Building a Mezzanine?

I'm looking at putting a mezzanine in my new shed some time in the not to distant future but haven't quite come to a conclusion as to how best to to it.

I'm leaning towards making it freestanding, but possibly attached to the existing steel shed frame to add stability. Galvanized steel purlins look a good option, and would match with the shed frame well. The biggest problem im having with that option though is the lack of span tables available to work out how to spec it adequately.  It's mostly just going to serve as storage for low use and bulky items, I'm not trying to store whole cars up there or anything, but realize weight can add up rather quickly.

I'd also like to build it sturdy enough that down the track I could frame up wake and enclose the mezzanine level to make a room, be it a games room, office space, spare accomodation, whatever really.

At this stage, I'm not interested in permanent stairs, they'll take up too much space, so either a ladder against the end of it or potentially an attic ladder through the floor will be used for access. I'll most likely rig a gantry trolley or similar for hoisting larger or heavier items up.

Overall size of the mezzanine will be somewhere around 3.2x3.5m². it'll need to be 2.4m off the ground and I'd like to keep the overall thickness of the floor as thin as possible, the thicker it is, the more it will eat into the upstairs headroom. Floors will most likely be structural chipboard flooring.

Something like the below picture would be pretty much perfect, but I've got no idea how to ensure I've spec'd it adequately.

I'd be willing to consider timber construction as an alternative

The most important thing to know is, what will you be storing up there?  If it's a man cave with 4 chairs, a coffee table, and a fridge, you can span 10' with 2x6 pine on 16" centers.  If you'll use it to store 15 spare engines, not so much.  Since you're not sure and would like the increased flexibility of putting whatever you want up there, go big and beefy.

Two things you need to know are live loads and dead loads.  Dead loads are things like kitchen cabinets, refrigerator, water heater... things that get installed and don't move.  Live loads are things like people, furniture, cars, dogs, etc.  Do a google for floor span calculator.  Most of them default to 10/30 psf which is a common residential load.  That covers things like your couch and 5 people, but is also enough in case you have a party with a keg and 40 people.

Commercial loads are often higher.  Things like stores, gyms, auditoriums, schools, bowling alleys, etc usually require 100 psf floors.  My theater floors are 125 psf live (using engineered wood I-beam joists and 3/4 ply) and I can drive a 2500- lb scissor lift across it and only feel very minor flex.  I should think that 100 psf would be glorious overkill for you, and you could store all the engine blocks you want up there.

To get 100 psf with wood installed on 12" centers, you really need 2x10s, but 2x8s would get you really close, like 90 psf or better.  So overall thickness of the floor would be 8" (7.25" for the 2x8 and 3/4" for the subfloor).  If you can spare the headroom, that is the easy button.

I won't comment on steel since I rarely work with it in structural applications.  There are some rough estimates you can do, but it seems that most steel structural manufacturers do their own testing and make their own ratings.  It's kinda hard to find a standard chart where you can plug in 4x8x 1/4" steel I-beam and get an answer.

A good rule of thumb(apparently not a PC term I just found out) when framing flooring or decking is to figure out your span. Less than 4' use a 2x4, 4' to 6' use a 2x6, 6' to 8' use a 2x8, 8' to 10' use a 2x10 and 10' to 12' use a 2x12. Code will determine what you will "have" to use in the long run, if it is a permitted project. Spans should be 16" on center.

Just my 0.02¢

In reply to Curtis73 (Forum Supporter) :

Just a note...

Furniture, appliances, etc are not dead loads.  They are live loads.

Dead loads are the components of the building itself.  The weight of the wood, roofing, drywall, etc.  

Water heater is a dead load.  Fridge is a live load.  Cabinets are a dead load IF they are installed- if they are free standing like European cabinets, they are a live load.

In reply to daeman :

You need to give more info about the shed you are building into.

The picture you included is beautiful, but the vertical posts in that structure were DESIGNED to hold the loads of the mezzanine.  If your shed is a metal structure, you can't just hang extra weight on a structure that was not designed for it.  You may need additional posts to support the weight of the mezzanine independent of the existing structure.

If your shed is a wood framed structure, it is likely overbuilt enough to support additional weight of the mezzanine.

SVreX (Forum Supporter) said:

In reply to Curtis73 (Forum Supporter) :

Just a note...

Furniture, appliances, etc are not dead loads.  They are live loads.

Dead loads are the components of the building itself.  The weight of the wood, roofing, drywall, etc.  

Water heater is a dead load.  Fridge is a live load.  Cabinets are a dead load IF they are installed- if they are free standing like European cabinets, they are a live load.

Good clarification.  I knew that movable things were live, but thought that a fridge was one of the "permanent/installed" things.

Curtis73 (Forum Supporter) said:

I should think that 100 psf would be glorious overkill for you, and you could store all the engine blocks you want up there.

I won't comment on steel since I rarely work with it in structural applications.  There are some rough estimates you can do, but it seems that most steel structural manufacturers do their own testing and make their own ratings.  It's kinda hard to find a standard chart where you can plug in 4x8x 1/4" steel I-beam and get an answer.

 

Agreed not knowing the end use makes this a trickier problem to solve, so I'd like to head towards heavier than needed as opposed to underspec-ing and not being able to use it to it's potential.

Not being able to find a plug and play calculator for steel is what prompted me to ask, timber is pretty easy to figure out due to how commonly used it is, but I'd honestly prefer to use steel if I can.

I really appreciate you being able to give some figures on wood though, because I hadn't given it much thought and it looks like if I used lvl supported on its own legs/uprights I can actually have a comparable overall floor depth to steel, potentially with a higher load bearing capacity. It'd also have the bonus of making putting stud walls on top of the mez easier in future if I wanted to enclose it as it would be nail gun assembly friendly.

In reply to lotusseven7 (Forum Supporter) :

Rule of thumb not pc? Is it because its regarding the thickness of an object that was able to be used in a not very nice domestic nature?

That's a really simple break down of span v size of timber, thanks mate. Code is pretty lax for this project, for arguments sake, if I put it on its own independent legs, it's would be seen as a shelf, not part of the building. Being a shed and not a residence, my local authority wants very little to do with it past the primary structure being compliant.

In reply to SVreX (Forum Supporter) :

Yeah, fair point. More information would have been good, my bad.

What I'm working with is essentially the same as what you saw pictured. The uprights are c15015 purlins. 152x64x1.5mm . The end wall is single uprights, the center posts are double/back to back uprights. Slab is 100mm thick, all uprights are on pier holes 450 wide by 400mm deep.

I'm more than happy to put the mez on its own uprights if need be. Whilst I love the packaging of the included picture, I understand that my current upright purlins may not be enough alone to make that possible.

My understanding is z purlins would be better than c purlins for the mez floor. Apparently they're stronger in that kind of application.

I can probably dig out a table with the information required to calculate load/area. But I wasn't confident in calculating that myself and getting it correct.

I'll go and take a photo or two close up of the actual area I'm working with after breakfast. 

Would something like this work for you ?

Metric measurements... I forgot you are in Australia...

I respect your desire to double check and get the calculations right... don't ask on the internet. The only people here who are qualified to do the calculations probably wouldn't do it online. 
 

I build with steel, but I don't design with steel. Only wood. I just follow plans that someone else designed.

There are 2 ways to do it- hire an engineer (shouldn't be cost prohibitive), or use your gut and overbuild it. I'd do the latter. 
 

The details I was looking for are the loads you are gonna put on it.  I already know your existing structure isn't designed for the additional weight- they are never over-designed.  Like Curtis said- if youre gonna load it with engines, it's different than if you're gonna put a couch up there.

The mezzanine you pictured is a really simple structure. I'd feel very comfortable winging it - just add legs under your new floor system so it's not counting on the existing columns. 6" 16 ga C-joists with 3/4" AdvanTech T&G subfloor should do fine- but not if you load it with 15 engines.
 

Steel is gonna cost you 3X what wood will. 

Good luck!!

In reply to californiamilleghia :

Dexion or similar pallet racking crossed my mind, but because it's in the middle bay it will really hamper access. There's no doubting it's an easy button answer though, so appreciate the suggestion.

In reply to SVreX (Forum Supporter) :

Haha, yeah, bloody foreigners and their metric measurements. 

Thanks mate, I can recognize when I'm out of my area of expertise, so don't feel any shame in asking for input from people with more knowledge or expertise than myself. I can appreciate that people would be reluctant to give a firm or definitive answer online though.

Yeah, I hear you, I mean I built the shed, but I didn't spec it or design it. I probably would have gone a bit more overkill if left to my own devices haha.

I totally understand how my lack of knowing exactly what will end up up there makes this much harder in terms of just how strong the build needs to be. But I guess if I build to worst case scenario and under utilize the space it's far less harmful than underbuilding and overloading... Except maybe to my wallet.

I was initially thinking along a similar path to what you said, but probably 200mm c purlins for the legs and perimeter frame with 150mm z sections for the joists. At least I was in the ballpark.

Given I'm considering lining the end 3 bays to create a separate workshop space, wood isn't completely off the table, and if I can get the same or better strength than steel, I'm definitely prepared to consider it as an alternative. Especially if it ended up costing half the price.... Money talks haha.

Thanks for your help, I've always got alot of respect for guys like yourself and Curtis and others who are willing to share their hard earned knowledge and experience.

Ok, seeing as I'm entertaining wood, let's change directions here for a minute.

So as mentioned, my structure is essentially the same as what I posted initially. The bay right of center with the PA door will be getting built in to enclose a small bathroom and kichenette etc. So given that I'll be already framing in some of the end of the shed, I have previously considered putting an 8ft ceiling right the way across the 3 end bays. That would give me 2 additional loft like spaces that I can stash long skinny things, say ladders, lengths of wood, pipe, etc.

Center bay I'd like a large opening to the rest of the shed, possibly using sliding doors or something so I can air-condition the workshop section effectively.

The bay to the left can have a solid wall, but I'd probably prefer to have at least a double door size opening or a window or something in it so I don't end up with a little cave across the end of the shed.

Given you guys like wood, how would you go about something like that? I can sketch up (pencil and paper not the software haha) a couple of rough drawings to give a better idea of what I'm talking about if what I've said isn't overly clear.

Let me preface this with the fact that I am not an engineer or a licensed contractor at all.  I'm a guy who builds sets for a theater and I used to do general contracting/building.

So the following is an idea for how I would proceed if there were no inspectors involved, but not a blueprint.  Forgive the English/SAE measurements, but you'll get the idea.

Since you had mentioned that walls are a possibility, I would frame up typical stud walls with 2x4 or 2x6 (yellow) with a double top plate, and span it with 2x10s (one shown in orange, too lazy to draw the rest).  I, personally wouldn't continue the second level for the entire span, A) because as you mentioned it might make a whole cave, and B) the second floor would be primarily useless except for maybe sliding some boxes in.

But, if you did want to continue the span the whole way, you would just continue the 2x10 joists the whole way to the outside walls.  Where I can't advise is the best way to attach the joists to the outside walls.  I don't know if the steel posts are designed to handle additional weight.  If they are, you could bolt a ledger board to the steel and set the joists on it.  If not, you could build another stud wall against the side wall to be sure.  That way you're transferring the weight to the floor and not the walls.  Having an additional stud wall against the outside might be nice anyway if you're going to enclose it and put up some kind of wall board.  Easier to attach drywall to wood than a steel pole frame.

If you wanted to 

Another possibility that avoids the walls and also eliminates the question of how much weight the steel posts can take...

Using some 6x6 posts bolted to the steel at each corner (yellow) with an appropriately-sized LVL (brown) and then 2x10s between them (blue) with joist hangers would also be a possibility.   The only times I worked with LVL, someone else did the engineering and calculations, so I can't advise what size to get or what it can support, but like I said.... ideas.

Basically, you are using the steel posts for vertical stability, but the weight is carried by the wood 6x6s, not the steel

Don't need the walls.  Just add a 4x4 alongside each existing column supporting a beam to hold up the floor joists.

In reply to Curtis73 (Forum Supporter) :

Appreciate you taking the time to have a play with the drawings. The second image is pretty much what I have in mind for the mez be it wood or steel.

I probably didn't explain myself right regarding walls though, I'm thinking about walling off the whole width of the shed to create a separate workspace from the main shed. Same rules apply more or less though, so I can definitely adapt what I'm doing to suit.

So I did some pricing and investigating yesterday.

Either we pay substantially more for wood or substantially less for steel here, because cost per lineal meter of steel is within 10 percent of wood. It may work out cheaper for steel if I have to use a wood 6x6 for the legs (svrex, you're thinking I could get away with 4x4?) or have to use 10x4 for the beams the joists hang off. 

Interestingly lvl is very competitively priced with normal wood. So a 240x45 (10x2)mgp10 pine length is approximately the same price as a 190x45 (8x2) f17. Figures suggest the lvl has about a 40 stiffness increase over the pine. So would I be out of line running 2x8 lvl's as opposed to 2x10 pine?

Also managed to make a bit of sense out of some steel spans. If I can spec steel to over 5kn/m I should be over 100lb/sf. Just need to speak to one of the tech guys to confirm my working and joist spacing. I'd also need to find what kind of vertical loading the purlins can take. 6 inch c or z joists in 16ga are cheaper than 2x8 lvl. And about the same price in 10ga (10ga will put me up around 6-6.5kn/m)

In reply to daeman :

There is no such thing as speccing the size of the beams and joists (regardless of if they are wood or metal) if you can't guess at the load. 
 

You gotta build for SOMETHING.  It would be irresponsible for me to say an 8" LVL would support the weight of the floor and then have you load it with engines. 
 

The LVL beam is the issue (not the floor joist). It holds ALL the floor joists. LVL beams can be taller, thicker, or several laminations to help carry loads. Sometimes 4 or more laminations. 
 

You gotta take a guess at the use. Figure worst case scenario. 

In reply to SVreX (Forum Supporter) :

Fair enough, I should have said I'm aiming towards the 500kg/m or 100lb/sf range. I feel like if I can get between a result capable of between 400 and 500kg/m2 that's going to take pretty much anything I can throw at it, without being stupid about it.

I had a look at a few commercially available mezzanines yesterday and that would seem to be considered fairly heavy duty. 300kg/m being light, 400kg being medium. Whilst not a standard, it seemed a pretty common theme amongst several providers.

I figure building anything will help regarding storage. And working out what weight it will hold is important  but I can look at it kind of like buying a set of premade shelves.... If I know the shelf will hold 100kg per shelf, it'd be dumb to then try and put 200kg per shelf on it 

Unless I'm totally missing the mark, if it's roughly 3x3m at 500kg/m2 that's 4.5ton... or a metric berkeleyload of junk.

I realize I'm working kind of backwards here, but I figure if I build the shelf, I load it accordingly. So if that means I only achieve half of what I'm looking for, then I just have to make peace with that and not overload it.

Sorry, I'm not always great at explaining myself or putting forward information in a useful or digestible manner. I get that that can be frustrating, especially when someone's trying to help me out.

In reply to daeman :

Ok...

First off (this is important!)... Floor loading is a weird calculation. You CAN'T take a 10x10 floor that is rated for 50 psf and assume that means it can hold 5000 lbs.  It can't. I know that sounds stupid, but engineers have some weird language they calculate this in... it is an AVERAGE of the total floor space (including aisles). Which means that a 50 psf floor can't hold 50 psf.

If you want to actually calculate the floor loads, here is how it's done:

https://www.google.com/amp/s/nationalofficesystems.wordpress.com/2011/11/30/10-things-i-know-about-floor-loading/amp/

Now, forget that stuff. Let's build you a reasonably strong floor....

(These are just my swags from a lot of experience- no science)

Yes, a 4x4 leg is adequate to support the floor, especially if it is bolted to the existing steel column.

After that, I would use LVLs for the support beams.  2 lamination 11 7/8" x 1 3/4" for each side.  
 

2x8 floor joists hanging off the side of the beams should be fine. 16" o.c. If you want to beef it up, switch to 2x10.  LVLs for the joists would be really nice, but it's overkill. 
 

The floor decking is important. 3/4" AdvanTech T&G would be awesome. 
 

That will build you a really solid floor. 
 

You can do the same thing with metal. Just add structural tube columns next to the existing columns (instead of 4x4s). Don't add load to the existing columns.

Hope that helps!

I will second the AdvanTec flooring.  It's what I used to re-do my subfloor in the house and it is far better than even plywood.  They have several grades.  I got the top-of-the-line, mostly because I knew I would have to store it outside and the top-grade stuff is rated for 100 days of wet exposure without water infiltration.  If they don't sell AdvanTec in Australia, I'm sure they have a similar product available.

Another product (if you have them down there) is HeadLok screws and TimberLok screws.  Replacement for a 10mm lag bolt.  Instead of drilling big 12mm holes in your steel posts for big bolts, you can drill a few 6-7mm holes and screw right into the 4x4.  I call them orgasm screws because it feels like getting a little orgasm when you feel them tighten up.

In reply to SVreX (Forum Supporter) :

Yeah, that's what I was afraid of, that I was completely off on my Understanding of exactly how to calculate a floors load carrying capacity. An engineer I am not....

Building a really strong floor and using it sensibly sounds like the best way forward. What you and Curtis have proposed will hold a decent amount of stuff without going full nuclear and spending half the cost of the shed .

So, given the choice, 2x8 LVL or 2x10 pine for the joists? Neither are a major cost increase over pine 2x8s and both are within a few cents of one another cost wise.

Side note, it's interesting seeing the different standards between the countries. Standard joist spacing here is either 450 or 600 O.C in nearly all applications I've come across. Meaning insulation bats are sold as 430 and 580mm widths respectively.

OSB based structural flooring isn't common here, but looks like it's about to be. I had a discussion with a supplier yesterday and he said theyre being swamped with orders lately. Lighter, stronger and cheaper than the standard compressed particle board flooring has helped it pick up popularity, but what's really pushed it forward is a prominent particle board maker has recently changed their standard board size from 3600x900 (12x3ft) to 3600x800. It's left a lot of guys in the lurch because their builds have been based around standard board size.

While steel is still on the radar, I feel like steel ceiling joists and timber stud walls will probably give me plaster issues.

Mate, it helps plenty, I appreciate it alot.

In reply to Curtis73 (Forum Supporter) :

I had a bit of a look into the headlok and timberlok screws, they look like stud tie screws. A couple of companies here make them so I'll keep them in mind.

While we're talking fasteners, I'm thinking joist hangers for the joists. But also running bugles (big countersunk  in-hex drive drive screws) through the bearers and into the joists. Overkill? Or should I go more overkill and run the big flat headlok types (given they'll be in shear, I feel like bugles will achieve the same thing)