Understood. The stove/fireplace would be a backup energy source and a source of ambiance. In the place we are currently renting we have NG fireplace. No way in hell that would be in my actual home...
Electric vs. NG Boiler
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I think the hack being used on super tight homes is redirect the outdoor air makeup system vents to the heating appliance in place of sending it to the bedrooms when the stove is being used. It would require one extra diverter valve and a extra duct run to the appliance. Oversize the air to air heat exchanger and even with a higher air exchange the building would still be quite efficient The biggest problem is the stoves need to be tiny and most folks want a big one with glass door so they can see the flames. The older small Jotul's (original 602 and 606) had 5" outlets.
EbS-P
Minister of Fire
So with 1 AHC are you installing an energy recovery ventilation appliance? Seems that with one of these and ballanced to a slight positive pressure along with an oak you could be alright. I know my jotul has a single well sealable air inlet. No idea of the leak rate.
Seems that a stove of the correct size and an air inlet of the jotul type, ERV or not you should be ok. I would plan on a hepa filter while burning anyway tight house or not.
I’m envious of your opportunity but not sure how I would survive the build process. I know just enough to really feel my constant oversight is warranted.
Yes, we'll have an HRV or ERV. Need to discuss with builder. I'm leaning towards ERV because we're in a low humidity part of the world.
Yes, planning on HEPA filter for sure, mainly because we're subject to occasional smokey summers here in BC.
It seems that the biggest issue with the OAK is how it connects to the stove/fireplace. Some/most units just dump into a general, but leaky, area and that's good enough. But for a house that is tight, it sounds like this is the weak link. However, reading some additional GBA articles last night, there are some stories of true Passive House designs out there that have used just normal stoves and didn't have issues.
Yes, my constant oversight is just beginning. I'm sure our builder (and eventual neighbor), will hate me by about week 3. I'm a structural engineer, so reviewing this kind of stuff is kind of ingrained in me at this point in life.
Here's my thoughts on your wall.......
if you think you can get 4" of insulation on the outside of your assembly and still stack stone on the wall, then your going to need a pretty thick foundation?
I think it's hard to beat a 2x6 flash and batt wall with 2" of eps foam on the outside. The thermal brake is achieved , air seal can be virtually perfect, and use cellulose blown behind 2" of sprayfoam in the wall cavity. The performance is great and structure sound.
Also be aware all truss packages do not come with energy heels.
Unless you plan on no windows in your house, too much thought can be put into the perfect wall.
I can heat a mcmansion and a ton of large windows with a 3cuft firebox 5 cords of wood and a very little amount of forced air propane in the shoulder season, with the above said wall assembly.
The stove room is large with 16ft cathedral and typically never gets to a "Holy cow it's hot in here" point,which I think is key.
Initial cost vs efficiency vs longevity and comfort of your dhw system is important for sure. I'm not sure what that answer really is now a days vs 5 years ago when I looked last. In those days I thought a 50 gallon electric for 400$ was hard to beat??
if you think you can get 4" of insulation on the outside of your assembly and still stack stone on the wall, then your going to need a pretty thick foundation?
I think it's hard to beat a 2x6 flash and batt wall with 2" of eps foam on the outside. The thermal brake is achieved , air seal can be virtually perfect, and use cellulose blown behind 2" of sprayfoam in the wall cavity. The performance is great and structure sound.
Also be aware all truss packages do not come with energy heels.
Unless you plan on no windows in your house, too much thought can be put into the perfect wall.
I can heat a mcmansion and a ton of large windows with a 3cuft firebox 5 cords of wood and a very little amount of forced air propane in the shoulder season, with the above said wall assembly.
The stove room is large with 16ft cathedral and typically never gets to a "Holy cow it's hot in here" point,which I think is key.
Initial cost vs efficiency vs longevity and comfort of your dhw system is important for sure. I'm not sure what that answer really is now a days vs 5 years ago when I looked last. In those days I thought a 50 gallon electric for 400$ was hard to beat??
Yes, I am not sure what the foundation detail looks like yet for walls that will have rock/masonry elements. We are going to use ICF with 6" concrete and 4" thick (each side) foam.
Trusses will have energy heels. My builder is on it.
I understand about too much thought. I have spent many late nights for the past 3 weeks reading all that I can. Not fun. Current thoughts are as follows:
1) drywall, 2x6, roxul batts, sheathing, WRB, 4" comfortboard (availability of CB concerns), 3/4" furring, rainscreen
- time tested. will work. worried that there will be a lot of screwing around with furring strips/siding. don't necessarily like the window being an "inbetweenie" (set in ~5" from exterior)
2) drywall, 2x6, sheathing, WRB, 4" rigid foam (XPS, maybe, but environmental impacts + questionable long term) shrinkage/performance issues; EPS, lower R-value, but maybe better on the shrinkage front), 3/4" furring, rainscreen
- time tested. will work. sim concern on "inbetweenie" as #1. i have doubts about vapor transmission, but apparently with foam this thick, sheathing will be "warm" and thus there is no issue with whether house dries in or out
3) drywall, 2x6 (or 2x8) staggered 2x4 studs, dense pack cellulose, sheathing, WRB, 2 or 4" comfortboard or rigid foam, 3/4" furring, rainscreen
- blend of issues from #1 and #2, dense pack installer is critical so no longterm air gaps form at top of cavity
4) drywall, 2x4 double stud wall, roxul batts or dense pack cellulose, sheathing, WRB, 3/4" furring, rainscreen
- double stud walls are seemingly controversial (strong arguments in both camps). biggest issue is whether the cold sheathing is a long term issue with wetting/drying cycles. i like the deep windows and having the windows be "outties". easy to handle cladding and rainscreen. highly dependent on cellulose installer (if used) - and not sure if it's cost effective if using roxul batts to fill the cavity. if doing roxul, i'd do 3.5", 5.5", 3.5" batts (vert, horiz, vert). this option loses a lot of interior square footage.
5) ICF (same as basement)
- some doubts on claimed R-35 performance. air tight. no long term flexibility of house modifications (hopefully there would never be any). would likely require interior 2x4 walls throughout house for drywall, MEP, etc. sim to #4, this loses a lot of interior square footage. should have best reduction of thermal bridges of all options
I'm leaning towards #4 because I think holistically it is the most efficient (cost and time and material) to build and I like how the windows would feel being trimmed out 12" deep. All the anectdotal stories of long term performance are favorable for cold climates, but I do have concerns with the wetting cycle due to cold sheathing. I understand that you cannot put exterior insulation on these walls, so you do end up with a lot of thermal bridging locations. Additionally, how this would integrate with the 4" of ICF sticking out is something to consider.
If supply chain issues weren't a thing, I think #1 would probably be at the top of the list, but I question if we can procure comfortboard. Gutex multitherm was another option (more $), but it too is not available to us in Canada with any reasonable supply chain.
With #4 you won't have thermal bridge with your 5.5" "space" between your studs and your second stud won't be load bearing which will allow for a standard 9" thick foundation. If I'm following your description correctly.
Is condensation inside your cavity a big worry?
Just curious what your thoughts are about a drywall,3.5" batt or cellulose,2" spray foam, in/on a 2x6 stud with 2" foam on the exterior vs #4?
Condensation in the cavity is my #1 worry with #4.
The thermal bridges with #4 occur at top and bottom plates, truss heels, and rim board (maybe). I suppose the rim and heels could be set back 2" or so to allow for 2" of exterior insulation.
I'm trying to avoid spray foam (environmental + long term performance concerns with shrinkage).
EbS-P
Minister of Fire
Seems like #4 comes with solvable issues and cuts the number of sub contractors and provides fewer opportunities for mistakes. which means less oversight on your part which equals overall happier mood during all of this.
I think the North American Supply chain is going to take 6 months to normalize no real info just a gut feeling. Any items that rely on Chinese components or materials I don’t have a good sense of when that might return to normal. China getting through winter will help some.
But in general we are not addressing our labor shortage so we will see how long that is an issue.
I think the North American Supply chain is going to take 6 months to normalize no real info just a gut feeling. Any items that rely on Chinese components or materials I don’t have a good sense of when that might return to normal. China getting through winter will help some.
But in general we are not addressing our labor shortage so we will see how long that is an issue.
I don't think you'll have an issue with wetting on the exterior sheeting, as long as the exterior housewrap and siding is installed correctly and again assuming the interior vapor barrier is done well. Rot can't take hold when it's froze in the winter, and come spring it should dry out relatively quickly should it get wet, plywood will also perform better than OSB if it does get wet and right now is pretty close in cost.
IMO I think you're leaving a lot of performance on the table by percluding spray foam, closed cell spray foam has a high insulation value and also works wonders for air sealing and keeping interior moisture off the outside sheeting. Flash and fill or flash and batt are relatively cost effective for the performance achieved.
IMO I think you're leaving a lot of performance on the table by percluding spray foam, closed cell spray foam has a high insulation value and also works wonders for air sealing and keeping interior moisture off the outside sheeting. Flash and fill or flash and batt are relatively cost effective for the performance achieved.
I'm leaning towards post 18 and 19 found here in the replies:
Details for Insulating a Double-Stud Wall With Cellulose - GreenBuildingAdvisor
Michael Sterner is ready to build a new house in northern Wisconsin: a simple, two-story box of about 2,000 square feet. After studying many possible wall assemblies, he has settled […]
www.greenbuildingadvisor.com
The biggest issue is figuring out how the wall aligns with the foundation. But, it seems to solve the cold sheathing concern and is a hybrid of traditional double stud wall + exterior insulation.
maple1
Minister of Fire
I've been wanting to re-side our house the past while, and improve air sealing and insulation while at it by putting a layer of foam board of some kind on the outside under the siding. I've lost touch with construction materials and techniques since we built 25 years ago. But I've been getting the heebie jeebies thinking about moisture getting trapped in the walls by doing that, with the layer of vapour barrier on the inside of the walls. How best to accomplish that without laying a moisture trap?
Unfortunately I don't have a specific answer for you, my research has centered around new builds (intend to buy some land and build our own house) and I haven't really considered installing foam over the existing sheeting.
I do know a few people that have done just what you proposed, ripped off the old siding installed 1" foam and put on the new siding, 10-20 years later none of them have experienced moisture issues. If the vapor barrier is good and moisture can't get in from outside I don't see where moisture is a very big concern, but we also have a fairly dry climate and it's common knowledge here to keep house humidity low in winter to avoid moisture/mold issues. I have looked some at the Durospan product and think something like the R10 version would improve insulation considerably.
My parents took a different approach when they resided their house, they had existing 2x4 walls and r12 insulation with plywood sheeting. They built entirely new 2x4 walls to go over the existing secured with horizontal 2x4" straps. Giving them a total wall thickness of 9" including the existing 1/2" plywood that was left in place in the middle of the wall. The new cavity was filled with 2x6 R20 fiberglass batts, sheeted with osb, tar paper (I didn't agree with this and believed tyvek or typar should have been used instead) as the water barrier with vinyl siding on top. The difference in heat loss was immense, and all 2600sqft is now easily heated with a PE Super 27 consuming 4-4.5 cords of softwood per year. Noise transmission was also greatly reduced, and the house no longer shook in high winds. The problem with this is the amount of work involved, at least equivalent to framing a the outside walls of a new house, and it also requires creative approaches to allow existing windows to work with a now much thicker wall.
Here's is an interesting video I cam across a while ago as well, tyvek drain wrap that is supposed to eliminate the possibility of moisture between the sheeting and foam:
maple1
Minister of Fire
Regular 2x6. T&G sheathing. Fiberglass batts. Plastic vapour barrier under the drywall, Tyvek under the siding.
With having plywood on the stud exterior then adding insulation on top of that you can create a possible dew point thats on the surface of the plywood. The fiberglass batt is not helping a ton in this situation either, as it has the potential to allow the warmth of the house enter the cavity more than other types of insulation. My last deep dive into wall construction concluded that if your putting any type of foam insulation ONTOP of plywood you want a minimum of R10 in a cold canadian climate to stop the possible dew point. R10 = 2" foamboard in most cases. With that 2" you have to consider your existing windows and how to cap them effectively as it can be a easy point of entry for rain water.
In your type of construction, the general weak spot is the sill plate and joist ends. Is your basement finished? If accessible I would highly encourage you to spend your money in that area,(sprayfoam) as well as having a good look at your attic insulation levels. In the attic I would recommend topping it up to a R60 with cellulose. Increasing your wall insulation would be after those 2 areas are addressed, and in a retrofit from the exterior Increasing wall insulation comes with some complications if not done correctly. In general it sounds like you have the fairly common and fairly decent wall construction that has stood the test of time. 2x6 is alot better than only having a 2x4 batt for insulation and is probably 75% of existing homes. You can add more to walls but it needs to be done correctly with proper r value and care for water penetration. Hope this helps
sloeffle
Minister of Fire
Worked on a Habitat for Humanity house last week and we put R5 ( last Habitat house I worked on we put up R10, was told they've cheapened their builds because of cost ) over the existing 7/16 sheathing. House wrap wasn't applied over the sheathing, but all joints on the insulation board were taped. In Ohio ( very humid in the summer time ) I've never seen a house with plastic under the drywall, so maybe that's how you can get away without using any house wrap.
maple1
Minister of Fire
Yes. Basically reinforced some of my thoughts. I think around here it's pretty common to put a layer of thin foam board under siding when re-siding, but I've always been suspect of it. My rim joist area is full of batts with a layer of vapour barrier over it (that was painstaking), and I have a double layer of 6" batts in the attic.
That's awesome you make the time to work on the habitat homes.......
the sheathing in the middle of tha cavity is the issue....
@iron why do you want to use plywood then insulation. Metal windbracing will provide adequate wall strength and if you use a eps type foam it too will add strength vs the comfortoard you have mentioned.
I just read an article that there is/was some pretty generous energy grants for insulation in N.S.
IIRC this was in Halifax (not sure if the program was local or provincewide) but the story was how the person had there exposed basement walls spray foamed and fireprotected for very little out of pocket cost.
sloeffle
Minister of Fire
Can you explain more please ? If I ever build a new house myself I want to make sure that's it's done correctly.
Ok, this what "they" say. .. cold climate is trickier than a warm climate and cold climate poses these issues with a dew point inside the cavity.......sheathing in the middle of the wall is the topic and its potential problem.....1. air infiltration into the cavity....moisture laden air enters the cavity and is stopped at the sheathing,where it can collect and rot. 2. In the winter the sun beats on the wall (siding,brick)where there's not enough insulation between the brick and plywood. (R10 minimum suggested).The plywood is cold from the night temperatures the sun comes out and starts heating the plywood (due to a lack of sufficient R-value) and dew forms on the plywood. Both these situations create a potential disaster of trapped moisture in the cavity leading to rot and mold...........remove the plywood from the situation and the organic is removed (no rot) , and there is no surface to create a dew point from solar gain.
I wouldn't want to rely on EPS to provide diaphragm strength.
Plywood in the middle because it would be on the interior wall which is the load bearing wall.
Anyway, I've ultimately selected to go with a full ICF build. Not as carbon friendly, but certainly simplifies a lot of details and concerns and should provide a really quality build.
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