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Episode-1089- Jacob Nielson on Energy Efficient Housing Options

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Jacob Nielson is a home energy consultant.  He helps builders and homeowners build more efficient and effective homes along with improving the efficiency of existing housing.

He also consults on designs of Net Zero homes.  Jacob has been a certified HERS rater for more than 6 years.  He also holds several other certifications including NAHB Green Verifier, BPI Building Performance Analyst, BPI Building Shell, and Texas Hero Home Energy Auditor.

Jacob is originally from Utah but is now living in Lindale Texas with his wife and 3 kids.  One of their goals is to establish a small permaculture farm in East Texas, a goal they are only about a year away from achieving.

Jacob blogs about his families efforts to live a sustainable life at ourprovidentlife.blogspot.com and they also run a Mason Bee Partner Program.

Jacob joins us today to discuss various energy efficient housing options such as SIPs, ICFs and other “green technologies”.  We begin with a discussion on energy efficiencies and the importance of an “energy audit”.  We discuss common and also very expensive mistakes that often fail to provide any real results and how to avoid them.  This show will help those planning new construction and living in older homes equally.

Resources for Today’s Show…

Remember to comment, chime in and tell us your thoughts, this podcast is one man’s opinion, not a lecture or sermon. Also please enter our listener appreciation contest and help spread the word about our show. Also remember you can call in your questions and comments to 866-65-THINK and you might hear yourself on the air.

Comments

Episode-1089- Jacob Nielson on Energy Efficient Housing Options — 52 Comments

  1. On why ‘less studs is better’..

    Thermal bridging. In an insulated wall, the wood or metal studs have a lower R-value than the insulation. So they act as temperature conduits.

    A 2×4 has an R-Value of 4.38.

    So if you have R-11 insulation in the cavities between studs your wall isn’t R-11. Its R-11 for 15.5″ then R-4.38 for 1.5″ and this has a larger effect on the overall insulative effect of the wall assembly than you’d expect.

    For existing construction you can reduce this effect by adding a layer of rigid insulation to the outside of the building..

    • Insidious,
      absolutely, thermal bridging is a factor that should be addressed. When looking at the overall average R-Value of the wall, each stud draws that average down as does each window.

      Adding foam board is a good solution to interrupt that thermal bridge and a conventional wall.

      Advanced Framing techniques also help a lot in eliminating lumber in the walls as well as dead spots i.e. wall intersections and corners.

  2. On roofs..

    To get a ‘double roof’ there are products that are a piece of rigid foam, some spacer blocks and a piece of sheathing material. When roofing, you screw these to your existing roof deck, and then put the roof on top. So what you get (sorry I don’t have a picture).. is old roof deck, insulation, air gap, new roof deck, roof. As part of the new roof you add a continuous soffit vent and a ridge line vent. Now when the roof heats up, it heats the air in the gap which exits through the ridge line vent, which actually COOLS the house.. the hotter it gets, the faster the air moves.

    In Africa I saw double roofs where they just put a 2nd roof on polls eight feet or so above the main roof (so there was no radiant heat effect).. this was for flat roofs, but it kept the building in constant shade.

    There are also ‘roof ponds’ which are exactly what they sound like (also for flat roofs).

    • Solar Panels mounted over the roof will also provide some shading effect. Depending on how hot it gets where you live, you may want to space them further from the roof to reduce radiant heat transfer.

      • One thing you would loose by spacing the panels out out is the stack effect created by the space behind the panels and the heat differential.

        Also spacing the out also would probably mean more roof penetrations, and possibly exposed wires.

      • Waterproofing ICF’s…
        Below grade – some type of bituminous membrane or spray on membrane (essentially a tar). More importantly, dealing with subsurface water is vital.
        Above grade – depends on what the house will be clad with, brick, siding, stucco etc.

        • I’ve built using Rastra and Faswall blocks and for below grade, we used a product that has a dimpled plastic sheet bonded to filter fabric. The plastic is stiff and waterproof and goes against the building. The dimples hold the filter fabric away so any ground water will run straight down to be carried away with perimeter drain pipe. It effectively eliminates and hydraulic pressure below grade.

  5. I think one thing that should be reviewed when considering SIPs and ICFs is labor cost. Yes, you are paying a premium on the building materials but there could be a significant savings on labor.

    If we look at ICFs, normally the process for a concrete wall is you assemble a wooden form, fill it, then disassemble the wood form and haul it away. With an ICF the forms go together more quickly and when you are done with your pour they stay in place so you aren’t paying for tear down costs.

    For SIPs, often the main frame can be assembled in a day or two. It can take weeks for the framing on a traditional stick-built house, not to count the time to insulate and sheath the house.

    I haven’t done this research yet, but the question would be do you save enough on labor to offset a significant portion of the premium cost for these materials?

    • The labor is a real factor there. Regionally these costs will vary. Also an experienced ICF or SIP crew can run circles around inexerpienced crew. Worth weighing the costs in money and time.

      There are also times when theses differnt systems will be an “easier” option, here in my area, basements are not done, so there is amost no one who does it or have all of the forms, driving costs up consideably. Up in my old area in Utah there were foundation guys all over….supply and demand takes over.

  6. For getting rid of humidity… A counter flow heat exchanger (which looks like a duct inside a duct, sealed at one end) with a liquid cooled coil (at the sealed end) will wring out the dew and humidity and return air the same temperature as it was when it entered as long as it’s properly built. Just make sure the moisture has a good place to go (maybe a cistern?).

  8. So how do you get rid of the old fiberglass insulation? I have been thinking that a good layer of spray in foam insulation was the right direction for me to go ( I live south of Dallas).

    • Aaron,
      There in Dallas, you will need a minimum of 5.5 inches of open cell spray foam on the roof deck( sloped part and any gable ends).

      Pulling out the fiberglass is easily done by an insulation company. They pull up their truck with a fiberglass blowing machine, they basically reverse the machine and suck out all of the old insulation.

      • Thanks Jacob I will have to call around and see what it will cost me to get this done. In the interview Jack gave the impression that the attic space would need to be semi “finished”. Is this true or would it be just fine to remove the fiberglass and spray the unerside of the roof with foam insulation. I may have a bad picture of the process and the result any help would be appreciated.

        • Aaron, yes, removing the old insulation and spraying the new is all you need.
          Jack, if I remember right was refering to adding some decking(plywood/osb) down on the floor of the attic for a good storage place.
          One other consideration is what type of furnace you have…gas,heatpump or electric. If gas there can be some special considerations depending on the type and location of the gas unit.

  9. Jacob thank you for the clarification. At the moment we use electric space heaters, I know very inefficient but it is all there is. I plan to this year put in either a wood stove or a rocket mass heater.

    • Electric heat is the most expensive way to heat a home, however you have to use what you have sometimes. I see people all the time that have electric furnaces who’s winter electric bills are higher than summer… Paul Wheaton displayed to us that heating just yourself is also very effective in comfort and energy costs (though not for everyone).

      The reality of our area in Texas is that while some heating is needed, great expense should not be put out to do so. We have cool months but few very cold days. Looking at thermal mass, window exposure etc is worth while to reduce your electrical draw. Even considering the Steven Harris solar window heater may make sense for some homes.

      I see all the time when people will put these 5 or $6,000+ wood inserts in their homes, that if fully cranking would cook everyone out of the house. While only be used a few times a year. Rocket Mass Heaters make sense since you can run them for less time with less fuel and reap the same benefits over an extended period.

      • I a thinking that Paul Wheatons “portable” rmh is the way to go for me. I don’t think that a full rmh is advisable due to the weight it would add th the trailer (which is where it would need to be). My house is a ’72 mobile home with an addition. Half the mobile and all the addition are under a steel panel roof, with about a 45 degree pitch. There is one spinning turban to vent heat build up but that is it.

  10. One thing that was mentioned with air conditioning is for the startup of the air conditioner the efficiency is really low, I think 15 minutes was mentioned. I have a heatpump up in the Pacific Northwest. It is my only source of heat at this time. It seems to run for 10-20 minutes and only kicks on when the thermostat drops below the set temperature. It shuts off when it is a degree above. You have me thinking now that it is not running optimally. I am wondering if a thermostat that does a range would be better. Such as I set it to 69 degrees and it warms the house to 71 and lets it cool back down to 69 before it kicks on again. This way it runs longer and more efficiently. My house was built in 2005 and the heatpump is that old.

    • The run time when in heating mode does not follow the same rule exactly, there are other variable that are a play like outside temperature. On mild day there is more heat that can be extracted and pumped into the house. When the temps drop down to 17 to 25 degrees your system will only put out about 1/2 the rated output and run a long time. This is why most Heat Pumps have and emergency mode which is electric strip heat.

      When summer rolls around, watch how long your system is running then.

      There are some good thermostats that give you some added control as far as how far below or above your setting it will allow it to go before it kicks on again. I also like thermostats that have humidity control, you can set the level and it will run your AC to keep it down, (sometimes running a few degrees lower than your setpoint).

  11. Hey Jacob,

    You said in a previous comment that there are special considerations for the type of heat you have. I am in SW Ohio and we have a fuel oil furnace with the exhaust pipe going through a brick chimney in the center of the roof. Any special considerations if I wanted the spray foam? Also, I am going to be putting in a wood stove this year with a free standing stainless steel stove pipe going through the roof. Same question.

    How do I find a credible home energy auditor in Ohio? A google search brings up 2.3 million hits, any resources you know of? Are there any certifications I should look for? Thanks for your help.

    Patrick

    • To find an auditor I would start at either
      RESNET http://www.resnet.us/directory/search or
      BPI http://www.bpi.org/tools_locator.aspx?associateTypeID=CTR&accreditedSearch=N&splash=Y

      I hold certifications with both organizations. Shop around, ask for referrals or sample audit reports… Also it is worth asking if they carry any certain products (are they an insulation company, HVAC company). If they are, don’t rule them out but be cautious.

      Typically I would recommend avoiding “FREE Audits”.

    • As far as the issues with combustion appliances and foam… Most fuel fired equipment used have an open flame, meaning that they draw air from the surrounding space to supply the flame. These types of furnaces require outside combustion air sources in the proper size and location to keep the unit exhausting the gasses. If there is inadequate combustion air, the unit can back-draft exhaust gasses into the home, this creates a real CO (carbon monoxide) poisoning possibility. When foaming up a house you are decreasing the amount of natural air that can leak into the home and supplying the naturally drafted furnace/appliance.

      The other option for fuel fired furnaces is a “closed combustion” unit, typically this is a high efficiency unit or a 90% + AFUE unit. Typically these units will have two PVC pipe running from the unit, one bringing in air from outside and one exhausting air. The flame is completely contained and back-drafting is not an issue.

      This is where following code is a good idea, maintaining the proper combustion air to the unit(s) is vital for safety. Depending on location (basement, hall closet, garage or attic) there are some options to make your unit work and still foam, though the sealed combustion units solve all the issues.

      On the fireplace, bringing in outside combustion air is also important. This helps avoid the need to crack a window or having a hot middle of the house and cold rooms outside. Fire draws a lot of air and will quickly make the house go to a negative pressure trying to feed the flame. Adding some type of combustion air is good, though hard with a freestanding stove. Adding some type of dampered outside air source would work to bring in that air. This can be worked into a hearth or adjacent to the stove area, closing off the damper when out of season or not in use would minimize the amount of air leaking into the home.

      The foam will usually need to have some level of offset from the stove pipe as it exits the roof, a metal collar is usually the best way to block off the chimney and still allow some insulation to be applied near the stove pipe.

  12. Just wanted to mention that I with the help of my wife over the last 6 years have built a solar powered off grid ICF home with a contra flow masonry heater / pizza oven. My ICF’s are 8 inch blocks (8 inches of concrete) 2 and 1/2 inches of polystyrene on both sides. I live in southern Colorado in a desert climate beneath four 14 thousand foot peaks just below 8000 feet above sea level. The ICF walls go all the way up to the roof which I put on with trusses that I had built by a truss company. Like adobe the ICF’s are cool in the summer and when heated stay warm in the winter. They are also very quiet. You will immediately notice the difference from a normal stud framed home. My contra flow masonry heater / pizza oven is our heat source and sits almost in the center of the first floor on a 4 by 8 foot foundation and is approximately 7 feet tall. I read about them (like ICF building) for several months before self designing and building this abode. I am available for any questions if anyone has any via my website. I also recently completed several eBooks that chronicle the construction of the home and a few of its components. I appreciate your comments and insight on this blog and look forward to more great information in the future. Many thanks and don’t hesitate if I can be of any service. George

  13. Thanks for the terrific show, Jacob. How much should one expect to pay for such an audit? And can you give a ballpark on fiberglass insulation removal/spray foam insulation for a 2000 sq ft home.

    • Thanks, togeteherless!

      For these types of audit’s national average is $400 to $900 for a 2000 sq ft home. There is some variability depending on location, local utility programs, if the house has gas etc.

      Foam for a 2000 sq ft home, really depends on a few factors:
      – Roof pitch?
      – Gable roof or hip roof?
      – Climate Zone – Do you live up in Minnesota or down in Tallahassee Florida?
      – Near a large city? (larger cities have more competition = lower price)
      – Shingle Color? A darker roof will absorb more heat.

    • Ball park on foaming an attic, pulling out the old insulation… assuming there is no need to frame any walls to separate out a garage or porches.

      In my area it would run $4000-$5800 depending on some of those factors I mentioned before. Every house is different and really affect what price we can expect. That is 5.5″ of foam, ignition barrier, pulling out old insulation etc.

  14. Mr. Nielson,
    I am researching to build a 1900 sq. ft. home with a 12/12 pitch roof on the front and 8/12 on the back, 2 story 8′ ceilings with a small cathedral ceiling area and small loft. I’m looking into SIP’s (OSB-foam-OSB), however I have a builder telling me he can build a stick frame home with 1-1.5″ spray on foam and 2.5-3″ of cellulose and achieve nearly the same energy efficiency as the SIP’s at lower cost. Is the additional cost of the SIP’s actually going to be worth it for energy efficiency gain. The house will be in Northern Kentucky – Ohio River Valley area.
    Floor Plan:
    http://www.houseplans.com/plan/1897-square-feet-3-bedrooms-2-5-bathroom-farm-house-plans-2-garage-25860
    SIP’s Company I’m Looking At:
    http://www.fischersips.com/

    • Sure, I need a little more info from you…
      – How thick are the SIP’s you are comparing to?
      – Based on a 2×4 wall? or 2×6 wall. what you have in you comment adds up to 4″, but there is only 3.5″ in a 2×4 wall.

      With a 2×4 wall with 1″ of closed cell foam (usually about R-6-7 / inch) and 2.5″ of cellulose you would end up with total R-Value of 16.7 – 17.7. Cellulose by it self in a 2×4 wall is typically an R-15 or an R-23 in a 2×6 wall. This method of foam skim coat and blown cellulose/fiber is used by some to boost the wall’s R-Value and added air sealing.

  15. Thank you for your reply Mr. Nielson. I got some more numbers from my builder and some “ballpark numbers” from the SIP manufacturer. The walls of the stick built would be 2X6, 24″ on center, with 1-1.5″ spray on foam and 4-4.5″ cellulose, and really thick R-40 cellulose in the ceiling. The builder says the R value of the walls would be approx. 24, by my calculation it would drop to approx. 21-22 accounting for the studs. The SIP’s would be 6.5″ total thickness (5 5/8″ of foam, 7/16″ OSB on each side) for the walls R-25, and the roof panels would be 8.25″ R-33 or 10.25″ R-41 depending on how thick they had to be to span from the ridge beam to the top of the 2nd floor wall.

    According to the numbers I got from my builder, and ballpark numbers from the SIP manufacturer I am looking at approx. 10,000-13,000 $ additional cost for SIP’s. This would only be about an extra 5-7% additional construction cost, I’m just concerned about how long if ever I would get my return on investment. I am already working with the builder to install Geo-Thermal to heat and cool with, and he estimates 300$ per year each for heating and cooling. Are these estimates realistic for the cost of heating and cooling with geothermal in the above described stick built?? And if so, how much room would there actually be for the SIP’s to save me any money with energy efficiency??

    Thank you so much for your great interview on TSP and for taking the time to respond to questions from the community. Thanks Again!!

    -Kurt

    • Just a couple of questions for clarification. You are comparing a SIP roof and a conventional vented attic with R-40 cellulose? I am understanding that correctly? If so that is one element that will sway the numbers a bit, because it’s apples and oranges… a fully enclosed house or one with a hot attic.

      Are you on gas or electricity out that way? Gas furnace or Heat Pump?

      I have a very similar house plan I have already ran through the Energy Modeling and I will play with it with your specs. Get back to me with the info above so I can further fine tune it.

      • If I went with the stick built yes it would be vented attic with blown in cellulose. If I went with the SIP’s I would do the whole house in them including roof. I would be on electricity or propane, no natural gas, however I plan to do geothermal.

    • Using a very similar house that I tested and Energy Star certified last year, the difference between the two wall options is very minimal… only about $28 a year difference.

      This is based on a 1746 square foot house facing west. This house was a full foam house, foamed walls up to peak of roof. It was tested and and exceed the current Energy Star standards. I changed the weather site to Shelbyville (northern KY).

      I took the two wall types you asked about and changed out the walls on this reference home. Going to the R-25 SIPS on this house would only save $28 a year over the R-24 2×6 wall. This is based on a fully electric house with 16.5 Seer Heat Pump.

      I have rarely seen a decent payback on geothermal, it does have application, but the premium cost is there. Lets not rule it out, I would like to run the geothermal info through these two scenarios compared to a super simple 13 seer system up through the 16 seer system I used on this house.

      Can you give me any specs/brand info on what Geothermal you plan to put in? I will run them through on this same house for comparison.

      • Sure, I will break out just Heating and Cooling.

        In kWh:
        Heating&Cooling R-25 SIP walls – 5202kWh / yr
        Heating & Cooling R-24 2x6walls flash&cellulose – 5489kWh /yr

        In Therms:
        Heating&Cooling R-25 SIP walls – 17.8 MMBtu (or 178 Therms)
        Heating & Cooling R-24 2x6walls flash&cellulose – 18.7MMBtu (or 187 Therms)

        • ty. That’s very useful.

          So there’s a 287 annual kWh difference. Or 0.780 kWh/day, which at my location would mean ONE 155W solar panel.

          🙂

        • There is a tipping point in all energy efficiency items where stepping up to the next level, adding more, etc. does not payback enough to justify the added cost.

          This is a great example, using the additional 5-7% of the construction cost to other items with a better return might make sense, if we are only looking at the money/return aspect.

          In Insidious’ case, that is a level that justifies more solar to meet the slightly more demand for far far less than the 5-7%, even with installation on additional panel will run $2-4 per watt $310-620. Likely less on an existing system, panels alone can be very low per watt.

        • In my case my panels cost me $0.90/watt. And adding one more panel would require no additional wiring or inverter upgrades.. so the cost would be $139.50

          It certainly makes the case to plan the entire housing system at one time, even if you can’t or won’t be implementing it all at once.

          🙂

      • Thank you very much, that will make the decision much much easier. As to the geothermal…… I was under the impression that geothermal was by far the most cost effective way to heat and cool, it just takes approx. 10 years to see return of investment. I plan to live in the house I’m building for 30,40…..50 years (retirement and beyond). Also, the state of Kentucky is running a tax credit program where I would receive $6,000 back in a tax credit. My builder is telling me the geothermal would only add approx. $7,000 in cost over the conventional electric or propane furnace and air conditioner, in turn making the additional up front cost to me only about an extra $1,000.
        With this being the house I plan to say in for that length of time, is geothermal worth it??
        I do not know anything about what brand or type of geothermal unit my builder uses, I will try to find out.
        Are there any specific brands or types of systems you would suggest??…….. Or suggest staying away from????????
        Thank you so much for your time Mr. Nielson, I know this is what you do for a living and your basically donating it to me. If there is anything I can do to support you, your business, or anything I can do to help you advertise/spread your name please just let me know. Thank you again.
        -Kurt

      • Kurt,
        Sounds like with the state incentives you have make a winning combination. One nice thing about geothermal is the lack of noise outside, you can have it running in the middle of the day or night and there is not the condenser outside whirring away. In tough times, this could be a handy.

        I would recommend sticking with a name brand, one that the HVAC company can produce an AHRI number on. This ensures that it is not just a shop built unit, but one that is has the AHRI certification. http://www.ahridirectory.org.

        My other recommendation is to make sure that you have a Manual J done for the house. This is a load calculation that defines exactly what size AC the house needs based on all house components, walls, windows, orientation, use of rooms, occupant habits etc. Too big for AC’s is a problem for cost, energy, humidity and comfort. Any one who uses a “rule of thumb” on AC sizing is not worth your time. No house is like the last house and each house must be considered separately. I run Manual J’s all the time and I am still surprised on some houses either needing more or even less than I had expected.

        A Manual D is also a good practice, this will ensure proper duct design, helping to get the right amount of air to the right area.

  17. I’m currently looking at purchasing an older farmsted as it fits my needs but I am concerned about the efficiency of the place. I understand about getting an energy audit but do you have any more resources on the internet that a person can study on ways to make an older farm house more efficient? (Insulation, windows, HVAC, ETC) This is in the heart of Nebraska so we get the Nasty Cold & Snow along with very Hot/Humid summers. Any information you can share is much appreciated…

    • https://www.energystar.gov/ is a good start for general info on energy efficiency and self evaluations. There is a lot of resources there.

      Here’s a few….
      One good place to start on any home is air sealing, a box of caulk and expanding foam will do a lot for an old drafty house.
      Check your door’s weather stripping, adjust your door thresholds.
      Attic insulation levels should be checked. Before attic insulation is added, run though the attic an seal off cracks, seams and electrical/plumbing penetrations.
      Check your ducts (in attic, basement etc). Seal duct seams, joints etc.
      If new HVAC is required get a Manual J! make sure your are getting the right size, too much air is a problem!
      Replace windows after you have exhausted all other options (payback is typically 15+ years often 30+). Though consider window replacement for comfort and functionality, I.E. large picture window near the dining table, makes you feel cold when sitting down for dinner but is not really a huge energy issue, for comfort a new modern window would make the space feel more comfortable.

  18. Jacob, not sure if you’re monitoring this but I have a question about mold in an air-tight house.

  19. We finished our house last fall, my parents live there now and my family will move in in a few years. It’s has ICF exterior walls with spray foam insulation on the roof decking, a totally sealed attic space. This past winter there was condensation dripping from the windows, now there’s mold in different areas of the house. We’ve had a couple different HVAC guys come out and they said to run the AC and heat more often to pull the humidity out.

    The whole purpose of having an energy efficient house was to run the heating and cooling less and have lower energy costs. Would an air exchanger do the job or do we need a dehumidifier. If the house is this air tight I think I want an air exchanger just for air quality issues. Do you think they are worth it?

    From time living in Germany I know they have the same problem, their solution is to open the house up for 10 minutes, twice a day. That’s a low cost solution but I think there’s a better way. What are your thoughts.

    • A few questions to narrow down an answer…

      General Location?
      Was a Manual J done on the house? AC/Heat sizing calculation
      Rough square footage?
      How large of an AC is installed?
      What type of windows? Vinyl, aluminum etc.
      Are bathroom exhausts used/how long?
      Are kitchen exhausts used?
      Are those exhausts exhausted outside of the home? I.E not into “attic”

      If you can get back to me with as much of that info I can better answer to your issues. I will also address the Air Exchange and/or dehumidifier questions as well.

  20. Central Arkansas
    I’m sure it was but I don’t know the results
    Approximately 2600, 3200 with garage
    4 ton
    Vinyl, median grade low-e
    Bath fans are used during shower time and they vent to the exterior
    Kitchen, not usually but it’s just a filter that vents back to the kitchen

    We finally had the original HVAC guy come back out. He said he recommended an air exchanger and dehumidifier to the builder but was told no. I asked the builder about them at the beginning and was told they weren’t necessary. The builder was pretty good, had a bunch of energy certifications and qualifications. He was just a little difficult to work with and set in is his ways on certain things.

    • Bathroom exhaust fans should be used during the time of a shower/bath and usually about 20 minutes following those activities. Beyond that it is important to have a fan that is large enough to clear the moist air out of the space. Adding a timer switch is an easy way to ensure it is running long enough.

      Kitchen exhaust fans that just recirculate are just noise makers and really don’t do anything. If they cook a lot it would be good to put an exhaust fan in or duct the unit there outside.

      An air exchanger (an Energy Recovery Ventilator or Heat Recovery Ventilator) do not help with moisture, they are there just to cycle air into the house. They could help some in the winter, as the winter air is drier. They do help to maintain good air quality, though they are expensive. I would have a Blower Door test done on the house. Just because it is foam and ICF does not entirely mean it is “air tight”. A Blower Door test and it’s operator could let you know where you house falls in the scale. At that point if you need an ERV then you will know how long you would need to run it to meet the standard for good indoor air quality.

      If the AC is properly sized (Manual J) the AC will act as a Dehumidifier, adding a dehumidifier will only burn more energy and add heat into the home.
      I recommend installing a thermostat that has the ability to measure and cycle the AC on to control humidity. They allow you to set your desired humidity level and it then runs the AC accordingly. I can make a recommendation if you like. The target humidity in a home is 45-60 percent. I keep mine at 50percent, most foam homes I know stay at 45 or less, with properly sized AC units.

      I see “sweating” windows often with Aluminum windows where the frames have poor thermal properties. Condensation is all relative to the difference between temperature inside vs. outside. The other unknown here is the level of humidity in the home during that time in the winter. Is the glass or the frame sweating?

      Is the garage attic separated from the house attic?

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