Exposed Ceiling Joist Project
RSanchez
| Posted in Building Code Questions on
Hello,
I have looked on this site and many others but can’t find the answer to something I’m thinking about. Some similar questions, but they always seem related to attic insulation. My situation is different. I’m a homeowner and I’m currently doing some renovations on my 1962 single level ranch block home in Phoenix Arizona. Electrical and plumbing upgrades etc…The roof framing is stick built with 2X6 rafters and ceiling joints. In the living room and kitchen we currently have the ceiling sheetrock removed for another project. The ceilings are 8 feet tall.
Something I’m thinking about if it meets building codes etc. – I like the look of exposed ceiling joists (I know they are not “real beams”.). The ceiling joists are in very good visual shape as well. Now that the sheetrock is removed I can easily visualize it. I’m not talking about exposed rafters, just the ceiling joints. The ideal is to place some type of material (shiplap, v-grooved wood, sheetrock etc.) above the ceiling joints. They would actually be installed directly on top of the ceiling joints. The attic would still be insulated in a standard way with blown-in insulation laying above the new ceiling material….This is not a cathedral/vaulted ceiling, just standard 8 feet high flat ceiling. So the blown-in insulation would lay directly on top of the product I install on top of ceiling joist. I’m not an expert, but I don’t see a difference between sheetrock on the interior side of the ceiling joist or a product like shiplap or even sheetrock on the attic side of the ceiling joist other than fire building codes I guess. All the electrical would be ran in the attic like normal. Since the ceiling is only 8 feet tall I don’t want to sheetrock the ceiling like you normally would do and build fake beams on the exterior of the sheetrock, it would be too low since my ceiling is 8 feet.
Another thought is to just use sheetrock instead of shiplap installed directly about the ceiling joist to provide some fire protection. The wood of the ceiling joist would still be below the sheetrock if there was fire, but the sheetrock could slow the spread to the above roofing structure.
Attached are 2 pictures of a look I’m thinking about.
I’m I crazy? Any feedback would be great! Thank you! I’m tempted to just sheetrock like normal and move on with my life. LOL… I just like the visual lines of the exposed ceiling joist look and I would create some increased ceiling height visually.
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Replies
RSanchez,
Definitely pursue it if the ceiling joists are in good shape. It will lend a lot of character to the space. If you go with T&G wood, make sure to include an air barrier above that.
Here you would not need a fire rated assembly, and as far as I can see the IRC doesn't require it, but I'm not that familiar with US codes, so hopefully someone better informed will chime in.
Thank you for the reply. That does makes sense regarding air barrier.
You're going to have to do something about air sealing and insulation where the joists meet the roof.
Normally the joists will sit on top of the wall. The ceiling drywall is the air barrier, and it meets the wall drywall. Above the ceiling drywall is your insulation, which goes over the wall and up to the underside of the roof. If you want to move the ceiling to the other side of the joist you have to figure out a way to connect the ceiling drywall to the wall drywall for an air barrier, and you have to figure out how to insulate that area between the roof and top of the wall.
It's not impossible, it's just out of the ordinary. You could probably run drywall parallel to the roof from the wall to the ceiling. You'd have to seal carefully around the joists. The insulate above that drywall. Since your roof is vented you'd have to vent the underside of the roof there.
Thank you! I have been thinking about that the more I look at the fine details of each step. It might be tricky, but as you state possible.
From my understand different US cities can have their own modifications to the IRC building codes, but in general for IRC codes, has anybody seen where a code for a single family single-level home has to have some type of fire protection like sheetrock/drywall on the ceiling to protect the roof structure about the ceiling in case of a fire?
Another idea I have that would be easier, is to just install shiplap on the underside of the ceiling joist like you normally would do with sheetrock. In this case the ceiling joist would be in the attic like normal. I'm assuming I would still need an air barrier in this case since the shiplap is not a solid surface like sheetrock. I see that most people install shiplap directly on the sheetrock because they don't want to remove the sheetrock, which makes sense. But in my case the sheetrock is already removed for another project.
From what I've seen, residential fire codes are more about limiting fire spread than limiting fuel available for the fire to burn. Commercial codes tend to involve the "limiting fuel" part more (requiring non-combustible materials). You're probably OK with just adding blocking at the ends of the joist bays, and possibly firestopping them (the orange Great Stuff, or the yellow fire stop caulk). There are local variations on these codes, with Chicago being especially strict, so I would check with your local building department before you get too far along with your project.
You can air seal easily from above if you have attic access: a layer of cheap panel product like luan would probably be all you need. I've wondered for years about the possibility of using a fluid applied WRB as an air seal layer for a project like this, but I've never actually tried it.
Bill
Thank you for the info!
From the 2018 IRC (just the last version I had to reference, your local jurisdiction may adopt a different version, also look out for local amendments) Section R302.9 Flame Spread Index and Smoke-Developed Index for Wall and Ceiling Finishes spells out the requirements.
The benefit of using gyp board is the manufacturer deals with the ASTM or UL testing, gets their product to pass, and then makes a nifty data sheet available that you can look up and reference if you building department kicks up a fuss. My guess is it would not be economical to prove that you old ceiling joists are compliant if someone bothered to ask.
That being said I've seen much sketchier things fly. If you can't turn up some kind of resource that discusses the typical flame spread and smoke developing characteristics of sawn lumber then maybe try running it by the building official. If you are comfortable with it they might not even care.
I also live in AZ and own a block house. you can definitely do what you want, but you'll have to overcome some obstacles. You'll need some form of fire retarder between living space and attic. 1/2 inch sheet rock is the most common thing used. You can install whatever finish you would like (ship lap, v-grooved wood, tongue and grove panel) by code you still need fire retarder. Typically its installed on the bottom of the joist but because you plan on attaching to the top you'll run into two issues. 1~ the sheet rock is both an air barrier and fire retarder, so you'll want to run it continuously over the entire attic space above the joist and either tape all the joints or add an additional air barrier.Then just add the insulation. 2~ You'll need to block and insulate between the walls top sill and joist You'll need a good insulation since there wont be a whole lot of room. Since you're going to do that you'll loose the ability to vent your attic space because you block the soffit vent between the joist. So you'll nee d to find a different way to do that.
Good luck