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Julie2Oregon
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# Posted: 26 Jan 2016 11:29pm
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So my question about a gambrel roof has been how to effectively insulate it (preferably on the inside) and then how to finish the interior once that has been accomplished. I'm going with a half-loft that will be my bedroom and the other half will be open to offer an airy feel to my living room.
I love natural wood but wasn't sure I wanted ALL wood in the loft. However, I didn't want a traditional white "plaster-looking" ceiling, either. Tin would be cool for the upper portion of the gambrel roof.
Turns out, it's quite possible that a "drop" tin ceiling might make my insulation quandary a bit easier, too. When I was Googling tin ceilings, I read that "furring" is the traditional manner of installing a tin ceiling and this basically means that the tin is nailed to an installed grid rather than plywood. There are a variety of ways of doing a "drop in" tin ceiling now and different products for installation.
But it seems that I may be able to install the rock wool insulation and build this 2' X 2' grid over the spaces on which to attach tin panels. There are benefits -- it's a fireproof ceiling and one in which a section can be easily removed in case plumbing or wiring needs to be altered or fixed. A caveat is that codes in seismic areas require wiring for fixtures to be secured to the house framing. That's fine -- no biggy.
I am wondering a bit about humidity, propensity toward discoloration or rusting over time and if there are ventilation recommendations (I am planning on having some solar attic vents in my loft, anyway) or dehumidifying requirements.
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bldginsp
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# Posted: 27 Jan 2016 08:19am - Edited by: bldginsp
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Tin is the 'new look' in hip restaurants in my area. It has a practical, industrial look, to contrast with the glitz of other styles.
Condensation shouldn't be an issue if you have enough insulation above the tin ceiling. Condensation occurs where there is a difference in temperature- warm, moist interior air contacts the cold surface of an exterior wall. But the inside surface of adequate insulation should be the same temperature as the room, so there is no difference in temperature and no condensation. But the inside surface of the plywood above the insulation will be cold, and the insulation warm, so condensation can happen on that plywood, that's why you need ventilation above the insulation.
It's also very important to provide an air barrier in the ceiling. I don't mean a plastic moisture barrier, but some means of keeping air from moving through the ceiling. Taped drywall does that well, but you don't want that look. The problem I see with corrugated tin as a ceiling finish is sealing up the edges so air doesn't get past. This is also an important fire issue. If the edges leak air then a fire can get into the roof assembly.
You could drywall and tape the ceiling first, then put on the tin, or put plywood first. I'd go for the drywall.
Incidentally 'drop ceiling' means a lowered ceiling suspended with wires- with the 2x4 foot tiles placed inside T bar. I don't think that's what you meant.
Furring the inside of the ceiling joists with 2x2s isn't necessary except if you don't want the tin to run perpendicular to the joists. You can screw the tin to the joists, but not if it is parallel. If you do fur it out, be aware that that will create additional air passage space that needs to be closed off to prevent heat leakage and fire spread. A fire can spread very quickly inside a closed ceiling assembly if it isn't sealed off.
Sounds like you are having a lot of fun designing your project!
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Julie2Oregon
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# Posted: 27 Jan 2016 07:32pm
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Quoting: bldginsp Sounds like you are having a lot of fun designing your project!
I am! It's so cool to work on a small place because I can consider interesting elements that there's no way I could afford to do on a big home! 
If I were to do the furring, wouldn't packing the rock wool insulation in the joists close up the air space sufficiently to install the tin over that? Or could I use something like this, in combination?
Otherwise, yes, I'd go with dry wall.
I did throw out the traditional drop ceiling with the wire and T-bar, too, in case anyone was interested in that. But not for my application.
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Julie2Oregon
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# Posted: 27 Jan 2016 07:38pm
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I'm actually pondering whether I could buy tin and "distress" my own pattern. I've worked with tin before and own tin snips. The patterns I've seen are too foo-foo for my taste.  I want something more rustic. I'd hire some guys to help with installation, though.
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bldginsp
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# Posted: 27 Jan 2016 08:48pm
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Not sure that packing the insulation in would provide positive enough air seal. Think of your roof as an upside down sieve, with the heat filtering through the insulation. Insulation isn't an air barrier, it just slows heat, but it must be in a space where the air isn't being forced through it.
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MtnDon
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# Posted: 27 Jan 2016 08:57pm - Edited by: MtnDon
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Quoting: Julie2Oregon If I were to do the furring, wouldn't packing the rock wool insulation in the joists close up the air space sufficiently to install the tin over that?
Packing insulation reduces the R-value, as it is not so much the material (fiberglass, cellulose or rock wool) that does the insulating, it is the entrapped air that provides the insulation. Same goes for foam, spray or sheet, it is the empty spaces, the bubbles that insulate.
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Julie2Oregon
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# Posted: 27 Jan 2016 10:17pm
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So, tin, furring, insulation, (joists), decking, vapor barrier, and metal roofing panels wouldn't be sufficient, then? (Can't recall if tar paper goes beneath metal roofing or not.)
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Don_P
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# Posted: 27 Jan 2016 10:18pm
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Apply drywall or osb now, glue and tack your homemade ceiling to it later, gets it done and sealed now. This is probably a 2x12 rafter bay to get fiberglass, cellulose or rock wool insulation and a vented space above it.
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bldginsp
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# Posted: 27 Jan 2016 11:17pm - Edited by: bldginsp
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No vapor barrier between roofing and roof deck, just tar paper or other waterproof layer.
I'd go- tin, furring if necessary, drywall, joists (with insulation), roof deck plywood, paper, roofing, pigeons.
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Steve_S
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# Posted: 28 Jan 2016 06:00am
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Julie, what kind of tin are you talking about here ? The corrugated metal roofing stuff ? Square 1'x1' or 2'x2' stamped tin tiles ? The repro tin ceilings they make now that look like the stuff of old ? The installation method really depends on what product/material you are considering.
Some of these can get insanely expensive in a hurry. There is also some made to look like tin but made of lightweight materials (ABS plastics I think) which are much cheaper, some even come in rolls (only saw it on display once, looked neat).
If you do a Google Search for images "tin ceilings" a vast array of possibilities shows up. I found this Canadian Site www.tinceiling.ca which has some cool pics, and lots of interesting info/details on the old style stuff.
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Jabberwocky
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# Posted: 28 Jan 2016 09:43am
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Julie, tin ceilings are awesome looking, I don't blame you for wanting them!
Perhaps another way to explain the dilemma bldginsp is presenting is this: Where is your "building envelope" going to wind up? That is to say, where does the conditioned space start and the unconditioned space end? This matters in terms of energy efficiency and what you should or should not use as ceiling material. Notice I said "should or should not" rather than "can or can not." As I'm sure you are well aware, you can do anything you want after the building inspectors leave, but that doesn't necessarily make it a good idea.
In a traditionally insulated home, the building envelope is below the roof deck. The insulation is sealed up behind a layer of drywall on the ceiling, etc. Drywall is a good air barrier, but especially so if it is sealed up nicely around all of the edges. When you restrict air movement, you also in turn greatly restrict the movement of vapor, since vapor has to piggyback on air to go anywhere. Conventional methods therefore, employ some sort of method to allow the insulation to dry to the outside of the building envelope rather than inside - hence vented roofs, etc.. where the idea is to create air movement above the insulation in order to keep it high and dry.
Now then, let's apply that theory to your ceiling tin/tiles idea. Since they cannot be taped and bedded together (as in sheetrock) and therefore air sealed, they are extremely air permeable. They will subsequently allow humid air from inside the home to leak through the ceiling, through the insulation, and up and out through whatever venting system is designed into the roof structure. They are basically an energy leaking sieve. Also, since this is the case, any perceived fire protection the metal offers is somewhat negated by the fact that convection would carry right through them to the flammable materials above.
Now then, if you're still with me: The fact remains that tin ceilings are cool, you want them, so the question begs: How DO you make them work?
Option 1) Do what bldginsp and DonP have suggested: Do normal sheetrock and then glue/fasten them to the sheetrock substrate.
Option 2) Don't build a vented roof in the first place, and change where your building envelope resides. (See?! I DID actually bring this around back to where I started!)
If you want to spend a good half hour or more learning about roofs, read this: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral- ceiling
Here's the deal, if you insulate your home on the outside of your roof decking, as I have been describing in your other thread, you don't have to ventilate your roof. You change the whole dynamic. The humid air inside the home stays there, the outside air stays outside. There isn't a need to somehow marry the two and make them reconcile their differences as in a typical vented roof. As long as your foam insulation on the outside is thick enough, you won't have a problem with condensation building up inside the home.
Theoretically, if you were to insulate sufficiently on the outside of your roof, you wouldn't need ANY type of insulation inside your rafter bays OR covering over them. You could leave the whole thing open and look up at the bottom of your roof deck if you so desired. But of course that isn't usually preferable, but the point is that any ceiling treatments in such a design are purely cosmetic. They don't have to be air sealed, and therefore..... and this is the important part..... you can put as much tin on your ceiling as you want, and still be energy efficient. 
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Julie2Oregon
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# Posted: 28 Jan 2016 06:15pm
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Steve_S
I was looking at the 2' X 2' stamped tin tiles. The site I was interested in showed installation via furring or over plywood. Cost was about $8 per tile. I would only be doing the uppermost two angles at the very top of the gambrel ceiling.
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Julie2Oregon
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# Posted: 28 Jan 2016 06:23pm
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Jabberwocky
Thank you! Very, very clear and written in a way that even a non-numberical, construction idiot like myself can understand! (Have you yet gotten the impression that I'm more of a creative type than a logical one, lol?)
One question: If I didn't vent the space, will it meet building code? That might be a good question for bldginsp.
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bldginsp
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# Posted: 28 Jan 2016 07:46pm
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The code requires ventilation, and it requires cross ventilation, so that the air can come in and go out. But the codes don't specify exactly how to do it. You propose that to the building inspector, and he will accept or reject your suggestion, based on whether he thinks it meets the requirement. At least that's how it's supposed to work, but some inspectors don't know ventilation from ventriloquism, and you want to make sure your house is properly vented so you don't get mold in the ceiling and start breathing those yucky spores. Bad for your health.
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Julie2Oregon
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# Posted: 29 Jan 2016 03:07am
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bldginsp
Too true. I want air moving. I plan to have windows upstairs, the solar celing fan, and was going to have the builder install solar vents up on the non-lofted side (below the cathedral ceiling). Perhaps that will be sufficient.
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