Lisa Ann Pasquale from Six Cylinder Limited explains what thermal imaging is and how it can be used in quality assuring the construction of low energy buildings.
Interview with Lisa Ann Pasquale
Lisa Ann Pasquale is an architect by training but after several years supervising construction works in Boston, USA, she took a masters in building physics from the Architectural Association.
With practical experience under her belt she frequently found herself shooting holes in her professor's theories about perfect construction! It was at this point he suggested that she might be suited to becoming a post occupancy building performance evaluator and that's exactly what she did.
Lisa now runs Six Cylinder Limited.
Thermal Imaging Allows Us to See Differences in Temperature
While part of the electromagnetic spectrum is visible to the human eye (visible radiation – light) there is a lot more that we do not see.
Thermal imaging allows us to look at infrared radiation, which is a slightly different wavelength, and deals with the heat of objects.
If you point a thermal imaging camera at your hob when you've just cooked a meal, you'll see it glowing red. Likewise if you open your fridge it'll be black or blue. So it allows us to see differences in thermal temperatures.
When it Comes to Buildings, Thermal Imaging Helps Identify Anomalies
Thermal anomalies are significant differences in temperature which wouldn't normally be expected.
For example, you would expect a wall to have a fairly consistent temperature from top to bottom and thus it would be the same colour on the thermal image.
This image below shows air infiltration where some sealing tape was accidentally missed around a door and window. This caused large amounts of cold air (the black patches) to flow into the room, through the interior wooden wall cladding. This was noticed using thermal imaging in the later stages of construction and corrected by the builder before the building was handed over to the client.
Rainscreens Can Mask the Defects
In certain situations it may be difficult to get meaningful thermal images.
Rainscreens, which are often cladding that is a certain distance away from the rest of the building fabric, make it very difficult to see if there's a problem (from the outside). However, the defect would still show up on the interior pictures.
This is one of the reasons why thermal imaging should be carried out on interior surfaces as well as exterior surfaces.
Depending on the Project, Thermal Imaging is Useful at Different Times
Ahead of a retrofit it makes a lot of sense to carry out a thermal imaging survey. This is because you want to be certain you know what is going on and that you're not about to insulate damp building fabric.
In a new build, thermal imaging is unlikely to take place until the heating system is commissioned.
Most Defects During Construction are Accidental
Lisa says it's relatively rare that a building defect is down to blatant negligence on the part of a contractor. More often than not a tradesperson has forgotten to do something and just needs to go back and fix it.
An example of this might be an electrician who scoops out some insulation to install a socket and then just slaps a plate over it without putting some insulation back. Therefore a cold spot would show up on the thermal image.
Poor Design Can Lead to More Significant Issues
Detailing is very important to get right. If it's not done correctly, heat can be conducted directly from inside to outside. This also increases the risk of condensation (where warm, moist air will come into contact with a colder surface).
Beware of the ‘Drive-by' Survey!
When it comes to organising a thermal imaging survey Lisa says: “It's not a particularly well-established practice. It's not super common to do it. It's becoming more common which is really positive.”
Even people who are certified to do this as a service may not be a good choice. This is because they are not invested in the process and are just there to take a few snaps. You want someone who takes the time to understand what's going on and looks for specific details that might be an issue.
The Right Conditions are Necessary to Achieve a Meaningful Survey
The weather conditions need to be right to conduct a thermal imaging survey. They are mostly done in winter and on overcast days. If the sun is out it will heat up the external walls and if it's rainy or windy there will also be issues.
Doing it at night or early in the morning can be an option, too, because this is about the infrared spectrum and not the visible light spectrum.
At Least a 10-Degree Temperature Differential is Necessary
The temperature inside needs to be at least 10 degrees hotter than outside and this is achieved by artificially boosting the temperatures by running the heating system for a few hours.
Before the photos are taken the radiators are allowed to cool (so they don't show up in the pictures!).
The Images Must be Calibrated Properly
It's important to make sure that the camera is calibrated for the emissivity of the material that's being measured.
While bricks, woods and concretes are all in a similar range other materials, such as zinc, are not. Therefore you'll get a false reading unless the camera is re-calibrated.
Thermal Imaging Provides a Quality Assurance Process
Lisa tells a story of how she spotted a serious building defect when just messing about with a thermal imaging camera on-site at a children's centre.
After hearing about it the contractor quickly realised that a sloppy tradesperson had slapped up some trim and cladding without putting in any sealing tape around the windows and doors, etc.
The issue was quickly fixed. If it hadn't been remedied the client would probably have ended up with mould, condensation and rot on the inside of building.
Interpreting Images Requires Expertise
Thermal imaging is a great tool but it's important not to overestimate what it can do.
These photos will be no good without a person who can interpret what is going on from the image and suggest the best course of action.
The example below shows the outside of a building on a cold morning (pre-dawn). The bright red/yellow colour indicates that heat is escaping the building via a detail around a large beam. This is creating a thermal bridge at the top of a glazed curtain wall, allowing heat to move from the inside of the building to outside.”
Ask Your Architect a Few Questions about Thermal Imaging
If you are building a low energy house then thermal imaging should form part of the quality assurance process.
So when you are hiring an architect, it is worth seeing if they are familiar with it.
Lisa says: “If this is something that is completely foreign to an architect I would be a little bit hesitant about working with them to design a low energy building.”
A sample report
Certain Information Should be Included in a Report
- The day and time that photos were taken
- The emissivity of the target surface
- The approximate distance that the camera was looking. Ideally all images should be taken at right-angles to what's being photographed (so that the whole image is at the same distance from the lens), but that is not always possible with building details.
- The building plan or relevant detail is often helpful to have alongside the images so that you can orient the images or see which detail caused an issue.
- The reports should have a covering page noting the time/day of the survey, the site weather conditions (wet, snow, overcast sky, sunny,wind speeds, etc) and the conditions for the previous 4-6 hours and matching visual and thermal images, amongst other details.
Find Out More
Our Question for the Comments Section
How has thermal imaging helped your project?
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