Journey into the depths of how sub floor airbricks work

Over the past few months the PCA has been working in partnership with Historic England to examine the effects of airbricks on the atmosphere in the voids below suspended timber floors.

With the assistance of a number of PCA members, atmospheric data has been collected from the subfloor voids, the occupied space above the floors and from the atmosphere outside. Existing airbricks were opened and then sealed for week-long periods to see what effect, if any, opening and closing the vents had on the condition below the floor and within the occupied space.

At the same time as data was being collected by PCA members, Brian Ridout of Historic England has been monitoring his own property.

What has the data shown about airbricks?

Data collected by PCA members was processed and interpreted by Graham Coleman. What the figures appear to show is that airbricks do indeed have an effect on the subfloor environment even when the “flow” of air is negligible. However, it does seem that the benefits of subfloor airbricks are varied and are dependent on a great many factors.

Data collected by Historic England also shows an effect from airbricks with a clear divergence in vapour pressure between the occupied rooms, the subfloor void and the external environment.

So what’s the next step?

A great deal of work now needs to be done to understand the implications of the data we have collected. It follows that we anticipate that further debate and collective working will be needed to reach conclusions that can be agreed by both PCA and Historic England.

What we are hoping to do in the medium term is to promote further academic research in partnership with Historic England into what we concede is a subject that is not fully understood. That said our preliminary findings suggest that airbricks help reduce the amount of water in the air within subfloor voids in the winter. We consider this to have a beneficial effect to both the condition of timber floor and possibly the quality of the air in the occupied room.

We remain committed to the use of airbricks

Our long standing commitment to the use of airbricks and ventilation to protect ground floor timbers from decay is valid and defensible, and to ignore vents that are blocked or missing is extremely risky. It is conceded however that more work is required to understand how best to quantify the number and location of vents needed in any particular situation.

We hope to produce more detailed findings from these experiments in the coming months and be able to feature some of this work at our Ventilation Conference in November.

We could not do this without our members!

Special thanks are extended to: Cormac Rooney, Matt Tucny, Phil Smith (and his next door neighbour), Adi Dawson and Hector Altamirano for helping with the collection of data. Particular thanks goes to Graham Coleman for working on the experimental design and the interpretation of the data.

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