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Cedar Fever
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# Posted: 22 Mar 2022 09:00am
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Hi fellow cabin builders, first post here.
We are doing the small cabin thing in the south in an area that gets about 18 inches of rain a year. Its a somewhat arid place but I have seen some pretty heavy dew in the morning. There are a lot of hot days, and not many cold days so I am trying to run a small AC off a generator is the goal.
My Cabin was built on-site. The roof is not ideal but I dont want to take it off and mess with it if I dont have to.
What i've got: 16x24 foot cabin, 2x6 roof joists, metal roofing directly on the joists with no underlayment. Has a ridge vent and gets some air ventilation through the ridges in the metal roof.
My plan to insulate it: My best plan is to put rockwool insulation between the joists and then put my ceiling on. Will this work? Some wind and bugs will get through on top of the insulation from the ridges in the metal roof. I dont want to create a fire hazard. My first plan was to shove foam block insulation in the roof but I moved on after reading that stuff burns good. Anyone have a better plan? The cabin was supposed to be built with 2x8 ceiling joists but the builder messed it up.
Currently I am working on wiring up the place for a generator.
Also I could use some advice on the floor. What do I do under it to insulate it? Is my best bet spray foam insulation on the bottom? Right now the treated plywood floor is just exposed underneath as you can see in the picture. I was going to put some kind of laminate on top or vinyl planks seem low maintenance.
I appreciate your thoughts on this, thanks for checking it out!
Cabin_Roof_Outside.J.jpg
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Cabin_Floor_Under.jp.jpg
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Cabin_Ceiling_Inside.jpg
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Tim_Ohio
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# Posted: 22 Mar 2022 10:14am
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It looks to me like the way the ceiling joists were run as purlins (to support the tin), the only venting is in the ribs of the tin. That really reduces the air flow from the soffits. There is probably some calculator for how much air flow you will need (mostly to allow to keep it dry). I'm inclined to say, whatever insulation you use, a vapor barrier will be very important. Most of the water vapor that condenses on a ceiling (especially metal) is from inside the cabin. You will need space between the bottom of the tin and the top of the insulation to allow the air to flow. You may have to drill some holes in the upper most part of each "purlin" to enhance air flow,
before installing the insulation. If the insulation you choose does not have a paper vapor barrier, you will have to cover all of the ceiling with plastic and seal the seams. Even on the paper faced insulation, you will have to go back an seal the seams. If there is any water vapor passing through, it will condense on the metal, drip onto the finished ceiling below the insulation and cause a stain or cause rot. I like the paper vapor barrier since it has flaps for stapling it to the joists. I used it on the ceiling for this reason, but it's just a preference. Plastic over top of your insulation is probably way better.
Tim_Ohio
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jhp
Member
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# Posted: 22 Mar 2022 10:22am
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Wouldn't this be a good case for spray foam+air exchanger?
Basically spray foam the whole thing, block off whatever ventilation may exist, then punch a hole in the side somewhere and use an air exchanger to vent on demand?
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Brettny
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# Posted: 22 Mar 2022 10:27am - Edited by: Brettny
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Insulating under metal roof properly is prety difficult and much less with only 6in to work with. Your only real option if you dont want to take the metal off is foam. Either way it should really have a proper underlayment. What's going to happen is the warm air from in the building is going to leak out through bat insulation around the studs and condense on the cold metal. Then it will either drip, make mold, rot your framing or all three.
You really need to remove the metal. At that point I would put down 2in foam board ontop of the rafters, then underlayment for any possibly drips then the metal back on.
Also I see a huge looking beam in the center of the building..yet only 1 wall stud actualy supporting it? What ever stud is under that beam is actualy holding up half your building. Also when that single stud starts to sink your door isnt going to open because it's not framed as a load supporting wall.
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razmichael
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# Posted: 22 Mar 2022 10:29am - Edited by: razmichael
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Edit: By the time I hit "post" two others suggested foam. Anyway ...
Is spray foam within your budget for the ceiling? "Hot" roof - no ventilation needed, great insulation from both heat and cold plus sound.
Insulating the floor looks like a tricky process given you already have the floor down and looks like little room to get under. Likely easiest option (before putting in the floor would have been to Trim the cavities with ledgers and drop plywood in then insulation (assuming not much room to get under and seal from the bottom). If pests are a concern some sort of wire would be good as well. Given the current situation I'll be interested in options others come up with.
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Cedar Fever
Member
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# Posted: 22 Mar 2022 11:22am
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The budget is not bad, I can afford spray foam if that is the best option. I would rather not take the roof off as this is out in the middle of nowhere and I am short on help. But I also don’t want problems so if I need to slow down and rip off the roof so be it.
Also I can get under it to install whatever is the best kind of insulation. There is about 15 inches of clearance and I have been down there adding screws into the skids and hurricane straps.
Thank you for calling out that single stud holding up the cross beam. I will reinforce that. I was going to add some angle brackets to that connection but I will put another stud in there or a 4x4 or something to try and limit downward movement.
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Tim_Ohio
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# Posted: 22 Mar 2022 11:30am
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I've never used spray foam. I'm not real fond of the thought of using it in a living space. From my chemistry background, I know that all polymers out-gas. This is especially true when they are in hot environments. Have you seen the film on your windshield from all of the plastic components in your automobile. Fortunately, there is a ton of air exchange in the cabin of an automobile. I like spray foam for a garage or industrial building with a large ratio of fresh air to work with. Just food for thought. If you are ole like I am and closer to the end, then the beginning, go for it.
My two cents ain't worth much, but worth voicing.
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Cedar Fever
Member
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# Posted: 22 Mar 2022 11:35am - Edited by: Cedar Fever
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I’m at the age where I have a few small kids running around so I am trying to be reasonably non-toxic here. They were in that loft coloring right after that picture.
I could screw on some 2x4’s onto the joists to make them deeper. And then put in 2x6 rock wool and that would give me a few inches of ventilation. Any vapor barrier I do will be less than perfect. I will likely puncture it a little when I put some wood up on the roof.
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Tim_Ohio
Member
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# Posted: 22 Mar 2022 11:46am
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I think, if you have enough air flow from the soffit area (not much to work with there) from the ribs of the
roofing, to the ridge cap (all of which should be open)
the natural convection current will move the air above the insulation. I used 2x4 fiberglass kraft faced insulation in 2x6 rafters and this left a nice space. However, I have a vented soffit/overhang (18"). My tin was on a wood decking on the roof, so the air flowed under that decking up to the ridge and out the vented ridge cap. I installed a ridge venting under the cap, not unlike a scotch guard pad (this stuff comes as a roll) to keep out insects and critters. The soffit I had was with holes for venting, so I did not need to use anything there. You could probably use this material above your walls to screen the openings of your roof rides
there. At least, that's what I'm seeing...I dunno, pictures are not always completely showing what's going on.
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Tim_Ohio
Member
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# Posted: 22 Mar 2022 11:53am
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By the way, I was just in my cabin at 10 degrees Farenheit and the wood stove had it at 90.........I had to open the windows. This was with R13 in the ceiling, R23 in the wall and floor. The cabin is 12x24. All of the walls and vaulted ceiling are covered with drywall. Overnight,
I got up the next morning to see that none of the snow melted on the roof, not even around the wood stove chimney.
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happilyretired
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# Posted: 22 Mar 2022 12:19pm
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Quoting: Cedar Fever Thank you for calling out that single stud holding up the cross beam. I will reinforce that. I was going to add some angle brackets to that connection but I will put another stud in there or a 4x4 or something to try and limit downward movement.
It's a triple beam, I'd support it with 3 studs.
Also, is that load transferred to one of the pads on the outside?
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Cedar Fever
Member
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# Posted: 22 Mar 2022 12:34pm
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Quoting: happilyretired It's a triple beam, I'd support it with 3 studs. Also, is that load transferred to one of the pads on the outside?
If it is directly supported by a pad it is luck. I helped laser level the pads and there was not much measuring going on. I will check it out and add supporting these to my list. There should be a pad within a few feet at this time.
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gcrank1
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# Posted: 22 Mar 2022 12:42pm - Edited by: gcrank1
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Looks like a nice place 
No inspections required?
No snow load? If not the 2x6 rafter/purlins will do for practicality.
Insulation priority is roof, walls, floor.
My roof wasnt built as well as yours, and should come off. He 'glass batt insulated and put up rough-cut sawmill random size boards as ceiling. Lots to pull off! Id like to pull it, put down boxcar siding to be exposed, vap/bar, then styro, and reroof (with Good squirrel blocking This TIME!). But im 70ish and not that spry anymore. You are a lot closer to be able to do it better than it is.
Walls would be batts unless I could afford to pay somebody to spray foam. Wire first!
Some have put down rigid styro on the existing floor and covered with a new floor; gotta have room for door swing to do it. Id probably use some thin styro, carpet pad and carpet it.
I have to balance 'its a cabin' with Im not required to make it a 'small house'.
If you worry about fire a wood structure will always be a thing so maybe dont worry too much about foam, instead mitigate fire danger?
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Cedar Fever
Member
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# Posted: 22 Mar 2022 01:05pm - Edited by: Cedar Fever
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No snow load, no inspections.
My first plan for the roof was to put 3/4 inch spacers against the roof. Push in 2†foam board. This would create a small ventilation space. This area has a lot of wind so it’s almost forced air ventilation. Seal that up and the. Smash in some insulation and the cover it up.
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Brettny
Member
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# Posted: 22 Mar 2022 01:50pm
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Quoting: Cedar Fever I’m at the age where I have a few small kids running around so I am trying to be reasonably non-toxic here. They were in that loft coloring right after that picture.
You could also use the "cut and cobble" foam method. But honestly getting some kind of continuous seal between the roof rafters and metal is prety important so the roof should come off any way. And if your going to have the roof off any way put foam ontop of the rafters.
You also need to support the bottom of the vertical stud under that beam..right to the ground.
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Brettny
Member
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# Posted: 22 Mar 2022 01:53pm
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Quoting: Cedar Fever I’m at the age where I have a few small kids running around so I am trying to be reasonably non-toxic here. They were in that loft coloring right after that picture.
You could also use the "cut and cobble" foam method. But honestly getting some kind of continuous seal between the roof rafters and metal is prety important so the roof should come off any way. And if your going to have the roof off any way put foam ontop of the rafters.
You also need to support the bottom of the vertical stud under that beam..right to the ground
.Quoting: Tim_Ohio think, if you have enough air flow from the soffit area (not much to work with there) from the ribs of the roofing, to the ridge cap
The ribs alone are not enough ventilation. They make up a very small percentage of the actual pannel and metal can sweat a ton.
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Cedar Fever
Member
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# Posted: 22 Mar 2022 08:26pm
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Ok I sent some pictures to a roofer about an hour away from the cabin. He immediately asked where the decking was under the metal roofing. Then said the best thing to do is foam the roof in.
So is foam as toxic as the internet says it is? I know my house had some and we’re not dead yet.
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razmichael
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# Posted: 23 Mar 2022 06:51am
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Do your own research as you will get a large spectrum of responses from a forum. IMO there is certainly some off-gassing initially but, assuming properly installed, this is only limited. I suspect you will also be sealing in the roof anyway. Given the wide-spread use of foam nowadays, I consider the risk limited - especially true as it is is cabin not full time. Obviously others will be more concerned.
When I had mine done I included doing the upper end walls of the gambrel roof (as I had already insulated the lower floor with batts). The added cost was minimal.
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Aklogcabin
Member
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# Posted: 23 Mar 2022 09:13am - Edited by: Aklogcabin
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Hello nice little cabin there. I've been researching spray urethane as we are planning on building our retirement home.
I haven't found much information about off gasing being a problem. The cold climate research center which designs cold climate structures suggests the closed cell spray urethane. I am planning on filling the wall cavity. With 5-1/2" @ r-6 per inch should be near r-32 insulation.
I believe that you could easily have this done. And they could do under your floor also. Using the spray urethane you will not need to add a visqueen vapor barrier.
You may want to install vents on the gable ends. Or a vent or 2 on the roof that spins with the wind to help move the air.
The spray urethane against the bottom of the metal roof will make noise such as rain quieter also.
Good luck, you have a great start to some great memories. Stay positive n have fun
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spencerin
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# Posted: 29 Mar 2022 12:52am - Edited by: spencerin
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Get that cross beam fully supported ASAP, both from floor to ceiling and floor to ground.
Looks like your best option is spray foam. Not only for the reasons already discussed, but it also looks like it'll free up loft space. Space is at a premium in small cabins. Putting in a ceiling will cut out space you'll want to have. Also, I recommend you avoid removing the roof - not a good idea to unscrew and re-screw something that should be watertight.
UPDATE - just saw that the roof joists/rafters run parallel to the long wall. First time seeing that. Wonder if having all that spray foam pulling down in the underside of the roof will bow the joists down - they're spanning a larger space, and it doesn't look look like they're firmly fastened at the ends (although it's difficult to determine that in the picture). In that case, Tim_Ohio's recommendation is probably better.
For proper roof ventilation in this second scenario, you would need to have soffit/eave vents and vents at the top, the latter of which you appear to already have (a ridge vent). Typically with metal roofs like yours, there's a decent gap separating the 2 sides at the peak, and the peak "cap" if you will goes over it. That should allow plenty of ventilation at the peak provided foam closure strips aren't already installed. If they aren't, you can install screen on the underside of the gap and fill the gaps between the roof and screen with foam closure strips (and adhesive and staples) to keep bugs out. To further complicate that, though, it looks like you could have a beam just under the ridge vent. But, can't tell in the picture how much a hindrance that may be.....
The good news is that you have a "problem" you can solve!
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Brettny
Member
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# Posted: 29 Mar 2022 09:17am
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If you spray foam there is no need to vent.
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gcrank1
Member
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# Posted: 29 Mar 2022 11:26am
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Roof looks pretty much like how they do pole buildings around here.
But most dont insulate those roofs.
Guess Id be looking online, or taking to pole building folks, on how to insulate that.
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Cedar Fever
Member
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# Posted: 29 Mar 2022 02:21pm
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Thanks!
The beam is getting supported on Thursday with more 2x4. This cabin is built on skids so there are 2x6’s under the beam at the floor.
The guy who built this has been doing “sheds†since the 80’s and I asked him about insulation. He said to nail pink up there and it’s good.
My plan right now is to design out a nice double roof design with eaves, block foam. And rip it off and build an all new roof next year.
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gcrank1
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# Posted: 30 Mar 2022 10:00am - Edited by: gcrank1
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2x6's under the foot of that load supporting upright doesnt sound like enough to me; ie, would think you need a support from under the 2x6's to ground?
The roof....money and work into it then tear it off next year? How about stapling up plastic or vapor barrier now to block the heat from going out then properly rebuild it later?
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Brettny
Member
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# Posted: 30 Mar 2022 11:20am
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Why are you going to rip off and totally redesign the roof on a new building?
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Cedar Fever
Member
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# Posted: 30 Mar 2022 11:29am
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Because I want the roof to be very solid and able to be worked on. I watched them put this roof on in about an hour. It’s more quick work than a forever roof. I also realize I am converting a shed into a cabin so a complete roof upgrade does not seem crazy.
I agree I need to look at how the walls are supported, I’ll shore it up with supports or another rail.
Thanks for the feedback everyone!
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Cedar Fever
Member
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# Posted: 30 Mar 2022 11:45am - Edited by: Cedar Fever
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Quoting: gcrank1 How about stapling up plastic or vapor barrier now to block the heat from going out then properly rebuild it later?
We’re on the same page. This is the kind of temp solution I need while I figure out what a real long term roof will look like on this.
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Brettny
Member
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# Posted: 30 Mar 2022 07:34pm - Edited by: Brettny
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If your not going to get any snow the way is physically built now is totally fine besides a few boards under that big beam. Really the two biggest things anyone needs to worry about how a roof is framed is how its going to handle weight (not in your case) and how it's going to keep the top of the walls from bowing out. Both seam to be addressed in this building becids a few little things.
Also if you feel the need for deeper insulation you can fur out the under side of the roof rafters or even sister them up. Sistering them up can add a bit of strength but that's not something I would really worry about with no snow load.
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Cedar Fever
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# Posted: 30 Mar 2022 09:04pm
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Yes no snow. I just need insulation against the 100+ degree heat. I just need to figure out how to insulate it and not have moisture issues. I worry about condensation rotting away the rafters over time but I also don’t want to over react here.
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gcrank1
Member
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# Posted: 30 Mar 2022 11:21pm
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Within the past year we've had other discussions regarding venting roofs, the one I particularly like has kind of a flow-thru dbl roof design. Hope someone with a better memory can post up the link here or direct you to the site.
Iirc, member Steve_S has great info on this stuff.
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