open beam for cathedral ceiling

[nanook]

I want to build a cottage roughly 30'x30' with the front part an open space kitchen and living/dining room. I would like this space to have an open cathedral ceiling. It has been suggested that I use scissor joists but I would like to create my own beams etc. Can anyone point me to pictures, plans, info, on this type of project. I have a wood mizer and saw my own lumber so I can produce whatever lumber I want. Thanks for any suggestions anyone can give.

[icolquhoun]

sounds like a nice plan, however 30' is a pretty serious span!  Do-able, but if you don't have a good working knowledge of statics and figuring out load paths, I'd recommend you contact a qualified designer/engineer.  It will indeed have to be some type of truss, and which type depends on the look you are going for coupled with roof pitch and how you frame the rest of the house below it.  Start looking around online to see what other have done both here on the forums as well as some builders in your area.  I think heartwood up in NS has a few "off the shelf" log homes that have 30' clear spans using either king post trusses or a bay thats 12' wide and supported at both sides using a common purling style roof frame. 

 

[Thehardway]

Nanook,

You are describing the cottage I have built









I used a 25X33 foot print for the span reason previously mentioned.  24-26' seems to be the maximum practical span if anything has to be transported to the site.  If you have a tree large enough on site to make a 30' tie beam for a kingpost or queen post truss and have the ability to handle it then there is no reason you can't do it. Since its only one beam you could even hew it so you wouldn't need bed extensions for your WM.

That said, I used a splined tie-beam so I could use two shorter timbers.  I placed them on ICF walls with extra steel reinforcement and short spans to serve as a sort of buttress and limit thrust and the stress on the spline and dovetail rafter joints.
I am not recommending this, especially with a 30' span, however, it can be engineered.  I would stick with the 24'-26' wide dimension and add more length if you can.  If I were building my house over again I would go to a 24'W X 40' L with 10'OC bents.  The 25'X33' is just a little tight around the kitchen island and spiral stairs.  If you don't need the stairs/loft then it would work fine although it is rather compact for furniture placement  etc.

Notice used pocket doors to save space and there are no halls. All mechanical equipment will be housed outside to save space as well.  We are in the process of completing the inside right now and I haven't got to building the porch yet.  Everything is still in pretty rough form.

As a kid, My aunt and uncle had a 2 bdrm, 1 floor cottage on Lake Erie that turned the floor plan sideways.
It was about the dimensions you describe and a similar floorplan with open living/kitchen/dining.  Turning it sideways allows you to have a vaulted ceiling with exposed beams but your max unsupported span is 16' as posts/support can be used in a center wall.  A nice additional touch to this is a balcony/loft with clerestory windows or even a rooftop deck.

Hope this helps and give you some ideas.  I am more than willing to share plans and info should you like.  This was all my own design work so there are no copyright infringement issues involved.

[nanook]

Thanks to my two  early respondents. All info is helpful. Will consider suggestions and let you know how I am making out.

[Thehardway]

Nanook, I sketched up my aunts cottage from memory.  It is 30'X30'. you would not have any span issues here and framing would be very simple.








A modified version with clerestory windows

[nanook]

Thanks for your work on the second reply. This design is very close to the one I am considering with two bedrooms and bathroom in  back and living space in front. I am O. K. using scissor trusses in back with 8' ceilings but would like the living space to have a cathedral ceiling. I believe my area [Nova Scotia, Canada] calls for r40 insulation in ceilings. My intent is to board in the roof and cover with asphalt shingles. I would insulate up  to this from the underside and then cover with pine paneling which would be what you would see from the living space. Is this possible under your concept and if so, what would the framing and ceiling beams look like? Again thanks for your time and interest.

[nanook]

Just took a more careful look at your plans. My cottage will face a lake and I want the gable end facing that way with lots of glass...similar to the one you built but with a gentler pitch[no loft or ladder]. I guess that eliminates your second plan. Maybe consider scissor trusses with a false set of beams to give the impression of beam construction.

[beenthere]

We put a 24' addition to our home a few years back that has cathedral ceiling and is 30' wide. Mostly windows. The gable end can be seen through the woods.


There is a 24' king beam, 2x12 rafters on a 7:12 pitch. 10" of fiberglass insulation, and cedar ceiling paneling. King beam and paneling shown here before the king beam was wrapped in cedar.

[witterbound]

If I've got the mental picture right, you're not trying to span 30'.  You're going to have an outside wall (gable end & bent #1), which can support the 30' span, and you can have a load bearing wall between the living room and bedroom area (bent #2) that can support the 30' span at several points.  The only thing you're really spanning is the 15' ridge beam, which can be supported by a king post that runs all the way to the footings, can't it?  What am I missing?

[nanook]

Thanks to Beenthere and Witterbound. The pictures of the 24'x30' addition are pretty close what I hope to achieve. I guess my problem is that although I have built quite  a few buildings I have not tackled something like this before. I've always used traditional framing with either trusses or rafters and ridge pole. From the last two replies I believe I can use the gable end with a bent[not familiar with the term so I guess its a support beam] running from the roof ridge to the footing and use my weight bearing wall dividing the two areas of the cottage in a similar manner. These would support a 15' king beam [ridge beam] at 12"x2" or whatever code says. The rafters would then run from the outside walls to the king beam[????].Are there other beams running parallel to the king beam?[ which I guess would be difficult if the rafters run perpendicular to it] Is there no need for collar ties? What would the framing/support for the insulation look like? Again please excuse my lack of knowledge but although I can do a good job of producing projects from plans I have poor ability to visualize things in three dimensions. Thanks for any further help you can give.

[clif]

Just think of your ridge beam (or another beam running parallel to the ridge beam between the ridge and the outside wall) as a really large header that requires support all the way to the foundation at both ends.  The rafters sit on top of the beams.

[beenthere]

nanook
The ridge beam is 18" deep, consisting of three parallel-laminated 3 x 18's nailed together and sitting on 6 x 9 posts to the foundation. After the ceiling panelling was installed, I made three false 'beams' to break up the expanse of cedar board.



Will gladly show more of the construction if you have interest.

[nanook]

Thanks.I guess your rafters ran perpendicular to this beam.What dimensions were they?Attached to king beam by metal brackets?Centers at 16"or 24". What keeps this type of roof from spreading and folding inward?

[beenthere]

Rafters are 2 x 12, and rest on the king beam. The kingbeam keeps the roof from spreading (at least it has worked so far  ;D).
A pic of the rafters going up. 24" oc, no brackets (although plywood gusset plates at top and metal ties at the birdsmouth)

[nanook]

Great pics.....Thanks! Looks like the rafters have birdsmouth cut at top[on king beam] and at the side wall. The rafters were then covered by cedar boards and insulated as you worked your way up[or down]? If your span is 30 feet what is the total length of the rafters?

[beenthere]

Yes, notched at top and bottom. There is a 3' overhang, and I believe the 2x12's were 24' if memory serves me.
Sheathing on top of rafters, foam venting panels, then 10" insulation bats, with plastic vapor barrier, then the pre-oiled cedar paneling.

[Thehardway]

Nanook,

Check out the link for the Glossary at the top of the page.  It will be very helpful in ongoing conversations.  The building that is shown in Beenthere's posts is what is called Post and Beam style construction.  It differs from true TF construction and utilizes engineered lumber and usually has steel hardware joinery vs. mortice and tenon. For the "kingbeam"the correct term for this is ridge beam as you have already identified and it is supported by a ridge post at either end of the span. This is much different than a traditional truss frame or bent post frame.  (A bent is a pre-assembled timberframe section that may or may not include rafters.  They are typically stood up and connected to each other with purlins and girts to form what is called a bay)

Long spans in post and beam construction utilize engineered lumber to reach higher strength values than you would get with solid sawn lumber of the same dimensions. They are also typically quite expensive.  I would not attempt to saw lumber of the same dimension and use it as depicted.  It would likely fail under the load.  The effect can be replicated however with a few modifications.

16' is considered  the max practical limit for a bay which you would be inside of at 15' for a 2 bay design. I have drawn a line diagram showing how this could be framed using traditional  TF design on top of conventional stick framed walls.

Red is the TF portion supported on stick frame 2x6 walls.  The dotted lines are purlins..  Blue is the stick frame portion with lightweight fabricated scissor trusses to give you a vaulted ceiling in the bedrooms and bathroom as well.    The black lines are the 16" OC studs.  Does this make sense?  You can overlay this on the previous 30X30 2bdrm cottage floor plan with the gable end to the front.  The Purlins would be exposed to view as would the timbers.  You could do the entire house true TF and then do a stickframe infill between the timbers as well.

[Norm]

You'll also want to put in some ceiling fans along the  beam to keep the heat up there circulated down in the winter.

[nanook]

I'm learning a lot and I guess there are, as is usually the case, several ways of doing things.                              Thehardway...am I right in assuming that rafters would then go on top of the purloins? Your diagram is great.                                    Again, Thanks to everyone.

[beenthere]

Right Norm.
Have two     and they make a big difference.

[Thehardway]

Yes, you could do common rafters over the purlins or you could do T&G deck over the purlins, then "wrap and strap" foam insulation in layers over the T&G deck until you achieve desired value or you can do as I did and put SIP's over them.  Lots of options.
.
Whatever your approach you will need to make sure your finished deck is all the same plane.  My diagram did not reflect that if you go with rafters over purlins. 

PS.  Spell check does not accept purlin. You have to add it to the dictionary. It is correct however and is pronounced purr-lin.  Purloin is a different word which means "to steal" or "commit theft".  I'm definitely not advising you to steal anything! ;D

[nanook]

Thanks. If I did a king beam and purlins with rafters  on top and then fitted pine panels between the purlins with my insulation on top of the pine would this be be what you suggest as being "on the same plane"? What did you mean by SIP's?

[Thehardway]

SIP stands for Structural Insulated Panel  They are constructed of foam between two structural skins of OSB, plywood or steel.  They are rated for a specific span without need for additional structural support.  They also perform the needed insulation duty and give an exceptionally tight envelope.  Here are a couple links to manufacturers for starters.  They are also commonly used as wall enclosures for Timberframe structures.
www.murus.com/t.sips-overview.html
www.foardpanel.com/
www.fischersips.com/

being on the same plane just means that if you use two different types of roof construction, ie. lightweight trusses insulated with fiberglass batts on one end and timber frame with common rafters over purlins  on the other you will need to make sure that you allow for the different thicknesses when you calculate your roof truss dimensions otherwise your roofline will not be straight.

I would highly reccommend you get three books.

Tedd Benson:The Timber-Frame Home: Design, Construction, Finishing
Steve Chappell: A Timber Framer's Workshop Joinery, Design & Construction of Traditional Timber Frames
Jack Sobon: Timber frame construction: all about post and beam building

These books will give you a good overview of both traditional and modern timberframe techniques tools and planning and a wealth of other useful facts.  It is the best place to start.

I'm not sure what you mean when you say "pine panels"  so I can't answer that question.

[nanook]

Again thanks! Originally I thought that by "same plane" you were referring to the under side of the roof but now that I know you meant the top side I understand that the two roofs will have to be in the same plane. By pine panels I was referring to pine "boards" which I milled at half inch and hope to plane and use as my under roof cover. Similar to the tongue and groove cedar used by Beenthere. I will probably go on line and order one of the books you suggested. Which you recommend as the first/best read?

[Thehardway]

The Benson book is a broad overview and has lots of pretty pictures.  It covers a lot of ground and information but is not a how to book.  It is more inspirational in nature and thought provoking than hands on.  If you are still interested after that book, the Chappell book is very good.  It covers basic tools, layout, and structural considerations. It is very much a how to book.  The Sobon book has a lot of meat and covers a lot of the finer points of timberframing and reasons to go Timber Frame vs. stick built.  It is philosophical as well as earthy and very practical.  It has fewer pretty pictures and is more hand sketches of which Jack Sobon is the king.  His historical knowledge of timberframing is probably unsurpassed in the US and he gives some basic designs and plans that are time proven and free for the cost of the book.

If I had to choose one of the three it would probably be the Chappell book but I really like Sobon.

Try and pick them up used and maybe you can get all three!

The Timberframers Guild and website is a good source andonce you are familiar with basic terminology they have a good forum full of professionals.  It is not quite as active as this site however which is my favorite and covers a broader scope and knowledge base.

Merry Sawdust making!