Plans for 12x16 Saltbox with shed, greenhouse & deck add-ons

[KristopherCR]

Hola Timber Framing Community,

And thank you for offering such valuable advice through past discussion!

This is my first post, so as an amateur, I'm holding my teeth clenched in anticipation of feedback... Well here goes...

A bit of back story, in June 2019 my wife and I made our exit from city living to greener pastures. Costa Rica was where the dart hit the map, and in October we found our place in a Quaker Community, Monteverde, in the mountains. Before long, we found a place to live in exchange for building work. It was decided that the owner wanted to build a Studio, and after coming across Steve Chappell's - A Timber Framers Workshop in a library of a friend, I set out to make it a timber frame. After three months of sporadic study and design back and forth with the owner, I've managed to draw up something I hope to be respectable, which we will see about soon!

So the plan is to build a 12 x 16 FT saltbox frame with loft, a shed on the backside (4.5 x 16ft) a solarium/ greenhouse on the right side (6 x 12ft) and a deck on the front (7x16ft) . The basic structure has been inspired by the 22' x 16' Saltbox frame in Steve's book ... But more so on a photo which is included in the front of the frame plans section. The sizing of the timbers have been inspired by the 12x16ft Heartwood Class Frame in the Timber Framers Guild book - Fourteen Small Timber Frames, as well as other sources.

The plan is to build a strip footing and foundation wall to support a concrete pad 18 "  off grade.  The posts will to be anchored to the concrete foundation so no sills.

The wood is sourced onsite, it is Cypress and I've Heard from others who have build in the area that I can work it as soon as it's cut.

Im wondering if the rear rafter can run from the back shed post to the apex with a connection on the back post of the main building,without the need for collars. Also, which detail could support the rear rafter on each post respectively. I've also downsized my rafters (3x5's) as that's what the local timber framed structures use. I've omitted a ridge beam between rafters in hopes that the rafter/post joinery will suffice.

Standard practice is tin roofing here, and so chosen 1.5 x 3in purlins to support the sheathing between rafters.

I recently changed the detail for the wall plate on the front of the main structure to sit above the ties, to avoid overbearing at the joint, but I am unsure if this is necessary, as it will create a visual issue with the joists supporting the loft.

I've added girts around the greenhouse & shed, I wonder if these are necessary , if anything I'm sure it will help tie in the structure in and assit with the heavy wind loads we receive here.

I'm considering calling in the mill to get started so I can move forward despite not having considered the joinery details just yet.


Any thoughts, suggestions or encouragement is greatly appreciated !

Muchísimas Gracias!
Kris in CR


 

 

 

 

 

 

[Don P]

Darn, an engineer friend just emailed yesterday that he was back from CR, not sure where he was visiting. Do you have the latin name for your cypress or design values to check member sizes with? You will need to have made joinery decisions to know net sizes of the notched timbers you would be checking. Generally 20psf is good up to about a 90-100 mph burst.

Personally I'd use a ridge beam. It would make keeping the rafters in line easier and be stronger. The rear rafters are basically balanced over the main/shed plate negating much thrust there but the front on that tall post is going to want to thrust, I suspect those 3x5's will not be particularly stiff if we are counting on the long cantilevered rafters supporting that. I'd post the ridge beam all the way to the foundation. Trench or bevel that plate slightly, maybe about 1-1/2" wide to bear the passing rafters without notching them there.  No collars needed in the shed. If the joists sit on top of the ties with their tops at plate level might solve a couple of problems, notching the tie and sheathing the floor but you would need to revisit heights. Anyway just some quick thoughts.

[KristopherCR]

Thank you for your suggestions Don,

Unfortunate about the engineer!

The cypress here is called Cupressus lusitanica or Mexican Cyprus. I've struggled to find the mechanical properties for this species online, so my sizing is based mainly on the other cypress timber frames which have been built in Monteverde by Fox Maple and Steve Chappell, although ive beefed them up by an inch in places, posts & ties..

I came across a structure used in one of Steve's workshops that includes a braced 5x5 kingpost with a 6x6 ridge beam ... I am considering this as a good remedy to prevent any thrust at the top of the high posts. 

I have 10 days to get my joinery details in order, as the mill comes 3 days after the full moon... Something about insect resistance! 

[Don P]

Yeah, big bummer, for this vs home quarantine, you probably could have gotten him to hang out there.

Here's the tech sheet from the USFPL. Can you, or anyone, translate the title at the bottom "additional reading (27)"
https://www.fpl.fs.fed.us/documnts/TechSheets/Chudnoff/TropAmerican/html_files/cupres1new.html

Stiffness, E, looks pretty good, density is "average", I'll try to find comparables for bending to try to find some kind of average allowable for Fb. Sounds like pretty nice stuff.

Post some sketches of what you are thinking/come up with.

[KristopherCR]

Yeah, big bummer, for this vs home quarantine, you probably could have gotten him to hang out there.

Here's the tech sheet from the USFPL. Can you, or anyone, translate the title at the bottom "additional reading (27)"
https://www.fpl.fs.fed.us/documnts/TechSheets/Chudnoff/TropAmerican/html_files/cupres1new.html

Stiffness, E, looks pretty good, density is "average", I'll try to find comparables for bending to try to find some kind of average allowable for Fb. Sounds like pretty nice stuff.

Post some sketches of what you are thinking/come up with.

Many thanks Don for the tech sheet, and the valuable insights. I will have a read of the Spanish article on woods of costa rica.  ;D

The 5x5 king posts supporting the 6x6 ridge beam and braced at the interior bent twice and exterior bents once each side. I've modified the sketch to include joist layout which will pertain to only one 8ft bay, not continuous throughout.

If the braced tiebeams are insufficient to support the additional weight of the king posts & ridge beam, posting the ridge to floor is always an option. I'd like to avoid an interior post on the middle bent, so I wonder in the case that I post the ridge to foundation , could I increase the depth of the middle bent tie to maintain the 12' free span..?

 

 

[Don P]

Aaargh, ate my post!

It looks like 1000 psi Fb would probably be a reasonable allowable bending strength. I'd use 1.4 E. Shear isn't going to be a control here anywhere but 145 psi should be safe.

The ridge;
It supports 2' to the front, 3' to the rear so 5' x 8' span=40 sf x (20psi LL+10psi DL)=1200 lbs
https://forestryforum.com/members/donp/beamclcNDS2.htm
Check

Main Rear top plate;
 3' of rafter bearing on it to the front + 2.25' to the rear=5.25' tributary width x 8' of span=42sf x 30psf=1260lbs
Enter that into the calc above, check

Tie;
Check the center one. Floor:12'x4'= 48sf x (30psfLL+10PSF DL)=1920. We're going to use a center point load calc and that is a uniform load so divide this in half = 960lbs + 1200 lbs ridge post load=2160lbs center point load. Use this calc;
https://forestryforum.com/members/donp/beamclc_ctrpointload.htm
Bending is a little over stressed, a 7x9 passes easily.

Joist;
2'oc x 8'=16 sf x (30psf LL + 10psf DL)=640lbs. Back to that first uniformly loaded simple beam calc. Check

Rafter: looks like the front one is the long span 7' x 2.66' spacing=19sf x 30 psf=570 lbs. Simple beam calc, check

Looks like beef that center tie or pick out a really sweet one and basic member sizes should be good unless someone sees an oops.

[KristopherCR]

Soooo happy to be confined @ Home  ;D

I hope y'all are holding up OK wherever that may be!

I've spent some time clarifying and giving my drawings a makeover in hopes to make the building process run smooth-er... Also, I've omitted the deck for the time being.

As for Joinery I'm floating the following ideas:

1. Post @ block-wall - Knife Plate (from reading the experience of others, it seems that knife plates drilled & epoxy'd after the concrete sets will make layout easier (for me) than cast-in tie downs)

2. Ties @ post - Wedged Half Dovetail ... (would a through M&T with dovetail shoulder suffice? Be easier?)

3. Posts @ Top Plates - Mortise & tenon (does the bottom of the plate need to be recessed/ housed? Or can it sit on top of the post without recessing...)

4. Intermediate Wall Plate @ Posts - non-load bearing - would a simple housed tusk tenon suffice?

5. Rafters @ Plates - to bevel the ridge to accommodate open mortice & tenoned rafters at peak, rear rafter lapped on supporting plates. Or, as depicted on drawings, lag bolts securing rafters lapped onto the ridge beam.

6. 4x6 Joists... I'm wondering what is the minimum I should recess the joists into the tie beams? ... to offer enough stability to support my decking, without the need to install joist headers.

7. King Post - square tenon into tie beam? Can I get away without a knee brace on these posts, as the rafters will tie in the ridge beam?

Some other questions & concerns...

8. Wall A - the original plan was to brace the post to the wall plate, but this will interfere with the 3' 6" door openings... Does bracing at the top plate instead, as shown on drawing, have any repercussions?

9. Bent 3 - the top right brace will interfere with a very small, future 2' bathroom opening. What solutions are available? Frame door with header in its place? (Shown in drawing with dashed lines)

10. Bent 4 - offset middle post is 8ft from end to accommodate future interior walls, will the 4x4 non load bearing girt free span the 8ft  
Without problem?

The mill guy seems content defying driving restrictions to come and cut my cypress on Saturday. (Shhhhhh...Exciting times under house arrest!
)

Also, anyone interested in a spring vacation to Costa Rica more than welcome to stop with us! I hear flights are cheap to non-existent at the moment.



 

 

[Don P]

1. That works fine
2. Or just a pegged M&T, the wedged 1/2 dovetail is more secure but not really necessary. It would be good to table the tie 1" into the post.
3. sitting on top is fine, for square rule get the bottom to reference dimension.
4. That would be fine
5. Either would be fine, if you do a birdsmouth notch on the rafter top keep that notch as small as possible, that corner induces splitting, so the beveled ridge or a beveled cant strip is better.
6. zero is stronger for the tie with joist blocking or header
7. ridge post, minimum stub tenon, again damage the tie as little as possible. no brace needed, the rafter provides the bracing triangle.
8. I see no problem with that.
9. Move the brace over to the door post?
10. Yes

Others feel free to chime in, those are just my opinions.

Have sanitizer for both of you. We are trying to work solo but the moment you step outside the plans fall apart. I broke down yesterday, ignition module took a dump, and was in contact with a half dozen people before getting that resolved, best laid plans and all :.