Weight Distribution: Flooring needed?

[MattRMagnum]

Hey Folks,

My new garage has a loft in it. For both convenience and safety, we're wanting to move my server rack there. That means I'm going to be putting 300-500lbs in one static spot. I think the flooring is solid enough to hold the weight, but someone suggested I put flooring in, as that could help distribute the weight, and it wouldn't all be sitting on one sheet of plywood. There'll also be a couple hundred pounds elsewhere, as my desk/office are going to reside in another part of the loft.

I know nothing about construction. I just know that if my server racks fall through the floor, I'm going to be out all of our critical files, plus a bunch of computer hardware. There should be photos attached to this post. If not I'll find somewhere to upload them, and link to them. One shows the joists underneath. I think they're either 12" or 16" spans, and look to be at least 2x6's, if not 2x8's (I can't get into a spot to measure them, currently).

Does anybody think I need to add flooring, or do re-enforcement? Oh, and please don't suggest I put the server rack elsewhere: that's the only safe/secure location that's also protected from the elements.

 

[MattRMagnum]

Failed to add photos to the first post, so here they are:

 

[dave*99]

Let's start with the ledger - the board above the flag with the number 12 on it. All the joists tie into it. It's notched and hung from a single joist hanger on the right side. That ledger is a weak spot.

The middle of the joists should have bridging (blocks of wood tying each joist to it's neighbor.)

 

[MattRMagnum]

Let's start with the ledger - the board above the flag with the number 12 on it. All the joists tie into it. It's notched and hung from a single joist hanger on the right side. That ledger is a weak spot.

The middle of the joists should have bridging (blocks of wood tying each joist to it's neighbor.)

How would I strengthen the ledger? Would the bridging you're talking about do that?

 

[larry_g]

how I did it

In the link above you can see how I did it. On the right side observe the blocking under the ledger board. The blocking is nailed onto the 6x6 and supports the ledger board.

On the left side is what I call my storage wall, 2x10's for studs and the joists for the mez set on top of that wall. You can see more if you look through the build thread in my sig.

lg
no neat sig line

 

[benjy]

how I did it

In the link above you can see how I did it. On the right side observe the blocking under the ledger board. The blocking is nailed onto the 6x6 and supports the ledger board.

On the left side is what I call my storage wall, 2x10's for studs and the joists for the mez set on top of that wall. You can see more if you look through the build thread in my sig.

lg
no neat sig line

What I did also, sorry for the upside down pic. Was in Australia when I posted I guess.

Get some high shear strength lag screws to anchor the blocking, GRK and
Spax are good brands.

My simplistic approach to structural engineering is to divide the weight of whatever will be stored up there plus the weight of the mezzanine (x 2 or 4 or whatever my comfort level is) by the # of anchor points. The shear strength of the anchor needs to exceed this weight, this I factor up as well and use multiple anchors as well.

I believe I used 5/16 spax power lags with a shear strength of 920 lbs each. I used at least 14 for my mezzanine.

Edit: I'm not a structural engineer & there's a lot more to designing structural connections so if in doubt, consult a PE.

Under the mezzanine, lifted Jeep on 35s still fits under here w/ a bit of room so I should be good once concrete is in.

www.garagejournal.com

 

[dave*99]

What I did also, sorry for the upside down pic. Was in Australia when I posted I guess.

Get some high shear strength lag screws to anchor the blocking, GRK and
Spax are good brands.

My simplistic approach to structural engineering is to divide the weight of whatever will be stored up there plus the weight of the mezzanine (x 2 or 4 or whatever my comfort level is) by the # of anchor points. The shear strength of the anchor needs to exceed this weight, this I factor up as well and use multiple anchors as well.

I believe I used 5/16 spax power lags with a shear strength of 920 lbs each. I used at least 14 for my mezzanine.

Edit: I'm not a structural engineer & there's a lot more to designing structural connections so if in doubt, consult a PE.

Under the mezzanine, lifted Jeep on 35s still fits under here w/ a bit of room so I should be good once concrete is in.

www.garagejournal.com

Is your mezzanine also hung from the trusses with steel cable? If so, are the trusses rated for that point load?

 

[benjy]

Is your mezzanine also hung from the trusses with steel cable? If so, are the trusses rated for that point load?

Yes, 29k rated 1/2" elevator cable with a short 2x4 block to protect from pinching the bottom chord.

Morton was ok with it, ran it by them beforehand, as long as I don't store a collection of engine blocks up there, I'm good.

Down the road I'd like to get a 30' angle iron up there to support the span, something with a good depth to it & bolt to a sistered 2x6 beam.

Might test out a sistered 2x6 with a 30' flat bar thru it, did a 18' span this way. Will move to a stout square steel tubing for support on either end.

 

[duneslider]

Its hard to tell what that beam is but those brackets holding the beam look like HUCQ's and they have a capacity of like 4000#. It almost looks like the ledger or beam is a 3" wide by 14" solid member, that's pretty stout. Those joists look like 2x12's. I don't think you have anything to worry about.

I think you would be just fine to put the server up there and a desk. It would be nice to get more details on the sizes of the members used here but it looks pretty stout to me.

 

[TobeyA]

As to the original question: Is that OSB adequate as the floor, or should he treat it as a subfloor and add something over it? For some reason, placing a point load on OSB makes me nervous. But I have no direct experience to validate that concern.

 

[Toomanytools?]

How would I strengthen the ledger? Would the bridging you're talking about do that?

You could add a post or a couple of 2x4's to the existing post under the joist ledger to support at least 1 1/2". Or run another ledger post to post under all the joists. I think the OSB has a live load of 175 PSF for 23/32", you should be fine. As long as the rack doesn't have 4 legs that concentrates the load. If anything cut a 4x4 0r 2x2 sheet to help displace the load. I don't like the way the plywood was put down, stagger the joints.

 

[MattRMagnum]

As to the original question: Is that OSB adequate as the floor, or should he treat it as a subfloor and add something over it? For some reason, placing a point load on OSB makes me nervous. But I have no direct experience to validate that concern.

I probably should've put more emphasis on this question, since it seems like most folks fixated on the other... I think the joists will split the load, but it still feels very 'thin' to me, even though I think it's at least 1/2" OSB.

 

[benjy]

I probably should've put more emphasis on this question, since it seems like most folks fixated on the other... I think the joists will split the load, but it still feels very 'thin' to me, even though I think it's at least 1/2" OSB.

I'd put at least a 1/2" sheet of plywood over the osb to spread the load of the server rack across multiple joists, just to ensure the load is spread.

Somewhat cheap insurance.

 

[dave*99]

Bridging and blocking looks like this. It won't help the ledger but it will stiffen the floor. And stop a tall server rack from swaying when you walk across the floor. You only need 1 piece of blocking at the midspan of each joist. So in your case, 9 pieces about where your fluorescent light is installed. You can stagger them and nail into their ends if you don't want to toe nail them.

 

[dave*99]

You could add a post or a couple of 2x4's to the existing post under the joist ledger to support at least 1 1/2". Or run another ledger post to post under all the joists. I think the OSB has a live load of 175 PSF for 23/32", you should be fine. As long as the rack doesn't have 4 legs that concentrates the load. If anything cut a 4x4 0r 2x2 sheet to help displace the load. I don't like the way the plywood was put down, stagger the joints.

All good - and the server rack will likely have 4 legs or wheels. So be sure to look at that.

 

[benjy]

Bridging and blocking looks like this. It won't help the ledger but it will stiffen the floor. And stop a tall server rack from swaying when you walk across the floor. You only need 1 piece of blocking at the midspan of each joist. So in your case, 9 pieces about where your fluorescent light is installed. You can stagger them and nail into their ends if you don't want to toe nail them.

Good point, doesn't hurt to add details like this to improve the structure.

I'll try & use something like these for my ceiling & floor joists. Planning on using 2x6 ceiling joists & 2x10 floor joists to reduce noise transmission. 2x10s to rest on a 3/4" ledge.

Simpson Strong-Tie LTB 19-1/2 in. 22-Gauge Galvanized Tension Bridging LTB20-R - The Home Depot

Get hands on a perfect tool for your home renovation project by choosing this exclusive Simpson Strong-Tie LTB 22-Gauge Galvanized Tension Bridging.

www.homedepot.com

 

[dave*99]

Good point, doesn't hurt to add details like this to improve the structure.

I'll try & use something like these for my ceiling & floor joists. Planning on using 2x6 ceiling joists & 2x10 floor joists to reduce noise transmission. 2x10s to rest on a 3/4" ledge.

Simpson Strong-Tie LTB 19-1/2 in. 22-Gauge Galvanized Tension Bridging LTB20-R - The Home Depot

Get hands on a perfect tool for your home renovation project by choosing this exclusive Simpson Strong-Tie LTB 22-Gauge Galvanized Tension Bridging.

www.homedepot.com

I wouldn't call this an added detail. I would say this is a necessary component that was omitted from the original build.

 

[MattRMagnum]

All good - and the server rack will likely have 4 legs or wheels. So be sure to look at that.

The server rack is currently on 4 wheels. Once I have it situated, there's retractable legs which will be set down. It's only a half-height track (25U), so swaying isn't a big risk. Especially since much of the weight is UPS batteries situated in the bottom of it.

I'll look into adding bridging. It's likely something I'll pay to have done, since I lack the time to handle that, currently.

Is it worth adding anything onto the OSB to distribute load, like Benjy was saying?

 

[duneslider]

It looks more like 23/32" osb to me, which will measure thinner than 3/4" but I would still probably add another layer of plywood under the server. Houses use 23/32 osb all the time for the flooring, its rated for floor assemblies to carry at least 50-60lbs/sqft.
I don't think you need bridging unless the server will be in the middle of the span but it sounds like it will be closer to the wall. Bridging helps distribute the load between joists but the floor sheathing is also doing that. Bridging never hurts (except creates more opportunity for squeaks) but I don't think it will do much to help in your case.

 

[MattRMagnum]

It looks more like 23/32" osb to me, which will measure thinner than 3/4" but I would still probably add another layer of plywood under the server. Houses use 23/32 osb all the time for the flooring, its rated for floor assemblies to carry at least 50-60lbs/sqft.
I don't think you need bridging unless the server will be in the middle of the span but it sounds like it will be closer to the wall. Bridging helps distribute the load between joists but the floor sheathing is also doing that. Bridging never hurts (except creates more opportunity for squeaks) but I don't think it will do much to help in your case.

It is 23/32".

I'm planning to place about in the corner of the room (close to where that server is sitting in the first photo), so hopefully that helps distribute the weight directly to the foundation, and not strain the joists.