Building a porch with log posts for a yurt

[ErieBuoy]

I've been a lurker for a long time and have learned a lot from you guys using the search tool.  However, I have a fairly specific scenario that justifies me to come out of hiding.

Last summer I built a yurt on our property in NW PA just a few hundred feet back from the shore of Lake Erie.  Here's a photo:


This summer, I'm going to build a porch, but one of the drawbacks of a yurt is that you can't attach anything to it.  So, I'm essentially building a pavilion very close to the yurt . . .  In any case, I plan to use ash logs that came down in a recent windfall as the posts.  They are long and straight and plenty long.  See the following drawing for details.  I didn't put any dimensions on it, but the posts form a rectangle of 12' x 16' and the rafters are 4' on center.  I plan to use 4 x 8 for the beams and 4 x 6 for the rafters.  I'll use 2" T&G for the roof sheathing.


I'd like to make the center post that supports the ridgepole be one log that goes all the way up (about 14' from the deck to the peak).  If I do that, what's the best way to join the beams to the post?  The way I've drawn it makes the most structural sense, but I don't like how the log will have to be cut.  One solution might be to bore a slot out of the log for the central beam, but I don't think I've ever seen that done.  Any suggestions about this, or suggestions in general about the porch?

Here's a top view so you can see more details.  The deck will wrap all the way around to the other side which faces a creek, but I won't get to that this summer.  Thanks for any advice!

[Don_P]

 
First, powderpost beetles are going to go wild in the ash if you don't treat it. I'd use a borate solution with glycol and multiple wet on wet coats.

Are you locked on having a ridge supported by midposts? I'd be tempted to build 2 trusses on 4 posts and run purlins horizontal across them. The decking would then run up and down the roof

[speedfunk]

Glad you came out of hidding   Nice looking yurt...I'd love to see some interior pics if your willing to share  

Really like your deck shape too.

Most people seem to want an overhang in the door opening of their yurts I've noticed.
very cool.

[ErieBuoy]

@Don_P:  Do you buy borate solution from pest-control places -- trade name Boracare? 

@speedfunk:  Thanks for the kudos -- overhangs are a key design feature left out of yurts, guess it didn't rain much on the Mongolian steppes . . . There isn't much inside yet, I hope to put a radial wood floor inside and build a loft.  Will share photos when there's something to see . . . meanwhile, you can see some of the build photos in this gallery.  I have a lot more photos, but haven't found the time to get them presentable yet.

[Don_P]

That is the standard borate/glycol solution. If you download the MSDS notice that the borate is DOT and the glycol is common antifreeze.

I use a formulation that was first published in the Journal of Light Construction some years ago. Solubor is chemically the same DOT in Boracare. It's an ag boron ammendment for soil... boron is a micronutrient required in tomatos, peppers, etc. Solubor comes in 50 lb bags and sells for between $1-1.50/lb here. Some farm supply's will bust a bag and sell small quantities. I buy full sacks and often have to divvy up mine among friends.

A 10% solution is 1 lb/gallon of water, it is stable at room temp but clean any sprayers well when done. I usually mix between a quart and a half gallon of antifreeze per 5 gallon batch. The glycol is simply a wetting agent, the longer and wetter you keep the wood the deeper the borate diffuses into the wood. I've kept a really buggy old log cabin wet for a month. Most fresh wood I dip for several minutes. Borate goes into green wood much better than dry wood, it travels on the wet. I skip the glycol if the wood is fresh, that mixture is then just DOT and water , commercially sold as Timbor. In all of these trade names the active ingredient is the same, DOT. For wood that is drier you need glycol to get it in. Antifreeze is toxic but does eventually dry and is the cheapest most readily available glycol. If there are concerns RV antifreeze is propylene glycol, non toxic, remember all we need is some glycol to slow drying. Shellgard uses PEG, polyethylene glycol, read the ingredients on a can of Dr Pepper. If you've ever had GI work done you probably remember chugging a drumful of PEG. Another PEG, PEG 4000 (big chemical chains) is a wood stabilizer, helps prevent shrinkage and checking. It is quite costly and requires heat though, woodturners sometimes use it to keep large green turnings from checking. One log home company was using it on their logs.

If I'm just going to hit something once I'll mix a saturated solution at 15% (warm water helps when mixing either) 1.5 lbs/gal. If you've ever made rock candy you've made a saturated solution. Use all of this that day, it'll crystallize.

Borate has low mammalian toxicity but do use care, plastic under your work or make a tank. I have had a small spill where I was dripping as I pulled wood out of the tank, although it is a micronutrient it doesn't take much at this rate to kill grass. The deer have excavated that spot licking up the mineral.

There is another old navy recipe using boric acid and borax... can't remember the formula off the top and it requires cooking.

Don't forget to brace the posts, you have a sail up on stilts.

I think in all that I neglected to answer the question, yes Boracare will work fine.

[ErieBuoy]

Holy smokes, Don_P!  That is a most excellent response and far more information than I had a right to expect.  Thank you very much.  As Boracare seems pretty expensive ($100 for a gallon of concentrate), I think I'll go your route -- and even if I didn't, having such a concrete idea of what the stuff contains is quite satisfying.  Thanks also for such specific mixing and application instructions.

I think that I'll open a can of worms (so to speak) with this next question, but since I'm the new guy (and purveyor of bad puns) I'll just bore (ha!) ahead.  I have been thinking for quite some time about leaving the bark on the ash posts.  I've searched many a forum for discussions of this, specifically for first-hand accounts of either where it went right or where it went wrong.  I really didn't find much, but most people suggest not to do it although from the sounds of it, they haven't tried.  However, that's still enough to make me hesitant, but not fully convinced it's a bad idea.  Then, I saw this book which shows a picture of a porch that uses bark-covered ash posts!  I bought a copy of it hoping it might contain more information -- of course, beyond the photo, it didn't really tell me anything more (although it is full of very fine ideas and architecture p*rn . . .).  Here's the photo:



Do you guys think that those posts are full of bugs (it's in upstate NY) and not going to last more than a few years?  I've considered writing the author and asking him to find out how they are holding up.  

Using a fairly sharp drawshave, I debarked some ash posts that I'm going to use to hold up my loft.  These had been sitting off the ground for a year, outside, and I was surprised at how tight the bark still was -- compared to cherry, the ash bark was really well attached and required a lot of elbow grease to peel it off.  In fact, it never really peeled like the cherry did, it came off in much smaller pieces.  I did see some bug tracks under the bark -- most likely the emerald ash borer.

Do you guys think that borate solution would kill the insects (powderpost and/or ash-borer) if applied to a log with the bark still attached?

[Don_P]

I've never tried it with ash, but with any species that is where the majority of the food is concentrated, the cambium layer right under the bark, sugars. A big variable in how tight the bark is is the time of year. The bark in spring "slips" as the cambium divides to form a new growth ring. At the logging deck some trees can squirt right out of their bark at this time of year. I've removed a 2' diameter poplar from its bark in one sheet in spring. The bark is getting tighter this time of year and is glued down good by fall. My pines have gained 1/2" of girth in the past month or so, the light part of the annual growth ring. The dark part of the ring will be laid down over the rest of the year.

If you can poison the food supply to keep the bugs out and if they were felled at the right time you may have some success. You will not be able to easily see if the ash is getting buggy and will also have a harder time getting borate into the wood. Ash is pretty starchy, that is what the PPB's are looking for in the sapwood.

Aside, to wrap up the comments from above; Sugars are instant energy, starch is stored energy. Starch is a sugar molecule twisted a little, the tree can convert back and forth between sugar and starch. Cellulose is built from starch. Unwind that and you'll feed the world and never run out of energy.

Bark on is in general a bad idea... it does look cool though.

[ErieBuoy]

Are you locked on having a ridge supported by midposts? I'd be tempted to build 2 trusses on 4 posts and run purlins horizontal across them. The decking would then run up and down the roof

I'm starting to think that's a better idea.  What's the typical way to create a flat on the beam to fasten the decking?  Do people rip the beam and purlins, or do you rip a 2x4 to the right angle and attach the 2x4 to the top of the beam/purlin? 

Thanks for all the advice so far!

[Don_P]

Normally, rip a flat on the top surface of the log. If you don't have the means to do that you can also use a level at each end to mark a plane, chalk lines down each side and power plane or hew the flat.

[ErieBuoy]

I am planning to use rectangular (4" x 8") beams.  Besides a band-saw, what's the best way to rip a flat on these?

[ben2go]

Great yurt.Is it a kit or did you do all the work and sew the cover? 

What will you do about snow sliding off the roof and on to the yurt? 

[Don_P]

You can have a bandmill come in, haul them to a stationary mill or use a chainsaw mill. OlJarhead has some pics of one in use on his build thread.

[ErieBuoy]

Great yurt.Is it a kit or did you do all the work and sew the cover? 

Thanks!  This is a kit from Rainier Yurts.  I would have liked to build more "from scratch" and will do in the future (starting with the porch!) but being able to get it warm and dry in a short amount of time was a big benefit at this point in our lives.  We liked the price/sq.ft. and uniqueness, but there are some downsides that could have been avoided had I built a "real" cabin.

What will you do about snow sliding off the roof and on to the yurt? 

Unless I'm missing something, I think that the snow would have to "fall up" to slide from the porch roof to the yurt (or at least fall "sideways").

[ErieBuoy]

I'd like to place an order for beams and from the closest sawmill I can have four choices, all green:  red oak, white oak, hard maple and soft maple.  Any reason not to get oak?  Which species (red or white) would be preferable?  I used Douglas Fir 4" x 8" to support the yurt platform, but they were like $6 or $7 per linear foot -- the white oak is more like $2 per linear foot.  The Doug Fir was certainly easy to get fasteners into, is that going to be a problem with oak?

[Don_P]

Oh yeah. Of the choices white oak is considered the most durable wood, that would be my choice as well. prebore for screws or lags ~80-90% of the root diameter of the screw, the diameter between the raised threads. Try a sample and fine tune the diameter. It is easy to break lags in wood this hard. White oak dries at the same rate that glaciers melt, in antartica, prior to global warming  . Red oak is considerable softer, dries faster, shrinks less, is not decay resistant. The maples are less decay resistant still. I wouldn't consider them outdoors. Hardwoods shrink more than softwoods, expect movement and checking as it dries.

http://www.fpl.fs.fed.us/documnts/TechSheets/HardwoodNA/htmlDocs/quercussp.html
http://www.fpl.fs.fed.us/documnts/TechSheets/HardwoodNA/htmlDocs/acersp1.html

[ErieBuoy]

Thanks for the quick reply, Don.

White oak dries at the same rate that glaciers melt, in antartica, prior to global warming  Grin

Does that mean that an upside to global warming is faster timber drying times? 

I just got off the phone with another mill that has hemlock available.  From what I understand, that's more rot-resistant that the oak -- is it easier or more desirable to work with?  I guess that it also may be less prone to twisting as it dries?  It's about 2/3 the price of oak, but since I don't need a lot of beams, price isn't such a big issue for this project.

So, white oak or hemlock: as someone with knowledge and wisdom, which would you choose?

[Don_P]

  no doubt, it'll dry quicker!

Be real clear with the mill that you will not accept any shake. Hemlock is notorious for shake. Look at the end grain carefully for black rings or portions of rings that are black and seperated. As the wood dries these open up and the timber comes apart. It is called wind shake but is really a slow moving soil borne bacterial infection that moves up from the roots, smalls alot like cat pith. (often root damage caused by grazing livestock in the woods) The rot resistance of hemlock is largely a well established wives tale but don't bother getting into an argument over facts  . It does have lower shrinkage and is easier to work and to lift. It is sufficiently strong to do the job, will move less and is less decay resistant... if you keep it dry it'll work fine. Notice the shrinkage numbers for the different species in question, you'll dry down to ~12% covered and open to the air. a big spread in radial and tangential = more checking. Specific gravity is a pretty good indicator of strength and weight, MOE is stiffness.
http://www.fpl.fs.fed.us/documnts/TechSheets/SoftwoodNA/htmlDocs/tsugacanadensis.html