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harrymanimus
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# Posted: 13 Dec 2018 04:32pm - Edited by: harrymanimus
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I have a 12x30 portable building with barn shaped ceiling and lofts that I'm finishing out. I recently did the insulation on the ceiling. Here is my plan for the ceiling with 2ft joists.
Ceiling Pic for reference https://photos.app.goo.gl/C9jNUuh7pc9uHcPf7
* The center 16 ft section of the ceiling will be done with tongue & groove pine
** This is my splurge area. Nice ceiling in center of the building right as you come in the door (where there isn't a loft) and a nice ceiling fan to greet you.
** Use 16 ga finishing nails, and construction adhesive to affix the planks.
* Other ceiling areas in the loft (and walls) use 3/8 inch sanded plywood
* 1x3 furring strips to prevent sagging where needed. (Good idea?)
** Furring affixed between for support of the plywood. Between the joists instead of under the joists because the loft area are already too tight on headroom, don't want to take another inch of headroom away.
** Using 1 inch thick furring to have less compression on the insulation.
** Use screws to affix between joists (what kind?)
* Use screws to attach plywood to joists (if good idea, what kind?). Use 18 gauge brad nailer to attach plywood to furring strips.
* Use trim to cover the seams with 18 gauge brad nailer.
Any tips? Or comments on the ?? areas above?
Thanks!
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rockies
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# Posted: 13 Dec 2018 07:41pm
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One of the big mistakes I've read about on the "Green Building Advisor" website is the practice of installing tongue and groove material on the inside of the roof system without first installing a layer of drywall.
The drywall (taped and mudded) prevents air movement through the tongue and grooved boards (which carries moisture into the ceiling cavities and causes rot and mold).
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Eddy G
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# Posted: 14 Dec 2018 11:50am
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I'm sorry, Its probably me but I didn't follow some of that to well.
Not seeing the building or roof type is kind of hard but I'll try and take a crack at it.
What I can tell you is this.
When it comes to insulating ceilings (under a roof) its all about ventilation.
Now if you used a closed cell foam insulation you could ignore that (for the most part). When sprayed directly to the underside of the roof deck between rafters closed cell foam doesn't require the ventilation that fiberglass insulation does.
But when using fiberglass bat insulation or loose fill insulation you need to ventilate the under side of the roof deck.
You don't need to drywall and mud the underside if you tongue and groove the ceiling.
You can but you don't need to.
It would serve no purpose in structure, insulation value or ventilation.
In fact if the space isn't ventilated right it will absorb moisture and cause more trouble.
What you could do is simply install vents on either side of the building just below the roof line so the moisture could escape under the roof deck and above your insulated ceiling.
3/8 strapping is a good idea for structure and the wall covering.
Screws, with 3/8 plywood I'd go with either heavy duty cores thread dry wall or a deck screw (deck screw may be a little over kill)
I hope that's helpful.
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rockies
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# Posted: 14 Dec 2018 07:16pm
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Quote: "You don't need to drywall and mud the underside if you tongue and groove the ceiling.
You can but you don't need to. It would serve no purpose in structure, insulation value or ventilation."
You do need to have a continuous airtight barrier on the underside of the ceiling rafters. usually taped and mudded drywall is easiest.
https://www.greenbuildingadvisor.com/article/insulating-and-air-sealing-a-vaulted-cei ling
See the second paragraph, point "B", in the section titled "This plan has some problems".
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harrymanimus
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# Posted: 17 Dec 2018 12:18pm - Edited by: harrymanimus
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Eddy G - But when using fiberglass bat insulation or loose fill insulation you need to ventilate the under side of the roof deck.
I did not build this building, purchased it.
Here are the layers for my building.
1. Metal roof
2. Felt paper (paid extra for this)
3. Plywood
4. Bat insulation (added by me)
5. T&G 1 inch pine (added by me)
So can I just add some vents near the ceiling peak just below the T&G on either end of the building? Put a wire mesh on it to keep bugs out?
I realize I dumped too much info in one thread, I did go back and clean up the edit. I'll stick to more specific questions from now on.
Thanks
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rockies
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# Posted: 17 Dec 2018 07:29pm
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No, you'll have to add a continuous eave vent from one end of the roof to the other in order to ventilate each rafter bay and a continuous ridge vent as well. Hopefully you installed baffles to keep a 2" air pathway over the tops of your insulation batts.
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deercula
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# Posted: 17 Dec 2018 08:06pm
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Quoting: rockies No, you'll have to add a continuous eave vent from one end of the roof to the other in order to ventilate each rafter bay and a continuous ridge vent as well. Hopefully you installed baffles to keep a 2" air pathway over the tops of your insulation batts.
YES! This is absolutely correct.
A friend put up fiberglass batts without the baffles. So much water condensed it was dripping down causing puddles. This was in winter in the N.E. when he heated the cabin. Do NOT put up T&G until you are sure you will not have to tear it down like this guy did.
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Eddy G
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# Posted: 17 Dec 2018 08:38pm
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Quoting: rockies No, you'll have to add a continuous eave vent from one end of the roof to the other in order to ventilate each rafter bay and a continuous ridge vent as well. Hopefully you installed baffles to keep a 2" air pathway over the tops of your insulation batts.
The continuous ridge vent isn't necessary if you have an open vault and have vents on the end walls.
The whole purpose of the vents is to get the moisture out. If you put the fiberglass right up against the deck the moisture will get trapped and cause problems.
I think we're all saying the same thing but in different ways.
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Eddy G
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# Posted: 17 Dec 2018 08:48pm
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Quoting: harrymanimus 1. Metal roof2. Felt paper (paid extra for this)3. Plywood4. Bat insulation (added by me)5. T&G 1 inch pine (added by me)So can I just add some vents near the ceiling peak just below the T&G on either end of the building? Put a wire mesh on it to keep bugs out?
That sounds like a recipe for disaster.
First, if you don't have eave vents then they are easy enough to put in. You can use round or square vents. The round ones are easier because all you need to do is use a hole saw and put a couple in each bay.
Second you need to put insulation chutes in each bay and then your fiberglass insulation so that the air can come in through the vents and travel up the roof deck and exit out the end vents.
Now of course a ridge vent is the better way and only way if its a cathedral ceiling but it you have any type of a vault at the top of your ceiling the end wall vents will work.
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harrymanimus
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# Posted: 17 Dec 2018 11:41pm - Edited by: harrymanimus
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This is what my building looks like but no porch.
https://derksenbuildings.com/building/z-metal-lofted-barn-cabin/
There are no eaves. Inside where the ceiling pitches down to the walls there are stacked 2x6 boards 2 high that form the top of the wall frame.
I’ve had part of the ceiling insulated since summer. Have not seen any moisture buildup anywhere. Lots of rain in the area.
The way this is constructed I don't see how air would get to chutes. *Maybe* if I drills holes under the lip where the roof meets the walls but there is not much room there and does not solve where the air vents as it goes up. Someone mentioned a 2" airway for chute size I think. These are 2x4s for rafters. If I do that, I have room for around 1.5 inches of insulation.
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neckless
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# Posted: 18 Dec 2018 03:59am
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i dont think u have to worry too much the felt u installed will take care of most of the problem.. the moister will form on tin and felt will protect the sheeting, after all its a cabin.... in thirty years of work never had a bad roof with felt down.... just my 2 cents..... would be nice to have a air space above insulation but that roof kinda makes it hard ...
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Eddy G
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# Posted: 18 Dec 2018 08:24am
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Quoting: neckless i dont think u have to worry too much the felt u installed will take care of most of the problem.. the moister will form on tin and felt will protect the sheeting, after all its a cabin.... in thirty years of work never had a bad roof with felt down.... just my 2 cents..... would be nice to have a air space above insulation but that roof kinda makes it hard ...
I have to agree.
Having a little time to think about it.
It isn't a full time residence/home.
Your design is almost impossible to fully vent it properly.
It would be great to treat it that way if possible but in this case I think you'll be okay.
I still wouldn't put drywall, tape and mud up there.
Just remember "moisture" is the enemy. If its in a basement or in the attic its always best to dry it out.
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harrymanimus
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# Posted: 18 Dec 2018 12:06pm
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Thanks guys. I'm feeling better about it. I should have mentioned the buildings use. This is a hunting/getaway cabin that is not going have AC/Heat going in it much at all in a years use.
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