Looking for Tips on Unconventional Build
Eric_U
| Posted in General Questions on
Hey All, first I’ll apologize for the long post to follow. The TLDR is I’m looking for a few tips for the barndominium I’m building including insulation details and air systems.
Backstory: My dad has been a handy man and amateur carpenter my entire life. I’m a too-independent and frugal person. This combo has led me to be a big time DIYer. My first solo project was a chicken coop ~12 years ago which is still in great shape today. My next big project was a 20×40 pole barn that my dad and I built together in 2015. My third big project was gutting and remodeling a single-wide that my father-in-law gifted my wife and me. That last project was slow since we were living in it while I was doing the work, so I started around 2019 and finished early last year. Around 2020 my wife decided she wanted to go back to school to get a third degree, this time to be a veterinary. Since we were both from South Carolina which has no vet school, I knew we’d be moving once she did her prerequisites and got accepted to a vet school. I decided to go ahead and start researching home building and very quickly stumbled upon Matt Risinger who has been my unofficial, YouTube mentor ever since; I don’t believe I’m missed a single video of his in three years.
House Plans: Due to the fact that my job is of pretty average pay, I planned from the start to do as much as I could on my own. I figured I would pay someone for site work, foundation, and framing as I wanted to make sure those things were absolutely perfect. I juggled for two years on what type of building and decided I wanted an ICF house. However, where we ended up moving (Central New York) I couldn’t find someone with any experience in ICF beyond basements. I then bounced around looking at everything else from steel buildings, pole barns, traditional stick built, prefab SIPs, modular, etc. While I was deciding on that I also went through multiple architects and house designs to find something that fit our unique needs. I wanted a two car garage so we wouldn’t have to crank our cars for 15 minutes every day all winter long and to avoid digging a car out of the snow. My wife has horses and we didn’t want to deal with feed and water in single digit temperatures so we wanted an attached barn. Then we wanted a house with three bedrooms and two bathrooms with one large great room. Long story short that summer of 2023 we had plans for a 40×104 barndominium. Exciting! We chose a pole barn style for fast construction and the ability to pour concrete in winter.
Details: This is where things get sticky. Because I’m a self proclaimed “building science guy” there have been some back and forths with my builder and a lot of time spent on my part trying to get the best of both worlds (and hoping not failing both!). For example, most barndominiums in this area have a wall assembly of metal siding–>framing–>close cell spray foam–>dry wall. I was ok with that but then the spray foam installer I found said the manufacturer wouldn’t warranty the product if it was direct applied on metal, so I then had to spend a good chunk of money on 7/16 OSB on the entire house. Since I was doing spray foam on OSB I decided to get Tamlyn Drainable Housewrap to give me an airgap per buildingscience.com. I also made sure they taped the OSB with a 3M tape I found here on GBA (6087 I think?). However, after thinking about it more, it seems inefficient to be heating the “attic” (more on this later) and very expensive considering the roof deck alone is 5500sqft. I also have come across a few posts here on GBA from people like Walta, Akos, and DC (love you guys’ comments) that make me question spray foam.
More House Specs: The eave height is 12ft, roof is all clear span trusses with a 9:12 pitch, sides and roof are all 28ga metal, there are three overhead doors (one on one gable end two on the other) which are 10’x10′ steel R18, there are fourteen 36″x60″ Andersen 100 casement windows, front door is a custom made douglas fir 36″x96″ 2 1/4 thick 3/4 lite door with a multipoint lock, the back door is the same as the front two of them (double door), the upstairs has become a three bedroom two bath space while the downstairs is great room, mud room, bathroom, and two spare bedrooms. I would love an ACH50 of <1 but not sure if it will happen. Barn will get some amount of ceiling/roof insulation only with no climate control, garage will get a 2ton ductless minisplit that I’ll most likely run in vacation mode to keep it around 50-55F in the winter, and the main part of the house will have central heat/air via cold climate heat pump and air handler with a 5kw backup heater. Foundation is just slab on grade, 4″ at 4000psi with R16 underneath it. “Separator walls” will be treated like exterior walls eg 2×6 framing with air tightness priority. All drywall in entire house will be 5/8s. House is full electric with a propane home standby generator. The heat, water heater, and even the ventless clothes dryer are all heat pump. Entire building has a two foot overhang and seamless gutters.
Questions: So here are some of my questions. Keep in mind I already have the shell of the building at this point so there is no changing framing, walls, or windows.
1. If I can reach good air tightness, should I get an ERV or HRV? A simple Google search results in ERV in hot areas and HRVs in cold areas, but I’m pretty sure I saw a Build Show video saying ERVs can be used in any climate. Where I’m at in Central NY there is a large yearly temperature delta. It was 90F this past summer for several weeks while it is 9F as I type this. It is also pretty humid, over 75% most days regardless of season.
2. Regarding insulation, should I bite the bullet and spray foam the entire shell of this building? I was originally going to do three inches all the way around, but a couple weeks ago decided it would make more sense to do 2″ in the wall along with a 3.5″ of mineral wool (flash and batt). However, after seeing this post: https://www.greenbuildingadvisor.com/question/are-conditioned-attics-the-only-_real_-answer-when-airtightness-is-a-priority?cid=266630&discussion=response#comment-266630 I’m second guessing. At the very least, it might make sense for me to still spray foam the living areas but using something like cellulose for the garage and barn ceilings. The crew that did my roof were Amish and the guys doing the rest are accidentally knowledgeable sometimes (they did “California Corners” in my dormers (which are standard 2×6 framing) but they aren’t technically custom home builders and miss easy things sometimes (caught them multiple times not using a roller on the sheathing tape and I have to teach them how to zip tape a window properly)) so I feel like I NEED spray foam to help with air sealing. It just seems weird to insulate and heat so much “attic” space though. Any recommendations here appreciated.
3. Air system. I want to do the ductwork myself so I Googled for a company that could provide a Manual J/S/D and picked one of the first results. Unfortunately, they did not listen to me at all in regards to the Man D and were also unable to provide ERV/HRV design nor did they do a makeup air system. I told them I wanted spiral ducts but they did high velocity and when I corrected them, they just did standard rectangular ducts. Question 3a: Can I take the cfm calcs per room and just use a chart such as this one from HVAC direct https://hvacdirect.com/hvac/pdf/Field_duct-sizing-chart.pdf to convert from rectangular to spiral? Question 3b: What is the best way to hide the ducts since I don’t have a basement? The upstairs has room in the truss for it but downstairs I think I’ll have to just have to run it along the ceiling and frame it off. A year ago I thought I could maybe wrap it to look like a wood beam but if the trunk is 14″+ I don’t think that will look right Question 3c: Due to the layout the first floor will have registers in the ceiling which I think I’ve seen on GBA is frowned upon, and that is before considering these are twelve foot ceilings. Is the house going to feel cold in the winters because of this or will it be fine? Question 3d: I’m aiming for zero roof penetrations. Will it be ok for my ERV/HRV to have a 24ft long exhaust and fresh air lines by running it through the garage attic and out the gable end?
I believe that is all of my questions. I apologize for the long post and for asking help mid project of a non-standard building. I will try to upload some files in case it helps. For some reason when I check Send Replies to Mailbox it never works but I’ll keep this post open a refresh in case I need to answer any questions about the build. Thanks again for any help!
PS We changed the floorplan just a couple of weeks ago so what is on the blueprint is not right, the other images are which we did in a program called Room Sketcher
PPS I don’t think you all will need truss specs but I do have those too, just can’t upload because they are 5MB
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The problem is the 1/2 story construction and dormers. It is possible to do that without spray foam but requires a bit of design up front and proper details at build. That ship has sailed.
You can still limit the amount of spray foam through. The only thing that needs to be spray foamed is the sloped roof sections including behind any of the knee walls and the dormers.
You can install a membrane as the air barrier at the 2nd floor ceiling to top it off. Once this is all done, before any batts or drywall is install, you can get somebody there with a blower door and see how things are and maybe touch up things as needed.
If the main floor walls end up being a large leak source, you can get the spray foam guy back for another round, but I doubt this would be the case with taped sheathing.
The rest of the insulation can be batts in the walls and blown fluffy in the attic.
You want an ERV in pretty much any climate outside of a couple of places in the PNW.
No issues with converting between hard pipe and spiral, either work great. The one you want to watch is flex duct.
For ERV ducting, I would look at a hybrid ducted setup with an autobalance ERV. Here you connect the fresh air supply to the return of your air handler and have dedicated stale air ducting and pickups in each bathroom and kitchen area. Long runs to the outside are not an issue as long as the duct is right sized. You want the outside connection including vent cap to be about 0.1" WG loss at your boost airflow (~6" flex for a 120CFM unit).
If insulating with spray foam at the roof deck behind the knee walls, I would run all ducting in the knee wall space on the 2nd floor. Ceiling registers are not an issue as long as they are above larger windows and have decent throw. Decent throw is the important item, I've been bitten by this even with 8' ceilings, standard ceiling register don't work ( you want adjustable commercial units or liner vents). If you have some very large windows, you might want to plan on a strip (say 2' wide) of resistance floor heat under the windows, won't cost much to run but would greatly improve comfort in cold climate.
Thank you so much for your reply, I've read through it several times and feel better. Seems I was somewhat on the right track, but I tend to second guess myself at crunch time.
One quick question about the last paragraph, the heat you're talking about is similar to what a lot of people put in bathrooms right? A mat that heat up under tile? If so, would that extra deltaT not cause condensation on the windows? My windows are three feet off the ground so it might not matter but I was curious so thought I would ask. Also, we are doing wood floors so I want to make sure the temperature change from one plank to its neighbor wouldn't cause a problem.
If your windows are 3' off the ground, it doesn't sound like they are all that large. Typically this is something you want for large floor to ceiling windows. doesn't sound like you need this.
Adding heat by the window actually reduces condensation as it warms the window surface. If you look at your local pool, you'll see there will be vents directed at the windows specifically to control condensation.
People often have sunrooms with flooring continuous between it and the house. Lot of those in the summer can get quite toasty and it doesn't create issues. The hotter floor will be significantly dryer so it will shrink more than its neighbors. This is not an issue with nail down or glue down, it will just gap a bit more.
Your barndominium project in Central New York is ambitious and reflects a deep commitment to creating a high-performing, sustainable home. Given the complexity of your project and your specific questions, here's a concise response tailored to your needs:
1. ERV or HRV?
Given the large yearly temperature delta and high humidity levels in your area, an ERV (Energy Recovery Ventilator) would be the most suitable choice. ERVs are effective in both hot and cold climates as they can transfer both heat and moisture between the incoming and outgoing airstreams, helping to manage humidity levels inside your home throughout the year.
2. Insulation Strategy:
Your consideration of a hybrid approach (flash and batt) with 2" spray foam and 3.5" mineral wool in the walls is a sound decision, especially for achieving a balance between insulation performance and environmental impact. For the attic and less critical areas like the barn and garage, considering dense-pack cellulose could indeed offer a cost-effective and environmentally friendly solution. Cellulose provides excellent air sealing when densely packed and has lower embodied carbon than foam. Ensure that any spray foam used is applied with meticulous attention to achieving an airtight seal, as this will significantly contribute to your overall building performance.
3. Air System & Ductwork:
3a. Converting Duct Sizes: Yes, you can use the CFM calculations per room and convert duct sizes using a chart. Ensure that the duct sizing appropriately matches the calculated CFM requirements to maintain efficiency and comfort.
3b. Hiding Ducts: For the first floor, running ductwork along the ceiling and framing it as a design feature could work. Consider creative solutions like decorative soffits that integrate with your interior design.
3c. Ceiling Registers: While ceiling registers are not ideal for heating in homes with high ceilings, ensuring your HVAC system is correctly sized and configured can mitigate cold spots. Strategic placement of registers and fans to circulate warm air can also help.
3d. ERV/HRV Venting: A 24ft vent run for your ERV/HRV is feasible, but ensure that the system is designed to handle the duct length without compromising airflow or efficiency. Minimizing turns and using smooth, straight ducting will help.
Additional Recommendations:
Building Envelope: Continue prioritizing air tightness across all aspects of your construction. Consider a blower door test pre-drywall to identify and address any leaks.
Heating & Cooling: With your high ceilings and the system you're planning, consider supplementary heating sources or fans to circulate warm air in winter.
Professional Consultation: Given the uniqueness of your project and the specific challenges you've mentioned, consulting with a local HVAC engineer or a building science professional for a second opinion on your HVAC design and insulation strategy could be invaluable.
Your project's success lies in the careful integration of building science principles with your specific needs and constraints. While you're well into the construction phase, it's commendable that you're seeking to optimize each decision to ensure the best possible outcome for your barndominium. Keep up the research, and consider reaching out to local experts who can provide tailored advice and support.