Shed Design

[bigmish]

I am building a shed that will be used for a sauna with a front changing room. It is a heavy modified Sobon shed. The joinery and dimensions are taken directly from texts including Sabon's and Gruber's books and discussions and postings on this forum. It will be made of green white oak.

I've included a rendering of the building and a detail of each of the joints. I'd like to build directly off of these. My questions are these: should I really submit these to an engineer? Do you all see and problems with the size or layouts of the timbers or the joints?

Thanks again for all your help, Mischa

Buiding:

Detail 1:

Detail 2:

Detail 3:

Detail 4:

Detail 5:

Detail 6:

Detail 7:

Detail 8:

[Thomas-in-Kentucky]

Mischa,

We built a frame like this in the Grand Oaks Timber Frame workshop that I attended (12x16), and the posts were 6x6's, not 8x8's.  Our rafters were also 6x6's, not 8x8's, but then again, the end bents had collar ties.  You could buy plans from Grand Oaks, or you could build what you have and feel pretty confident that you could park a dozer on top of that frame when you're done.  With the timber sizes you have chosen, there is a lot of room for sub-optimal joints that are still overdesigned for what you need by a factor of 5 or 10.  That's what I did for my house - we call it "gothick" architecture, not to be confused with gothic architecture. 

The only suggestion that I have would maybe be to make your dovetails taller than 3.5".  I think it's better if the bottom of the dovetail (major stress concentration) does not fall exactly in the middle of the beam it is supporting.  You could fix this by 1. housing the dovetail joint (a lot of unecessary work I think, but we did it in the workshop), 2. increasing the height of the dovetail to say 5" or 6" - especially if the receiving timber is 10" deep (which looks to be in your case), 3. adzing (or skilsaw and kerfing) the ends of the 5x7 joists so they are maybe only 5" tall at the ends.  (Sobon describes option 3).  I chose option #2 for my house frame.

and another little trick I used that works well - url=http://massiehouse.blogspot.com/2006/01/dovetail-details.html]wedging the dovetails so you know they'll fit...(active links to off site pictures are not allowed, modified by moderator)(if you wish to see this copy the above link into a browser)

One more thing... You might want to put some braces from each bent post to its corresponding girt.  Even though your timbers are plenty big enough, the frame will still rack (sway, lean, whatever) if you don't have sufficient bracing.

-Thomas

PS.  I have only built one frame in my life, other than the one in the workshop.  So please get some other opinions.

[Max sawdust]

Nice post! Mischa
I am by no means an expert, but consider shouldering those birdsmouth joints.  Really does not take any more effort.

I am some what of a Sauna expert.  If you need help or reference with the bench height or internal layout let me know.  You putting in a wood stove?  If not you should strongly consider it.  It is the very best for a proper Sauna..
Max

[bigmish]

Thomas, thanks for the catch: I forgot to unhide the layer with the braces ;)
I've updated the above image to include.

Max, I'll post up a model with the sauna benches and stove later (and yes, definitely plan for a wood stove – any less and it wouldn't be a sauna!). Would love to pick your brain some on the details once I get to that point...

Got to sign off now, but will review and incorporate your and Max's suggestions ASAP.

Thanks, M

[Max sawdust]

Mischa,
A great book on Sauna design is:
Finnish Sauna, Design, Construction and Maintenance.
It is put out by The building Information Institute of Helsinki.  Published by Rakennustieo OY (The Finnish Building Centre LTD)

This book has it all for bench layout and design, wood types and so on. 

Remember do not use any Pine on the benches or wall or you will get burned by the pitch
White Cedar, Red Cedar, or Redwood are the best for benches, there are others that will work too.  Make sure to get a wood stove that will hold lots of rocks.  (The rocks should be chunks of soapstone too..

Any way enough for know, back to my TF shed!
Max

[landrand]

Curious as to what you plan to use for the wall system and insulation?  I've been thinking about building a sauna as well.  Haven't decided yet if I should do a timberframe sauna or use a dovetail square log type sauna.   

[Max sawdust]

Curious as to what you plan to use for the wall system and insulation?  I've been thinking about building a sauna as well.  Haven't decided yet if I should do a timberframe sauna or use a dovetail square log type sauna.   

Wall systems and insulation on a stick built or TF sauna requires lots of thought.  (Lots of heat and moisture at work) 

Personally, I like the idea square log.  (built one, using red cedar 4x4's on the cheap)  With a proper size wood stove in a sauna, a not perfectly sealed building is actually a benefit to the environment inside the sauna. (In my opinion)  Additionally if you are using a non-pitch type of wood such as white cedar you have your finished interior walls already done, which saves money.

If you are serious about building a sauna, try to find the book I referenced above.  Lots to consider with venting bench heights and stove selection, to get that really good sauna  environment that is hard to find here in the states.

Max

[landrand]

I think I read the finnish sauna book you mentioned above.  I was suprised when author indicates white pine is a desirable wood for sauna's.  Most people around here, Northern Michigan, use white cedar T&G on a stick built walls.  Because I have all kinds of white pine timbers, I thought it would be a good project to build a dovetail timber log sauna out of white pine.  Since chinking isn't recommended on the interior of sauna's, I would need to build the log walls with no chink space.   I'm new to log building,  I don't think I could acurately cut the dovetail corners perfectly so the timbers rest on each other with no space.  The other alternative is to apply 1" T&G boards, perhaps cedar, over the log walls.  But, who wants a log building covered with 1" boards.

With a TF sauna, it would be visually nice to have the timber posts exposed in the sauna room.  Unfortunately, that isn't good for the wood posts.  I figured I could insulate the sauna similar to the "wrap and strap" Timberpeg solution.  See link below.

http://www.timberpeg.com/about-product.html

Any other ideas would be appreciated.

[TW]

I am not a sauna expert but I live in the wold center of saunas so I know a little.

About Finnish spruce and log buildings.
I think that it is harder than most spruces and there is not much resin in it. It is good for logbuilding in general and for saunas in particular. Our spruce has a tendency to twist so the walls need to be pegged a lot in log buildings. The traditional log building method is that the logs are hewn flat on two sides and the round edges are scribed together. The corners are either dovetailed or double notch. I use flax fibers between the logs and I have seen them used in log saunas as well. I can hardly understand why the Scandinavian method of log building has not spread furter abroad. It is not difficult at all, only terribly time consuming. Still it is said to be much faster than scribed round logs.



Present day saunas
The walls are often stick frame with insulation and a moisture proof membrane on the inside. The inside is covered with spruce tongue and groove boards. Between th boards and the moisture barrier is a air gap with vertical circulation. The ceiling is made horizontal with boards and air cirkulation behind them as in the walls. A wood stowe is considered the best heating. The bench tops and everything else that is intended to be touched is made from either aspen or a imported wood sold as abachi. Exposed nailheads and screwheads are avoided as far as possible because they burn the skin. Still many people prefere log built saunas (spruce logs). It is important to use a kind of caulking that dries well in a log sauna. Only a few boneheaded conservatives use chimneyless saunas theese days.

Rakennustieto use to have excellent information in everything they publish. It is a shame that most is only in Finnish. ( I belong to the Swedish minority)

And then a bit off topic about the old time saunas as the old people tell.
It was a square one room log building of spruce logs. The logs were hewn to 4" or 5" thickness and the edges scribed (normal log building method here).  They used moss between the logs so the walls rotted, starting from the caulking. The door was low but the sauna could be high in itself. The ceiling followed the roof pitch. The floor was packed earth with a few boards to walk on. Heating was by a big oven without chimney. They had some hatches in the walls where most of the smoke could get out. The oven was built with very little mortar so the smoke seeped out through the top. They fired first and then they bathed when the fire was out. In fact they used the saunas for smoking meat as well. No wonder that the lice did not survive.

[Max sawdust]

I think I read the Finnish sauna book you mentioned above.  I was surprised when author indicates white pine is a desirable wood for sauna's. 
I don't think I could accurately cut the dovetail corners perfectly so the timbers rest on each other with no space. 

Landrand,
I am pretty sure the book I mentioned did not recommend pine for area's skin will touch.  (But I could be wrong.)  If it did the book is wrong, and you fine folks in the state of Superior got it right ;)  I notice TW mentions Aspen as a good wood for Sauna's too.  Not sure about you but I got the stuff coming out of my ears.

It is my opinion a sauna would be the perfect project to hone your log building skills.  a couple of gaps will not hurt anything but your pride.  TW mentions the Scandinavian method it could be fun to give it a try.

TW
Thanks for the great advice from the world center of saunas :D  Did you know that the UP where Landrand is writing from is a major Scandinavian immigrant area.  The country side even looks a little like Finland and Sweden.  I have seen log structures built in the Scandinavian style there.

Only a few boneheaded conservatives use chimneyless saunas theese days.
No wonder that the lice did not survive.

Mita?
Bone head conservatives  :-[   I would say bonehead traditionalist  ;D  I happen to like smoke saunas.  Then again I like Terva soap and shampoo :D  Something about that low ceiling pitch black room with a big pile of heated rocks.  It is very primal, and well suited to prepare a person to jump through the hole in the ice  ;)
Maybe you do not care for it because you are Swedish minority
(Sorry I have many Finnish friends, some of them from the Swedish minority, and we always joke about these things.)

Max

[TW]

Max sawdust
No need to beg pardon. Life would be dull without irony and sarcasmn.

A thought about aspen: I am not sure if American aspen is similar to north European aspen. Ours is very porous and soft, splits easily, usually straight grown and tends to rot from the inside. It is the poriosity that is important in this case.

If I build a sauna for myself some day and have time and money to do it well it would be a log sauna with wood fired stove. Spruce logs and flax fiber caulking.

No I did not know about the lot of Scandinavians in Michigan (if that is what MI means). What is UP?
I too have relatives somewhere in the area south of the Great Lakes if I have'nt gotten it wrong. We have lost contact.

[landrand]

I don't believe the Finnish Sauna book recommends white pine for benches, but it did rate white pine logs as a suitable material for sauna log walls.   White pine being relatively easy to work, somewhat decay resistant, with good thermal properties.  I've notice when I mill logs that been sitting around in the weather for a few years, white pine is much more decay resistant than other pines such as jackpine and red pine.  Other than some blue stain and bug holes, there is minimal rotting.  Aspen/Popple and white cedar is usually used here for benches.

I need to look into the flax fiber caulking for the gaps between the logs.  If that is the way to go, my next project is to build a jig to make all those dovetail corners with a chainsaw. 

Yes, I'm a finlander that lives in the Upper Peninsula of Michigan.  Although I've never been to Finland, I've been told this area is very similiar to Finland.  Lots of lakes, trees, and plenty of snow in the winter.

[Max sawdust]

TW,
I think our Aspen is very similar. We have two types Big tooth and Quaking.  Both have similar qualities that you mention and they are very light and porous.  (Does not get hot to the touch.)

Landrand,
I need to try Aspen in the sauna.  The one I use now is full scribe white cedar log with white cedar benches.  (I did not build it).  The area south of Marquette with lots of exposed bedrock really reminds me of Finland.  I worked for a Finnish company in Tuusla for almost 20 years had to travel to Finland 2-4 times a year during that period.  Good people I like it, try to get there someday.
Max

[TW]

About the flax fibers

When they process flax to yarn they cannot use the short fibers. That means that short fibers (called blånor in Swedish) mixed with some straw is a major biproduct that they have hard to get rid of.
The flax we have used on the two loghouses I have been working in has come from a local factory and costed 20 euro (24 $)per bale. The consumption is about two bales for a one family house. A bale is as big as two men can handle. There is a factory that makes strips of flax insulation intended for logbuilding but those are very expensive so I have never used them. We fill the long grove with flax as the oldtimers did with moss. We block up the log so ther is a 1"gap under it and fill with flax and remove the blocks and bang down the log and peg it. The peg holes must be drilled before the flax is inserted. Otherwise the flax will wind up on the drill and jam it. It took two hours to get the drill loose once.
The flax does not hold moist like rockwool does. In fact it seems to dry better than moss too. It does not seem to mould fast either.

I am not a very experienced logbuilder but this seems to work and others have used it before me with no problems so far.

[bigmish]

landrand
In answer to your questions about the insulation: I plan to add another post detailing my plans for the insulation and walls once I finalize the timber frame structure. I plan to do similar to the "Lap Strap" method on the website you mentioned.

[landrand]

The book I have on Sauna building is "The International Handbook of Finnish Sauna", by Allan Konya and Alewyn Burger.  It is a very good and detailed book on building sauna's.  In one section, the authors list the properties of various wood types and it's suitability for Sauna construction. 

For N. America, they list the following timber most suitable for sauna construction in order of preference:  Eastern White Pine, Sugar Pine, White Cedar, Ponderosa Pine, Western Red Cedar, Incense Cedar, Redwood, and Western White Pine. 

Wood NOT suitable for sauna construction is listed as follows:  Silver fir, English cedar, Alaska cedar, Yellow cedar, Easten red cedar, European larch, Western larch, Jack pine, Pitch pine, Maritime pine, Pond pine, Southern Yellow pine, Virginia pine, Baldcypress, and Swamp cypress.

[FrankLad]

Hey Bigmish!

Nice design there!  My dad and I built a shed recently that is very similar to this (also based on Sobon's).

I was looking at the braces between the middle posts and side girts and they don't look necessary given the timber size and 16' length BUT that is only my opinion. 

[bigmish]

Yea, I see what you're saying: the end braces are all that's needed to arrest the racking. Interesting....
Just looked at Sobon's and he dosn't use them.

Thanks FrankLad!

Any pics of that shed you built?

[bigmish]

Thomas-in-Kentucky, I think I'll go with your option 2 and increase the depth of the tenons to 6".

Max sawdust, I've looked through several books and can't find any that describe a shouldered birds mouth. Can you direct me to a book or website or perhaps post a picture of one you've done in the past with dimensions?

Regarding the sauna posts
-   I've purchased Spas and Hot Tubs Saunas and Home Gyms and will let you know my thoughts once I receive. Anyone read this one?
-   I looked into Finnish Sauna: Design, Construction and Maintenance but I could only find it for 35.00. I'm hoping the book above will cover all the topics covered in this one so I don't have to shell out the cash
-   I'm going to make an other post soon with the sauna plan (with bench layout, insulation, etc.) and look forward to all of your feedback on that

Thanks all, Mischa

[FrankLad]

bigmish:  I have some pictures of the shed in my gallery here:
https://forestryforum.com/gallery/index.php?cat=12895

However, I've been lazy and haven't uploaded the rest.  It has long since been finished with lapped cypress siding, metal roof, etc.

[Max sawdust]

Steve Chappell's book "A Timber Framer's Workshop: Joinery, Design & Construction of Traditional Timber Frames"  shows how to design and cut a shouldered birdsmouth.  My thought is having a shoulder to carry some of the weight is a good thing.  Here is a pic of a template being held on a post cut to receive a shouldered birdsmouth. 

max

[bigmish]

Cool, thanks. haven't seen this before.

Not sure about it though, seems like the force from the rafters is directed out at a 45 degree angle and not down perpendicular to the ground. I suspect that this is why they aren't seen more often.

Any one else used these, have any thoughts?

[Max sawdust]

By all means I am NO expert, just in the EARLY stages of learning!
Max

[Jim_Rogers]

This type of design, rafter foot to post top is truly a contemporary design. It was never used in traditional timber framing designs.

In traditional timber framing the rafter always sits on either a tie beam above the plate or on the plate. And most rafters were common rafters. Or if there were principal rafters (at each bent) then there were common rafters in between. Unless these principal rafters had purlins in between. As you can see there are many types of roof systems.

The outward pressure on a post by a rafter foot is called thrust. Your design has to reduce or eliminate the thrust to a level that the post can withstand. This is done by securing the rafters to each other at the ridge, adding a supported ridge beam and hooking the rafters to it with joinery, adding king posts, adding queens posts.

You also have to limit the length of post above the tie beam and make sure that the tie beam to post joint is strong enough to resist the thrust. And that the area where the tie beam goes into the post doesn't weaken the post to the point where the rafter thrust pushes the top of the post over or breaks it off.

These are all dependent on the slope angle of the roof, the lower the slope the more thrust is pushing out, as gravity works on the roof.

There are lots of things to consider......


Jim Rogers

[landrand]

Bigmish,
Was wondering what computer program you use to develop drawings of your timberframe plan?