Air Tightness Membrane - worth it?

GoneShootin

Many of you will say yes, definately.

BUT

I ditched the HRV (sorry sinnerboy et al ) - sorry but I couldn't be convinced. To maximise the benefit of air tightness, I'd need to have HRV really wouldn't I?

SO

My dilemma. My PM was onto me about the air tightness membrane. At the very start I was saying to seal it like a ducks arse. But of course now I've learned so much that my concern about such an air tightness membrane are:

1- Moisture & Damp:
How breathable are these membranes, and who here really has experience of these membranes being installed for 10+ years?

2- Maintaining the envelope
Say you install the membrane and somehow by magic it's integregity is maintained by those installing it. What about fitting those bits of kitchen, shelving, wall mounted tvs etc. It's like a slow leak in a tyre - it might hold for a bit but eventually the damn thing will leak and run flat.

Also - the cost. I've been quoted 3K supply and fit. To me I'd rather spend 3K on my fascia + soffit!

Opinions?

sinnerboy

Cart before horse GS

If you achieve the TDA - you must have HRV to stay healthy

It's not an unreasonable strategy to aim for good air tightness - say Q50 7-8 and not install HRV

You are not the 1st and only person to query the lifetime performance of these membranes and tapes . They are new . Not tried and trusted yet .

.

Carlow52

Re

To maximise the benefit of air tightness, I'd need to have HRV really wouldn't I?

I would have thought :
To maximise the benefit of HRV, I'd need to have air tightness really wouldn't I?

I suppose it depends what you learned:) as per

But of course now I've learned so much

soldsold

How about:

...Aim for "seal like a camels arse in a sandstorm", using wet plaster finish and 9mm OSB taped and clamped tight (proven air barrier?) then add tricke vents to reach an air leakage level that doesnt need HRV.

Then you have controlled ventilation and if at a later date you decide to go the HRV route, install HRV and seal the trickle vents?

Steve

GoneShootin

soldsold wrote: »

using wet plaster finish and 9mm OSB taped and clamped tight (proven air barrier?) then add tricke vents to reach an air leakage level that doesnt need HRV.

Yep - most likely the route I'll be taking.

Thanks one and all.

Carlow52 - to me air tightness and hrv go hand in hand, they act in a symbiotic relationship

sinnerboy

Draft part F requires that if you exceed Q50/7 - you must increase "hole in wall" or trickle vents by 50%

sinnerboy

HRVs can be retrofit in most existing homes, but a blower door test (check with your electric utility or heating contractor) should be performed first. HRVs are generally only used in homes which require mechanical ventilation, usually homes with a natural ventilation rate of less than .35 ACH

text above from this Canadian site

http://www.oikos.com/library/energy_outlet/hrv.html

At this point I declare

1. I don't have HRV in my home
2. none of my clients do

I have tried with others to determine the AT "cut off " point for HRV , i.e. at what degree at air tightness do you need to consider HRV

The Canadians are ahead of the pack here . Heres an interesting point

Q50/7 equates to 0.35 achr ( divide Q50/20)

So this Canadian advice dovetails to the Draft Part F requirement to add +50% to holes in walls / trickle vents . ( Or by implication - install HRV )

Q50/7 is not very difficult to achieve - having said that it is also not difficult to fail to achieve if you are a careless builder .

You MUST have an air tightness test done anyway ( for all 1 offs ) .
So a little careful planning with DEAP calcs is required now GS