Ventilation in Retrofit
We come unstuck far too often because we fail to take the time to consider the fundamentals of ventilation.
And nowhere shows this up more than in a retrofit.
Specification by product
We often fall into the trap of ventilation by product specification.
This means we get comfortable with a preferred product and assume that as long as I specify one of those in those types of rooms, everything else will be fine.
This can be a risky approach even in the homogenised environment of large-scale new build construction, but out in the world of retrofit, you can come unstuck and quickly.
A white paper by Neil May and Chris Sanders later became the foundation of some of the latest BS 5250 revisions called Moisture in Buildings.
This white paper well describes the difference between the as-designed and theoretical (ADT) world of a new build or imagined use and the real world of the stock we inherit, the as-built or in-service (ABIS) profile of the existing building stock.
It leans on risk management principles for spaces that consider the realities of managing moisture, for example.
This is where the 4 C’s come from.
Context
Coherence
Capacity
Caution
Link at the bottom (well worth a read)
The hunger for blanket solutions and the need to speed up retrofit and find repeatable solutions is entirely understandable, but the risk with ventilation, like any other measure, is that we don't take the time to stand in a building and honestly try and understand the context of its place, and use.
Taking the time
Take the time to think about how a solution is coherent with other measures and has the capacity to manage risk. And lastly, caution. The many uncertainties, complexities and unknowns in retrofit mean we have to view the proposed solutions through this lens.
This means we often need to take a minute to stand in a building and think for a while about what our goals are, what good looks like for this building and its use, and how the systems we are proposing will fit that.
We need enough fundamental knowledge of how systems work to sanity-check those assumptions.
It is possible for repeated archetypes to work towards a repeatable solution, but what we want to do is compound a workable and favourable outcome, not compound a bad one. And that, my friends, is what often happens!
Avoiding this requires a more fundamental understanding of ventilation, than what flow rates to target or what system is allowed at what air tightness. It requires an understanding of the risk we are trying to manage, how ventilation and air movement actually work in a building and how these principles apply to some of our standards.
I have been covering this in my half-day workshop to equip attendees with some basic grounding of why we see the success and failures we do.
Standards
In some ways, the softer element of some of the standards we use, like PAS and SR 54, cover these broader elements of managing risk with ventilation but often run aground between those and the requirements they have to impose.
Often they are standards that are reached through consensus with industry and professional bodies, and what comes out the other side has been watered down, certainly. But sometimes, you lose some of the elements of the softer, more subtle intent, some of the original thinking.
It's where we end up with a “do no harm” approach, inevitably doing some harm. Or dancing around language so aggressively to appease interest groups that you come out the other side dizzy, and the original intent is all but lost.
But standards are a backstop, a marker in the ground that can give us some targets to reach for and surpass.
Example
I'm working on an almost weekly basis at the moment with organisations looking for retrofit strategies for various programmes of work they have. And I see this fan or this system marked up on drawings, a reflection, no doubt of previous work.
Even off plan, I see failures to consider the context and potential use of the building, the potential occupancy levels, layouts of the space and implications of proposed designs.
An excellent example of this is De Centralised Extract systems. It's very attractive for improving a system beyond Natural Ventilation and Intermittent Fan systems, as only a few changes are required.
What is rarely considered is the level of air movement we now want the system to achieve and how that translates to the individual fan unit. Often in retrofit, we don't have many wet areas to work with, unlike modern buildings with en-suites and utility rooms and w,c’s.
This means we can push any decentralised unit beyond comfortable noise levels before we even consider any extra capacity in the system to deal with unknowns.
I can't tell you how often I see some poor little fan expected to achieve flow rates usually reserved for boost settings. It has no chance of delivering. In more compact housing, these fans may only be a matter of metres away from sleeping zones and the likelihood of them being turned off or disabled would be high.
As these systems are seen as an improvement from natural ventilation, I often see the legacy of the previous system thinking (if you can call it that) causing issues on the new.
For example, the retention of supply inlets in the wet areas now causing severe issues in the performance of the new system.
Or the realistic ability of the proposed supply vents to deliver the flow rate required by the extract side of the system.
Or the realities of air movement and flow paths within a building not matching the placement of inlets and extract points. That somehow air is going to magically bend to our will within a building and defy fundamental physics.
In Summary
Much of this stuff is simple, but it does take ventilation to be valued enough to learn and think about in the context of the retrofit you are designing or standing in today and how it may be used tomorrow.
Link to the half-day workshop
https://www.airqualitymatters.net/housing
Link to the white paper
https://sdfoundation.org.uk/downloads/BSI-White-Paper-Moisture-In-Buildings.PDF