Hello,
I currently building an addition and plan on putting up a knotty pine tongue and groove (1x6, 3/4" thick) ceiling attached to the bottom of scissors trusses. The trusses are 24" on center. I plan on putting up 5/8" drywall first to get an airtight assembly. The tongue and groove pine is end matched (ends are tongue and groove as well). My question is this, with the drywall up, am I ok not ending each piece of pine on a truss seeing that the ends are also tongue and groove, or am I asking for trouble if the boards aren't nailed on the ends?

 

IMO since they are T&G that will be acceptable.

 

I'd be looking at the boards, if they seem straight and flat then you would probably be OK but I might apply some const. adhesive near the ends of pieces that may fall between framing.

It would be wise to allow the load of t&g to acclimate in the room for a few weeks prior to installation. If you get some wild ones showing up you can either eliminate them or cut them for piecing in the ends.

 

I'd recommend staining and apply 2 coats of poly/varnish prior to installation. It's easier/quicker to stain the wood while on saw horses! That way all you have to do after installation is a light sanding, colored putty where needed and the final coat of poly. You do need to be careful to not apply too much poly on the tongue and grooves - a heavy coat or runs/drips can affect how they fit together.

 

A question for the pros: Are trusses/ceiling joist selection intended to support the extra weight of an additional layer of 3/4" wood? Will it sag over time?


How long is the span of those trusses? The jumbo-sized drywall and T&G will add a significant amount of weight. Why not use 3/8" drywall and 1/2" planks? Or eliminate the drywall and achieve your air barrier (without trapping moisture) with Tyvek?

 

I'm mostly on the painting end of those types of ceilings but I've seen it done various ways. Some locales require the drywall as a fire break. My son's house has 1x6 T&G pine nailed directly to the ceiling joists. The pine was installed a few yrs before he bought the house [7 yrs ago] All his ceilings appear to be nice and flat/straight .... wish the same could be said about his laminate flooring.

3/4" thick boards shouldn't sag any. I've been on some jobs where they used real thin bead boards [3/8"?] and they would sag unless they were installed over drywall along with a dab of adhesive between trusses.

 

5/8" drywall is used on ceilings that will have blow in insulation resting on the drywall, so that the ceiling doesn't sag. The planks aren't taken into consideration when determining the thickness of the drywall. 5/8" is the only thickness that should be used, especially since the joists are 24" on center.

Hard to say what the load rating of the trusses are without that info being provided for us, but suffice to say it should handle the distributed weight of both the drywall and the t&g planks with no problem whatsoever.

 

Thanks for all the replies. I'm out of town right now, so I'll check the load rating on the truss paperwork when I get back, however I can't imagine 5/8" drywall and 3/4" tongue and groove boards even comes close to being too much weight, but I'll check. Also, 5/8 drywall is code for trusses that are 24" oc. The truss span is 24' 6". I plan on putting 2 coats of poly on the front and 1 coat on the back prior to putting them up. Oh, the boards are also tongue and groove on the ends as well. Again, thank you for all the info.

 

Guy48065,
Here are a few links that might be good reading:

Info-401: Air Barriers

How to Build an Insulated Cathedral Ceiling | GreenBuildingAdvisor.com

with special attention paid to the section titled "Do I need to install an air barrier under the insulation?"



These sites provide some very beneficial information.

 

It's best to leave the tongue and groove uncoated or if you do coat those parts, make it a thin coat. Too much poly on the t&g can complicate fitting them together as any excess might have to be sanded or scraped off so the tongue can slip into the groove. I normally spray them on saw horses and don't make a direct pass over the tongue, the overspray on the t&g usually isn't an issue.

 

The bottom chord load is 10 psf.

 

That's about what I expected... (that's the normal ceiling rating) As long as the area of a 4x8 sheet of drywall along with the t&g and the insulation doesn't exceed 320 lbs you'll be alright.

 

XSleeper,
Thank you for all your help and info. By the way, I finished shimming and nailing the window jamb extensions as well as foaming the ro last week. The dap foam is great to work with as you suggested. Again, thank you

 

Does anyone know what the psf of 3/4" pine is? I've found that r38 fiberglass batt insulation is approximately .7 psf and 5/8" drywall is 2.75 psf, however I can't find a number on the pine. Any help would be appreciated. Thanks

 

I have no idea what the weight of pine is but all lumber weighs more before it's dried. With the moisture content playing a big part it might be hard to find a definitive answer.

 

It is kiln dried material that was 6-8% moisture content when purchased several years ago. It's been in storage for a couple of years now.

 

That's pretty dry but is it still that dry? Unsealed wood can pick up moisture from the air ... dependent on the environment it's exposed to.

 

its probably around 1. Wow, you're all the way up to 4 1/2 lbs sq ft.

 

Decided to email the manufacturer of the knotty pine about whether or not I should end on a stud/truss. Here is their response:

You shouldn't have to worry about the knotty pine paneling bowing at all. We have had installations on 4' centers without any problems. It's no problem letting the paneling "run wild" past a stud and it's all the more reason that end-matching is the unique feature of our paneling that we've sold for years and years! The End-match locks all the boards in place once each row of paneling is installed.

With the use of drywall as a backer, you would want a finish nail somewhere in the 2.00" to 2.25" range. You will be nailing on a 45 degree angle through the base of the tongue, so you would be going through basically, 1" of drywall on an angle. You would like to have at least .75"- 1.00" of nail into each rafter. We would lean toward the 2.25" length and you could even go to 2.5" if your gun shoots those. Neither would be overkill.