What Not To Do when Building a Home During An Iowa Winter
(And what to do instead!)
If you’ve survived a winter or two in Iowa, then you know how extreme they can be. We see ice, snow, subzero temperatures, and overnight 50-degree temperature swings every year. All of this, not even to mention The Wind which is a totally separate but equal force in and of itself.
So it’s winter. In Iowa. And Iowa’s winter is beautiful and crazy and cold and dark and long and some might say, miserable. But you’re building a house. And this is exciting!
And because you’re smart, you want to mitigate any potential issues that Winter might create for you as you make progress on your build. You want to work with Winter, not against it- because (as we all know) that plan will probably fail. No one can control the weather. But we can all be smart about how winter wind & temperatures affect humidity levels, the dew point, and scheduling the various stages of your build.
And so here we have it. Without any further ado (and no, in case you were wondering, we’re not fired up about this at all):
How to Create Totally Preventable Problems During the Mid-Winter Build of Your Home
😂 😂 Just kidding! What I actually meant to say was:
What Not To Do when Building a Home During An Iowa Winter
(and what to do instead!!)
What NOT To Do #1: Not changing your installation schedule when you see sub-zero temperatures on the forecast
Installation types have a window of tolerance in terms of temperature and humidity (which create moisture and condensation). For example, you most likely won’t be able to install spray foam once it gets colder than 20ºF, it simply won’t stick to the surface you’re working with. Or, it might be a bad idea to install paint or drywall mud when it’s 0ºF or colder (unless you have a serious plan for humidity mitigation). And while it is possible to mitigate condensation and moisture during these installations, changing your schedule might be the better option. You’ll lower your chance of moisture and condensation ever becoming an issue. And, it’ll be less work!
This home was built during the winter of 2024-2025 in Northern Iowa.
What NOT To Do #2: Planning for humidity-increasing Installs on Sub-Zero Days
Something that needs to be understood right away is how humidity and temperature interact to create the dew point (the point at which moisture in the air will condensate and create moisture on the walls, the floor, the roof deck…everywhere).
For example, if the ambient air temperature is 20 degrees (as if often is during an Iowa Winter) and the relative humidity inside of a new home is 80% (perhaps due to the use of a diesel heater without ventilation while the MEPs were installed) the moisture in the air will begin to condensate on surfaces with a temperature of just 17 degrees. When it’s 20 degrees outside, all surfaces will be at least this cold, if not colder.
So now we have a problem, because yesterday the diesel heater got turned off when everyone finished their work and today the insulators are showing up and tomorrow, the drywallers will be around. And the drywallers will tell you that their tape isn’t sticking to the drywall because it’s too cold and wet. So now you have to delay your mud and tape and texture and paint while you wait for the house to dry out, but it’s been 20 degrees outside for a week and it seems that there is no end to this ridiculous problem!
So, how could this have been prevented? We have a few options. Our favorite option: don’t add humidity to your house or building on sub-zero days. This means no drywall mud, no texture, no paint, and no use of a fuel heater without fresh air ventilation.
If you’re thinking “that’s great and all…but I didn’t read this article in time and I do have high humidity in the middle of my build and I need to mitigate it…” then no worries, we’ve got your back. Here are a few steps you can take to begin to mitigate the moisture levels in your home or building:
Set up dry heat sources like electric space heaters
If a gas furnace is installed, turn it on!
Set up fans to circulate the air
Set up a temporary fresh air intake system (aka: leave a window slightly open)
Set up an industrial dehumidifier
Schedule a few days in between humidity-adding installs and whatever follows to allow the house time to “dry out”
What NOT To Do #3: Not Mitigating Moisture or Ventilating
We did hit this topic just a bit in WNTD #2, but here we are going to elaborate here just a bit.
Consider this- when it is 0ºF outside, humidity levels inside a home should be below 15%-20% in order to control condensation. That’s not a comfortable humidity level! That air would feel dry to the throat. Most people find a range of 30%-50% humidity comfortable for breathing indoors. As temperatures drop outdoors, humidity needs to follow suit indoors in order to avoid moisture build-up, and potential damage by mold. A tell-tale sign of humidity levels getting too high is condensation on windows, typically towards the bottom of the window. If this is happening in your home, open the blinds/curtains and keep the air circulating to dry it out.
Something else to consider- condensation, and frost if it gets cold enough- can form on any surface in a home. Exterior Walls. Roof decks. Floors. No surface is “safe” because they all follow the same equation: the interplay of ambient temperature and relative humidity create the dew point. And the dew point changes on an ongoing basis, as the temperature and humidity levels fluctuate.
Some good rules of thumb:
If you are going to heat with fuel heaters, you need to ventilate with fresh air. Without fresh air, you are circulating the same air over and over again, and it is getting heavier with moisture each time.
The more ventilation, the better!
Avoid all moisture-adding installs on sub-zero days.
If humidity levels increase inside a house, set up dry heat sources.
We were delighted to see this thermometer at a Cedar Rapids multi-family construction site in early 2025.
This building also had heaters, fresh air intake, and fans to circulate the air on every level.
What NOT To Do #4: Installing Attic Blow before Ventilated Soffits AKA: How to rile up an insulator.
It is extremely important to install your ventilated soffit before your attic blow. Ventilated soffits help to control and direct wind as it moves into the attic. Fluffy attic insulation, without ventilated soffits, is vulnerable to strong winds, which could create insulation blow-back in the attic, exposing drywall. If drywall gets exposed, guess what happens? The surface temperature of the drywall drops, and it becomes a condensing surface. And…now you have wet spots! Neat! Wet spots are obviously a problem for many reasons:
If mud, texture, and paint are finished, it could ruin them. Yay!
If drywallers, texture and paint workers are trying to finish the job, they won’t be able to with a wet surface. Awesome!
If the humidity was already too high in the home, this will make it higher. Yes!
If the wet spot doesn’t dry out right away, mold could grow in the attic. Our favorite!
Please, please please please please: plan your building schedule specifically so soffits go in before attic blow. It will save you (and probably us) a lot of wasted time/energy/stress!
What NOT To Do #5.0: Installing Water Lines in Cantilevers
Cantilevers are exposed to extra unconditioned air as they extend out over open space, with nothing underneath them. While cantilevers can obviously be insulated and insulated well, several days in a row of sub-zero temperatures with wind chill to boot will take their toll, especially if the cantilever in question has any air infiltration issues.
If you’re running water through a cantilever on a sub-zero day, that line is liable to freeze, even with insulation! Think about it: insulation doesn’t only keep things warm. It can also keep things cold. Insulation slows thermal transfer. And that can go in either direction, so it is up to us to design reliable systems that keep warm and cold air exactly where we want it. If insulation finds itself between a waterline and freezing exterior temperatures, guess what? That waterline is likely going to freeze. And it isn’t bad insulation- it's unfortunate design.
What NOT To Do #5.1: Insulating Around the Entire Water Line In Exterior Wall/Cantilever
Hopefully, this one is already starting to make sense after reading through WNTD #5.0. As we’ve already said, insulation can block or maintain heat and cold depending on where it finds itself in a system. If you are installing insulation to keep waterlines from freezing, please don’t insulate the entire waterline. This could end up insulating for cold once the temperature drops below freezing. Instead, insulate the waterline, but leave a pathway that warm air can travel from other spaces in the home to keep the waterline warm. If, for example, your goal isn’t to stop a waterline from freezing (maybe it’s on an interior wall) and instead you’d like to keep hot water hot as it travels to its destination, then in this case you could insulate the entire waterline. Different goals in different parts of the home create different systems, which in turn create different installation types.
What NOT To Do #6: Not Installing Adequate Energy Heels
Energy heels are raised heel trusses. They help to reduce thermal bridging (cold spots), moisture, and heat build-up by providing enough space for proper ventilation and adequate insulation. Without them, insulation in the corners and edges is likely to become compressed, and less airflow can get through. In climates like ours- where the winter is dynamic and temperatures range in the extremes- energy heels keep homes warmer, more efficient, and therefore more economical. In fact, homes without adequate energy heels will have more wood (which is a terrible insulator) than actual insulation in those corners and edges. So it doesn’t surprise us when cold spots show up in these houses! (And after reading this article, it shouldn’t surprise you either). As we’ve learned, condensation often follows cold spots, as the dew point shifts in response to fluctuating surface temperatures. And after condensation, mold. Install energy heels, folks, 7”-12”, minimum.
What NOT To Do #7.0: Not Installing a Continuous Air Barrier on Outside of Home
We’re going to switch gears here for a moment and talk about insulation’s partner in crime: air-sealing. Insulation is the wool sweater, and air-sealing is the wind breaker. You need both to feel comfortable in cold weather. The main air barrier in a home or building is not insulation. It’s the exterior weather barrier (like Tyvek or Zip Sheathing) and interior drywall. It’s their job to keep unconditioned air from moving into conditioned space. Insulation’s job is to maintain whatever temperature you happen to set for your conditioned space. One without the other will not perform adequately. There is a lot of opportunity for improvement on the exterior sheathing/weather barrier. We are big fans of continuous WRB like Zip System Wall Sheathing or liquid applied.
This new home uses Zip System Wall Sheathing as its continuous WRB.
What NOT To Do 7.1: Not Leaving Enough Space during Rough-In Framing for Air-Sealing
Other opportunities for air-sealing include around windows and doors. Proper air-sealing in these locations is hugely important for reducing the amount of air infiltration in homes. Especially since windows, and oftentimes doors, are terrible insulators. However, if adequate space around a window or door is not left during the rough-ins framing stage, then only a tiny amount of can foam or caulk can be applied, which doesn’t bode well for our air-sealing hopes and dreams. A ½” gap around all sides of a window or door leaves plenty of room for foam to be adequately applied, and for air infiltration to be stopped in its tracks!
Just for Current Homeowners
Unfortunately, not every home is built with all of the above in mind. Another thing that typically doesn’t get as much attention as it should is the location of bathrooms inside a home. Showers and baths tend to produce a lot of hot steam. During the winter, when this hot steam rises and meets the cold attic- guess what? It can condensate, especially if the bathroom is not properly ventilated, and/or it finds itself on an exterior wall of a home.
It is a well known fact that Iowa winters can get seriously cold. If you combine cold weather, a bathroom on an exterior wall, and not enough ventilation…guess what? The temperature discrepancy between the cold exterior and warm interior will create condensation. This can lead to wet spots, and if left unchecked- mold.
So, you’re a homeowner and you have a bath or shower on an exterior wall. You live in Iowa, and it’s winter. What do you do? Here are a few steps you can take:
Make sure your bathrooms are properly ventilated, and that your bath fans are working properly. You may have to go up into your attic to take a look at where your bath fan vents exit your bathroom. We’ve seen vents that go right into attic insulation, have giant holes in them, or that don’t exist at all.
Buy and install an Energy Star bath fan and let it work for you!
Don’t use that shower on sub-zero days, or at all during the coldest months of winter.
Conclusion
If you’re building a new house during an Iowa winter, implement as many of the above recommendations as possible. Look at dew point charts, buy a humidistat, and keep an eye on the weather. Make air-sealing, energy heels, and ventilated soffits a priority. If you can, avoid cantilevers altogether, and if you can’t, at least avoid putting waterlines in them. If moisture and condensation issues arise, address them immediately with the list from What NOT To Do #2. Your home will stay warmer and healthier for longer, and the process of your build will be much smoother. Not to mention, you’ll feel less stressed and more in control of your work site.
It is possible to build during an Iowa winter by understanding how temperature and humidity interact to create the dew point, working with (and not against) the weather, and 😉 by hiring Thermal Shop to do the insulation scope of your project.
