Tennessee, Climate Zone 4A – plans are on the way
I live in the Climate Zone 4A in Tennessee, just barely north of where it intersects with Georgia and Alabama. Over the last few weeks, I’ve been reading a lot of articles on this site and have even joined as a member. We are looking to build hopefully to start in the next few months. My research has led me in a thousand directions as in our area, though Zip systems are becoming more popular, there’s still a lot of basic OSB sheathing with housewrap. I wanted to understand the best practices from waterproofing to insulation. I’ve been amazed at the options that are available and all the various factors to consider. Now the part where I get to hang my head. After an almost full day of reading articles on this site, I find one about planning ahead and working with a designer. Because we just don’t see exterior rigid foam used in my area, like I’m sure many folks in my region do, I assumed that I was safe as long as I planned before construction. If there’s one thing I’ve discovered, it’s that building a home is overwhelming if you’re trying to not just follow what everyone else is doing.
Now that I have my confession out of the way, here’s the meat of my question. My preliminary plans are approved and we are expecting our final versions to be completed any day now. In our county, they are looking to adopt code changes requiring R19 in the walls with 2×6 studs and an ERV/HRV. We are hoping to insulate well anyways and were planning on an ERV even if we start ahead of the requirements going into effect. We are also planning on using Zip sheathing and I’ve done a lot of reading on building the “perfect” wall in hopes of building a home that will be around a really long time and will be comfortable. Forgive me, I’m an EE and it’s in my nature to understand the engineering and not do things just because. My wife and I are also hoping this will be our home when I eventually reach retirement.
1. Most articles discussing the best wall structure (including Lstiburek’s) tend to describe it with rigid exterior foam. That in my mind made we wonder about using the Zip-R sheathing. A GBA article on sizing calculations indicated that my zone doesn’t necessarily require it due to average temperatures and that any exterior insulation could be beneficial. The best I could find is that it would help provide thermal break from the studs, add wall insulation, and provide some sound-proofing. Like I said, that’s not normal around here and I didn’t know to ask about it before walking through the design process. In a somewhat similar GBA Q&A, someone else in the 4A zone settled with I think cellulose insulation (they just said CI) and a focus on air-tightness in lieu of exterior insulation. Is this the best and most cost effective approach? I’ve heard there are horror stories with cellulose, but am not sure what there is to look for in my region. I did see where there were concerns about moisture in double-stud construction in a cold climate which neither applies to me. So maybe it’s safe?
2. Lstiburek/Straube article on recommended levels of insulation in our climate calls for R-25 in the walls. Can this be accomplished with basic 2×6 studs or will it requiring furring the interior studs with rigid insulation so far?
3. I plan to keep HVAC equipment out of the vented attic space and though we may have recessed lighting, I plan to encapsulate IC rated lights with rigid foam to make it part of building envelope. If I can get similar results from a thin-mount, may go that route too. I may also let them put a drop-down access into the attic from the garage, but plan on the access door having insulation on it and partitioning with OSB between the garage attic space and the rest of the house (as much safety as insulation). Is cellulose the best for the attic space as well?
4. Our plans do have two rooms with vaulted ceilings (cathedral). With a vented attic, I’m planning on baffles and venting channels between the trusses to the ridge vents and as much insulation as I can get in it. I would like to shoot for R-60 (I think that was in the recommendations from Straube and Lstiburek in an article they wrote a few years back). Can that be done?
5. The preliminary plan shows the air handler in the garage at the lowest elevation on the lot (meaning I should have room to punch underneath into the crawlspace. We live on a mountain and though there’s plenty of depth to the lot, there’s a 13 foot cliff edge behind where the home will go. There’s lots of shale rock to work around and so we’re planning on water being dealt with. That means we’ll be encapsulating our crawlspace. If this works out, does it make sense to also mount the ERV in the garage and run the ducts through the crawlspace? Just the little I’ve seen, these don’t seem to have large ducting so I was thinking that there may be a bit more flexibility with them.
6. Since I mentioned encapsulating the crawlspace, I might as well ask if there are any structural/insulating best practices we should be thoughtful of?
Thank you,
Jason
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Replies
A few things to keep in mind. When it comes to wall moisture, there isn't a practical difference between a good wall and a better wall - neither one has problems.
When it comes to insulation and air sealing, more is useful. But there are lots of ways to get to the same values and so it's a ROI issue. Once you satisfy code, only you can decide where to call it good enough. Consider using BEopt.
IMO, cellulose is a good choice.
Good wall R value calculator here:
http://cwc.ca/resources/effective-r/
Remember, interior side foam (strips or continuous) is also an option.
Jason,
I'm in a similar climate as you at 4c (marine). A few questions the experts here will probably ask are 1) Did you design raised heel trusses; 2) What are your current electric and gas prices; 3) Is the electric from a clean or dirty source; 4) How much solar potential does your house site have; 5) Is your builder on board with energy efficient building practices?
In simple form, building energy efficient will keep the air in (low ACH), the water out, and the thermal bridges broken (framing factor).
Have you read about the Mooney Wall (interior cross-hatching) and it's variants?
Keeping ducting inside is easy with the Mitsubishi or Fujitsu ducted minisplit.
Is a frost-protected slab practical for your home?
With solar prices having come down so much, the latest trend is to exchange some of the cost of insulation for more solar.
Good luck.
Thanks Jon. I'll give the BEOpt a try and see how it can help. I've seen it referenced on this site many times, but haven't looked much further.
Thanks Mark. 1.) Nope, that's why I went ahead and fell on my sword. I didn't know to ask about that as it's not common in my area. 2.) Electric should be around $0.10/kwh and my last month's gas was around $0.90/therm. 3.) Electric is a blend of sources (hydro, nuclear, a little fossil left, solar from cogen sites, and wheeled wind). 4.) The house faces south, so it should get a lot of sun running side-to-side, though on a mountain we have a lot of trees which is part of its attraction. I would like to be solar ready but don't want to jump straight in if there's not a lot on return for me. 5.) Yes, I don't think he'd have a problem at all. He's fairly new to using the Zip system and seemed ready to jump in with that.
As for the Mooney wall, is that the same as what I had read in a Fine Homebuilding article where foam strips were used on the interior side of exterior walls to "help" with thermal break (though it doesn't perfectly accomplish the break)?
I've wondered about the minisplits and have heard that there's been a lot of improvements.
We decided to stick with the crawlspace because of the sloping (front-to-back) of the lot. Backside of the foundation is estimated to come to around 5 ft or higher on the back side. With the shale rock underneath, we are wary that there will be sitting water underneath the earth which is why we plan to be extra cautious about water management (keeping away from the footing/foundation, etc) as well as encapsulating the crawlspace.
I wondered about the solar part of that, but our electric infrastructure is different than much of the country and the local energy efficiency programs focus more on insulation, air-sealing, and use of technology. I've begun discussions with our local distributor though as we get a rebate for our efforts. I'll ask them though as it can't hurt to see how things have changed. I suspect it's a lot easier to do that today than it used to be.
Jason,
It sounds like your plans don't show raised-heel trusses. Is it too late to fix this problem? Or can you just order raised-heel trusses if you want them?
You wrote, "I’ve heard there are horror stories with cellulose." Really? Where did you hear that? What terrible outcome occurred?
Q. "Lstiburek/Straube article on recommended levels of insulation in our climate calls for R-25 in the walls. Can this be accomplished with basic 2×6 studs or will it requiring furring the interior studs with rigid insulation so far?"
A. With cellulose or fiberglass, you can expect a maximum of about R-3.7 per inch -- so the center of your 2x6 stud bays will have an R-value of about R-20. Of course, the studs will be the weak link -- they are thermal bridges. With mineral wool batts, you might get as much as R-4 per inch -- so up to about R-22 in the center of the cavity. Whole-wall R-values are lower.
If you want better performance, you need continuous exterior insulation or a double-stud wall. More information here: "How to Design a Wall."
Q. "Is cellulose the best for the attic space as well?"
A. Yes. More information here: "How to Insulate an Attic Floor."
Q. "Our plans do have two rooms with vaulted ceilings (cathedral). ... I would like to shoot for R-60 (I think that was in the recommendations from Straube and Lstiburek in an article they wrote a few years back). Can that be done?"
A. Yes, but only if you plan ahead with appropriate framing. For more information, see "How to Build an Insulated Cathedral Ceiling."
Q. "Does it make sense to also mount the ERV in the garage?"
A. No. You don't want to install a furnace or an ERV in your garage, because the air quality in your garage may be dangerous.
Thanks for your response Martin! Great information.
1.) First, cellulose horror stories? I don't recall where I read it, but regardless the author didn't state. I had also watched a video of a professional insulation installer state he was trying to debunk myths of cellulose use. His concern was mostly regarding moisture problems and he did admit in his comments that the vapor barrier was critical to his success and needed careful planning. I don't personally have a lot of experience and so these two things peaked my interest which is why I asked. I did look online today to see if I could find more info and all I could find was concerns regarding: settling (supposedly by as much as 20% with time), termites (due to the wood content in paper), carcinogenic (due to the chemical treatments), moisture (both due to the application technique and properties of paper). Maybe you have thoughts or info supporting or to the contrary? I have to admit, the chemical treatment part definitely raises my eye brows.
2.) Exterior walls with mineral wool batts and exterior foam seems to be the way to go. I'll probably use the Zip-R to keep it simple since our area doesn't typically do this.
3.) Attic insulation. Thanks, if there are valid concerns with cellulose, what would be the next best thing? Mineral wool batt layers with vertical and horizontal crossing? Or blown in? As I read more on insulation today, it struck me that I should be able to do the insulation myself. In fact, I'd probably feel more comfortable that it is done right if I do. Is something it possible to accomplish what I'm attempting with a loose fill mineral wool product? And if so, where would I find that? I discovered HD doesn't carry that, only batts.
4.) Cathedral ceiling. Good info in that article and I'll plan on the vented approach with the furred strips as necessary. I assume it'll be the same as the exterior walls in this case, i.e. mineral wool batts.
5.) ERV in the garage. Good point about the handler. I think I just took the drawings for granted, but you're right it needs to be outside. However, as for the ERV, does it really matter since it will have ducting through an exterior wall to pull outside air in? I assume they should be relatively well sealed.
Also, just got a response back from the designer. They've already slightly raised the heel at 8 inches. In my zone, and being as close to a 3A zone as I am, does that sound reasonable?
Jason,
Q. "All I could find was concerns regarding: settling (supposedly by as much as 20% with time), termites (due to the wood content in paper), carcinogenic (due to the chemical treatments), moisture (both due to the application technique and properties of paper). Maybe you have thoughts or info supporting or to the contrary?"
A. It sounds like you have been visiting the wrong web sites, or reading exaggerations from rival insulation manufacturers. Termites aren't attracted to cellullose insulation, due in part to the borate content. The borate treatment reduces flammability. Borates aren't carcinogenic. If you want accurate information, seek it out on GBA. You can start here:
"Cellulose Insulation"
"Blown Insulation for Attics: Fiberglass vs. Cellulose"
"How to Install Cellulose Insulation"
"Buyer’s Guide to Insulation: Blown-In"
Q. "If there are valid concerns with cellulose, what would be the next best thing?"
A. The concerns you have about cellulose have no basis in fact.
Q. "ERV in the garage. Good point about the [air] handler. I think I just took the drawings for granted, but you're right it needs to be outside. However, as for the ERV, does it really matter since it will have ducting through an exterior wall to pull outside air in? I assume they should be relatively well sealed."
A. You misunderstood my point about the air handler and ERV. I'm not implying that they should be outside. They should be inside -- in your home's conditioned space. For example, they can be installed in a mechanical room. It's extremely difficult to make sure that the duct seams of your air handler and ERV are perfectly sealed, which is why installing these pieces of equipment in a garage is unwise.
Thanks for the cellulose info and helping to set that straight. Like I said, it was only mentioned there were horror stories, but I wasn't sure what was meant by that. Thanks also for setting me straight on the ERV. I should've thought of the ducting. I'm not sure there's space in the plans for a mechanical room though, so this may take some thought. My fear is that codes may require a substantial distance around the unit(s) for working space. I'll have to pull out my copy of the NEC, but I think it may be something like 3 ft. Though that may only apply to electrical panels, I'll need to verify either way. Your suggestion makes sense though, so I'll try playing around with some ideas. May even look at the crawlspace as an option as suggested by Dana.
Did you see my comment on the raised heel trusses? The designer sends their drawings/specs to the truss manufacturer who evidently completes the truss design. They've evidently specified a slightly raised heel at 8 inches. Will that suffice in my area?
Jason,
In Zone 4, most codes require a minimum of R-49 ceiling insulation. If you want to leave 1 1/2 inch for the ventilation baffle and the vent space above your attic insulation, that means that you need trusses with a raised heel of 15 inches.
Martin,
Thanks for taking your time to help walk me through this process. It's definitely been an adventure. I get what you're saying about the heel and makes sense considering the R-value per inch of the cellulose and ventilation channels.
I hope you don't mind me asking two more questions:
1.) Does it make more sense to use cellulose in the low-lying areas and in the cathedral use mineral wool batts? I ask because I wasn't sure about the packing method in a cathedral ceiling and I'm thinking I may do the insulation myself.
2.) Assuming I do the insulation myself and stick with cellulose all the way through, should I be able to get and blow the cellulose dry and get the proper R-value? I know HD rents the machine and has cellulose, but wasn't sure if the method matters and/or to get the most requiring professional services.
Jason,
Q. "Does it make more sense to use cellulose in the low-lying areas and in the cathedral use mineral wool batts? I ask because I wasn't sure about the packing method in a cathedral ceiling and I'm thinking I may do the insulation myself."
A. I'm not sure what you mean by "low-lying areas." If you mean, "on the floor of a vented attic," then using cellulose at that location makes sense.
When it comes to insulating a cathedral ceiling, the insulation method depends on many factors, including (a) your R-value goal, (b) the depth of the rafters or framing members, (c) whether you want a vented assembly or an unvented assembly. (Note that if your cathedral ceiling areas include skylights or roof valleys, you'll probably want to create unvented assemblies.)
For more information on all of these issues, see "How to Build an Insulated Cathedral Ceiling."
Q. "Assuming I do the insulation myself and stick with cellulose all the way through, should I be able to get and blow the cellulose dry and get the proper R-value? I know Home Depot rents the machine and has cellulose, but wasn't sure if the method matters and/or to get the most requiring professional services."
A. It's possible to screw up any construction project, unfortunately. Of course "the method matters." You may find it helpful to read this article: "Borrowing a Cellulose Blower From a Big Box Store."
>"2. Lstiburek/Straube article on recommended levels of insulation in our climate calls for R-25 in the walls. Can this be accomplished with basic 2×6 studs or will it requiring furring the interior studs with rigid insulation so far?"
BA-1005 recommends R25 "whole wall", which is AFTER factoring in the thermal bridging of the studs, the R values of the wallboard & siding, etc. A typical 2x6/R19 16" o.c. wall comes in at about R14-R15 whole-wall, partly due to the fact that R19s only perform at R18 when compressed to 5.5" in a wall cavity.
https://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf
An easy upgrade would be to use R23 rock wool or R21 fiberglass instead, which raises it to the R17-ish whole-wall range. Rock wool is far more fireproof (fiberglass melts), and higher R, and easier to install. While it's going to be more expensive than R19s, it's probably not going to be a huge upgcharge.
To get it from there to R25 whole-wall would take 1.25"-1.5" of continuous polyiso.
R23 rock wool + 1" of polyiso would get you north of R20, which is probably "good enough", given that with climate change the house be in climate zone 3 well within it's full lifecycle. Most siding can be mounted on 1" foam without furring using longer fasteners.
>"4. Our plans do have two rooms with vaulted ceilings (cathedral). With a vented attic, I’m planning on baffles and venting channels between the trusses to the ridge vents and as much insulation as I can get in it. I would like to shoot for R-60..."
With an energy heel truss it's cheap & easy to hit R60 on the attic floor. BA-1005 calls out R45 for "compact roof" (aka "cathedral ceiling). Even with 2x12 rafters packed with high density cellulose that's going to take 2.5-3" of exterior rigid polyiso.
>"6. Since I mentioned encapsulating the crawlspace, I might as well ask if there are any structural/insulating best practices we should be thoughtful of?"
Pouring the foundation in a minimalist 2" + 2" insulated concrete form and finishing the EPS with a cementicious material such as stuccos designed for direct application to foam makes that pretty easy. In termite zones it's worth installing copper clad sill gasket that extends out over the foam on both sides.
Any chance the furnace & ERV can all live in the crawlspace? The heating & cooling loads of tight code-min homes are pretty small compared to leaky older construction with clear glass windows- it doesn't take much HVAC, and unless someone did a careful Manual J it's almost certainly oversized by at least a factor of 2. Going with a right sized (per the Manual-J/D/S heat pump instead of a fossil burner + split AC and installing it in the crawlspace can work. I've been pretty impressed with just how much house can be heated/cooled with a 1.5 ton ducted mini-split (even in colder areas.) Your 99% outside design temp is about +20F- a 1.5 ton Fujitsu delivers bout 22,000 BTU/hr at that temp, which would cover the loads of a decently designed & construction 1800-2000' house with some margin (but do the Manual-J!)
1.) Thanks for the link to the article. With your and Martin's comments, I'm now thinking mineral wool batts with Zip-R sheathing.
2.) Regarding cathedral ceilings, I'm assuming the gusseting approach should get me close without exterior foam, but if I was to assume it didn't is it possible to only use foam on the cathedral ceiling portions of the roof assembly? I assume that would require the flashing to occur off the foam? Also, thanks for the reference to the R-45. Good to have the right bearings.
3.) Furnace and ERV in the crawlspace? I'm not sure. The builder has not elected for any site elevation studies by the designer as it's not required in our area. The back side of the lot may be 5 ft or higher at the floor joists, so it's possible. But as I mentioned with my response to Martin, if the ERV input ducts are directed to an exterior wall, then does it really matter? Though it definitely makes sense to get the handler out of the garage. I may be looking more into the mini-splits as well.
4.) Do you have any diagrams regarding your approach to the foundation? Am I understanding you right, 2" foam on both sides? I think what I had seen so far involved foam on the interior, with the exterior being coated and layered with a dimpled rain screen directing water to the drainage tiles below the footing. I'm also considering graveling the ground underneath, layering dimpled rain screen on top (possibly), and then the vapor barrier.
5.) Interesting idea on the copper clad sill. Thanks for the info. I'll definitely be looking into that. We have no shortage of termites in our area and where we live is very wooded, though I do plan to ensure we take all the fundamental measures as well (like keeping mulch away from the foundation, etc). But this sounds like great insurance to help mitigate up front.
Also, did you see my comment about insulating myself? With exception of the Zip-R exterior foam of course. I'm thinking that would help me feel better about how it's done and help offset costs to apply the additional (in the sense that in my area it's mostly the minimum done) insulation. Wanted to go ahead and mention that in case that changes things.
It's possible to use exterior foam on just the cathedralized ceiling portions, but it presents an aesthetic issue since there will a ~3" facia board on the edges of those sections of roof. This is easier to resolve on some houses than others.
A mini-ducted mini-split cassette is less than a foot thick by ~35" wide- a 3-4' crawlspace is plenty of room to allow mounting it (and the ducts) to the underside of the floor joists.
With an ICF foundation and 2x6 framing with no exterior foam on the framed wall it's common to cantilelever the still plates 2" off the edge of the concrete (3.5" is still on the concrete, as it it were a 2x4 wall) so that the plane of the exterior side foam is roughly aligned with the plane of the wall sheathing.