Week 6: Fan Test Result

Posted by on Apr 23, 2013 in Warm EnerPHit office | Comments Off on Week 6: Fan Test Result

Just continuing from where Emma left off last week!  We carried out an air tightness test on Friday and received some pretty illuminating results.  In short, we achieved a figure of 4.5 air changes per hour (ach), which is significantly better than our last result of 6.4, but still means that we’ve got a task on our hands to reach the 1 ach that we’re aiming for.

We decided that a little summary of our progress so far, with some simple diagrams, might help:

 

Week 0

Week 0 (Before Work Began)

At this stage, the building was so leaky that we couldn’t get the pressure inside the building up to 50 Pascals, which we always need to do before measuring how airtight the building is – a very poor start!

The ceiling in all of these drawings is represented by a dashed line, to remind you that it’s full of holes where the services (wiring, pipes etc) were being run through.  The box in the ceiling is the loft hatch.

 Week 5

Week 5

This one was cause for minor celebration, being an enormous improvement on the previous result.

There were three main changes affecting the air tightness that had happened since the previous test:

  • The roof tiles and felt had been removed and most of the OSB sarking had been put on
  • The office floor had been made airtight, meaning very low air leakage into the shop below
  • We had temporarily blocked up any holes in the wall that won’t be there, or will otherwise have been made airtight, when the project is finished.  An example is the hole for the soil pipe from the bathroom.

This tells us that in the previous test there had been a very large flow of air through the office floor and through the holes we’d filled.

Week 6

Week 6

For this test, we wanted to simulate a situation where our shiny new Passivhaus windows had already been installed and had airtight detailing round the edges, so we taped up the existing windows with air tightness tape.  Not only had the roof sarking been finished, but we also had an airtight membrane on the roof.  We were slightly nervous to see if the still-wet glue would withstand 50 Pascals of pressure, or if the membrane would part from wall.  The loft hatch was left open.

Well, although the roof membrane held just fine, we did get a surprise –  there was a fair old gale blowing down from the loft.  Often you don’t need any fancy kit to tell you where to look!  Once in the loft, we soon identified the culprit – the gable wall on the West side of the building.

Being a cavity wall, it is made of two “leaves” of brick/block work.  What we felt was lots of air coming over the top of the inner leaf and into the loft space, and air forcing its way through the blockwork of the inner leaf.  What this led us to believe was that air was entering the cavity from the outside (through cracks, holes for services and the like), making its way up to this part of the wall and thus entering the loft.  The air is represented by the blue arrows on the diagram.

So, as a result of this revelation, the decision has been made to fill the cavity with polyurethane foam, which will prevent this infiltration.  This is expected to be completed by the end of this week, at which point we can do another fan test and see what our progress is like – watch this space!