Week 11: Airtightness

Posted by on May 23, 2013 in Warm EnerPHit office | Comments Off on Week 11: Airtightness

Fan test number 3

We finally got to carry out the next air tightness test! The team were joined by delegates from the Plymouth Carbonlite training course, getting a hands-on visit to the EnerPHit site as part of the Building Services training.

The results we get each time are key to moving the whole project along. “Airtightness is driving this whole project” Pete tells me, “and it’s the hardest thing to manage.” He’s right: it’s relatively easy to specify the different insulation and materials required, but it’s the results from each fan test that flag up the issues, problems and areas of focus, some of which are expected, and some not.

Airtightness lies at the core of Passivhaus design; it’s fundamental to achieving a low energy demand in the final building, improving the performance of the insulation materials and attaining good comfort levels (for example getting rid of draughts and cold surfaces). It’s something that standard builds in the UK just aren’t good at, and it isn’t always widely understood that airtightness plays such a key part in building performance.

The test gave us results of 2.2 ach depressurised, and 3.5 ach at 50Pa pressurised. The important thing is the difference between the two numbers – it tells us that something is wrong and air is leaking somewhere.  Luckily it was easy to locate the problem. Putting the new lintels in unfortunately ripped where the air tight roof membrane had been beautifully sealed to the wall. We have more sealant ordered now, and will have to focus on ensuring that the roof is completely sealed to the wall once more and that all of the airtightness is repaired before any work is started on the external insulation.

 

External insulation

The big story on site this week is that the external insulation arrived yesterday morning – 40 cubic metres carefully unloaded and stored….only to discover that it wasn’t the right insulation! It was the colour that gave the game away when Pete arrived on site – Neopor, our chosen insulation, is grey (due to the particles of graphite inside it). This insulation most definitely isn’t. There are several lessons to be learnt and things not to be repeated here, but in the meantime it’s already taken the team a half day of wasted time in unloading this, now there will be another half day or more with getting it back out and the new insulation in, plus of course the delay in getting the new insulation to site.

On a more positive note the cavity fill went without a hitch and the wall cavities are now sealed up from draughts and air movement. You can see from the photo below that in some places the PU foam has spilled right through to the inside through the internal cavity wall.

Doors and windows

The Rationel front door has gone in and the team are now starting work on fitting the shop windows downstairs.

outside wk 11 rs

The outside of the building in week 11 – Pete just leaving site!