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Building a Shop Mezzanine for Storage

Bigslice's picture

I recently built a workshop (2x4 construction for the walls) with 16' wide by 24' deep dimensions. I want to build a storage mezzanine that spans the front 16' wide by 8' deep section above the garage door but I am unsure of how to do this without installing a post along the span.

Any suggestions on how to build this? I need an adequate "floor joist" system that will support the load above, on 3/4" T&G plywood, without sagging across the 16' span. I was planning on running 2x?'s across the 8' span, 16" O.C., but this also ads to the weight that has to be supported on each end.

The roof above is conventional "A-frame" construction, so I don't think it is wise to attach a load to this, though a friend of mine did it on an 18 foot span, using a cable to tie the centre of the shop to the roof. I'm skeptical on this one.

If anyone knows of a formula for calculating loads for this thing, I'd be interested.


Edited 8/12/2003 3:03:58 PM ET by Bigslice

Edited 8/12/2003 3:06:03 PM ET by Bigslice

(post #93207, reply #1 of 27)

If I understand you correctly, it's no different that figuring the size for floor joists on a 16' span, but I'd assume a far greater load per SF, since you're using the space for storage (ie: lotsa stuff piled up there).   You'll probably end up going with engineered lumber, or spacing 2x12's at 12" o.c. (don't know what the load capacity of that would be, as I don't have span tables in front of me).

I wouldn't tie anything up to the roof- let the roof focus on supporting itself, and have the floor do the same.


"Brilliance!! That's all I can say- Sheer, unadulterated brilliance!!" Wile E. Coyote- Super Genius

(post #93207, reply #2 of 27)

Your understanding is correct. I couldn't figure out how to add a jpg sketch into my message but you have the right idea. I forgot to mention that my space above is limited because of the garage door. I was hoping to be able to join several 2x's together on each end, and run joists across from front to back, using joist hangers on each end.

I am also not opposed to using steel beams or engineered lumber, but I would like to know how to do this before I start. Ultimately, I am likely to hire a framing carpenter to do the work, but there is no shortage of people who want to hammer this together without any concern with whether it will hold the heavy stuff.

It will probably hold a lot less weight than a household floor. Without furniture up there, I expect it to hold 2 people carrying stuff up there and some lumber supplies and boxed items that I don't use very often. I should plan for it to be as strong as a house, though.

There has been too much love in building this dream shop (skylights and all) for me to screw it up by not installing a proper storage mezzanine.

(post #93207, reply #3 of 27)

I happen to have a table for 100 lb live load and 25 lb dead load which shows 2 x 12" Sel. Structural on 16 OC, good for  a span of 14' 9" (you have 15' 4"    16 feet less two 4" walls).

2 x 10" Select Structural on 12 OC are good for 14' 1"

Most residential floors have typical spans of 16 feet and use 2 x 10 on 16 OC.

Throw some 2 x 10 up there on 12 OC (to be good, only cost you two more joists).

(post #93207, reply #4 of 27)

So if I understand this correctly, I would run 2x10 at 12" O.C. and I tie them together with cross bracing (just like a flooring system). Can I hang them on joist hangers, since the roof does not permit me to hang them off the top plate? Secondly, do I need to double (or triple, or quadruple, etc.) the 2x10s anywhere, in order to avoid sagging?

(post #93207, reply #5 of 27)

You can not place them on top of the top plate next to the rafters?

Secondly, I read a second post of yours stating that you would like to run the joists from in front of the door back to a carrying beam.  Is this correct?   If so I don't know what the deminsions should be for the carrying beam.   However, I don't see why this tactic would be more or less better for your garage door.  Can you explain your thinking?

Lastly, I should say that I am not an engineer.  I just know a bit about building, codes and structural tables.

(post #93207, reply #6 of 27)

Originally, I thought that I would run 2x's from front to back and join them to tripled beams on the front and back using joist hangers, as one of my neighbours did. However, this is the same guy who hung the mid-point of the span off the roof rafters and I am skeptical about his design. Time will tell.

I happen to be an engineer who should be able to figure this out, but as an engineer from a family of tradesmen, I recognize that there is theory and practice (and I haven't worked in my field since graduating). This thing called a mortgage had me chasing higher paying jobs and now I do a lot of my own home renos. I know when to hire the pros, though, but for this job, the framing carpenters have contrasting opinions and nobody seems too concerned with the end result (after all, it's only a workshop to them, but to me, it's the workshop where furniture will be created).

Anyhow, I wouldn't hold anyone to their advice here but I enjoy breaktime and often find that opinions and experience often converge into a common pattern that sets me in the right general direction.

The situation, if you don't mind using your imagination a bit, is that I have to build a storage mezzanine across the front of the shop, just above the roll-up garage door. Becuase of this, there is little room between the garage door and the roof rafters on a 9/12 roof. So, between the garage door opener and the roof rafters I have limited space. I suppose I'll probably end up replacing the garage door track with a low headroom version, which should open up some space above. I could then run 2x10s along the outer two walls, each 16' apart from each other, and then nail 2x10s spanning the 16' length, and hanging these on joist hangers nailed to the 2x10's on the outer walls. Just a thought. If I was confident in the design, I would actually consider framing this thing myself. Or if one of the carpenters was convincing enough, I'd trust him to do the job. If this was concrete, it would be a snap. I know a lot of good concrete guys!

Anyhow, any advice/references would be appreciated.

(post #93207, reply #7 of 27)

Here are some schematics that I sketched up.

(post #93207, reply #8 of 27)

I still say get the 2x10 joists up on top of the top plate between the rafters.   I do see that the space height will be pretty low.  Even with a 9/12, the distance from the level of the top plate to the underside of the ridge is only 6 feet.  If you add 2x10s on top of the top plate you drop to 5'3"+-.  Not walking room, but good enough to slide some lumber up there.  And with that limited amount of space, if would be hard to over load the space.

(post #93207, reply #9 of 27)

I think this is the first direction I will go in preparing to build this thing. My brother's an architect. I'll get him to check with one of the structural engineers, but I think I'm on the right track with your suggestion. Better to have some idea to start than none at all.

Thanks for the angle. I appreciate it.

(post #93207, reply #10 of 27)

What is the height requirement in your town? Will your ridge exceed that?

You have standard framing there. Who told you you can't sit the 2x's on the top plate, everyone who builds a house does, unless you raise the 2x's up and have a clipped ceiling but other then that run your 2x's the 16' foot way on top of your plates.

If you have no problem with the height and you need more attic space you can raise the pitch of the roof or keep the pitch and when you run your 2x's on the top plate with a rim joist/box, you can nail a plate on top of that and set your rafters on that plate. If you use 2x10 you wont loose the 9-1/2" that way in height.

Put a row of 5/4 bridging or solid blocking right down the middle.

Joe Carola 

Joe Carola

(post #93207, reply #11 of 27)

I can't remember the height restriction but I do know that I built to the max. according to the local building code. The structure is already built, and it has passed inspection. The mezzanine was an after thought that was not planned into the original design.

I would like to put the mezzanine joists on the top plate but the space between the top plate and roof rafters won't allow me to squeeze a 2x10 in there, unless I cut the ends at an angle that corresponds to the roof. But wouldn't that weaken the joists? See diagram attached.


shopmezzroofmeetstruss.jpg10.7 KB

(post #93207, reply #12 of 27)

I didn't have time to carefully read everyone's thoughts or look at pictures.  I can tell you this--before I moved in 27 years ago the first owner built the same thing you described.  This house has a solid steel garage door (two car) and because that type of door operates on lower tracks there is more room (height) for stuff on that shelf. 
A 5 gallon bucket with stuff sticking out the top fits easily.  I have never said a kind word about the building practices of Owner #1 but....    The storage area is nearly full width (16') and 4' deep.  I haven't loaded the space with full buckets of drywall compound but it has carried it's share of stuff.   It is made with a 2X4 frame, plywood over the 2X's (1/2").  It is held in place by more 2X's nailed to the jack rafters in the hip roof.  One center support from a common rafter.  No beam, no trimmers, no king studs.  One long side of frame nailed to header over door, other long lide suspended as described.  I have a cut roof.  Uses 2X6's.  Been through blizzard of '82 and '93.  Still there.  Simpler (and Owner #1 was simple) seems to be better.  PS  I can't park my 4X4, 3/4 ton w/rack in the garage.  But that is due to door.  Change garage (bad word--used by wife) to "shop", (good word--used, really used!--by me).

Now, if I can just find all the wiring this guy did behind the gyp board--it's aluminum with copper extensions, no J-box, just taped!  Thor 


Things are not always what they seem; the first appearance deceives many; the intelligence of a few perceives what has been carefully hidden.... Roman Poet Phaedrus 15BC–50AD

(post #93207, reply #13 of 27)

What's the size of the garage? Someone I know has the same design as you, and it seems to hold up okay, but it's a single car garage so the span is smaller. Also, I'm not crazy about adding additional load to the roof (and neither was the building inspector when I discussed the idea with him).

I suppose any design will work if done right. I just got onto the "floor joist" idea because it seemed logical that a "floor-type" design would be stronger, and not add stress to the roof.

(post #93207, reply #27 of 27)

As I said, it is a double garage.  It measures about 19'6" in width.  The storage shelf in above the door tracks by about 5".  The 2X4 frame could have been taken full width to the stud walls and supported there (like a header) instead of "hung" from the roof.  The span would need support from somewhere or total redesign.  I planned on tearing it so I could install a sectional door.  But.....I use it for things I don't want to freeze (heated garage).  I beefed up (or added more) everything that acted as ceiling joists, decked it over, insulated like crazy and framed in the ends leaving an access door.  So now my garage (shop) has an attic and I can leave a light going in it for a heat source.  Otherwise, the heated air from the shop rises (which I rely upon alot) and heats the storage area.  But it no way as handy as the 16' wide X 4' deep shelf above the garage door!  So I haven't taken it down, haven't installed a sectional door and keep rebuilding the big one piece door (which I have started to insulate with foam board).  Thor

Things are not always what they seem; the first appearance deceives many; the intelligence of a few perceives what has been carefully hidden.... Roman Poet Phaedrus 15BC–50AD

(post #93207, reply #17 of 27)

Check with your engineer, but a beam or joist's load presures are greatest at the center and near zero at the ends.  Ever see beams on some bridges that taper to the ends and are wide at the midspan?  You also know this to be true if you read codes regarding drilling holes in joists.  They are allowed only in areas which are not critical to the strength of the carrying body.

(post #93207, reply #18 of 27)

Thinking back to many years ago when I studied engineering, I remember some of this when it came to load distributions across a beam. The edges were most stressed while the centres were least stressed. We did tons of stress and deflection calculations, etc. This explains why an I-beam or engineered joists are designed the way that they are. The "thicker" edges reduce deflection in the beam and handles stresses where it's needed most. Notching or drilling a hole in a beam at the edges weakens it where strength is needed most. The problem that I had with engineering was that, as a practical person, I didn't come to appreciate all that theory until I could relate it to something like homebuilding, which I've only taken up in the last 6 years.

Anyhow, on a Friday afternoon, I'm having trouble seeing where you're going with this in relation with this mezzanine idea. Can you help me connect the dots?

(post #93207, reply #19 of 27)

Well, you ask about cutting wedges off the top of you 2x10's where the rafters close on the top plate.  The material at the ends of the joist is just not where the strenght is or is needed.  So you can clip the corners without comprimising the joist.  That is all I was saying in response to that specific question of your.

(post #93207, reply #20 of 27)

2 more cents in the pot...........

First, size a carrying beam to go across the 16' width of the garage.

I know a pair of 1 3/4 x 14" LVL's would work as the beam since I just completed a structural change which placed a 20' LVL across the gable end of a house so we could remove that whole wall and then took out a perpendicular bearing wall between the kitchen and living room and hung a 9 1/2" x 13' set of LVL,s from the center of that 14" beam to carry the ceiling joists that were on top of that bearing wall and then hung another LVL set (11" x 16') from the opposite side to carry the center of the ceiling joists of the addition on the outside of the original house. Without doing the math I'll venture an opinion that a pair of 11" LVL's would work as your carrying beam.

Second, all you have to do is have the bottom of the lofts joists clear the top of the operating garage door. Therefore, the carrying beam would not necessarily have to be ON TOP of the double top plates, as long as you place it far enough into the garage to clear the back of the garage door operating mechanism. The bottom of the beam could be even with the headroom you'd have when the garage door was in the open position.

Third, the beam bearing points could then be within the framing of the side walls of the garage (a 4x4 would do it) and the end of the beam would not be scarf cut to fit to the roof pitch but would have a simple notch cut in the ends to clear the double top plate. With a lowered beam this cut would be very small. What's the height off the floor of an open garage door?

2x6 joists should do it for the floor of your loft.

Are you intending to set those on top of the garage door headers or is there enough room over the top of the door to use hangers to get them a little lower, affording more headroom in the loft?

Also, are the headers over the garage door of sufficient size to act as the opposing carrying beam????

(post #93207, reply #22 of 27)

Going to go with the 2x10s sitting on the top plate. I don't have more than a few inches above the door. Before realizing that I could do this with the 2x10s I thought I would have to lower the track for the door by replacing it with a low-riding track. The 2x10s on the top plate keep everything else in place, simplify the operation, and are listed in the tables as sufficient for both dead and (very rarerly) live loads that will resting on this floor.

By the way, what does LVL stand for? Sorry, I'm still pretty green at this stuff.

(post #93207, reply #23 of 27)

I am not an Engineer, or a professional framer, but I doubt that they are laughing at you and your questions.  What is most likely to get laughs is when a know it all, that was to proud to ask, calls for help to fix the mess they have created.  Sounds to me as though you have it figured out now, good luck on a speedy and quality conclusion.  LVL is a type of engineered wood, Straighter sstronger and flaw free.  Man made new stuff, better we think, woof woof woof.


(post #93207, reply #21 of 27)

Makes sense now. Been dealing with "the big blackout" and couldn't see things clearly.

Thx again

(post #93207, reply #14 of 27)

My first post to you I thought that the rafters weren't on at first.

I must not understand this to well. It sounds as if you framed it without ceiling beams and maybe just put collar ties in and would like to add a 8' x 16' platform in it and keep the collar ties there and just get to this platform from a ladder.

Are there any ceiling beams now? If so are they nailed on the top plate or up on the rafters as collar ties?

I've attached two drawings. Tell me if I'm close.

Joe Carola


Joe Carola
garage_platformx1.jpg27.39 KB
garage_platformx2.jpg22.18 KB

(post #93207, reply #15 of 27)

Why not build a 16' x 8' x 9" box beam? very strong!

use 2x8s for joists, cut to fit roof line (leave 1/8 to 1/4" clear for venting) 12"OC.

Use  solid blocking at the 4' mark. Use flat 2x4s top and bottom at the 8' mark with a solid block next to them. Use solid blocking next to walls.

Sheath top and bottom, with perimeter gluing and a 4" OC nail schedule at perimeter and 8"OC in field. 1/2" ply on bottom.

After sheathing bottom, push a 2x8 ledger tight to bottom of box beam at the walls and lag it to the top plates and studs.

This stress skin type construction requires all plywood edges to be stitched together with glue and a lot of 8d nails top and bottom to the blocking. 2x4 blocking allows you to place the nails a little farther from the edge.


"Law reflects, but in no sense determines the moral worth of a society.... The better the society, the less law there will be. In Heaven, there will be no law, and the lion will lie down with the lamb.... The worse the society, the more law there will be. In Hell, there will be nothing but law, and due process will be meticulously observed."

Grant Gilmore, The Ages of American Law (New Haven: Yale University Press, 1977), pp. 110-111.
From 32866.117

A Pragmatic Classical Liberal, aka Libertarian.

I'm always right!
Except when I'm not.

(post #93207, reply #16 of 27)

Thanks a million! This is bang on! Since reading these messages I remembered a house framing book that I had bought years ago so I looked up a loft (which is like my mezzanine). I found exactly what you referred to in the first diagram, with the angle cuts in the end.

The mezzanine was a last minute thought, so we added the ceiling beams spaced at 4' O.C., screwed in, just in case we had to remove them and add the mezzanine later. There are no collar ties in the design (thinking back to the permit drawings, they were in and then were removed as they were not necessary due to the rest of the design). The rest of the shop (the remaining 16' behind the 8' at the front) is a cathedral ceiling framed in scissor trusses with skylights. It's dream shop that I built myself to be able to do cabinet-making work, and it enables me to move tall pieces of trim and full sheets of plywood without worrying about hitting the ceiling. Where the back 16' roof meets the front 8' roof section, there are tripled trusses (the engineer who spec'd the trusses wanted to be sure that the front was solid, in case we added the mezzanine) and the front is conventionally framed, so as to provide more headroom for storage.

At the time, I was thinking about a 2x6 mezzanine floor that I had seen elsewhere, but I didn't like the fact that the person who built it had suggested a cable at the centre, suspended from the roof, and used doubled up 2x6's at the front and back, with joist hangers holding 2x4's across the 8' length, totally suspended from the 2x6's (one of which hangs at the front). I hadn't realized that angle cutting the 2x10's where top plate meets roof rafter was a acceptable, as my carpentry skills are limited to the basics (built a garage and a shed) and I am always one to hire the right person for the job rather than pretend I can do it all. Problem three different carpenters had three different perspectives (from steel beams to quadruple 2x8's, etc.). This  got me thinking that for something this basic, there has to be an easy and "proper" way.

So, your diagram and the other postings got me on the right track with this. Thanks again! I'm sure the professional framers out there are laughing at me but I hope you give me credit for trying to do this "the right way". I've seen too many botched up jobs out there to know that while they may look okay, and seem acceptable, there's always a better reason for doing things right.


(post #93207, reply #24 of 27)

So, your diagram and the other postings got me on the right track with this. Thanks again! I'm sure the professional framers out there are laughing at me but I hope you give me credit for trying to do this "the right way".

I'm glad that everything worked out and everyone was helpful for you.

I've been framing for 20 years and still ask a million questions all the time and if I come into a situation that I've never been in before, I wont stop until I figure it out right or ask another framer what they've done it that situation so the job gets done right or it doesn't get done at all.

I call architects up if I'm bidding a job and something doesn't look right structurally or a roof line wont work the way they have on the plans and that they forgot to put a structural beam under a roof. This way it can be addressed before I bid it and the problems are solved before the jobs starts.

I'm not an engineer and can't quote loads and all that but I can tell from experience on framing so many houses and additions and comparing your situation with the jobs that I have done like yours and can tell you my thoughts.

No one should be Laughing at you at all. Your taking the time out to do the job right. I see a lot of contractors that have been in the business for years that don't do the job right and know it. I respect what your doing and so should everyone else and keep up the good work.

Joe Carola


Edited 8/16/2003 8:41:40 AM ET by Framer

Edited 8/16/2003 8:44:41 AM ET by Framer

Joe Carola

(post #93207, reply #25 of 27)

It's refreshing to know that there are skilled tradespeople out there who are committed to doing the job right...the first time!

Thanks to all for the support and advice. I subscribed to Fine Homebuilding because it's what I am interested in. Anyone can hammer nails and cut wood. Doing this right and with pride is another story.

Above all, I learned a great deal more than I anticipated, from all that responded to my inquiry.

Thanks again!

(post #93207, reply #26 of 27)

Laminated Veneer Lumber.