Air tightness test - will too high or low be bad news bears?

[Mr Punter]

I am building some new flats and have installed DMEV fans, which, together with trickle vents and wall vents will provide ventilation.  I am about to get an air tightness test.  The design stage SAP is stating 4.0 design value for air permeability. What if the testing shows 2.0 or 10.0?

[ProDave]

In Scotland, if it is better than 3 you must fit MVHR

[MikeSharp01]

Good question - at the low end you might not be able to show enough ventilation - but you can always drill some more holes, at the high end won't you be outside building regs? 

[kandgmitchell]

So your SAP design assumes 4.0, if it comes out more than that then your "as built" SAP will not be at least equal to the design SAP assuming everything else remains the same. Thus it will not comply.

 

If you come in at less than 3.0 then you may no longer comply with all the provisions of Part F - Ventilation, if you have gone the natural ventilation route to show compliance.

 

This is a very simple summary of what are complex regulations that interact with each other, you'll need further advice if the figure varies a lot from 4.0.

[Jenki]

Don't let them publish the figures until you are happy with the results. Maybe get a preliminary test done to assist your build..if it hits the required numbers ask them to formalise it.. otherwise do some rework. The worst case for you would be less than 3, ( this should be easy to resolve, by opening a window handle after the tester has checked it's closed😉)

 

[saveasteading]

57 minutes ago, Jenki said:

opening a window

If there are window vent holes, its easy to slide one or more open or closed.

 

It's years since I did one. Do they still ask what number you are aiming for?