting possibly a year for the market... then you do have the time to allow green beams to do an awful lot of air drying. Saw or buy them now, sticker and cover the top of the piles, they'll either be dry or a whole lot better than dead green when you need them.

[RIjake]

Don,
I want to start building as soon as I can get in on the land.  There's still plenty of snow in the woods, gonna be a while yet.

[RIjake]

I haven't had any luck in finding load and span data for 4x8 hardwood timbers but I'm figuring 4' centers with 4"x1.5" T&G plank should be plenty solid for just bedrooms.

[John Raabe]

A 4' span on 2x6 T&G is standard. I've seen 5' + done with a subfloor screwed to the decking topside.

[Don_P]

For timbers less than 5" thick you can use the AWC spancalc for some work.
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
For instance if the proposed joists were 3" thick and 24" on center you could use the table entries for 2x material at 12" centers. Likewise if it were 3" thick and 32" on center the entries for 2x on 16" on centers would work. At 5" and thicker a different set of design values are used so heavy timber should not be checked with the AWC calc. I have span calcs for other situations but it does take a good understanding to use them.

[RIjake]

Don thanks very much for that info! 

I think for it to look "right" I'm going to have to go with 6x8s though.  I have not been able to find a span calculator online that will tell me if a 6x8 hem/fir timber will span 20'.  I'm guessing there won't be an issue(?)

[Don_P]

You can download the WSDD manual from the awc.org website. That dimension is too small in that species at 4' centers. Can you go deeper or put a support in the middle?

[RIjake]

I'm really trying to avoid the center post if at all possible.  How about if I went with a 4x12? 

I believe that's what was used on this http://countryplans.com/smf/index.php?topic=6311.msg116600#msg116600 house

[Don_P]

Hi Jake,
I looked in the NDS supplement of wood design values (The strength tables of various species) and the WSDD manual (Safe load tables for various wood strengths) hoping to find something that would work in "official" referenced tables. Unfortunately eastern hemlock is below the WSDD's lowest strength listings. I used my simple beam calculator, which is not "official". http://www.windyhilllogworks.com/Calcs/beamcalc.htm

20' is a long span and hemlock is not a particularly strong species, you're taking a hit from both ends. It took me a 6x12 full dimension to make it work at 4' spacing. I took a screen shot and will explain how to use it in case you want to try other options.


The load is calculated by taking the clear span X the joist spacing which gives the square footage supported by each joist. Then multiply that by the total load per square foot. The minimum load for a floor is 30 pounds per square foot Live Load ( the weight of people and furnishings) + 10 psf Dead Load (the self weight of the floor system itself)... or 40 psf total load.

Your clear span is 229" (20'...240"-two 2x6 walls) 229"/12"=19.08'
Multiply 19.08' x your desired 4' joist spacing =76.33 square feet supported by each joist. Multiply this x 40 psf= 3053 lbs bearing on each joist.

The span, width and depth inputs are self explanatory, use the actual lumber dimensions.

The last three inputs relate to the bending strength, the stiffness and the shear capcity of hemlock in a #2 grade.

The outputs show it passes well in bending strength, deflection is very close to maximum at about 5/8" under full design load, shear passes easily.

I've been working with some 20' 6x12 white pine that is pretty dry. It's not bad for two people to handle. If green it'll be a handful.

[John_M]

I used 4x12 Hemlock beams for my 18X32 structure.  The beams were green when I installed them.  After about 4 years or so everything looks good. 

I originally was going with 6x8 beams, but my building inspector advised me to go with the 4x12 beams.  I do want to mention again however that my structure is 18 feet wide where as yours is 20 feet wide!!

I'll try a dig up a photo if I can.  I think you can see what we did at my blog:

www.ourlittlecabin.blogspot.com

[RIjake]

Don, that's exactly the info I needed.  Thanks.  I saw that calculator but didn't know what all the values represented.

After more research, eastern white pine is what's predominantly sold in my area in building centers.  I'm sure if I went with a small local mill I could get whatever I wanted.

I'll run some numbers with the pine..... 

[RIjake]

I just ran the calculations and a eastern white pine 6x12 passes all categories.  Looks like that's what I'll do!

Thanks Don and John for the help