Good Morning all,
We are in the process of building a bio-compatible house in the Piemonte region of Italy. It is a double frame house (about the 2000 sq ft), with fully insulated 14" walls. We hope the house will be certified CasaClima Gold (kind of like PHI). We have completed all framing, 80% insulation, Vapour barrier, windows, doors. All services are installed, but not drywall.
The cost of doing Blower Door Tests here is very high, so we invested in a tester so we can monitor our progress, and when the project is done, we'll go do blower tests around the countryside.
Anyway, we ran the first test yesterday, and obtained what everyone tells me is excellent. A 1.32 ACH50. However, this appears to be a long way from the 0.6 that I need for CasaClima Gold.
I have chased around the house looking for that "smoking gun" hole that explains where the air is coming from, and have determined that it probably doesn't exist (all penetrations have been checked). It appears to be many very small areas that I'm not sure are easily fixed, short of foaming the inside of the house, which we would prefer not to do, hence the "bio" house. We have used no foams or chemical insulations to this point, only non-formaldehyde fiberglass insulation and perlite.
So my question is this. Given the level I am at now, what can I expect to see if the inside were completely drywalled (taped and mudded, but NOT ADA)? I should also mention that the exterior wrap is NOT complete, so not sure what the effect of this will be when done.
I am trying to determine if is it worth (or necessary) to chase every minute air leak.

Thanks for everyone's time.
Alec

No it is not worth finding every minute leak. Do the best you can during construction. Doors and windows will still leak, exhaust fans and dryer vents will still back draft

Carefully taped exterior wrap, caulked drywall and perhaps an interior film/wrap air barrier will certainly help. I don't know your energy rates, but you are probably at the point where air infiltration will contribute very little to heating/cooling costs (I've done the calculation once).

jonr
Thanks. Energy in this part of the world is very high. You are probably right tho' chasing the ghosts will probably not add much to our overall costs. We are going to use 4 ROTEX thermal panels and 500l technical water tank, along with an integration of a 6KW air/water heat pump for cold/cloudy days.
The wall profile is: Weathermate/10mm OSB/2x6 insulated/5 inch rigid fibreglass/vapour barrier/2x4 technical wall, insulated/drywall.
R is about 60 or so.
The whole house is rated at about 7kwh/m2/yr, not sure what that means in NA terms.

Thanks for the input.
Alec

bio- I was reading a report, can not remember what it was and where. But they were in a very similar situation as you...pretty low before drywall. However they did air tight drywall with a lot of attention to caulking plates and around openings. I cant remember the exact number, but they reduced it to nearly .5-.7 range. I would say you are really close, good work!

Hi lzerarc. Thanks for your comment. I too found an old report by the University of Colorado (I think). They were trying to determine the impact of various types of insulation as related to air tightness. They found that the 2 types of insulation they used (wet cellulose and fiberglass) had virtually no effect on the air tightness. They did discover that the presence of finished (not necessarily sealed) drywall improved things by an amazing 70-80%. I don't remember the start and end values, but I'm pretty certain that the improvement would largely depend on how much improvement was possible. Or rather, if I start at 50, and get to 10, I've improved by 80%, but if I start at 1, is it really feasible to think I can get to 0.2 (same 80%)? I am just trying to understand the impact of drywall at low ACH50 values.
Thanks again
Alec
 

I would have guessed that cellulose would have a beneficial effect on air infiltration in a typical (ie, not so perfectly sealed) house.

wish I could be more help, but I can not really. I guess you just do the best, sealed gyp you can and see where it gets you.
Just know that most of the passivehous buildings do not use spray foams to achieve their impressive rating.

Is the outside OSB glued/sealed with some type of mastic to seal for air infiltration? Was SIP tape appliied over the seams of the OSB to seal for air infiltration? The outside shear wall is an excellent place to stop airlieaks if you don't have condensation problems in the wall that requires the outside shear wall to release moisture to the outside. The next place to stop air infiltration is all doors and windows. A thermal imaging gun can help find temperature changes caused from air leakage and can be sealed up with mastic and SIP tape. After all this has been addressed, the next area is whether to use a plastic vapor barrier on the inside wall before placement of the drywall. Another area to check is the electrical outlet boxes for air leakage.

With fiberglass insulation, I suggest having some type of air barrier on both sides of the wall. You don't want any air flowing vertically or horizontally either (vs through the wall). Two air barriers are better than one.

Hello all, and thanks for the comments.
At present I have NOT sealed the exterior of the house. We plan on wrapping the house and then stuccoing the outside. I have not sealed the exterior joints, as there seems to be some continuing concern over completely sealing a wall cavity. At present we have 1 barrier located at about 80% (80% outside and 20% inside) of insulation. My plan was to seal the bottom of the wrap, and then seal all the joints in the wrap, and allow breathing through the wrap and stucco (not sure how much the stucco will breath!). So while pretty sure this too will tighten up the house, I'm still trying to hedge my bets. So my next plan is to proceed with drywall, sealing as much as possible, and then run the blower door again. The exterior should improve things, but I was still trying to understand how much drywall alone would improve ACH50. Can't seem to get any answers, even though the U of C study indicates impressive improvements, but starting with much higher values. Oh well, I guess we just plug ahead!!

Alec

I've never heard anything contrary to completely air sealing a wall cavity. But air sealing is not water vapor sealing.

OK. I'll bite. What's the difference? If air is sealed then so must be vapour???
Alec

I believe that house wraps are considered air sealers but not water vapor sealers.

Exactly.

http://www2.dupont.com/Tyvek_Weatherization/en_US/assets/downloads/K01472.pdf

(although their curves look suspect to me)

Posted By biocasaitaly on 31 Aug 2011 05:57 AM
OK. I'll bite. What's the difference? If air is sealed then so must be vapour???
Alec

The bulk of the gases in air are diatomic and comprise of atoms with multiple electron shells, (N2 & O2 comprise the bulk of it), whereas H2O has single-shell hydrogens sharing their lone electron with a single oxygen. From a gas-diffusion point of view it's a molecule about half the cross section of air molecules, and a vessel that can hold a sustained and considerable  AIR pressure can still pass water vapor molecules (in either direction), if made of a vapor permeable material.  (Liquid water has surface tension that keeps it from passing through many vapor-permeable materials as well- waterproofness  of a material alone is not an indication that it's a vapor barrier.)

When referring to vapor barrier/retarders in building materials we are talking ONLY about water vapor.  A vapor barrier such as 6 mil poly  or foil with lots of cuts, slashes & nicks can be a very LOUSY air-barrier- it'll leak like crazy when there's a difference in air-pressure, but it can still be a very effective vapor barrier, since it will still block migration of moisture between the two sides in the presence of a difference in vapor pressure (a difference humidity/dryness from one side to the other).

That said, moisture problems in building materials are far more likely to be caused by air-transported moisture than it is by vapor diffusion.  Air sealing is thus more critical than vapor-sealing, and an air-leaky vapor barrier can be worse than having no vapor barrier at all, since it inhibits drying after air leaks during condensing conditions.

Posted By biocasaitaly on 30 Aug 2011 07:14 PM
Hello all, and thanks for the comments.
At present I have NOT sealed the exterior of the house. We plan on wrapping the house and then stuccoing the outside. I have not sealed the exterior joints, as there seems to be some continuing concern over completely sealing a wall cavity. At present we have 1 barrier located at about 80% (80% outside and 20% inside) of insulation. My plan was to seal the bottom of the wrap, and then seal all the joints in the wrap, and allow breathing through the wrap and stucco (not sure how much the stucco will breath!). So while pretty sure this too will tighten up the house, I'm still trying to hedge my bets. So my next plan is to proceed with drywall, sealing as much as possible, and then run the blower door again. The exterior should improve things, but I was still trying to understand how much drywall alone would improve ACH50. Can't seem to get any answers, even though the U of C study indicates impressive improvements, but starting with much higher values. Oh well, I guess we just plug ahead!!

Alec

Air seal the exterior behind the stucco and leave a gap, or the moisture drives from sun-heated stucco can be too intense.  From an air-transport point of view, venting the air-gap behind the stucco at both the bottom and top will dry the stucco more quickly after rain/dew absorption, purging the moisture to the outdoors rather than into the wall cavity. Vented or not, stucco is VERY vapor permeable (its "breathable" to water vapor even when air-tight), and is not waterproof- it's porous- it wicks dew & rain moisture toward the interior.  To avoid moisture issues with the timber frame and any wood products on the interior, a waterproof semi-impermeable element needs to be inserted into the stackup.  Standard grades of Tyvek etc are often too vapor-permeable for application behind stucco- whether it can be used depends a lot on the overall material stackup of the building, and whether a ventilation gap is provided. More info:

http://www.buildingscience.com/docu...fect-storm

Air-sealing the drywall can make a huge difference in the ACH/50 number,  but if you have low-density fiber in the wall cavities, air leakage at the exterior can still reduce it's insulating performance at very high or very low outdoor temperatures.  Whether it changes YOUR ACH50 numbers depends somewhat on where your leakage is. (If most of it is somewhere other than the exterior sheathing, air sealing the drywall may not affect the numbers much at all.)

While it's true that from an ACH50 point of view there's no appreciable difference between low-density wet-sprayed cellulose and low-density fiberglass (both require air barriers on both sides to get the full effect),  low density cellulose has far less convection within the cavity than low density fiberglass during high temperature-difference conditions. (It also has almost no gaps or compressions creating whole convective-bypass currents inside the cavity as happens with batts,  but for the moment we'll assume it's blown-fiberglass with no gaps too.)  These convection currents cause low density fiberglass to lose some of it's effectiveness at the seasonal temperature extremes, whereas even low-density cellulose R-values remain nearly constant over a large range of temperatures.

At higher density "dense-pack" installation of either cellulose or fiberglass (especially super-fine blowing wool such as Optima or Spider, (widely available in N. America, not sure about Europe) the whole house air-sealing performance can improve from an ACH50 point of view, and stabilizes the R value of fiberglass over temperature to comparable levels. Dense-packing reduces or eliminates settling of dry-blown cellulose over time, but the density required is climate-dependent, since it's dependent upon seasonal humidity fluctuation within the cellulose.  See:

http://www.nordicinnovation.net/nor...rep565.pdf

Dana1,
Wow! Thanks. All very informative (and concerning to say the least).
I guess now would be a good time to describe my wall profile. we have starting from the outside:
Dow housewrap,
3/8mm OSB,
2x6 studs insulated with fibreglass batts (50 kg/m3),
5 1/2" Fiberglass panels (4ft x 9ft),
vapour barrier,
2x4 walls insulated with same fiberglass,
drywall.
We are (were) planning stucco exterior over the wrap and a metal lathe.
Perhaps we should reconsider the wall profile, but we haven't closed in the interior or exterior, so it's not too late. The climate in our construction area is not Vancouver, perhaps closer Toronto. We get quite a bit of rain, but also hot summers and cool winters (lows of -10C).
Any further thoughts are always appreciated.
Alec

Posted By biocasaitaly on 31 Aug 2011 09:08 PM
Dana1,
Wow! Thanks. All very informative (and concerning to say the least).
I guess now would be a good time to describe my wall profile. we have starting from the outside:
Dow housewrap,
3/8mm OSB,
2x6 studs insulated with fibreglass batts (50 kg/m3),
5 1/2" Fiberglass panels (4ft x 9ft),
vapour barrier,
2x4 walls insulated with same fiberglass,
drywall.
We are (were) planning stucco exterior over the wrap and a metal lathe.
Perhaps we should reconsider the wall profile, but we haven't closed in the interior or exterior, so it's not too late. The climate in our construction area is not Vancouver, perhaps closer Toronto. We get quite a bit of rain, but also hot summers and cool winters (lows of -10C).
Any further thoughts are always appreciated.
Alec

Unless you have some amount of vented rainscreen gap, and preferably a modest vapor retarder somewhere between the stucco and OSB you run some risk of summertime condensation on the mid-wall v.b. due to the extremely high moisture drives that occur when sun hits rain/dew wetted stucco.  Something like 1/4" fan-fold XPS (0.6-0.8  US perms for most, but up to 1.7 perms for some products) would limit the migration of moisture into the wall but still allow the exterior studwall to dry to the exterior.  The fan-fold can go over the housewrap, or under- your call.

Alternatively a purpose-made semi-permeable combined rainscreen/drain-plane system over the housewrap works, eg:

http://greenguard.pactiv.com/reside...ainage-mat  (<<<1.1 US perms, per spec)

With unvented stucco up against hi-perm housewrap your exterior OSB would be susceptible too.

Hi dana,

Thanks for the input. Sorry no XPS or EPS. This is a bio house, so no "synthetic" products. We have used no PVC or Polyurethane or EPS/XPS etc.

I will review the article you mentioned.

Alec