Measuring Buildings

I’m British, and like many British people I live in an old house. In my case, a brick one built in 1949.

It may be 71 years old, but for a British house that’s fairly young. In fact, 80% of our housing stock was built more than 60 years ago. Old houses are cold, draughty and poorly insulated. For every house built to modern standards there’s hundreds more that aren’t. This isn’t just a British problem. It’s worldwide.

If we want to reduce emissions while still living comfortably, we need to use less energy to heat our houses to the same temperature. There’s essentially 2 ways to do this.

  1. More insulation. Insulation is like a duvet for your house. Increasing the amount, and making sure everything is covered, reduces the amount of energy needed to keep the house at the right temperature.
  2. Seal it up. Draughts and leaks mean hot air leaving and cold air entering. If the house is sealed, less heat is lost.

This seems straightforward - what could be simpler than insulating a house? But when you start looking into what you can do, it suddenly becomes overwhelming. There’s so many types of insulation and places to put it. Which one is most important?

Most people don’t want to obsess over this. We need to identify the actions which have the most impact for the least effort.

In the UK we report the efficiency of buildings with an Energy Performance Certificate (EPC) rating. This is generated by a computer based on a few observations - does the house have loft insulation, are the walls solid, does it have double glazing. What this rating doesn’t do is actually measure the house performance. Regardless of whether insulation has been carelessly scattered or methodically laid out, the score is the same. It ignores that every house is different, and that insulation and air tightness can be damaged over time. Poorly laid insulation, thermal bridging, damp insulation and air leaks can mean that even if we fit insulation it doesn’t necessarily have the desired effect.

That’s where measurement comes in.

In almost every area of engineering we like to measure. When you can measure things, you can be objective about them. Houses are no different.

What we need is a way of measuring how well a house is insulated. Then when we change things we can immediately see if it’s better.

There are a few industry standard tools for measuring a houses thermal performance.

The co-heating test

The co-heating test is a method of measuring the energy performance of a house. The house is raised to a set temperature and held very close to it using special heaters. All other heating is turned off, and the total heat input is measured. The outside temperature is logged, and together these numbers give us a good picture of how the house performs.

This test is the gold standard of house insulation tests. However, it is also incredibly invasive and expensive. The test is run over multiple weeks, during which the house must be completely empty. Special heating equipment needs to be brought in and carefully monitored. This works for academic studies, but not for you or me.

Thermal camera measurement

Thermal imaging of house

Wikimedia / CC BY-SA

This one is fun. You take a thermal imaging camera and point it at your house. It shows the hot spots - this is where heat is getting out. Then you go inside the house and look for cold spots.

This is a very effective way to see what parts of a house need work. If you have a draught, it’s likely that the area near the leak is cooler. If your loft insulation is a mess, you’ll have cold spots across your ceiling.

Although it’s a very good way of seeing relative performance across different parts of a house, this type of test can’t compare performance at different times or between different houses. This means you can’t judge if fixing a problem has made a huge difference or a tiny one.

Air leakage test

This test measures how draughty your house is by measuring how quickly air is leaking out. A big fan is placed in one door, and all the other doors and windows are sealed. The fan is used to blow air into the house, and by measuring how much air is blown in you can get a picture of how draughty the house is. While the test is running you can use smoke to find where air is leaking (often around pipes or through cracks).

Low Cost Measurements

A barrier to improving buildings is the cost and invasiveness of these measurements. The best way to fix a leaky building is to repeatedly run an air leakage test, hunting down leaks until the major ones have been sealed. This means having the equipment for an extended period of time. The best way to know you’ve fixed faulty insulation is to re-run the co-heating test after the insulation has been fixed.

To get these tests used widely and often, we need to find cheaper and less invasive ways to run them, and to develop new tests which are quicker and easier to run.

Title image Wikimedia / CC BY-SA

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