What is my best insulation strategy here?
Hello,
I’ve been reading and watching videos on everything insulation lately, but nothing I read or watch seems to cover my exact situation so I wanted to ask here.
My info:
1. Central, Missouri, climate zone 4
2. New construction house with scissor truss vaulted ceilings for 2/3 of the roof, and 1/3 is normal flat bottomed trusses. Attached 24×48 garage with normal flat bottomed trusses creating an attic space. 5/8 Zip System on the roofs as decking with Hytech #80 Barrier Coat painted on the underside (radiant barrier paint with aluminum particles and tiny ceramic spheres.) 7/16 Zip System for wall sheathing. Everything liquid flashed with either Zip System Liquid Flashing or Dymonic 100.
3. 4 ft crawlspace with a full concrete floor which has plastic under the concrete.
Insulation Options:
I want to go with Rockwool batts AND/OR open/closed cell spray foam where appropriate. But my biggest fear is creating a condensation problem which will lead to mold and rot.
Would like R-60 in the ceilings/attics and R-23 or so in the walls.
For the Vaulted ceilings:
From what I’ve researched, closed cell in the vaulted ceilings is best (and do NOT install a vented ridge cap), but again I’m worried about creating condensation somewhere – so if I did this would I need to cut vent holes in the drywall for registers to get air in and out of the ceiling space? Also, getting to R-60 using closed cell would be insanely expensive, so maybe there is a better option?
For the walls:
Was thinking about using Rockwool’s 5.5 inch thick R-23 Comfortbatts – but being as they are friction fit and are unfaced, do I need to install a plastic barrier on the drywall side of the Rockwool for Climate zone 4?
For the Garage attic:
Was thinking about blowing in R60 deep worth of Greenfiber
For the crawlspace:
Was thinking 2 to 3 inches of closed cell foam on the 4 ft concrete stem wall and in between each floor joist in the rim board cavity
All of this is just my best guess based on what I’ve studied. If anyone has any better ideas/strategies, I’m all ears.
Thank you.
Replies
You might want to check out the flash and batt approach if you are doing an unvented assembly. Enough closed cell to keep the dew point away from the fiber insulation. You want to make sure you provide an air barrier and vapor retarder to keep the moisture out of the attic spaces. Don't want to put in big holes and registers.
See these articles for flash and batt information:
https://www.greenbuildingadvisor.com/article/flash-and-batt-insulation
https://www.finehomebuilding.com/2011/01/20/why-flash-and-batt-makes-sense
You don't want the plastic sheeting in a cooling climate. You do need an air barrier - but not plastic sheeting as it becomes a condensing keeps the wall from drying to the inside during a/c season when it is hot and humid outside and cool and dry inside.
Will the spray foam adhere to the radiant barrier paint? Does it need an air gap to work best?
>Will the spray foam adhere to the radiant barrier paint? Does it need an air gap to work best?
Yes it will adhere, but as to whether it needs an air gap for best effectiveness, that's a good question and one I'm not sure of yet. Will try to find an answer.
Radiant barriers do not work without an air gap. Generally 1" is considered good practice. If you spray foam directly to the underside of your paint-on roof sheathing radiant barrier, then you've just pissed away money on your Hy-tech barrier.
My understanding is that radiant barriers work best when reflecting solar heat from entering an attic space laying adjacent to, but outside of, the thermal envelope of a dwelling. It reduces the ambient temp. in an attic which is perpetually trying to equalize with the cooler temperature of a conditioned dwelling. Thus, instead of a 130 degree ambient attic temperature trying to equalize with a 70 degree dwelling space (which is obviously a 60 degree temperature differential that a thermal envelope has to mitigate) a radiant barrier can reduce ambient attic temps to, say, 100 degrees which presents a more effective 30 degree mitigation by the thermal envelope. Thus, a radiant barrier makes for a more effective thermal envelope which, in turn, makes for a more cost effective conditioning system and can save money.
Keep in mind that just as lower temperature differentials render a loss of radiant barrier effectiveness, so to do higher thermal envelope R-value render a loss in radiant barrier effectiveness. Said another way, the higher your thermal envelope R-value, the less cost effective the installation of a radiant barrier becomes.
Lastly, remember that radiant barriers actually work against you during the heating season. In other words, they appear to be most cost effective in their use in climates zones 3 and lower.
Condensation is caused by warm air meeting a cold surface.
My understanding is that an unvented roof cavity should be insulated in such a manner that the underside of the roof sheathing avoids reaching dew point conditions in your climate zone. I believe zone 4 means that you should try to reach at least an R-6 insulation level and use an air barrier between the conditioned space and the underside of your roof sheathing. I believe open cell sprayed directly on the sheathing @ nominal 3 inches would provide a reasonable R-15 rating and also qualify as a code required air barrier. You could spray deeper to get to your R-60 (open cell will also be more cost effective than closed cell to get this level of R -value), or use a variety of cost effective fibrous insulation materials to build upon your spray foam thermal barrier layer. I would recommend mineral wool (rockwool) or fiberglass batt in addition to the air barrier qualified spray foam. A typical paint film on finished side of drywall will also give you a level of vapor barrier protection from any warm, moist air migrating through cavity insulation.
Why you would want to introduce venting (convection) within a thermal envelope layer is beyond me. This could easily short circuit your thermal barrier and possibly introduce condensation upon your building materials that "care" about moisture (namely your wood roof sheathing). Venting would be similar to going out into a winter wind storm with a woolen sweater base layer top coated with a nylon wind breaker that you tore open with a bunch of holes.
The holes would allow convection and massive wind wash to easily move your body's warm thermal micro climate away from you and toward the colder outdoor temperature via the open weave (air channels) of your woolen sweater. Likewise, drywall vents could carry warm, moist interior air more easily toward your cold roof sheathing surface where a dew point could be reached.
Lastly, be careful when using closed cell polyurethane spray foam in crawl spaces. Closed cell can promote the migration of liquid water from the earth up into framing members (moisture naturally moves from wet to dry just as heat energy naturally moves from hot to cold) via capillary action (wicking). I believe it is recommended to use open cell foam for insulating crawl space walls that are in contact with the earth and form the structural basis for crawl space wall thermal envelopes. The physical nature of open cell foam does not promote capillary action. Also, be aware that open cell foam off gases over time and can introduce toxic fumes into the conditioned building envelope. I only recommend the use of closed cell for insulation under concrete slabs with an additional layer of 6 mil polyethylene used between the closed cell and concrete slab as an insurance policy against migrating toxic off gases into the conditioned space. I see few areas in a typical residential thermal envelope that closed cell polyurethane spray insulation is of practical use. One (albeit rare) exception might be where the structural nature of closed cell foam is needed between and/or over framing members to provide an unusual level of rigidity. Even then, I would take care to isolate the closed cell foam from building envelope with a zero perm vapor barrier that won't case condensation issues in the heating and cooling seasons. That could be easier said than done.
> I believe open cell sprayed directly on the sheathing @ nominal 3 inches would provide a reasonable R-15 rating and also qualify as a code required air barrier.
3 inches times R3.6 per inch gives me about R11. I was thinking do 2 inches of closed cell minimum and then fill in the rest with Rockwool batts. That gives me a vapor barrier/air barrier and then the added insulation on top of that. Not sure whether to install those plastic air channel baffles on the underside of the roof deck through or just spray it directly to the underside of the roof deck. With the Hytech Barrier Coat I already applied to the bottom of the Zip 5/8 roof sheathing, it might be good to have a small 1 inch or so air gap between it and the spray foam. Not sure about that yet.
>Why you would want to introduce venting (convection) within a thermal envelope layer is beyond me.
I was thinking that if I have closed cell on the ceiling, anything in the cavity can't dry to the outside due to the closed cell vapor barrier, but would instead need to dry to the inside and I wasn't sure if it could dry through the Rockwool batts and drywall or not.
>Closed cell can promote the migration of liquid water from the earth up into framing members (moisture naturally moves from wet to dry just as heat energy naturally moves from hot to cold) via capillary action (wicking).
This would not apply to my crawlspace which has a fully concrete floor, right? There is no exposed ground in my crawlspace whatsoever. It's all concrete with 6 mil plastic under all the concrete. Below that is gravel and below that is actual dirt.
Since you have the radiant barrier paint already applied, you might want to reconsider the vented roof - if you can still add the soffit and ridge vents.
See this for both vented and unvented recommendations.
https://www.greenbuildingadvisor.com/article/how-to-build-an-insulated-cathedral-ceiling
There can be drying towards the interior through the rock wool and drywall. But you do want the ceiling to be air tight as the air movement can account for more moisture movement than the drying to the interior through the rock wool and drywall.
Do you have a capillary break between the sill plate and the concrete? That should help minimize moisture movement from the concrete into the framing members.
With the radiant barrier on the bottom side of the sheathing, it should reflect the radiant heat back into the attic during the heating season.
>Since you have the radiant barrier paint already applied, you might want to reconsider the vented roof - if you can still add the soffit and ridge vents.
See this for both vented and unvented recommendations.
Thanks for the link. Yes, it's still not too late for me to go with a vented soffit and ridge vent. Haven't ordered the metal for the roof yet and the trusses aren't yet set.
>Do you have a capillary break between the sill plate and the concrete?
Yes my 2x8 sill plate has a foam sill seal under it. As does the 2x6 sill plate for the garage.
>With the radiant barrier on the bottom side of the sheathing, it should reflect the radiant heat back into the attic during the heating season.
Yes that's what Hytech claims will happen. The paint has aluminum in it, as well as tiny little ceramic balls with no air inside. The texture it leaves is a very rough silver.
Why would you have moisture in your ceiling cavity to vent out? If you expect moisture to be where it should not be, then you have admitted that you are planning to poorly insulate and do a sub par job barring air from passing through your thermal envelope. In essence, I believe you're admitting that you do not understand the science of building materials and are putting a supposed safety measure in place that will really only cause more of a problem. My advice is to hire someone that does understand the science because the science is not sinking into your cerebral cortex.
Ground moisture can (and will) enter through your footing and concrete stem walls.. Enough to be a problem? Maybe. But I do know that your vapor barrier under your slab will not prevent that from happening. Spray those walls with closed cell foam on the inside and it can wick ground moisture up to your framing. You don't have to take my word for it. Do your building science homework elsewhere on the web and you will find this to be true.
Definitely need closed cell. Also, just as important it needs to be installed at the right depth. The depth depends upon climate zone. I believe MO is in the same climate zone as me. Here we need 3” min in roof and 2” min in wall. Foam is amazing stuff b/c the water vapor will not condense at dew point. I’ve used the flash and batt method about as soon as it was introduced. Have never had a call back for moisture issue. I will be using the same method on my house when I build in a couple years. Only way you can have a problem is if you are creating way too much moisture in your house. I repaired a home for a few sweet old ladies a few years back. They set thermostat for 80 and turned humidifier all the way up b/c they liked the heat and moisture. Long story short, mold on both sides of the wall, was nasty. No proper insulation method to remedy a situation like that.
Thank you for the input. What you said about closed cell depth confirms what I read from the SPFA. The big issue will be cost.