Raised Floor Framing Systems

[T_Bat]

Hey everyone,

I've got an interior build out I'm assisting with and we need a floor surface raised around 16" to 18" inches (think like a raised access floor). The existing floor is a steel composite floor system (3rd story). My plan was to use light gauge framing with sheathing on top to form the elevated floor - similar to how you may frame auditorium/theater seating. I'll add some diagonal studs every so often for stability.

Before I go too far down this road detailing/designing, has anyone got a better system they've used? I'm also toying with using wood. It can't be a typical data center type pedestal floor because it's a kitchen and will get mopped or even potentially sprayed down for cleaning so it needs to be reasonably water resistant.

 

[KootK]

Depends how much weight you can tolerate and how "institutional" the client needs that floor to feel. A topping slab over rigid insulation would feel nicely institutional but may be too heavy. I like sheathing over cold form for economy and weight but it's probably going to feel/sound a bit cheap. Given the nature of the occupancy, one should probably give some consideration to moisture potentially getting trapped in the interstitial space and initiating corrosion issues.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dik]

There are proprietary raised floor systems, often used for computer or lab floors.

Dik

 

[klaus.]

you can get raised floor system on the market
for example : MERO

 

[XR250]

I've got an interior build out I'm assisting with and we need a floor surface raised around 16" to 18" inches (think like a raised access floor). The existing floor is a steel composite floor system (3rd story). My plan was to use light gauge framing with sheathing on top to form the elevated floor - similar to how you may frame auditorium/theater seating. I'll add some diagonal studs every so often for stability.

I have done a few of these similarly. Are you using wood or cement board sheathing? If wood, can use use wood studs as well?

 

[T_Bat]

All great points - I think we want to stay away from foams since some program elements will have to run through the space. I've looked into the proprietary systems but none make me feel great about water resistance. The area is a commercial kitchen - so it doesn't need to feel like crap but certainly not as nice as you may need for an office build out or lab. I'm not 100% clear on the floor finish yet. It could be tile but it may end up with some kind of membrane coating. Would a gypcrete topping help with the "feel" issues?

XR250 - I was thinking initially steel stud with wood sheathing but I'm open to wood framing. My concern was similar to KootK's - I'm worried about moisture in the interstitial space. Steel studs don't fix that but would probably hold up better than the wood framing. Not really sure what one does to properly mitigate any corrosion issues...

 

[XR250]

XR250 - I was thinking initially steel stud with wood sheathing but I'm open to wood framing. My concern was similar to KootK's - I'm worried about moisture in the interstitial space. Steel studs don't fix that but would probably hold up better than the wood framing. Not really sure what one does to properly mitigate any corrosion issues...

You could use PT wood. You could also vent the space out the sides if needed although i have never heard of moisture being a problem in these situations on upper levels.

 

[BridgeSmith]

If the floor finish is rigid tile (ceramic, porcelain, etc.) the subfloor will need to be really stiff, especially with the potential for heavy pieces of equipment with small feet that sometimes show up in commercial kitchens.

 

[XR250]

ahhh, did not see the Kitchen part. (I am so A.D.D.) I guess moisture could be an issue. PT lumber would be my preference over LG steel. Also, providing an access underneath and venting would make sense.
HotRod made some good points.

 

[DBronson]

T_Bat:

Be careful with wood framing - you may need to add a sprinkler system to the interstitial space. Check with the architect or the local building official to see what's required.

Regards,

DB

 

[NorthCivil]

Please - the answer to moisture isn't to pressure treat! you will have to use all stainless fasteners. Typically framers like to use nail guns, try to source coils of stainless nails, good luck.

If it is to be a cavity, it will need to get vented.

I might be more keen on a scaffolding, staging type temporary platform.

 

[dik]

Can you use Stonhard floor covering? or maybe a heavy duty vinyl, or 'battleship' linoleum? This can go over your concrete or wood decking, and can be tough and waterproof/resistant. Stonehard can wrap up the wall, similar to a molding.

See:

http://www.stonhard.ca/

and, it can even have a traction 'grit' to prevent slips...

Dik

 

[T_Bat]

Thanks for the insights everyone. The kitchen designer is using an epoxy coating similar to what dik describes. However he (or she)is concerned about the durability of the wood sheathing under everything, particularly since floor drains will be involved. A few options I've discussed with the my client:

1) Stick with CFS framing and wood sheathing but provide a gypcrete topping - maybe a membrane under the topping? Not sure how effective this would be.
2) CFS framing with 1/2" form deck and concrete slab. Constructability issue? - the area is on the third floor of a finished building.
3) Some option I don't know yet (that's where you come in).

Any opinions on 1 or 2? Any options for 3?

Also - there is now an separate area that we'll need to raise that will be exposed to the weather. It's a mechanical yard on the third floor. For this I'm thinking we'll have to go with CFS framing, form deck, and concrete. The elevation change it 16" - so I'm thinking I could use rolled steel placed directly on the existing slab with the new deck on top. Any other (cheaper) options you know of?

 

[structSU10]

I have used a cement board product for the floor sheathing before, like durock, over CFS.

 

[KootK]

Depends on the chosen philosophy. I don't know that it's practical to keep this thing 100% water/gunk proof. That being the case, you either:

1) Go light and allow for the access to the plenum so that it can be inspected periodically and things can breath or;

2) Lock it up tight and go as durable as possible. CMU pony walls and non-composite deck above. Pouring concrete on an existing floor won't be fun but it's certainly possible.

Even with #2, I'd be hesitant to not provide access for periodic inspection. It may well be the base structure that deteriorates first.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[T_Bat]

I see your point on providing access but what exactly would that look like? Some type of door/hatch in the floor? The plenum will be less than 16" (not including the CFS framing). How much will you reasonably be able to inspect with access?

 

[KootK]

The plenum will be less than 16" (not including the CFS framing). How much will you reasonably be able to inspect with access?

Access sounds infeasible unless you build the whole thing out of removable panels somehow.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BridgeSmith]

A wood framing system using 2 layers running perpendicular could give you the stiffness you're looking for with little restriction on air flow. Something like 12" engineered joists at 3' - 5' spacing in one direction with 2x6's running the other direction on top, for instance. The 2x6 spacing would be at 12-24" spacing, depending on the thickness of the sheathing and how stiff the floor needs to be.

 

[T_Bat]

I think I'm staying away from wood framing - I think the wood framing would need to be fire retardant treated since it's combustible. I may consider the (2) layer framing with CFS in some dryer areas.

 

[BridgeSmith]

Steel joists in the 2 layer system would also work, I suppose. Might be easier to connect - tek screws through one flange into the other, right? With wood framing, they'd either have to toe-nail or run the screws up through the TJI flange into the 2x6 blind.