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WILL1E
Moderator
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# Posted: 21 Oct 2021 08:06am
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How did you guys attach the foam to the studs/plywood? Same method for attaching the foam to the foam?
Since i don't have sheathing like NateR does in his picture, mine is currently wide open there. Should i put a 2x in here first and then the foam, or just use the foam?
I have alot of other things to do before insulation, including needing it inspected before insulation, but i want to at least get that area sealed off to minimize which critters can get into the cabin.
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Nate R
Member
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# Posted: 21 Oct 2021 08:25am - Edited by: Nate R
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I used 16ga stainless finish nails to go into the top plate, sheathing in my case, and into the trusses.
For yours, I'd think you could use finish nails into the rafters, top plate, and maybe some of the PL300 adhesive for foam board as well. I wouldn't bother with a board in front....my garage doesn't have that, my relative's cabin nearby mine didn't do anything there but baffles.
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WILL1E
Moderator
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# Posted: 28 Oct 2021 11:31am - Edited by: WILL1E
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While I know it’ll make more work when doing the doors, I think I’m just going to make use of all the leftover 2x6’s I have to frame the interior walls. Fells like less work than loading, transporting, picking out new 2x4’s, transporting back and unloading.
Any reason I couldn’t do 24†oc for the interior walls? None of them are load bearing. Only place I could think the 16†oc might be preferred is the kitchen wall the cabinets will hang from.
Another question. If my rafters are 24†oc, do I want 23†wide insulation or 24â€? I don’t understand why the have 2 different options when the space between is actually 22.5â€.
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Nate R
Member
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# Posted: 28 Oct 2021 11:55am
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I don't get that with the insulation either. Not sure if the denser stuff is wider to help hold it in place more, or what.....
Only issue with 24oc walls I can think of is the cabinets....and easy electrical box locations. But neither is a huge deal.
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ICC
Member
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# Posted: 28 Oct 2021 12:09pm
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Quoting: Nate R Only issue with 24oc walls I can think of is the cabinets....and easy electrical box locations. But neither is a huge deal.
Depends on what the interior wall will be... drywall needs to be 5/8" not 1/2" IMO. If wood boards T&G works well across 24" OC.
We would always install horizontal 1x4 or 1x6 where cabinets would be hung. That makes the cabinet hanging so much easier. Even for base cabinets. Kitchen , laundry, workshop.... Do the same for grab bars in the shower area. We would router out the notch before assembling the wall framing. That takes some planning but when you do several houses a year you figure it out. One can cut notches to inset the 1x after he framing is up, it just takes some time.
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WILL1E
Moderator
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# Posted: 28 Oct 2021 12:41pm
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My loft floor joist are sitting on a let in ledger...never thought about that for the cabinets! Good idea!
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WILL1E
Moderator
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# Posted: 28 Oct 2021 01:07pm
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Quoting: Nate R Or, use 1/2" foam, and the 6 1/4" R19 batts (Cheaper batts....), and you're at R21 or so total, but for less cost, too.
So this looks like the most readily available option or at least within a weeks timeframe. R19 (6.5" thick) Knauf insulation would cost around $350 for the entire roof and R21 (5.5" thick) would cost around $800 for the entire roof.
So if i do 1" foam as the spacers for the air channels, topped with .75" foam and then the R19 stuff i would have 1" of compression. So is it worth double the price to have no compression and a couple more on the R value for a roof?
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Brettny
Member
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# Posted: 28 Oct 2021 01:17pm
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Useing the foam board as a baffle also allows you to spray foam the edges and should make a very tight air seal. Its superior to the baffles.
You can use anything for the space, dosnt have to be 1in foam. For my little shed with perlins I didnt use a spacer. I just held up the 2in foam board with a few nails into the rafters and spray foamed the seams. The foam isnt moving once that spray foam cures.
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gcrank1
Member
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# Posted: 28 Oct 2021 01:43pm
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FYI, The rotten nasty little Red (Pine) Squirrels at our home and the cabin will gnaw access holes at any gap and through any insulation to take up residence.
At my old 1st cabin I blocked everything with 2x's, at the current cabin the prev owner/builder used what looks like pieces of 1/4" luan underlayment c/w gaps.
Guess which one has squirrel problems?
They mostly are nesting in the cath ceiling insulation.
7 down last year to the 410 shotgun, another 7 since the end of Sept this year with 1 for sure still eluding me.
Build 'Red Squirrel Tight'!
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Nate R
Member
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# Posted: 28 Oct 2021 06:30pm
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For 24oc ceilings, I agree drywall should be 5/8. But USG says 24oc walls is fine with 1/2".
Insulation...
The R19 batts here are 6 1/4: https://www.menards.com/main/building-materials/insulation/insulation-rolls-batts/r-1 9-ecoroll-trade-r-19-kraft-faced-fiberglass-insulation-roll-23-x-39-2/510499/p-144443 7011633-c-5780.htm?tid=7334631485073975674&ipos=8
So compressing those to 5 1/2" gives you R18 according to the chart I posted in the last page. Add the R4 in the 3/4" soffit baffles, and you've got R22 cavities. At $350 you say.
The R21 + the 4 for foam is R25. That's a 13-14% improvement in the cavity insulation.
But, when you look at the whole assembly (including the framing R value between the batts, etc), I come up with a best case TOTAL assembly R value of 21.3 for the cheaper version, and R23.3 for the more expensive. a 9% difference in the whole assembly. Not nothing, but not dramatic. (Calculator here: https://www.ekotrope.com/r-value-calculator )
IF the baffles are sealing off the wind/soffit air from the fiberglass entirely, making sure that no cold air is bypassing through the fiberglass....which I believe is your plan (Something to seal the batts between the rafters over the top plates), then I'd go right ahead with the R19 batts, and save the $ for somewhere else.
If it were say R35 vs R21, I'd be looking closer at it. And especially since this isn't a full time place....I doubt you'll ever see the full payback or feel the difference.
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Nate R
Member
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# Posted: 28 Oct 2021 06:31pm
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Quoting: gcrank1 Build 'Red Squirrel Tight'!
That's a good reminder I should put even some temporary covers over the 1- 1 1/2" gap where my soffit boards nearly meet at the peak..... Will do next weekend I'm up at my place! 
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travellerw
Member
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# Posted: 28 Oct 2021 06:44pm
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Quoting: gcrank1 FYI, The rotten nasty little Red (Pine) Squirrels at our home and the cabin will gnaw access holes at any gap and through any insulation to take up residence.
We don't got squirrels up here that do that.. but mice.. Damn we got a ton of mice and they will find any hole and get in.. I hate the buggers. I call them mammalian cockroaches.
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ICC
Member
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# Posted: 28 Oct 2021 07:18pm - Edited by: ICC
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Quoting: Nate R For 24oc ceilings, I agree drywall should be 5/8. But USG says 24oc walls is fine with 1/2
That IS what they say is okay. But, the panels do flex on 24" centers, more than we liked. So we quit doing that. YMMV
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WILL1E
Moderator
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# Posted: 29 Oct 2021 07:40am
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Man i love the feedback from you guys!!
Quoting: Nate R And especially since this isn't a full time place....I doubt you'll ever see the full payback or feel the difference.
The other thing i may have going for me is the pellet stove i bought. After talking with ComfortBilt it sounds like the unit, even though it's one of their smallest ones, may cook us out of the place....well at least my son and I as my wife is always cold. So maybe the less than desirably adequate roof insulation will be made up by the stove. TBD i guess.
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Tim_Ohio
Member
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# Posted: 29 Oct 2021 09:08am
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My two cents worth:
I did drywall on the inside over rock wool/mineral wool insulation in the walls with no vapor barrier and on the ceiling with fiberglass under a paper vapor barrier. I read both ways about using a vapor barrier over the mineral wool. I hate insulation installation and wanted it done as fast as possible. So, I chose no vapor barrier and just covered it up fast with drywall. A friend had a drywall lift and it was a wonderful thing to have when putting the drywall on the ceiling. The mineral wool cut easily with a bread knife. I also used it in the floor. It's said to be resistant to rodents and moisture so it was a good choice in a cabin. If it had come with a vapor barrier attached, I'd have put it in the ceiling. I couldn't find it like that. As for the drywall, using it
might be mundane in a cabin, but it is cheap and gave me a sense of security for fire issues, since the cabin is located far away from any help.
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Nate R
Member
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# Posted: 29 Oct 2021 09:16am
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Quoting: ICC Quoting: Nate R For 24oc ceilings, I agree drywall should be 5/8. But USG says 24oc walls is fine with 1/2 That IS what they say is okay. But, the panels do flex on 24" centers, more than we liked. So we quit doing that. YMMV
Interesting! I never tried it myself so far...thanks for sharing that experience.
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Brettny
Member
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# Posted: 29 Oct 2021 10:16am
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Quoting: WILL1E The other thing i may have going for me is the pellet stove i bought. After talking with ComfortBilt it sounds like the unit, even though it's one of their smallest ones, may cook us out of the place....well at least my son and I as my wife is always cold. So maybe the less than desirably adequate roof insulation will be made up by the stove. TBD i gues
Poor roof insulation means you can get condensation under your sheething causing it to rot out. It's even worse with metal roofing.
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WILL1E
Moderator
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# Posted: 29 Oct 2021 10:25am
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Quoting: Brettny Poor roof insulation means you can get condensation under your sheething causing it to rot out. It's even worse with metal roofing.
What other option(s) do I have?
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Tim_Ohio
Member
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# Posted: 29 Oct 2021 10:27am
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Quoting: Brettny Poor roof insulation means you can get condensation under your sheething causing it to rot out. It's even worse with metal roofing.
+1
Tim_Ohio
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Tim_Ohio
Member
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# Posted: 29 Oct 2021 10:30am
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Quoting: WILL1E What other option(s) do I have?
Don't fully insulate your ceiling between the joists. Mine were 2x6 ceiling joists. I used R13 for 2x4 studs and it left an air space above the insulation. Then, the slotted soffit allowed air to pass up through it to the ridge vent.
Tim_Ohio
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WILL1E
Moderator
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# Posted: 29 Oct 2021 10:38am
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Quoting: Tim_Ohio Don't fully insulate your ceiling between the joists. Mine were 2x6 ceiling joists. I used R13 for 2x4 studs and it left an air space above the insulation. Then, the slotted soffit allowed air to pass up through it to the ridge vent.
I'm going to build my own roof baffles out of foam like ya'll suggested...so how would that be any different?
Only other thing i can think of is to attached 2x2's to the inside edge of the rafters to regain the rafter depth i'm loosing to the custom foam baffles. This would allow me to get some R30 insulation that's 7.25" thick...which would put total insulation to the R35'ish.
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Tim_Ohio
Member
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# Posted: 29 Oct 2021 10:59am
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Hi, Willie.
Your idea has merit. Maybe I don't fully understand
the baffles idea. There is only so much room between the roof sheathing and the bottom of the rafters to work with. For me it was simple to just use less insulation. And, with the paper moisture barrier tabs, it stapled up in place quickly. Heating with the wood stove cooks me out of the 288 square feet I have. A ceiling fan in the center of the room brings the heat down and around the room nice and even without cold areas. The only thing that feels a bit chilling is the floor, since it's off the ground and cold air circulates under the building. The same mineral wool went into the floor. It was R23 bats.
Tim_Ohio
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WILL1E
Moderator
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# Posted: 29 Oct 2021 11:09am
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So my rafters are 2x8. The roof needs to be vented from soffit to ridge. I was going to do those plastic baffles but it was suggested to basically make my own out of pink sheet foam. So on the underside of the sheathing i'll use 1" thick strips of pink foam to create a standoff/airgap. On top of that i'll use .75" thick pink foam. So making my own baffles gives me a R4'ish rating vs. 0 from the plastic baffles. This leaves me with 7.25-1.75=5.5" of space left for insulation.
Since i'm being told here that having a total R value of mid 20's could cause problems, i was suggesting adding 2x2's to the inside edge of the rafters to increase my insulation space to 7". That way i can buy R30 wool batts. So the R30 plus the R4 puts me in the mid 30's...but will cost me about $1100 more than my other option for mid 20's r value.
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Tim_Ohio
Member
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# Posted: 29 Oct 2021 11:24am
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I don't see you going wrong with any of what you described. Like what Brettny said, the air space is critical for the life of the building materials.
Tim_Ohio
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WILL1E
Moderator
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# Posted: 29 Oct 2021 11:25am
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Or...do i just put full sheets of 2" pink foam to the underside of the current rafters? This would put me into the 30's and cheaper than the wool option. Not sure if it would be good to sandwhich fiberglass insualtion between 2 layers of pink foam...any might make attaching the finish ceiling surface a PITA.
Just thinking out loud here.
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WILL1E
Moderator
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# Posted: 29 Oct 2021 11:27am
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Quoting: Tim_Ohio I don't see you going wrong with any of what you described. Like what Brettny said, the air space is critical for the life of the building materials.
Creating the airspace is a given for me, regardles if it's the plastic trays or the custom foam. Just trying to figure out options for increasing the R value out of the mid 20's since Brettny said being under insulated is going to create problems.
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snobdds
Member
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# Posted: 29 Oct 2021 11:33am - Edited by: snobdds
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Closed cell spray foam solves a lot of issues, even just spraying on an inch think layer. Then you have no worry about venting or moisture. It gives the roof more rigidity and most importantly on a metal roof it locks in metal screws on the roof that may not have it a rafter. Screws have a tendency to come out over time, spray form will keep them where they are forever. One 600 sf kit could do your entire roof. Then just use the cheapest insulation you can find. You will save money in time...which is always the biggest hidden cost.
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gcrank1
Member
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# Posted: 29 Oct 2021 12:24pm
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2x8 rafters
Make the styro 'baffle', seal edges well
The above set at a 'depth' that std batting for 6" walls just kisses it.
My guess is you will be able to cook yourself out of your 'sauna' pretty easy.
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travellerw
Member
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# Posted: 29 Oct 2021 12:28pm
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Wow.. I think there is some misunderstanding here... or I wholeheartedly disagree with some information!
You plan to create a air channel (1") from the vented soffit all the way to the ridge vent. Then put insulation in the space remaining. Then vapour barrier, and then drywall?
YOU WILL NOT have issues with mid 20s R value rotting things out. Absolutely not. That is why you have an air channel. It allows the moisture and heat to be taken away preventing that.
Now as to sealing that 1" air chamber from the insulation below. There is debate here. All the experienced tradesman I spoke to up here said "Do not completely seal it". It was recommended to seal the first 16-20 inches to give the air a path up the channel and seal the soffit off. Leave the rest unsealed as a "tight fit". This will give a path for any moisture that might get into the batt area a way out (eg. a poorly installed electrical box without a poly hat). Vapour barrier that is fully sealed is a MUST in colder climates.
Rot happens in 2 ways.. Moisture or dry rot from overheating. Those channels are done to prevent both of those issues.
Thats my opinion based on my research with people building 100s of homes and buildings a year. I will be doing exactly like described above (with mid 20s R in the roof) and won't stress about it at all.
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WILL1E
Moderator
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# Posted: 29 Oct 2021 12:49pm
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Quoting: travellerw You plan to create a air channel (1") from the vented soffit all the way to the ridge vent. Then put insulation in the space remaining. Then vapour barrier, and then drywall?
Exactly
Quoting: Brettny Quoting: WILL1E The other thing i may have going for me is the pellet stove i bought. After talking with ComfortBilt it sounds like the unit, even though it's one of their smallest ones, may cook us out of the place....well at least my son and I as my wife is always cold. So maybe the less than desirably adequate roof insulation will be made up by the stove. TBD i gues Poor roof insulation means you can get condensation under your sheething causing it to rot out. It's even worse with metal roofing.
So maybe Brett missed the part about still venting it with the air channels?
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