Our very own retrofit journey
How checking the air-tightness of our office allowed us to make some important decisions
Since we moved into The Old Warehouse in 2005 it has seen plenty of changes, transformed initially from a gallery and studio to our office space and flat. But this is a 125-year-old industrial building at heart; what needs to happen to make it energy-efficient, how much would that cost, and should we improve or move?
Should we switch to a heat pump? Add solar panels? Where can we insulate, and what needs replacing? Will the cost of changes be softened by grants and incentives, and how long will it take for lower energy bills to pay back the capital investment?
Energy modelling
As with any retrofit project, to start answering these questions we need to begin by understanding what we currently have. Our Passivhaus Designer, Ele, has modelled the building using Passivhaus software, a service we regularly offer to clients. This gives us a good picture of the current energy demand as well as obvious areas for improvement. Things like windows, doors and un-insulated wall areas jumped out. Improvements to these are no-brainers for energy improvement, even if not always straightforward to achieve.
Pressure test
The Passivhaus model is fairly accurate, albeit with a few assumptions about materials we can’t easily check. But there’s one thing we simply can’t guess at – airtightness. A draughty building takes more energy to heat so identifying where there are holes to plug was our next step and we called in Darren Evans Partnership to do an air test.
So, what’s one of those? These tests involve fitting a big fan into an outside doorway, and sucking the air out of the building to create a pressure difference (between inside and outside) of 50 Pascals. The test tells us how leaky we are, measured in cubic metres per hour, per square metre of the building envelope (m3/h.m2), and – rather usefully – allows us to see exactly where the leaks are. We have an air permeability rate of 8.1m3/h.m2, which is better than we feared. For context the maximum under Building Regulations is 10m3/h.m2; when designing new buildings, we aim for 3 or lower, and for a Passivhaus we’d be aiming below 0.6.
Where were the leaks?
For the test, the known – intended – openings are closed up; windows, doors, extractor fans and vents. With the fan running we were then able to go around and identify the unwanted leaks, some were obvious, others, maybe less so, and some flagged up forgotten ‘snagging’ from previous building work. Old seals around windows and doors, a redundant chimney, and void spaces connecting to lofts, and our letterbox were obvious ones. Other typical culprits were present; gaps around waste pipes, behind the boiler and fuse boards, through recessed downlights, and even through electrical sockets. Forgotten snagging included gaps to pointing around doors, and a big hole (‘doh!) left where we moved a vent pipe.
Reducing Energy Demand
Reducing the energy needed for heating through what’s called a Fabric First approach could enable us to switch to a more efficient boiler, maybe even a heat pump, and this begins with insulation and air-tightness. There are some easy fixes, particularly for sealing air leaks, but we’re likely facing some big costs to properly address our fabric performance overall. Next up, then, will be a bit of a costing exercise…
