3 is the magic number

[NSS]

So the song goes, and that was the predicted air permeability number which went into our 'As Designed' SAP calcs (though our target was to be sub 2 'as built'). Well, we finally reached the point where we could delay the test no longer (we hope to move in in 3 weeks' time), and with some trepidation I watched as the blower door was fitted and the fan turned on. First thing to happen was the suction pulled the frame out of the door opening. Re-fitted,  the fan was  turned on again and depressurisation commenced. With inward opening windows I'd have preferred a pressurisation test but the tester wasn't planning on sitting outside in the light rain that was falling. 

 

The first run of recorded numbers were rejected by whatever software he entered them into on his laptop, it suggesting he needed to cover four of the eight holes in the fan cowling. He duly did so and re-ran the test. It was clear that the suction was again trying to rip the blower door out of the door frame as air was leaking past it on both sides, but the entered numbers provided a m3/h/m2 score of 1.74 - not bad (and inside my target), but both the tester and I knew it could be better if we could stop air leaking past the blower door frame. Tape was added and we had another go. Again, air was soon rushing in around the blower door, but the recorded numbers gave a score of 1.599 when entered and, as that was comfortably better than the original aspiration, we decided not to try again to seal the leaks round the blower door.

 

Okay, I know this is nowhere near the 0.6ACH (I estimate our test result equates to around 1.23ACH) required for Passiv House, but we were never aiming for that and the complex shape of our chalet bungalow and large dormers never leant themselves to such levels of air tightness. Frankly, I was delighted (and mightily relieved) to have achieved 1.6 but I'm now wondering what it could have been had that blower door sealed properly. Would I be being greedy to get them back for another go? Running it as a pressurised test would pull the frame hard into the door seal after all, and any chance of minor leakage past the windows would be reduced. Would it make much difference? Would I get a lower number and would that have any impact on the 'As Built' SAP score? Or do I just accept that 1.6 is my magic number?

[Nickfromwales]

After all the hard work getting it airtight, I'd definitely be having them back for a positive force test of it were me. "What if" is a question you'll be asking youself for a long time otherwise, and curiosity would get the better of me. 

[Jeremy Harris]

41 minutes ago, Nickfromwales said:

After all the hard work getting it airtight, I'd definitely be having them back for a positive force test of it were me. "What if" is a question you'll be asking youself for a long time otherwise, and curiosity would get the better of me. 

 

 

The test procedure requires them to do both a positive and negative test, then average the two results to get the permeability, so both tests need to be done. 

 

No need to go outside either, they just switch the fan.  There's often quite a difference between the positive and negative values, because some door and window seals will tighten on a positive test, some will loosen, and vice versa, which is why the procedure requires both tests to be done.  Looking at our blower test report, there was a 15% difference between the pressurisation test and the depressurisation test, with the latter giving the lower permeability figure (we have outward opening windows, inward opening doors).

Edited October 1, 2017 by JSHarris

[Ferdinand]

7 hours ago, NSS said:

the suction pulled the frame out of the door opening.

 

Is it a good sign when your test item breaks the equipment :-) ?

 

Good result.

[Jeremy Harris]

6 minutes ago, Ferdinand said:

 

Is it a good sign when your test item breaks the equipment :-) ?

 

Good result.

 

 

In this case is seems as if the air test company wasn't exactly on the ball, and that may have been the real reason for the frame coming loose.  50 Pa is a very low pressure, and I strongly suspect they made an error, didn't fit the restrictor rings to the fan before turning it on and accidentally depressurised the house to WAY below 50 Pa, hence the problems with the frame coming out, their software being out of range etc.  This also tallies with them not understanding the proper air test procedure and the requirement to take both readings and use the average as the air permeability figure.

[Jeremy Harris]

Just to add, doing both a pressurisation and depressurisation test is at the discretion of the tester,  but they must take into account the specific construction details of the house.  The key points here are the direction in which the doors and windows operate.  If a house has openings where every door and window operates inwards, then the tester could decide that a depressurisation test would give the worst case, and so use their discretion to just do this.  My personal view is that this is bad practice, looking at our test report, the depressurisation test was undertaken at 08:45 and the pressurisation test was undertaken at 08:50, so there was only 5 minutes to switch from one test to the other, and no real excuse for an air test company not to do this at all.

 

Most houses will have a combination of inward and outward opening doors and windows, so would need both a depressurisation and pressurisation test done, anyway, as I would question whether there would be adequate justification for just doing a single test under such circumstances.  The UK accepted compliance test method developed by the ATTMA  does vary slightly in this respect from the way other countries interpret the requirements of EN 13829, where bi-directional testing is the normal procedure.

 

For those that want the detail on the current recommended test methodology used in the UK, then here is the current (2016) document: https://www.attma.org/wp-content/uploads/2016/09/ATTMA-TSL1-Issue-3-Rev-0-2016.09.09.pdf

[NSS]

56 minutes ago, JSHarris said:

The test procedure requires them to do both a positive and negative test, then average the two results to get the permeability, so both tests need to be done. 

Actually, it doesn't. ATTMA guidelines for the test clearly state either * positive or negative pressure test is acceptable, but IF both are conducted then the average of the two should be used for the final result.

[Oz07]

I'd be happy and move on. You've got a house you're happy with. As long as it performs ok don't sweat about scores

[Jeremy Harris]

7 minutes ago, NSS said:

Actually, it doesn't. ATTMA guidelines for the test clearly state either * positive or negative pressure test is acceptable, but IF both are conducted then the average of the two should be used for the final result.

 

As I wrote above, with the link to a recommended compliance document for EN13829 in the ATTMA guidance (which is not the only way of showing compliance with the standard), but really only where there is justification for this, i.e. a case can be made by the tester that all the seals are unidirectional.  Given that it takes 5 minutes to switch from depressurisation to pressurisation and do another test, there seems very little reason not to do both.  It takes several times longer than that to fit the blower and tape it in place, then remove it again afterwards.

Edited October 1, 2017 by JSHarris

[MikeSharp01]

Great news but the professionals need to be rigorously encouraged to do the full job in exchange for the agreed fee. Hold some of the fee back or get them to do the proper job. Otherwise the next person will get a slightly worse service until some one down the line complains. It a classic case of keep reducing the quality of the service until it is just fractionally below acceptable then inch it up. That way you minimise effort and maximise profit albeit usually only in the short term because you will eventually get caught out by competitive companies who go the extra mile.

[le-cerveau]

In the ATTMA guidelines it says that the test must be done a minimum of 7 times, 10 recommended, with a difference between each of less than 10Pa.  So a comprehensive series.  It also states that he initial pressure is to be 20pa or 5 times zero flow reading from the initial setup calculations.  Did the tester do all the correct setting up, measurements and then steady ramp up?

[NSS]

1 hour ago, le-cerveau said:

In the ATTMA guidelines it says that the test must be done a minimum of 7 times, 10 recommended, with a difference between each of less than 10Pa.  So a comprehensive series.  It also states that he initial pressure is to be 20pa or 5 times zero flow reading from the initial setup calculations.  Did the tester do all the correct setting up, measurements and then steady ramp up?

Yep

[Jeremy Harris]

1 hour ago, le-cerveau said:

In the ATTMA guidelines it says that the test must be done a minimum of 7 times, 10 recommended, with a difference between each of less than 10Pa.  So a comprehensive series.  It also states that he initial pressure is to be 20pa or 5 times zero flow reading from the initial setup calculations.  Did the tester do all the correct setting up, measurements and then steady ramp up?

 

In our test report there are 10 measurements during the ramp up to 50 Pa for each of the pressurise and depressurisation tests, with the results for both plotted on a graph.  The leakage with pressure differential seems pretty non-linear, with zero flow rate being measured until the pressure differential reaches 8 Pa during the depressurisation test cycle and 9 Pa during the pressurisation test cycle.  The results show curves that are of opposite characteristics, and indicate that the the rate of change of air leakage increases with increasing pressure during the pressurisation test, and decreases with increasing differential pressure during the depressurisation test.  I'm guessing that's because we have outward opening windows that may well seal slightly tighter as the internal pressure decreases.

Edited October 1, 2017 by JSHarris