Help needed with 48" OC trusses

[dbenn0819]

I have a pole barn built with with trusses set at 48" on center. I'm working on finishing the building with electrical, heat, insulation, walls and ceiling.
Can OSB span 48" OC trusses with blown insulation for the ceiling? If so what size OSB?
Is there an easy way to make that span less (without toe nailing 2x4 every 16" or 24" in between every truss)?

 

[firebirdparts]

Generally speaking, if the building wasn't designed for a ceiling, you can't have one. You need to talk to the original truss company.

 

[rslaback]

Weight rating on the trusses is definitely something to look into. That said, you aren;t going to find any OSB options that are going to work for you acceptably. If you do end up with a ceiling my suggestion would be to run 2x firring strips perpendicular to the trusses 24" oc and then secure the ceiling to that. You'll lose just a bit of ceiling height but cutting blocking to fit would be nuts.

 

[bullnerd]

Look into the white metal rib panels.

They will span 48 easily and are already painted.

 

[dfiler2]

^^^This makes the most sense to me, the panel liner metal is rated to be fastened every 48" and will allow you to have blown in insulation on top of it. Just go down and talk to the guys at a lumber yard (not a big box store) and they will set you up.

 

[Krzewinskibe]

Look into the white metal rib panels.

They will span 48 easily and are already painted.

Thats how my pole barn is setup...4' truss centers with white metal rib panels. Blew in R42 on top of them.

 

[Orionrising]

Metal on the truss weighseffectively nothing and I would not worry about that with loading. Blown in cellulose does at up in weight and could definately matter.

Sent from my Moto G (5) Plus using Tapatalk

 

[Krzewinskibe]

Metal on the truss weighseffectively nothing and I would not worry about that with loading. Blown in cellulose does at up in weight and could definately matter.

Sent from my Moto G (5) Plus using Tapatalk

R42 of blow in fiberglass come in ~0.5 psf

 

[Orionrising]

R42 of blow in fiberglass come in ~0.5 psf

Yes fiberglass is light but nasty. R60 blown in cellulose is several psf.

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[Radix2]

R42 of blow in fiberglass come in ~0.5 psf

Super fluffy .5psf fiberglass is not going to give r42 especially in the cold. The manufacturers quote .7psf, building science places say more like 1.2psf and still suggest a cellulose cover to stop airflow.

With the modern cellulose R48 is about 1.6psf and will perform in cold climates, so not really that much different in weight.

Metal is the way to go every day and on sundays..

 

[tapered-pin]

your white ribbed panels run perpendiclar to the roof trusses?

what is your roofing surface above that?

 

[Krzewinskibe]

Mine run perpendicular along bottom of truss. Ribbed metal roof on the top of the trusses/purlins

 

[lakeroadster]

.... If you do end up with a ceiling my suggestion would be to run 2x firring strips perpendicular to the trusses 24" oc and then secure the ceiling to that. You'll lose just a bit of ceiling height but cutting blocking to fit would be nuts.

Yeah, don't do this ^^^. You're adding even more weight to the trusses.

 

[tapered-pin]

ALL truss manufacturers design using DL/LL (dead load/live load) calculations.

NOBODY builds a truss that can't handle having at minimum drywall and furring fastened to the bottom of it.

usually 50 lbs per sf is the dead load with upwards of 100lbs per sf as the live load (plus windloading, snow loading, etc depending on the region of the country you're in).

whomever designed your trusses would have provided a set of truss drawings which declare all this information in plain site. (look for 15-30 8.5X11 sheets of paper stapled together).

 

[firebirdparts]

ALL truss manufacturers design using DL/LL (dead load/live load) calculations.

NOBODY builds a truss that can't handle having at minimum drywall and furring fastened to the bottom of it.

usually 50 lbs per sf is the dead load with upwards of 100lbs per sf as the live load (plus windloading, snow loading, etc depending on the region of the country you're in).

whomever designed your trusses would have provided a set of truss drawings which declare all this information in plain site. (look for 15-30 8.5X11 sheets of paper stapled together).

You're crazy. OP, do not listen.

 

[cowboy73]

I would fir it out with 1x4s perpendicular to the trusses on 2 ft. centers. Then cover with the metal panels. I really doubt that your trusses are any different than the ones sold for houses. Meaning they were already designed for the load of drywall and insulation. truss manufacturers typically build them to size, making them special to handle more loads cost extra.....If you didn't pay extra for more engineering, you likely got trusses designed for a house anyway. House trusses are usually placed on 2' or 19.5" centers. The more trusses you have, the more the load is shared amongst them. If you don't get crazy trying to insulate with whatever you choose to use, you should be fine. You don't need R60 in a private building, commercial heated building...maybe. Depends on how warm you want to keep it, what you are using to heat. R30 is more than what is in most peoples' houses.

 

[tapered-pin]

I believe these are roof trusses. So no way they are anywhere near 50psf dead load and 100psf live load. Even a floor truss would maybe only be 40psf for LL unless specifically asked for more.

Trusses are designed without a DL requirement all the time on the bottom chord For his design, 4' centers, that additional DL can add up quickly. That could change the design of the truss, and thus make it more expensive.

ok, so it's 40psf, the truss doesn't know whether it's being loaded at the top chord or the bottom chord. as long as you're talking about an evenly spread load and not point loads, there is NO DOUBT that the truss design loads will handle plywood and shingles on the top chord with building paper and plywood or gypsum with 2X furring at the bottom chord.

we dont have to guess about it though.. wherever he got the trusses from, he can get the design calcs sent to him in a PDF document as fast as an email will fly. He should have used the bracing diagrams that came with the submittals to verify his carpenter/builder installed the blocking properly (most cut corners)

You're crazy. OP, do not listen.

lol..

yeah, why would he want to listen to a commercial general contractor that self performs more than 30 framing projects a year and has been doing so for over 20 years..?

 

[lakeroadster]

NOBODY builds a truss that can't handle having at minimum drywall and furring fastened to the bottom of it.

You're crazy. OP, do not listen.

yeah, why would he want to listen to a commercial general contractor that self performs more than 30 framing projects a year and has been doing so for over 20 years..?

Why? Because regardless of your experience, what you are advising is not only just flat out incorrect, but it is also dangerous.

As GMCGarage pointed out trusses are often designed with bottom chords that are not designed to support a ceiling. This is especially true for pole barns that utilize trusses that span wide buildings.

 

[Augus7us]

I have this problem. So if you did not build the building and have no idea where the trusses came from how would you determine if this is ok or not? And if not can you remedy this without replacing the trusses?

-Clint

 

[ard]

I have this problem. So if you did not build the building and have no idea where the trusses came from how would you determine if this is ok or not? And if not can you remedy this without replacing the trusses?

-Clint

Good question, Ive seen this come up before.

Have you carefully inspected the trusses for any tags, stamps, markings?

Maybe find a truss mfg, and ask for a favor/bid? As follows:

Draw a very detailed diagram, with precise measurements of all members -thickness, how connected, etc Go to a truss mfg and say "i have these, I want to hang XXlb/ft for a ceiling and insulation- can you tell me if I can, OR can you tell me what I can buy from you to add between to do so"? They might help

 

[GMCGarage]

yeah, why would he want to listen to a commercial general contractor that self performs more than 30 framing projects a year and has been doing so for over 20 years..?

He wouldn't want to listen because after 20 years you dont even know what a normal roof DL and LL is.

 

[dlawrence529]

I think building code requires trusses to be designed for 10 psf (minimum) on the bottom chord for drywall, insulation, etc. No idea if this applies to out buildings. It will depend on your local requirements and the age of your building.

 

[GMCGarage]

Back to the OPs original question, seems metal roofing would be better than OSB since the OSB would need to be quite thick.

 

[TractorJeff]

FWIW
My Trusses were stamped with their ratings on them and placed so you and the Inspector could read them!
Maybe you need to climb a ladder and see if yours are too?
Also rereading the first post, no where does it say what state he is in?

 

[tapered-pin]

As GMCGarage pointed out trusses are often designed with bottom chords that are not designed to support a ceiling. This is especially true for pole barns that utilize trusses that span wide buildings.

Uniform loading across the entire BOTTOM chord of a truss is absolutely NO DIFFERENT than uniform loading across the entire TOP chord of a truss.

I'd be happy to illustrate the point using a loading diagram, but I dont need to, OP has that information for EVERY truss on his building.

.. for the 3rd time now, just get the information from whomever manufactured the trusses, it will give you LL/DL/Deflection for each truss.

standard loading changes for every state and possibly by the county within each state so the "normal" ll/dl comment is erroneous.. (as another member pointed out, we dont even know where OP's building is located)

 

[cj7jeep81]

The specs for the trusses on my pole barn spec 1psf for dead load on the bottom chord, so I wouldn't go with OSB. Top chord is speced at 20psf ll, and 4psf dead load. But again, these are for mine, and yours very well could be different.

 

[tapered-pin]

Absolutely its different.

If I design my truss for top chord loading only, then the bottom cord will more than likely only have to take tension,

I stopped reading when you said something wrong..

bottom chord of a truss will NEVER see compression in relation to the loading over the truss as a whole.

There's no such thing as "top chord loading only" in design, assuming the load is evenly distributed on the top chord vs evenly distributed on the bottom chord and NO POINT LOADS are factored into the design, there is absolutely NO difference in the design of the truss. Trusses are designed based on total load across the member, span of the member, and reactions at bearing surfaces, and strengths of materials used.
THAT's IT.

Statics 101 (hell, they might literally have taught us that on the first day)

Lets say you're right and I'm wrong, you have absolutely NO IDEA what his trusses were designed to, since the OP still hasn't shown back up to tell us. you're trying to argue a specific position without knowing ANY of the facts.

As I've said before, all of this information is provided in the truss design package and layout that was provided with the purchase of the trusses.

 

[lakeroadster]

..bottom chord of a truss will NEVER see compression in relation to the loading over the truss as a whole.

Wind loading creates compression in the truss bottom chord.

Wind hits the wall, load is transferred into the truss.

 

[tapered-pin]

Wind loading creates compression in the truss bottom chord.

Wind hits the wall, load is transferred into the truss.

lol.. no.

the only thing that will create compression on the bottom chord is an open wall scenario where wind will create uplift from the center of the span. in that case, the truss manufacturer will have considered Xspf of uplift and the trusses wouldn't be spaced 48"oc. it would also nearly double the permanent bracing requirement and completely change the connection to bearing details.

 

[lakeroadster]

bottom chord of a truss will NEVER see compression

Wind loading creates compression in the truss bottom chord.

Wind hits the wall, load is transferred into the truss.

lol.. no.

the only thing that will create compression on the bottom chord is an open wall scenario where wind will create uplift from the center of the span. in that case, the truss manufacturer will have considered Xspf of uplift and the trusses wouldn't be spaced 48"oc. it would also nearly double the permanent bracing requirement and completely change the connection to bearing details.

lol.. yes.

With high wind loading on a light roofing deck (such as a pole barn without roof plywood sheathing and shingles) the wind load on the roof lifts the roof. This uplift along with the wind forces on the walls creates compression on the lower truss chord.

the only thing that will create compression on the bottom chord is an open wall scenario

It doesn't have to be an open wall scenario. Closed structures also have lift as a result of wind loadings. And the walls increase the compressive loads on the bottom chord.

and the trusses wouldn't be spaced 48"oc.

Uplift doesn't dictate truss spacing. My barn has trusses spaced 12'-6".

The uplift is real and the engineers design the structure, looking at the size of the roof and walls and their weight, along with how the poles (or walls) are affixed into the ground / foundation to ensure the uplift and resulting forces aren't an issue. There are limitless ways to address the issue.

 

[bczygan]

I TRUSSED what the manufacturer says.

And DISTRUSSED generalizations not based on missing facts.

I would want to know the engineering for the trusses.

But lightweight metal panels and light insulation, plus lighting would probably only slightly increase deflection.


Bill

 

[383]

There is a lot of bad information in this thread.

I have attached a truss drawing of a 40' truss. If you look at the loading info, this truss is designed with 30lb top chord live load, 5lb top chord dead load, 0 bottom chord live load, and 5lb bottom chord dead load. This loading is per sqft, so the truss is designed heavier for 48" spacing than it would be for 24" spacing with the same loading requirements.

the 5lb bottom chord dead load is not enough for drywall, but is more than enough for metal and insulation, the combination will probably be less than 2lbs per sqft.

This truss is designed with 30lbs top chord live load, and 0 bottom chord live load. If you load the bottom chord with 30 lbs/sqft, it WILL fail. It also had 5lb top chord dead load, enough for purlins and metal, not enough for plywood and shingles.

Trusses are not a one size fits all, most are designed for a specific application.

 

[renloy]

I just did the math for my ceiling a couple of days ago and the blown in R45 + metal came out to around 2.5lb psf. That's what i'm doing with my 48" oc 5lb psf trusses. Hopefully I don't end up on the news.

 

[bczygan]

There is a lot of bad information in this thread.

I have attached a truss drawing of a 40' truss. If you look at the loading info, this truss is designed with 30lb top chord live load, 5lb top chord dead load, 0 bottom chord live load, and 5lb bottom chord dead load. This loading is per sqft, so the truss is designed heavier for 48" spacing than it would be for 24" spacing with the same loading requirements.

the 5lb bottom chord dead load is not enough for drywall, but is more than enough for metal and insulation, the combination will probably be less than 2lbs per sqft.

This truss is designed with 30lbs top chord live load, and 0 bottom chord live load. If you load the bottom chord with 30 lbs/sqft, it WILL fail. It also had 5lb top chord dead load, enough for purlins and metal, not enough for plywood and shingles.

Trusses are not a one size fits all, most are designed for a specific application.

A couple of things.

The top chord LL of 30#/SF has a safety factor built in. It will not fail at that loading.

The bottom chord has a ZERO pound/SF LL. Live load is the force imposed on it, so there is NO capacity for adding anything to it. But the 5#/SF dead load is 800 pounds of dead load. I doubt that is all used up by the truss since the truss weighs in at just over 200#. And this is for a deflection limit of L/360. So I would be unafraid to use a metal ceiling and loose fill insulation, plus hanging lights.

Also note that bottom chord bracing is to be accomplished by a rigid ceiling or specific bracing. So there must be a weight allowance for that included in the dead load.

You could call the truss mfg. and ask exactly what it is.

Bill

 

[383]

A couple of things.

The top chord LL of 30#/SF has a safety factor built in. It will not fail at that loading.

Also note that bottom chord bracing is to be accomplished by a rigid ceiling or specific bracing. So there must be a weight allowance for that included in the dead load.


Bill

I mentioned that the truss would fail if 30#/ft is applied to the bottom chord because of earlier posts mentioning that it doesn't matter where the load it applied.

Another interesting point about rigid ceiling. Metal ceiling does not count as rigid ceiling (at least by code in our location) because it has never been strength tested for that application, the lateral bracing is still required if a metal ceiling is installed.

 

[tapered-pin]

I mentioned that the truss would fail if 30#/ft is applied to the bottom chord because of earlier posts mentioning that it doesn't matter where the load it applied.

Another interesting point about rigid ceiling. Metal ceiling does not count as rigid ceiling (at least by code in our location) because it has never been strength tested for that application, the lateral bracing is still required if a metal ceiling is installed.

This entire thread is nothing but conjecture without the OP providing the truss drawings for the system that HE installed.

Find a single reference to truss failure because a drywall ceiling was installed on the bottom chord..

 

[lakeroadster]

Find a single reference to truss failure because a drywall ceiling was installed on the bottom chord..

Typically the deflection becomes readily apparent, scares the holy hell out of the owner, and then the situation is rectified.

But if we can work together and help a fella from getting into such a mess... let's do that.

 

[tapered-pin]

But if we can work together and help a fella from getting into such a mess... let's do that.

impossible unless he posts those truss diagrams.

no truss ever failed (specifically) from getting a layer of gyp board attached to the bottom chord though.

ever.

 

[lakeroadster]

impossible unless he posts those truss diagrams.

no truss ever failed (specifically) from getting a layer of gyp board attached to the bottom chord though.

ever.

More bad advise from tapered pin. Your use of absolutes (never) reflects your haphazard advice.

Just because you have no knowledge of something, doesn't mean it's never happened.

I'm glad Columbus didn't have your attitude.

 

[tapered-pin]

Well, first Gyp board wont span 48", that will fail.

I stopped reading where you said something wrong.

all ceiling sheathing is installed perpendicular to the framing, so, unless you're cutting the drywall into 48" squares, you are wrong. if you're concerned about intermittent fastening, you can install 2X blocking between the trusses so there are intermittent fastening points.

a 12' board will span 4 fastening points on a 48"oc layout without blocking
a 8' board will span 3 fastening points on a 48"oc layout without blocking

maybe you ought to think about sticking to cars, leave buildings/structures/construction to the professionals.