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Old 09-11-2019, 02:55 PM
steronz is offline
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Unfinished garage ceiling question


I'm having a new garage built, the contractors are going to leave the interior unfinished and I'll take it from there. One thing I didn't anticipate was the ceiling isn't prepped for drywall, right now I've got 48" spans between the rafters, which are 24 feet long. I was looking into maybe shiplap but aside from being expensive for a ceiling that size, the internet doesn't recommend anything over 24" spans for 1" thick boards even.

What's the best way to move forward? Mount 4 foot 2x4s every 16" perpendicular to the rafters for drywall? Run additional 24 foot 2x6s between the rafters? Something else?

Last edited by steronz; 09-11-2019 at 02:56 PM.
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Old 09-11-2019, 03:42 PM
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I would be very concerned about hanging anything as heavy as a wooden shiplap ceiling from rafters on 48" centers as you describe. Yeah, it might support the weight but it might also pull the whole roof down during the next heavy snowfall.

You need to talk to your contractor about your plans and get his input.
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Old 09-11-2019, 03:51 PM
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I'd opt for 2X6s on 24" centers between the existing structure, with a few perpendicular 2x4s to keep everything in line. I assume you don't intend to store anything above the ceiling.
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Old 09-11-2019, 04:20 PM
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Correct, no storage up there. But ugh, Alpha Twits point has me concerned, I need to talk to the contractor.
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Old 09-11-2019, 04:27 PM
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You have more choices. You can install a drop ceiling. You can also use sheet metal roofing panels across the 48" span. For a real roof you'd use 36" centers, but there's no additional load on the panels besides their own weight so 48" should be fine. I'd run 2X4s or even 2x3s perpendicular to the existing rafters, and running underneath them for the length of the garage so you don't need to cut and nail a bunch of short pieces.

ETA: Pine ship lap probably doesn't weigh significantly more than drywall. If you want to use wood then get 4x8 bead board panels.

Last edited by TriPolar; 09-11-2019 at 04:29 PM.
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Old 09-11-2019, 06:27 PM
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What about some kind of marlite or Allure? Or even paneled?
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Old 09-11-2019, 11:44 PM
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What are these 'rafters' made of? Do you mean trusses? Is this even a wood structure? What Is the roofing material? Four foot centers for any kind of residential framing sounds extremely unusual to this western Canadian carpenter.

Why in the world are you thinking of doing a ceiling in shiplap? Tongue and groove cedar used to be a thing for ceilings, but only for decoration, and it never was a good idea to make a ceiling out of kindling.

Assuming this roof structure is properly designed the obvious thing to do would be to block it out with 2x4 at 2' centers and drywall it.

There was a building permit...right?
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Old 09-12-2019, 04:12 AM
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Apologies for the terminology, I suppose they're joists not rafters. The rafters are spaced every 2 feet, the joists tying the walls together are 4 feet. They're not trusses because the joints don't connect to the rafters with any kind of triangulation. It's a hip roof, they built it on site as opposed to buying trusses from a lumber company. To my untrained eye it appears to be made out of some kind of "wood" :P

This is a respected company that has done like 6 of the garages on my street alone, plans and permits exist and I have no doubt the roof structure was properly designed to hold its own weight and that of an amount of snow required by local code. In my naivety I assumed it would also hold drywall and insulation but i never thought to ask.
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Old 09-12-2019, 06:47 AM
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A common way to deal with this sort of thing is to add 1x3 strapping perpendicular to your joists on 16-inch centers. Then screw your drywall to the strapping as usual.
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Old 09-12-2019, 07:50 AM
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Okay that makes a little sense, as usually roof sheathing requires a maximum of 2' centers, and at that it is still flimsy. The ceiling rafters or joists would normally be spaced the same as the roof rafters and be fastened beside each roof rafter. It just seems very strange to me to install only half as many. Not only does it make for a weaker roof but it makes installing a ceiling very difficult. The labour to block it out to 2' centers is way beyond the cost of just installing the right number in the first place. I assume you must be some place with very mild weather, no snow load, or high storm risk?

I am not looking at span tables here but 24' seems like an awfully long span for dimensional lumber. Are these 2x8's? 2x6's? (yikes). Is there a center beam? I would never do what is being described without an engineer's letter and even then I would question it. Engineered joists would suffice I suppose but trusses are strong, cheap and less labour than stick framing. It all makes very little sense to me, maybe this is common where you live but it would never fly here. Maybe there is something I am missing.

I think the suggestion of installing a suspended ceiling made up thread is perhaps the best, being the lightest and least labour intensive solution.
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