Author Topic: 16 x 28 Shed/Workshop in Northern Delaware  (Read 8888 times)

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Offline Paul_R

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16 x 28 Shed/Workshop in Northern Delaware
« on: December 15, 2014, 07:50:11 PM »
I am a newbie to posting on the forum, but I have been reading here as much as I can in preparation for the spring building of a 16' x 28' structure that will initially be a storage shed with the plan of it one day becoming a proper woodworking workshop. For starters, I'm trying to keep the footprint under 480 square feet, but to also "future proof" it by thinking through how I might evolve and expand the interior usable space as time goes by.

To obtain center headroom in the 1/2 story of at least six feet, I have drawn up a preliminary sketch using the raising plate that Don_P demonstrated here (thank you sir!): http://countryplans.com/smf/index.php?topic=6732.0

Here is my design based on the raising plate concept. Twenty-foot 2x10 ceiling joists span the width of the building, extending almost 2 feet beyond the wall where they support a trimmed 2x12 raising plate that is tied into the 2x6 rafters that run from the ridge board. A trimmed 2x10 serves as the subfascia. Everything is lined up 16" o.c.



What do you think about the raising plate concept? There is so very little information online about it and I am wondering if it will be a tough sell to the engineer and/or building inspector. If I skipped the raising plate and used plywood gussets at the ceiling joist and rafter intersection and then again at the ridge to form giant trusses, would that improve the structure and my chances for approval? Do I need a short knee wall (see Don_P's drawing in the post above) to support or break up the rafter run? A no.1/premium 2x6 douglas fir rafter is almost maxed out on the horizontal span out to the rafter/joist intersection. Do I need to go to 2x8s for rafters?

I have looked into supporting the rafters with their seat cut resting on another plate that sits atop the ceiling joists. There is a lot more  information on that design, but unfortunately I can't figure how it will give me enough headroom in the 1/2 story with my 9:12 roof.

I also considered a ridge beam, a whopping 5-1/4" x 18" LVL, but that really would eat into the headroom, the pocketbook ($800+), and my lower back.

While the side walls are framed with eight foot 2x4s, I put 2x6 studs on the gable ends because I let in a 2x10 joist to support the ends of the top plates under the lookouts. There's only 1.5" of bearing there so it feels a bit flimsy, so I am wondering how else I might frame these gables. If I don't need the support, could I omit the let-in joist and go with 2x4 studs because they are supporting the plates sufficiently?

Here are some other details about the drawing for inquisitive minds. I am building the structure on 10 concrete pier footings (5 each side) because I have a lot of roots to contend with as well as a moderate slope (almost 2 feet over the 28 feet distance) that sees some run off from a nearby asphalt driveway. The frost line is 32" in Delaware. Short 6x6 posts will make up the varying height differences between the top of the piers and the beams. The built-up flush beam and floor joists will be pressure treated 2x10s under a 3/4" pressure treated plywood floor.

I am using three bottom plates as part of my "future proof" concept, thinking that I may put down 2.5" of rigid foam insulation (~R-19) with 3/4" tongue and groove plywood on top at some point. I thought I could make the insulation work in the floor joist bays, but the cost to keep it protected from the pests inspired me to put it inside. I'm not sure what the building inspector will think of my adding these as they serve no obvious, immediate purpose.

I'll likely use vertical 4'x9' 5/8 OSB sheathing on the outside. For the finished look, I just found local, full dimension 1x cypress stock that I hope to use for board and batten siding.

I chose eight foot studs to provide enough interior height between the raised floor and any suspended lights from under the ceiling joists. I've heard many woodworkers wish they had eight foot ceilings! Part of the bottom plate and additional blocking in the walls will give me support for interior sheathing down the road.

Thanks for taking a look and for any insights you care to offer. Really appreciate the great community here.
 

Offline Onkeludo2

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #1 on: December 16, 2014, 05:46:13 PM »
"I chose eight foot studs to provide enough interior height between the raised floor and any suspended lights from under the ceiling joists. I've heard many woodworkers wish they had eight foot ceilings! Part of the bottom plate and additional blocking in the walls will give me support for interior sheathing down the road."

This is about the only thing I can comment on.  Having horsed around enough sheet goods that tend to 8' long I can wholeheartedly say that any planned approach and departure from the tablesaw should have at least 8'1" of clearance floor to UNOBSTRUCTED ceiling for the first 5' before and the last 5' after the planned table saw working location.

As my house has 9' ceilings all built-ins tend to be made of a 6' high box topped with a 3' high box.  As my workshop area has 7' 6" ceilings I either break-down sheet goods in the driveway or nip off the first 22" of 8' sheets with a straight edge and a circular saw for this reason.
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Offline Don_P

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #2 on: December 16, 2014, 06:27:20 PM »
There are cantilever tables in chapter...5 I believe. The raising plate will be unknown to 99% of inspectors and engineers, whether they allow it is unknown. A more common approach is to build it as plywood gusseted trusses, that should be no problem. The kneewall stud in the truss, if gussested in or tied well to prevent it slipping, does count as a support for calculating allowable span.

The raising plate, or launching the rafters from a plate on the second floor does present some thrust and uplift considerations. I can make a case for viewing a properly sized raising plate similar to a ridgebeam in restraining thrust.

I just ordered a triple 18" x 18' built up lvl for supporting floor and roof alongside a set of stairs. Last week I helped bring inside and lift a 30' long x 18" x 63 lb/foot I beam to open up the living room in that house. We lifted the I beam with a pair of heavy duty come alongs.

I'd go with 9' studs to allow a standard garage door and track in the future if it will be a shop. I like 12' ceilings in a shop, and I can still clean out lights occassionally.

Quote
Here are some other details about the drawing for inquisitive minds. I am building the structure on 10 concrete pier footings (5 each side) because I have a lot of roots to contend with as well as a moderate slope (almost 2 feet over the 28 feet distance) that sees some run off from a nearby asphalt driveway. The frost line is 32" in Delaware. Short 6x6 posts will make up the varying height differences between the top of the piers and the beams. The built-up flush beam and floor joists will be pressure treated 2x10s under a 3/4" pressure treated plywood floor.

Although you will see this oft repeated here it is just about the worst way imaginable to build a foundation. The pier is poorly suited to resist horizontal loads, then stand a 6x6 on top of that. This does assure the pier is under very little lateral load, the 6x6 will tip over before the pier has the opportunity to, then at the top of the 6x6 try to fashion some type of adequate connection to prevent overturning under a story or more of sail and weight above. If you want to go this route build it post frame style with full height posts that run from footing to top plate, thus using the walls to brace the posts.

5/8 sheathing may complicate jambs and this is not the weak link here, overbuilding a strong area does not strengthen the weak areas, use the money where it does the most good. (That said, my house is sheathed with 3/4  :D)


Offline Paul_R

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #3 on: December 29, 2014, 07:04:05 PM »
Appreciate the good insights. I have been reviewing posts here and elsewhere and talking to others about my plans. My updated plan is below.



For starters, based on Don_P's input, I have elected to go with a monolithic pour of footing, foundation, and floor all in one shot. The slab will be around 6" above grade and the foundation wall will follow the grade so I'll have almost two feet of foundation wall at the rear. I can probably accommodate that with some fill and grading at a later date.

I have abandoned the raising plate in favor of a steeper pitch, from 9:12 to 10:12. That gives me an adequate amount of headroom, almost 16 feet below the beam to the floor,  should I decide to build out the half story using interior ledger boards and 2x10s supported by hangers to span the 16 foot building. I like the fact that I could determine at a later date the first level shop height. Nine feet is starting to sound like a possibility. The side walls are 10' 2x4s.

I have also gone back to the idea of the structural ridge, the big 18", 3-ply beam that was estimated for me. The 10:12 pitch helps with the headroom issue and I am thinking in the long run the structural ridge is better for "future proofing" my structure. This beam will sit in a short pocket supported by a 2-2x12 header that transfer to two built up posts that will follow down to the foundation. I like the option of having an opening below the beam should I elect to install a window and the spacing between the posts could accommodate a 36" wide door should I decide I need to bring larger items into the half story down the road.

Speaking of future proofing, I have also elected to design in an opening for a garage door should a future owner decide to convert the structure into a garage. I have merely filled in the opening with a short stud wall. Overhead is a 9-1/4 10.5' lvl. I may be that future owner if I decide I would like the space for a vehicle instead of a workshop. Maybe.

The full eave return across the gable end was a design consideration since I was going with the higher pitch and did not want to present a huge gable wall to the street.

Thanks again for your support in this build. Merry Christmas and best wishes for a happy New Year.

Offline Paul_R

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #4 on: December 29, 2014, 07:13:35 PM »
Here is another vantage point with the back wall (just studs) removed.



Anything missing or opportunities for simplification?

Offline Don_P

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #5 on: December 29, 2014, 07:49:40 PM »
I really like the eave return. Playing devil's advocate; look at the load that is on the column at each end of the building. On the garage door end, the load bridges over the window (check load for how many jacks needed and king studs to laterally stabilize the header). That load then drops to the garage door as a serious point load, have this sized. There is a hinge in the wall with the header breaking the 2x4...2x6 wall into two laterally unsupported halves. Without a floor to brace that hinge point that will be a weak wall. The return can be built as a horizontal beam or incorporating a sized beam to support that hinge and break the column length of the studs. A serious axial load on a column makes it want to buckle, think of pushing on the ends of a popsicle stick. You have that load and a lightly supported break in the middle of the popsicle stick. at the other gable calculate the column required, it probably isn't going to be in 2x4 at ~16', but again an opportunity for horizontal support, I like those returns.

Offline Paul_R

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #6 on: December 29, 2014, 08:24:28 PM »
Thanks Don_P. I am so glad you like those returns. They help solve some issues as well as add to the appearance. And my wife likes them. Here's what they look like fully trimmed.



I confess I have a lot to learn just from your reply and will be working to better understand your insights. Axial loads and your beam recommendations will be the first I take up. I can see where the garage door end has the hinge, with only six studs at the ends rising to the plates. Does exterior sheathing across this connection help with the hinge effect? I could potentially platform frame that wall and brace the top and bottom sections with a shallow (4 foot wide?) loft just to get a "floor" in there, unless the bracing needs to run more of the building's length (which I hope to do down the road with the ledger/joists combo). Does the platform frame with the floor or a beam running from side wall to side wall (trying to imagine this framing) help with the axial load? Platform framing could be easily done on both ends if the short lofts were an effective brace. The lofts could also help with placing the ridge beam.

I realize now that I must've attached my king studs for the structural ridge header on another layer that was hidden. They turned up on the other gable end.

Offline Don_P

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #7 on: December 30, 2014, 03:13:31 AM »
Floor sections would certainly help, it is beyond me how much is enough but any is going to be better than none. I was thinking the same thing though as far as helping to raise the ridge. The beam and column calcs here may help with understanding buckling in the posts; http://timbertoolbox.com/. Euler buckling is another thing to google and read up on for more on that. There is actually some amount of combined load from the ridge supplying an axial load, a load along the axis of the studs, with the wind providing a bending load perpendicular to the studs. Breaking the laterally unsupported length of the support studs in half with a loft floor will dramatically strengthen those posts. Sheathing effectively contributes nothing to the resistance to buckling, just as floor sheathing doesn't keep a floor from sagging, the girder at midspan on a wide floor does that. Remember the let in ledger on a 2x4 wall is a 1x with the joists resting on the ledger but running over the ledger and attaching to the wall studs

Offline Paul_R

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #8 on: December 30, 2014, 07:32:32 PM »
Thanks again.

Here is how that looks with 3/4" plywood resting on full-width 2x10 ceiling joists atop let-in 1x6 ledgers running for the first four feet from the gable which is now platform framed. Does this dramatically improve the load characteristics of these end walls, with or without the garage door header?



I recall reading that balloon framing was the choice for gable end construction given the problem with the hinge factor for regular platform framing. Is it the addition of the garage door header and/or the structural ridge supported by columns changing that rule of thumb? Did the garage door header in effect create the hinge with so few full height studs?

Still working on my calculations. How do you account for a built up 2x4 column when calculating the buckling load? If it is 3-2x4s, do you multiply the load of a single 2x4 times three, or do you consider the characteristics of a larger timber, say approximately a 4x6 for your inputs? Also, am I correct in determining that 1/4 the roof load is coming down each gable wall and then another 1/4 on each side wall if there are no mid-span supports for the structural ridge?

Offline Paul_R

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #9 on: December 30, 2014, 09:28:25 PM »
So here is what I've got on column load. 16' x 28' building, 10# dead load, 40# live load, roof load (16x28x(10+40)) is 22,400 lbs. Structural ridge supports half that, so 11,200. No mid span supports, so 5600 lbs on each end.

Using this calculator (http://www.timbertoolbox.com/Calcs/columncalc.htm) and these data sheets http://www.naffainc.com/x/IRC2000/TABLES/Properties-SawnLumber.htm and www.awc.org/pdf/2005-NDS-Supplement.pdf, I came up with the following for 96" douglas fir-south 4x6 (if it exists) columns.



This is if I were to have one post under each ridge, and those posts were "pinned" no more than 96" from top to bottom. Is this an area where the platform framed gable wall is helping (when backed by joists and plywood flooring at the hinge)? So does the fact that I've split the load path at the ridge, with a header, to two smaller columns divide the load for that end of the ridge in half yet again, so now it is 2800 lbs over each column? If so, either a 4x4 or possibly 2-2x4s can carry that weight. It would appear however that these two point loads overstress in deflection the 3.5x9.25 LVL garage door header (if it were actually used for a door) though it passes fiber stress and shear.

BTW, header under ridge beam passes if it is a 3.5" x 11.25" timber. Does that mean it has to be lvl or does a built up 2-2x12s with 1/2" spacer also suffice?

Thanks for the great lead on the calculator site. It has been an enlightening evening.

Offline Don_P

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Re: 16 x 28 Shed/Workshop in Northern Delaware
« Reply #10 on: December 31, 2014, 06:15:14 PM »
Quote
I recall reading that balloon framing was the choice for gable end construction given the problem with the hinge factor for regular platform framing. Is it the addition of the garage door header and/or the structural ridge supported by columns changing that rule of thumb? Did the garage door header in effect create the hinge with so few full height studs?
That's what worries me. Balloon framing also requires deeper studs the taller those studs get and the higher the load. The header and broken studs do redirect lateral loads to the full height king studs at either end of the header, which would be resisting that out of plane load in flatways bending. (check the NDS supplement for adjustment factors for that use). apawood.org has narrow wall bracing framing details in a couple of their publications. I'm all for that section of floor, it is creating a beam or diaphragm, although at one row of sheathing it is flexible, it is a big improvement. Block the edges at the center end joints and nail the perimeters very well.

Quote
Still working on my calculations. How do you account for a built up 2x4 column when calculating the buckling load? If it is 3-2x4s, do you multiply the load of a single 2x4 times three, or do you consider the characteristics of a larger timber, say approximately a 4x6 for your inputs?
I use the actual dimensions of the built up timber and fasten the pieces together very well. There is a section in the NDS that I need to review to answer that well. There is a section on columns in "Wood Structural Design Data" on the awc.org website, free download. The NDS is the code referenced document and is for sale on the awc site, the WSDD and all the info on that site is from the same people, so a good bookmark.

Quote
Also, am I correct in determining that 1/4 the roof load is coming down each gable wall and then another 1/4 on each side wall if there are no mid-span supports for the structural ridge?
Yes

Quote
So here is what I've got on column load. 16' x 28' building, 10# dead load, 40# live load, roof load (16x28x(10+40)) is 22,400 lbs. Structural ridge supports half that, so 11,200. No mid span supports, so 5600 lbs on each end.

Using this calculator (http://www.timbertoolbox.com/Calcs/columncalc.htm) and these data sheets http://www.naffainc.com/x/IRC2000/TABLES/Properties-SawnLumber.htm and www.awc.org/pdf/2005-NDS-Supplement.pdf, I came up with the following for 96" douglas fir-south 4x6 (if it exists) columns.

Use DF-L or DF-North and E will jump to 1.6, plug that in and notice what it does to the total load capacity of the column and to the column stability factor... This number gives a sense of the capacity lost due to slenderness, but stiffness (E) obviously plays a major role. Leave all the other inputs the same and enter 192" for unbraced column length. The column stability drops to 11% and the column fails.

Quote
This is if I were to have one post under each ridge, and those posts were "pinned" no more than 96" from top to bottom. Is this an area where the platform framed gable wall is helping (when backed by joists and plywood flooring at the hinge)? So does the fact that I've split the load path at the ridge, with a header, to two smaller columns divide the load for that end of the ridge in half yet again, so now it is 2800 lbs over each column? If so, either a 4x4 or possibly 2-2x4s can carry that weight.

For just the gravity load that is probably correct. The exterior wall studs are really under a combined load from gravity, the ridge load, and in bending, from the wind. Try this calc; http://www.timbertoolbox.com/Calcs/44axbend.htm
Start with #1 Southern Pine >5x5 P+T (to get design values similar to your 4x6 dougfir), 2800 axial and ~200 lbs bending load, a number I'm pulling out of air for a single stud bay in wind. Then imagine the header collecting 5' of wall width and delivering it to the studs on its' ends, maybe 1100 lbs in bending.

Quote
BTW, header under ridge beam passes if it is a 3.5" x 11.25" timber. Does that mean it has to be lvl or does a built up 2-2x12s with 1/2" spacer also suffice?

A double 2x12 would be 3"x 11.25" and the design values would be about half of those for an LVL, if it checks using the right numbers then it's good. Check bearing area of jacks, too little bearing area under a beam and the jacks crush and cut into the beam.

Wow, I think that was everything  :)
« Last Edit: December 31, 2014, 06:32:05 PM by Don_P »

 

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