Passive Design Strategies for our Cold-Climate New Hampshire House

By: Kate HambletMarch 7, 2024

I’m in the middle of the design process on my family’s future home.  We’ll be building in the summer of 2024 (just a few months away!).  Right now the project is in the Design Development phase of design, and I’m in the process of checking on the passive design strategies I incorporated into the design to make sure they’re going to be effective.  (Learn about all the different design phases here).

Passive design strategies use the natural climate conditions to control the indoor environment of a house.  They are the opposite of active design strategies such as mechanical heating, cooling and ventilation.  For some passive design strategies to work, you, the occupant, need to be active instead 🙂 

The more passive design strategies you can use in your home, the less you’ll rely on an energy source (whether it’s fossil fuels, hydro, PV solar, wind, etc.) to maintain comfort in your home. 

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Climate Matters:

Passive design strategies are incredibly climate specific.  If you live in a hot, arid climate, you will not be designing your house the same way I am in humid-summer / cold-winter New Hampshire.  

In this blog post, I’ll be sharing the passive design strategies I’m implementing into my NH home design.  But I hold a special place in my heart for hot, arid climates since that’s where I went to college and learned how to design buildings to work with nature rather than against it.  So who knows, there may be an upcoming blog post for the Tucson climate soon. 

A rendering of our house

Passive Design Strategies for a cold climate:

New Hampshire is technically considered a cold climate, but our summers are getting hotter and more humid year after year.  So designing in this climate means we need to consider both passive heating and cooling strategies.

Curious about Climate zones?

The town where I live in NH is in IECC Climate Zone 6.  IECC stands for International Energy Conservation Code.  Often referred to as the Energy Code, it's what most states use to define energy efficiency requirements for buildings.  You can Google ‘IECC climate zone map’ to find out what climate zone you live in.  Knowing your climate zone allows you to be more precise about insulation and other energy efficiency parameters.

IECC Climate Zone Map

Getting the basics right:

For passive design to work well, there are a few standard components that need to be properly designed - Insulation, air tightness, orientation, and building form.

Section through our house, showing insulation on all sides

Insulation:

In my cold climate, I need a lot of insulation.  I’ll have insulation below the slab of the basement, on the basement foundation walls, on the above-grade exterior walls, and in the attic (for roof insulation).  The plan is to use TimberHP wood fiber insulation for all above-grade applications.

The IECC calls out how much insulation you need by climate zone, but I recommend using more than the code minimum.  I’ll be well over code minimum for the R-value of the insulation on my house.

Air Tightness:

A building can never be too air tight!  The tighter it is, the healthier and more comfortable your house can be.  But please remember, an airtight house must have mechanical ventilation.  The balanced ventilation system (preferably an ERV or HRV) will be the lungs of your house, consistently bringing in fresh, filtered air and removing stale, toxic air.

Site Plan: The main part of the house faces south.

Orientation:

This is the direction your house is facing.  For most climates, a rectangular house with the long sides facing north and south is the best orientation.  This maximizes the best natural lighting throughout the day and takes advantage of passive heating and cooling strategies.  

Building Form:

I just mentioned it above, but typically a rectangular house is the optimal shape for passive design.  There are great alternative techniques for hot-arid, and hot-humid climates, but in my cold, New Hampshire climate, I want a rectangular house with the long side facing south.

The rectangular form is best for a cold climate because it is a compact shape, but elongates the south face of the house to take advantage of winter direct solar gain.

The compact shape is beneficial because it cuts down on the surface area of the exterior walls.  The more surface area of the exterior walls, the more we need to insulate.  So while I love the look of courtyard houses, they aren’t very practical in cold climates.

Passive Heating Strategies for cold climate:

Orientation:

I already talked about this, but it’s so important I’m going to mention it again.  You need to get your orientation right to have a comfortable, well-lit, healthy, and energy efficient home.

If your house is a rectangle, you want the long part to be facing north and south.  In a cold climate, you’ll want to maximize the windows on the south exterior wall and minimize windows on the north exterior wall.  

Our Floor Plan: The red arrows indicate the south-facing windows.

Direct solar gain:

In the winter, we want to take advantage of the free warm sunlight.  To get the most out of the sun, we want lots of south-facing windows.  The rooms where we spend the majority of our time during the day will be the rooms we want on the south side of the house so we can enjoy the sunlight and warmth from those spaces.  That’s why the kitchen, living, and dining areas are on the south side.

Open-ish Layout:

I don’t like the feeling of living in a completely open floor plan.  It’s hard to define zones and create cozy spaces.  And it can be rather noisy.  But an open plan is great for keeping a house warm in the winter.  So our main living areas have an open-ish layout with lots of south-facing windows to let in the warm winter sun.  

The rammed earth wall at the entry

Thermal Mass:

Thermal mass is the technique of using a building material that absorbs heat such as dirt, rocks, and concrete.  Thermal mass works for both heating and cooling.  We’ll be using it more for winter warmth, but in a hot-arid climate, thermal mass works really well to keep a house cool during the day.  The massive wall absorbs heat during the day, then releases the heat in the evening once the house begins to cool.

We’ll be installing a rammed earth wall on the inside of the house that will act as our thermal mass.  During the day in the winter, the sun will fill the living room with warmth.  The rammed earth wall will absorb that heat.  Then in the evening it will release the heat as the temperature of the house begins to cool.

Thermal mass can also be done with concrete or earthen floors.  But we’ll have wood floors, so we won’t be using the floor as a thermal mass.

Note: In a hot, arid climate you can make the exterior walls of a house out of rammed earth which helps regulate the indoor temperature even better.  But in a cold climate, it doesn’t make a lot of sense to use rammed earth on the exterior wall because insulation would need to be added to it.  That’s why I’m focusing on a thermal mass wall inside the house.

Passive cooling strategies for a cold climate:

New Hampshire is rather warm and very humid in the summer.  Insulation and exterior window shading will help with the heat, but the humidity is the tricky part.  We’ll use passive techniques as much as we can, but we'll also be installing a dehumidification system.  High humidity leads to mold and bacteria growth, contributing to poor (dangerous) air quality and structural damage to the house. 

Exterior window shading:

The key to keeping a house cool in the summer is to block the sun before it even reaches the windows.  Once the sun touches the glass, your house has to work a lot harder to cool everything down.  Blocking the sun is done by using exterior shading devices.  The easiest type of shading device is your roof overhang, but there are lots of ways to shade your windows besides roof overhangs.  I have deep roof overhangs on the south side of the house.  

South-facing windows want a horizontal shade, but east and west facing windows benefit better from vertical sun shades.  On our house, I’m minimizing the amount of east and west facing windows, so I’m not worrying about shading those windows. My main focus is making sure the roof overhang is deep enough to effectively block the summer sun from coming into the south-facing windows.

The blue arrows show cross ventilation strategies for most occupied rooms

Cross Ventilation:

Cross ventilation is the technique of having windows on opposite sides of a room to allow air to move more quickly through the room.  When the windows are both open, a pressure differential is created, making air move faster from one window to the other, thus creating a breeze in your home.  This can significantly impact your comfort since, even though the air temperature isn’t changing, you’ll feel cooler by having moving air flow past you.

Zola Tilt and Turn Windows.  Image on right is in the tilt position.

Windows on rainy days:

Rainy days in the summer are still pretty warm, so it’s helpful to be able to keep the windows open when it’s raining to keep the air moving through the house.  

I’ve designed our house so that windows can be left open without worrying about rain entering the windows.  First, the large roof overhangs will divert rain from coming near the windows.  Second, we’ll be installing tilt and turn windows.  A tilt and turn window can either be swung open like a door or tilted in from the top like a hopper window.  When it’s raining, we can have the window in the tilt position, allowing air to flow in while blocking any wind-driven rain.

Daylighting, and balancing light with south and north windows

Passive Lighting Strategies:

Orientation:

You’ll get the most natural light throughout the day with south-facing windows.  East and west facing windows will have fleeting light.  And up where I live, north facing windows let in a dismal amount of ambient light.  

Light shelf Example: https://www.designingbuildings.co.uk/wiki/Light_shelf

Sunshades and light shelves:

Sunshades are another name for exterior window shading.  See my notes above about exterior window shading to help control sunlight from coming into the house in the summer.

Light shelves go on the inside of windows.  I’m not using them in my project, but they can be a really effective way to get light deep into a room if you have tall windows and ceilings.  Light shelves are horizontal shelves that sit toward the top of the window.  When sunlight comes through the window, it hits the shelf and bounces light back up to the ceiling.  This allows the sunlight to bounce its way deep into the house.

Be aware of glare:

Our house is designed to allow sunlight to come directly into the windows during the winter.  This is great for heating, but it can cause some issues with blinding direct light and glare because the sun is so low in the sky.  A common place for glare to happen is when southern light bounces off a kitchen counter, so I strategically placed the kitchen on the north side of the house to avoid the glare issue.  Translucent shades can help if direct sunlight is a problem, but avoiding counter height surfaces near the south-facing windows is a good way to avoid the problem.

Adjacent Windows:

Have you ever been in a room that only has windows on the south side?  It can feel surprisingly dark.  To help even out the light and to make sure we aren’t creating glare and dark spots, I’ve added windows to the north side of the main living areas to balance out the light.

Final Thoughts

A healthy home will still need active features like mechanical ventilation, lighting, and may need heating and cooling.  If you live in a somewhat moderate climate, you may not need heating or cooling if you utilize passive design strategies and your home is well-insulated and air tight.  You will always need mechanical ventilation though!

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