Dog Trot Gable Roof Span

Started by fritz, December 16, 2005, 10:09:08 PM

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fritz

I'm playing with some ideas and I came across a Dog Trot in Dale Mulfinger's "The Cabin" (for those who know the book).

It's two simple cabins, covered by one gabel roof.  Between the two is a open air deck.  By guessing, the deck (running east west) is 16' by 44'.  A 12' x 24' is on the north end and a 12' x 18' on the south end.  This could easily be two versions of John's Small House.

But I'm trying to think through how to support the gable roof span across the 16' between the two.  I know some of you must have some good thoughts.  




glenn kangiser

I'm thinking headers from corners to corners then standard joists or trusses.
"Always work from the general to the specific." J. Raabe

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PEG688

Quote
But I'm trying to think through how to support the gable roof span across the 16' between the two.  I know some of you must have some good thoughts.  




 A LVL or Paralam would do the job . Go to your suppier / lumber yard a good one. not Lowes or Home depot . and they can or should be able to size your beams based on your location , potentail snow or lack there of loads .

 If your in a earthquake zone ask about required Brace Wall Panel Requirements , for window and door placements , and req. hold downs etc that will / could be required . Good Luck , PEG  
When in doubt , build it stout with something you know about .

Amanda_931

#3
I'd screwed up what I was going to say and it didn't make a lot of sense anyway.

There was a lovely two-story log cabin at the bottom of the hill, with a dog-trot on the first story only.  One of our local arsonists may have gotten it.  In any case, it burned.

The dog-trot part was probably closer to 10 than 16 feet, though.

John Raabe

#4
I've thought of this same project as a great expansion of the 14' wide little house.

You could span a beam (built up or LVL) at the ridge and side walls as headers and then have exposed rafters using shiplap sheathing for a nice underside look. Then, depending on climate, I'd drop in 2 to 4 skylights per the sliding glass door units in the Skylight and Greenhouse plans (that come with the Enchilada set).

You could set one up as the bedroom wing and the other as Living room or main social module.

Per the plan above... At the end of the long deck extension you could have a third (perhaps future) stand alone cabin as the office or guest house.

It would make a sweet little compound.
None of us are as smart as all of us.


fritz

Thanks for the thoughts ...

Sometimes I mis read so let me be sure I understand.  Use the LVL or similar as a 16' ridge and headers....over the open area?  if so, then what's the best way to tie into the end walls/ridge of the cabins.  A joist-type hanger?  Or are you thinking a LVL longer than the 16' gap?

Climate is southern Iowa: some sub zero in the winter, some high 90's summer.  Two really nice days in between.
;)

PEG688

Fritz .  A couple of questions first .

#1  Do you see the covered deck area as John discribed as open to the under side of the roof sheathing .


#2  What would the ceiling in the cabins (enclosed ) areas be like ?  Vaulted , flat w/ DW lid ?

#3  How much experience do you have in cutting rafters / beams if option #1 is selected .

 Much of const.  details are driven by design/ function  .   You'll need to figure out what you'd like to have .

 If your wanting truss's for the full roof all you'd need would be two LVL or solid beams , or a built on site header/ beam that would flush out with the under side of  top plates . Then your  top plate could run from the walls over the top of those beams , in the open area . That would give you a positive connection from the cabin walls to the open area .   All this is complicted if the cabins have a truss roof and the open area has a thicker roof sheathing than the cabins . Hence the above questions . PEG    
When in doubt , build it stout with something you know about .

fritz

QuoteFritz .  A couple of questions first .  

#1  Do you see the covered deck area as John discribed as open to the under side of the roof sheathing .  

#2  What would the ceiling in the cabins (enclosed ) areas be like ?  Vaulted , flat w/ DW lid ?  
 
I do see something like what John described -- and probably something similar in both cabins. I'm also looking at small lofts within the cabins per the little house plans.  The finish will be more rustic than polished, so exposed rafters and collar ties was the plan.
Quote
#3  How much experience do you have in cutting rafters / beams if option #1 is selected .  
What I lack --- I have friends.  But with the 12/12 roof, I'm leaning towards subbing parts or all of the roof out.  before I sub it out, I just want to think it through..so I know what to ask for.

PEG688

  Ok How will you insulate the roof if you go with the exposed to the interior roof sheathing ?  I'm thinking you'll want to insulate ,  in Iowa ,  the exposed roof sheathing. This  makes  it more work ,  will mean  more $ , it can be done it's just not the cheapest way to do it and Generally you end up with very wide facia and rake brds.

 So the next question is a $ question, are you willing to pay more for the look you have sort of lead us to ??     Just in material it will cost more , there are other ways to do it with stress skin pnls , and again they cost more tham a vaulted roof truss w/ conventional insulation .     Sorry to ask so many questions but to give good advice , sound in it's content and contex , all these ? need answered for the plan to move forward / take shape . PEG
When in doubt , build it stout with something you know about .


fritz

Let's see if I can give a better idea.  I won't insulate the  open area -- so visible sheathing and rafters and collar ties in the open area.

In the cabins, yes an insualted roof -- but the same rafters and same thickness sheathing over cabins -- but insulated with bats or similar (so probably 2 x 8 rafters per the little house plans)  Haven't gotten to thinking about cabin roof interior finish in detail -- but maybe ply, or beadboard.  

This will be a retreat mostly 3 season, with occasional winter use.

I'm thinking of a metal roof -- and your point about sheathing thickenss is well taken.


JRR

#10
I would use nothing but simple rafters, perhaps as small as 2 x 8's (depending on snow loads, etc) each 16' long.   They would be placed the "wrong direction" .... horizontally, looking just like stepped floor joists, the full width of the breezeway.  For the most strength, the joist-like rafters would be upright at perhaps 2' centers ... measured horizontally.  Actually these should be spaced to tie into the studs of the end walls.

On the tops of these, you would need to block in some nailers, perhaps on-side 2 x 4's, in the normal rafter direction ... for attaching sheathing.

I wish I knew how to include a sketch so this might make some sense.

glenn kangiser

#11
That's revolutionary, JRR -- count on you to come up with good ideas.  Like purlins on a steel building.  I'll see if I can do a simple sketch in paint.

Here it is -- a painfully ugly little sketch to look at but I think it shows the idea.


Brown = purlins  or joists -- Blue = nailers


I don't know why I didn't think of this-- I do it all the time with steel and have even made a carport that way at my other house with wood-- I was just thinking conventional house framing --- silly me -- just shows you how far the brain damage has progressed. :-/
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

PEG688

Ok   So how do we get a R-30 or 38 in a 2x8 rafter bay ? And if we use the purlin idea our T&G 2x6 decking is now running up the roof not perpendicular to the flow of the porch .

 John chime in anytime  :)

 We are drifting off task , which is fine , design is the time to drift , once ya start changes sort of grow on ya, in a bad way one change here effects yadad yada , etc  . Unless your remodeling then you flex to what the building sort of gives you as a / the lead.

 Ok now theres a word lead , is it metal or direction , contex / content drives that word .  A hound that is in front of the pack all the time might be called Lead , one that was always last could be called lead , the almost perfect word to show contex vs content .  Apples to oranges / apples to apples.

 So  fritz now will dwell on JRR revolutionary idea.   It does turn the whole project on end so to speak , at least for how it looks .

 Rethink those ideas lads , on the above facts / situation and the clients vision . fritz is the boss , it's his dream/ vision. Our job" If we choose to take it is " Now listen to the theme of Mission Impossible , is to #1 Destroy the tape . #2 complete the mission . #3 Call Martha  Steward . # 4 Ask John for HELP!!!

 That was fun , PEG      
 
When in doubt , build it stout with something you know about .

jonsey/downunder

Do away with the nailers, fix the iron straight to the purlins. If the structure is open both sides there is no point in insulating the roof.
jonesy.
:)
I've got nothing on today. This is not to say I'm naked. I'm just sans........ Plans.


glenn kangiser

#14
I guess being a 12/12 pitch it would be a bit steep for the purlin method as they would be laying over at a 45 degree angle.  If it ends up being a metal roof then this would work as Jonesy and JRR mentioned.  I guess that does look like a tin roof, doesn't it, and Fritz was thinking of a metal roof which is normally installed on purlins on many buildings -no need for sheathing actually so that in itself will cut costs.  As far as that goes - purlins could be used over the cabins also -again sheathing not required for metal roof as long as bracing requirements are met.  1x4 purlins over joists have to be cheaper than solid sheathing.  He is planning bat ceiling insulation so sheathing or lack thereof will not be visible anyway.

What is the purpose of insulating a space that has free air flow through it?  It doesn't seem that you would commonly insulate a breezeway roof.  

In the original posting I only see decking on the porch deck - not on the roof.  

I think part of our mission may be to come up with other options that may be more affordable - desirable or just a plain different way to do it.  Building methods are not set in stone until the owner has a method fixed in his mind, down on paper and contracted to be done a certain way or in the case of a DIY, materials and plans set for a certain way.  Much easier to make changes in methods before the job is in progress - this includes thought changes.  After that changes cost money and even value engineering can at least cost some to get the engineer or architect to redesign it in a more cost effective fashion, thereby reducing overall cost but increasing revenue to the designer.
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

PEG688

Ok I'll try one more time [highlight]read the whole post see the clients desires [/highlight]. Make those desires afford able and build able , for the client .

  Yes I see we do not need to insulate the dog trot but if we are using 2x6 T&G car decking to make this area a roof- able surface and a good looking to the eye porch ceiling , yet we have to tie that into two other small building / rooms that need to be insulated to at least R-30 min  with a potential loft area , for the area in question . How do we tie it all together so it sound as a unit / tied together/ strong .  

And  is buildable for a client who has "friends" to do the more tech building part . And affortable.  

 Contex / content  design can make it Mission Impossible / to big . to complicated / to much detail / not enought detail . All can make it a failure , can I build something with nothing , no , we need a plan, a starting point ,  a objective / goal . Planning . PEG
When in doubt , build it stout with something you know about .

JRR

#16
Glenn, your sketch is on the money.

But before you give me any credit for being a thinker,  perhaps you should know that during a vacation ride through Alabama ... we visited a state park ... known for its long old wooden covered bridge ... and oh yes, there was also an authentic "dog trot house".   Could be that that particular breezeway roof was supported in this fashion.

"Some of my best original ideas ... are ones that I've stolen from others".
                                                                                    JRR

fritz

First, I'm excited to see the interest.  I hoped I wasn't asking an obvious question, and looking at the replies, I like what y' all are thinking.  At least I have the winter to work through this on paper before having to plunk down cash for materials.  

PEG's last post described the "problem" very well.  I want to be sure the roof load is well carried and doesn't put the wrong stresses on the two cabin end walls that make up the ends of the open area.  (Do you call that a breeze way?  I guess that's what I would call it.)

Okay, also, to be sure my "metal roof" is the same as your "metal roof", The roof I'm thinking of is the standing seam metal roof, not a corugated roof as in the original photo for the design book.

JRR's plan seems straight forward.  I might think about using 2 x 10 for the end rafters of the cabins to be able to nail a hanger for the "roof joists" (purlins).

Then, thinking cosmetics (and some function) if we use the 2 x 4 nailers, flat, but running the typical rafter direction, the roof can be secured and then, from the underside, there is a nailing surface to nail a ship lap or other ceiling  between the roof joist/purlins.  

I played with some sketches yesterday.  Here's some basic ideas.  This cabin is in farm / cattle country -- the site is in a small valley visible from the highway.  Since it is an occasional use property, I want to be able to secure it when away, but have it be very open when in use, so I'm thinking of sliding barn doors over the breezeway entrances -- as well as over the doors/windows on each end.  (This will require a beefy header/nailer to hang the barn door track.)

The small side windows echo barn design....it blends in with the surroundings.  But not everyone wants to live in a barn.  ;)

Anyway, the colors aren't final -- although, it looks really good in barn red!



Again, many thanks, I really enjoy reading your ideas.....

Daddymem

Does the middle have to be tied to the end pieces?  You could tie the bottom together, but I think it would be interesting to raise the middle roof a bit higher than the ends?  This is a long structure that would benefit with a little breakup of the rooflines imho.  A little overhang under the open space and a little overhang over the ends.  Use some interesting posts for the open area and you have the look of the structure being built at different periods of time.  Or...make two pieces of the whole thing, one with the open area attached the other just an end piece with overhang ( you could step up or down one step to get into this section.  Just thinking from a different angle here, of course I have no idea on the details of framing that all up.  
Où sont passées toutes nos nuits de rêve?
Aide-moi à les retrouver.
" I'm an engineer Cap'n, not a miracle worker"

http://littlehouseonthesandpit.wordpress.com/

Daddymem

#19
Heh, wrote that one while you were writing yours..I see we are two ships in different directons  :D
Anyways..here is one with two pieces:
http://www.wheelerplantation.org/early_dogtrot_cabin.htm
Here is a compound project using dog trot influences:
http://themeridiancompany.com/cms/view.php?offset=1&sort=The%20Trot
Où sont passées toutes nos nuits de rêve?
Aide-moi à les retrouver.
" I'm an engineer Cap'n, not a miracle worker"

http://littlehouseonthesandpit.wordpress.com/


glenn kangiser

#20
[highlight]And let me try once again, PEG.  

Let creativity flow by allowing comments and ideas from all members. Please add your ideas without putting down the ideas of the other members.  No one is off topic as Fritz's original comment was "But I'm trying to think through how to support the gable roof span across the 16' between the two.  I know some of you must have some good thoughts."[/highlight]

There are a million ways to do things.  If the interested party is not yet set on a method and has not presented some of the ideas he is thinking of, we cannot know what may be of benefit and what may not.  All ideas should be presented then Fritz can take the good ones, toss the bad ones and have the most efficient cost effective structure possible.

Since JRR saw the purlin method in use on an actual building, it is obviously a viable alternative.  Bracing could be incorporated into the end cabins with the purlins only supporting the steel roof sheeting.  It could be screwed to the sheeting with neoprene sealed screws for strong fastening and long term water tightness. The sheeting visible below through the purlins would have a nice look to it and Fritz would save the cost and time of installing sheathing possibly on the whole house with the exception of that required for bracing.

A header could be put across the door openings to support the doors, but being non bearing in the purlin method, it would not have to be so deep thereby opening up a little more headroom in the breezeway.  

Lets kick around lots of ideas -even crazy ones -  not just one method we have set in our mind.

If I understand what you are talking about correctly, Fritz, the steel sheeting will still need horizontal supports approximately every 4 feet minimum and you may go down to every 2 depending on the sheeting and loading.  2 x 4 nailers, flat, but running the typical rafter direction would not provide that support.  You could fasten to the horizontal ones although for insulation and interior finish fastening it seems you would want to be lower down on the side or bottom of the joist -side if the joists are deep enough and you want the joist to show some.  Standing seam metal should be self venting above the insulation depending on the configuration.
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

PEG688

QuoteDoes the middle have to be tied to the end pieces?  You could tie the bottom together, but I think it would be interesting to raise the middle roof a bit higher than the ends?  This is a long structure that would benefit with a little breakup of the rooflines imho.  A little overhang under the open space and a little overhang over the ends.  Use some interesting posts for the open area and you have the look of the structure being built at different periods of time.  

[highlight] I really like this idea [/highlight],  Nice one Daddymen  :)the section of wall that is above  the two enclosed ends / rooms  could be left open so hot summer air would convect out making the porch area more interesting to look at and more confortable , Sort of timber framed , 6x6 post rough sawn with 3x8 R/S rafters say 3' OC overlayed with the T&G 2x6 decking .  

It also lends to the car decking to be used as the area won't be insulated so we get the nice looking T&G showing without the hassles of different roof sheathing becoming a issue .

 I think it would look cooler than the single long plane of roof as well. One of the little house plans a while back had that look , the winner of the contest IIRC, PEG
When in doubt , build it stout with something you know about .

Amanda_931

Looks like that traditional one was built--and re-built--in two sections, with the dogtrot roof being supported by huge old logs that do not quite line up with the logs in the upper roof cabin.  Looks, in the restored cabin, like it might be supported by being spiked into the other side (although a big post would work to, I expect).  With that, ceiling joist/rafter combination (or a king-pin truss) you'd probably be home free.

But if you don't have 8 x 8 poplar beams to play with....

southern living home plans has always had a dogtrot cabin--duplex type--in their catalog.  I'll post it if I see it.  Which I'm definitely NOT right now.

bartholomew

Hi there Fritz, I thought I'd post a pic of a similar cottage by Miller/Hull...



Your drawings didn't show rafter tails so maybe this is not an issue for you, but if you are planning to have exposed rafter tails then using standard rafter framing over the dogtrot would maintain the pattern of rafter tails along the length of the cabin. Of course you could also use the purlin method and attach fake rafter tails.

It seems to me that the purlin method saves lumber but that the rafter method involves a lot less head-scratching. It is easier to keep everything lined up at the right height just by keeping the tops of the dogtrot headers even with the cabin top plates. You can use PEG's top plate method to tie the three sections together, or if you want to raise the headers that extra 1.5 inch then use metal strapping instead.

On the issue of structural sheathing, I think you can skip it. Just use 1x or 2x purlins (aka skip sheathing) spaced a couple feet apart over the entire cabin and dogtrot. Given the length of the roof and the lack of dormers or other breaks, the metal roofing itself should provide adequate bracing (but check with the manufacturer first).

Good luck!

fritz

Just playing with the Daddymem idea.  It removes the sliding barn doors. The side windows would be re spaced.