11/01/2026
Here is our recent experience with aiming to build an airtight house. If you’re not aware the blower door test is for testing the airtightness of your home, which contributes massively to its overall energy efficiency & comfort. We’ve been building now for the past year and have at least a full body coat on the inside & out so it was time to see how the house was performing before we progressed past a point where we couldn’t seal up leaks behind linings & cabinetry. We came out with a number of 6ACH (Air Changes Per Hour), better than the average of 15ACH but no where near the passive house standard of 0.6ACH! (We’re not aiming for this by the way)
Problem areas were:
* Cracks in the body coat
* Transitions between materials - render/timber
* Bottom plate at the base of the wall
* Power/switch boxes.
Anywhere there’s a break in the skin of the render, air found its way from the outside through the bales and into the house.
We’ve sealed transitions between materials with a Sika 11FC flexible sealant and will have a final coat of render (crack free), when combined with airtight wrap & tape in the ceiling, from , it should eliminate the majority of air leakage.
Just some food for thought when you’re rendering and aiming to build an airtight house that will keep you toasty in winter, cool in summer, hopefully without any heating or cooling. Bear in mind that if your home is between 3-7ACH you should have mechanical ventilation to prevent build up of pollutants and gases.
And if you’re still reading and wondering why would we go through all this effort to stop a bit of air? We had our energy efficiency scorecard completed by with their Powerhaus app. You can adjust parameters and see a live update of your energy rating. The biggest change came through airtightness. We will hopefully achieve 9+ stars, and will update in a few months time when we do a follow up test. Blower door test conducted by Mat from 👌🏻
