Thermal Mass, What It Is and Where to Use It

Simply put, thermal mass is the ability of a material to resist temperature change. This should not be confused with insulation materials which resist thermal conductivity.

Thermal mass is related to the specific heat capacity of the material which defines the energy needed to raise said material by 1 degree, per unit of mass. For example concrete has a specific heat capacity of around 880 J/kg°C, water is 4182 J/kg°C and air is 1005 J/kg°C. This may seem confusing at first because air has a higher specific heat capacity than concrete but it is easier to heat up. The key here is that specific heat capacity is a function of mass, in this case kilograms, and concrete is much denser than air so in terms of physical size 1kg of concrete is tiny compared to 1kg of air. It is easier to use volumetric heat capacity which takes into account material density by multiplying it by specific heat capacity.

This is useful for example in a hot climate where a material with a high volumetric heat capacity (it takes a lot of energy to make it hot), will stay cool and lower the operative temperature (the temperature that it feels) despite the air still being hot. For example if you were in a stone castle where the air is 80 degrees inside and outside, its going to feel much cooler inside the castle despite the air temperature being very similar.

Heat that is stored in thermal mass is heat that would be increasing air temperature if it wasn’t absorbed. Heat is transferred to thermal mass through conductive heat loss from contacting a warmer object, convective heat loss like air or water, or most commonly radiative heat loss where for example the energy radiated by humans is absorbed over hours. Then at night you can perform “Night Flush Cooling“ which means opening carefully placed windows or doors so that the heat store in the material can be flushed out at nigh. This is caused by the thermal mass transferring its heat to the cold air flowing over it through convection. In scenarios where night flush cooling isn’t enough to fully remove the heat energy built during the day, you may need to use air conditioning to aid the process.

In a cold climate thermal mass can be used to passively heat a space by placing where it gets lots of direct sunlight which will be absorbed into the material and release throughout the night. Then if a hot spell comes you simply cover the openings that were letting light onto your thermal mass, place some rugs and cover the mass to resize it properly and you have a passive cooling strategy instead!

A few important notes are that the sizing of thermal mass is very important. Too little thermal mass means the material temperature will be closer to air temperature and remove any benefits whereas too much thermal mass means the material will never gain enough energy in a day cycle to flush it out at night.

Why Green Roofs are NOT Good Insulators

Its common to hear that green roofs will provide better insulation for your home, and that in turn your energy usage will be lower. However, the term “insulation“ here is quite misleading.

In the context of building science insulation is a material with low thermal conductivity, an example would be batt insulation. Now lets go back to green roofs which are primarily made of a watered growing medium, basically wet soil which compared to insulation materials does NOT have a low thermal conductivity. Just imagine laying in wet soil, its going to be cold because all of your heat is being easily conducted into the soil. So if you’re heating your house in the winter and your roof system only consists of a wet growing medium, all that heat is going to rise and conduct outside, meaning your heating costs go up.

The confusion of green roofs being insulating likely comes from them being used for “thermal mass”. Thermal mass is a term used to describe materials that can store lots of heat (energy), and are useful for passive cooling when you want to absorb heat from the environment and release it later. Read more about thermal mass

In short, green roofs are primarily wet soil that will conducts heat out of your warm house into the cold outside. Instead they should be used as thermal mass which means they absorb heat without getting too hot, making them good for passive cooling.

Mass Timber and Engineered Wood Products

Engineered Wood Products (EWPs) are just ways of combining wood components into stronger and more uniform products. Being based in the Pacific Northwest makes this a very prevalent topic as our native Douglas Fir is a very suitable wood for EWPs. This is a primer on EWP and what it means for design and construction.

I feel it is important to note that EWPs are only as sustainable as you plan for. This means planned harvesting of the lumber, replanting, and local sourcing. Many projects source EWPs from Europe, but luckily for us there are a few companies local to the PNW such as Vaagen, Freres and DRJ that each have their own specialty.

EWPs can be split into a few different categories by the size of their wood base components, from long fibers to short fibers, and width and thickness. The size of fiber usually corresponds to the application of the EWP being a panel product like Oriented Strand Board (OSB) or a linear product like Parallel Strand Lumber (PSL). Linear products will be best suited for spanning, while panels are often used for vertical applications or to resist shear force.

• Lumber

  • Lumber products have a wood base component of sawn lumber which consists of long fibers. The sawn lumber is then laminated together to form a larger and stronger composite.

    • Glue Laminated Timber (GLULAM)

    • Cross Laminated Timber (CLT)

    • Nail Laminated Timber (NLT)

    • Dowel Laminated Timber (DLT)

• Veneer

  • Veneer products have long fibers often from 2-8 feet long, similar to lumber, but have much thinner sheets which means they are laminated with adhesives.

    • Laminated Veneer Lumber (LVL)

    • Parallel Strand Lumber (PSL)

    • Mass Plywood panels (MPP)

• Strand

  • Strand products are shorter fibers that visually resemble shreds or chips usually less than 12” in length. These small strands are then laminated and pressed into a panel or linear composite.

    • Laminated Strand Lumber (LSL)

    • Oriented Strand Board (OSB)

• Other

  • Not all EWPs are just single laminate composites, and there are many other ways of increasing the size and strength of raw timber.

    • I -Joists

    • Finger Jointed Lumber

There are a few more things to take into account such as the lamination orientation being consistent, crossed or random, and the timber layup of your EWP.

High Performance Building Enclosures

To get the most out of a high performance building system, it is beneficial to understand the key components of an enclosure. The enclosure of a building most commonly refers to the walls, roof and foundation systems that protect and provide a controlled environment for the interior.

Since enclosure is all about separating the interior from the exterior environment it means that enclosure systems will change drastically depending on the location and climate of your project. For us here in the Pacific Northwest we expect a lot of rain, but are experiencing increasingly fewer extreme temperatures.

In a climate like the Pacific Northwest a high performance wall assembly would consist of the following “control layers“, each of which helps control a load on the building, whether it comes from the inside such as hot steam from a shower, or the outside such as a heavy storm.

• Thermal Control Layer

  • Controls heat transfer with insulation materials that have a low thermal conductivity. Often framing members create a large amount of thermal bridging, which can be negated through an exterior insulation layer. Its important to note that the material you use for insulation will change depending on the application. For example exterior mineral fiber insulation like RockWool is vapor and air open, meaning it can vent itself.

  • You can get a quick idea of how much energy will conduct through a enclosure using a one-dimensional Fourier’s Law of Conduction.

• Vapor Control Layer

  • Controls vapor from between interior and exterior, flowing either way to prevent condensation, mildew, and mold.

• Air Control Layer

  • Neutralizes the pressure difference between interior and exterior from driving water and fluids inside the building.

  • Divides the interior air from exterior air, meaning all the energy and money spent on heating or cooling your house isn’t escaping through cracks and openings. Heat exchanges can be used to exhaust stale air, and transfer its heat to incoming fresh air to conserve energy.

• Water Resistive Layer

  • Stops and controls water from going where you don’t want it, such as flashing or Water Resistive Barriers.

• Water Shedding Surface

  • The surface the rain will hit, such as cladding or roofing that reduces load on the rest of the building.

For all of these 5 layers to work it is key that they are continuous. This means no gaps, and that seams are taped or sealed. This shows up in the design and engineering process, where you may need to fasten exterior wall cladding through 4” of exterior insulation while minimizing the thermal bridging and holes you create. For this we can use special hardware like a Fero Fast Bracket. It also shows up in the installation and construction stage where control layers can be damaged and create holes in your enclosure.

By integrating designers and engineers on site, as well as routine performance checks we ensure that projects achieve a high performance through proper installation.

Here is an example detail of one such enclosure:

Wall corner detail for a non-brick rainscreen over exterior insulation

COVID 19 Update

Earthquake Fit is still open and operating. We are following the CDC's guidelines for risk assessment.  At this time, construction is still considered an essential service and protecting your home and families during a seismic event is probably still top of mind for all of you.  We continue to evaluate all worksites for risk and if we are able to work within your crawlspace, outside of your house, garage, or in your basement without having to work inside the house - we are able to still complete your project.

We are following all sanitation and cleanliness protocols by using antibacterial cleaners, masks/respirators, and gloves at all times.  As this situation continues to evolve, please call our office at 503-383-9482 for the latest updates with our business and your projects.

Good Earth Home, Garden & Living Show

We are excited to share that we will be conducting two seminars during the 15th Annual Good Earth Home, Garden & Living Show which is being held from Jan 24-26 at the Lane County Events Center - Convention Center.

Please come and join us, we will be located @ Booth 429

Our Seminars - Is your home “Fit” for an Earthquake?

• Cedars Stage - Friday, Jan 24th at 6:00 PM

• Cedars Stage - Saturday, Jan 25th at 4:00 PM

Eugene Emergency Preparedness Fair - KLCC - NPR for Oregonians

Services And Guidance Just a Tent Away at Eugene Emergency Preparedness Fair

By BRIAN BULL • SEP 18, 2019

ShareTweetEmail

The possible threats from a large earthquake, wildfire, or flood drew locals to the City of Eugene’s emergency preparedness fair at the Park Blocks today. 

The Community Emergency Response Team (CERT) tent staffers talks to several women on being ready for disaster.

While the prospect of a Cascadian event and its aftershocks has made news in recent years, concerns over global warming and its effects on forests have also increased. To that end, officials want residents to be stocked with about two weeks’ worth of water, food, and supplies regardless of the incident.

Eugene resident Cathy Eva says she feels fairly prepared. Her main priority after a disaster is her family’s safety.

“How to stay in contact with one another," Eva tells KLCC.  "Making sure we have an exit plan. Sometimes when an emergency takes place you never really know where the rest of your members will be.  So I guess that would be one thing for us to take into consideration.”

Caleb Doughterty (left) and Bill Blair (right) tend the Team Rubicon Tent at today's event.

A dozen vendors were present at the fifth annual observance of the fair, including EWEB, the Red Cross, and Team Rubicon, a disaster response team that recruits veterans. 

J.B. Carney is the owner of Earthquake Fit, one of many regional firms that’ve sprouted in recent years.   This is the first time they've set up a tent at the event.  He says their technicians and engineers work to safeguard homes against sliding off their foundations during a quake.

“We also do seismic gas shutoff valve installation for homes," explains Carney.  "Some of the biggest damage after an earthquake really comes from fires caused by gas lines breaking.”

J.B. Carney (right), owner of Earthquake Fit, at his tent where retrofitting homes for better earthquake resiliency is demonstrated and explained.

Scientists say there’s a 37 percent chance of a 9.0 point magnitude earthquake hitting the Pacific Northwest within the next 50 years.

And the State of Oregon warns residents that homes built before 1974 will suffer the most seismic damage.

Copyright 2019, KLCC.