Trinity Church (Rose Bay, NS) - Wooden Frame Exterior. Source: John Hayne

'Thermal mass' describes a material's capacity to absorb, store and release heat. Thermal movement – the transferring of heat – occurs much faster in materials with low thermal mass (eg. wood) than materials with high thermal mass (eg. bricks). These types of materials experience higher thermal conductivity than materials that absorb, store and release heat at a lower rate. Thermal Insulation helps to reduce the movement of heat between materials, especially of those with low thermal mass. 

Many faith communities have buildings with exterior structures that are made out of wooden framing– hence low thermal mass. Without insulation between the walls, such buildings typically experience thermal heat loss. This happens when the air from outside comes into contact with the exterior of the building, moves through the material, enters the cavity between the walls, heats up, and then rises. This process, also known as a convection loop, causes constant movement of heat – thermal movement – within the walls (imagine the air moving up and down like an elevator) and sucks the thermal energy out of the warm side and deposits it on the other side of the building. 

Because wood is a conductor, the wooden framing holding up the structures of these buildings acts as a thermal bridge. That means it is colder than the insulation, causing high amounts of thermal conductivity, and moving your precious heating dollars outside.

Breaking it Down: How Buildings are Kind of Like Winter Coats 

To explain how it works in more detail, consider your winter coat. In winter, to keep us warm, we pull on our parkas full of fluffy down or Thinsulate. On its own, the fluffy stuff doesn’t keep us warm; rather, it is the material’s ability to trap pockets of air. The better a material traps air pockets, the better it performs as an insulation. Similarly, adding insulation to the outside of your buiding holds the pockets of air, preventing them from moving, so they stay the same temperature for longer. Opposite to the coat's stuffing, the coat’s metal zipper acts as a thermal bridge  which is why it can feel freezing cold compared to other parts of the coat. Designers have reduced the process of thermal bridging in winter coats, by adding insulated flaps over zippers. This additional fabric helps keep that thermal bridge (and our bodies!) warm. Similarly, adding “outsulation” or insulation that it on the outside of your structure, will help keep your building’s conductors warm and toasty.  

What about Buildings with non-Wooden Exteriors? 

Many of our faith-buildings are thermally massive structures. This means, these buildings absorb, store, and release large amounts of heat. These buildings are typically built out of some sort of derivative of rock, such as stone, masonry, plaster, rubble, brick or block. Unlike wood, these materials perform differently, as they are solid and not full of pockets of air that hold heat. Instead, these materials act like a thermal storage battery. 

St. Augustine Church (Winnipeg, MB) - Stone/Solid Masonry Building Exterior Example Source: Mohammad Ziaei and Jesse Mass

Breaking it Down: How Thermally Massive Buildings are Kind of Like Stones

To clarify, imagine passing by a large stone on a cool but sunny fall day. If the sun has been shining on the stone all afternoon, the stone will be warm to touch; much warmer than the air or even the ground around you. This is because the sun has been “charging” the thermal battery of the stone, making it warm. When the temperature drops, the stone will release that energy to its surrounding environment. Thermally massive buildings act in the same way. They store the energy from the sun and from the radiators inside (which use the same kind of heat as the sun, that is, radiant). We may have all experienced the “stone cold” feeling of a faith building before the heating kicks on for the season. It takes a while for the heating to “prime” those thermal batteries, but when it does, the space stays thermally comfortable. 

However, unlike buildings with wooden framed exteriors, insulating the outside of stone and stone-like structures can be done, but is not always recommended. Though there are some occasions where covering the outside of the building with insulation would improve the performance, such as in brick clad or masonry post War structures, in the case of stone buildings, adding the “outsulation” insulation can dramatically impact the beauty of the structure. 

Getting to Know Your Building

The more you can learn about your building, the more you can save energy, minimize maintenance costs, and maximize the usage of your amazing faith community building. By understanding building science and how your building performs, you are able to make better decisions for the durability, and sustainability of the building that houses your faith community. 

Start with free guides available on the Faith & the Common Good website, such as the DIY Faith Building Energy Audit Guidebook and the Energy Star Action Workbook for Congregations. 

Faithful Footprints Program

The United Church of Canada (UCCan) Faithful Footprints program offers inspiration, tools, and grants to help its faith-communities reduce their carbon footprint. With the Church’s commitment to reducing its greenhouse gases (GHG) emissions by 80% by 2030, this one of a kind program offers up to $30,000 in grants towards energy conservation and renewable energy projects (conditions apply).

Faith & the Common Good is the delivery partner for UCCans Faithful Footprints program. To date, we have engaged over 300 congregations, camps, and buildings across the country. Your participation in the program puts your faith into action and helps the Church reach its target.

Stephen Collette is the Building Manager for Faith & the Common Good and can be reached at 705-930-1011 EDT, [email protected]