In planning my "dream house"  I have been giving a lot of thought to and researching how to reduce air leakage.  The airtight drywall approach + an exterior envelope that's well sealed as well to reduce "wind washing" of the insulation (dense pack cellulose) is what I'm planning.  The devil is in the details, here are some thoughts:   If I have a basement the basement becomes the bottom of the inner air barrier unless I teat the door to the basement stairway as an exterior door with weather stripping etc.  With a weather stripped basement door I still need to assure that the drywall on the interior walls around the stairwell is properly sealed and I'll need to seal all the penetrations of the sub floor as it is the bottom of the airtight shell.  On the other hand if I don't weatherstrip & seal the basement  I can ignore the sub floor but  must instead seal up the basement and assure a good air barrier in the connections between basement walls and the drywall on the inside of exterior walls.  This means sill plate gaskets, rim joist gaskets etc.  In either case the ceiling is a vital air barrier & penetrations of it must be sealed.  A particularly vexing set of penetrations occur at the places my ERV ducts enter or exit the living space.  I think I've come up with a plan for the ERV ducts.   First I'll use 6 " PVC thin wall irrigation pipe (SDR-81) for these ducts, the necessary fittings appear to be available but I haven't found someone who'll sell them to me, and at each penetration I'll install an EDPM "boot" normally used as a flashing to a plywood piece that'll be right behind the drywall. Has anyone else used these boots?  If I use the weatherstripped basement door I'll probably use smaller EDPM boots for all the pluming penetrations of the sub floor.

The biggest air leak into basements is usually at the band joist and foundation sill, which are best treated by insulating them with 1-2" of closed cell foam right up & over the rigid foam on the foundation wall. Sill gaskets don't really cut it, and unless you caulk the band joist to the sill, and the sill to the subfloor that micro-crack ends up being several square inches of cross sectional hole. But a spray foam seal & insulation should take care of it. (Closed cell is more reliable at air sealing jobs than open cell.)

Dryer vents are worth more air leakage than all the windows & doors you might have in the basement.

Sealing between the basement and first floor is a nightmare of 5 gianormous holes, 50 big holes, 10,000 small ones. It's better to use the exterior walls, as a rule. But air sealing between floors can still reduce stack-effect drives. In particular plumbing & electrical chases where a drain-stacks etc can run from the basement to the attic need treatment, sealed at both bottom and top (and anywhere it might be penetrated in between.)

There's no substitute for blower door verification and rectification if you're hoping to get it under 2ACH/50. Some of the bigger penetrations seem obvious, but may still leak after treatment, and there are myriad less obvious leaks that can still add up to something substantial.

"Sill gaskets don't really cut it" I agree the cheap ones don't.
One of the techniques I used to get my last house under 1.0ACH/50 was EDPM rubber sill gaskets from Conservation Technology.com. I used them at the foundation/PT and at the bottom wall plate/subfloor. Also used EDPM rubber drywall gaskets stapled to the top wall plates. (that or caulking is an Energy Star requirement; I thought caulk would lose the battle with the drywall hangers, so used the gaskets.) I avoid trying to seal the basement from the house; the basement should be within the envelope and well insulated anyway. We also used ZIP wall sheathing and spray foam at the rim joist.

Alot of steps for effective air sealing needs to be done during construction which goes against the grain of a schedule so you need someone in charge of it and onsite at all times to complete it.

For example, after floor framing but before sheathing the floor. After tipping some walls but before tipping others. Before wrb is complete. Before trusses are set, after trusses are set, before backers go in and on and on.

Defining the boundary is critical for those who are building the home so it will be apparent when construction work needs to stop and air sealing needs to begin.

If you don't do this you won't accomplish your target infiltration and you'll switch to band-aid mode after the fact which won't be as effective or durable.

If you do build your dream home and DIY your air sealing and plan to buy caulk by the gross, please learn about joint design and installing caulk correctly. Otherwise you may get a good number after the build, but after shrinkage and seasonal movement all your hard work will go by the wayside quickly.

I couldn't agree more with you, greentree. What I have found is that the very same tradesmen who can argue for hours over the finer points of sealing something up, or doing something "green", don't actually do ANY of it.

It's all laid out in detail, instructed, and the materials are supplied, but there are big surprised faces when the work is actually inspected. After surprise comes denial, then anger and then the argument about whether sealing makes any difference or not.

Goodness only knows what happens on spec houses if they can't be bothered to do it on custom builds.

Thank you all for very help full comments! Philosophically, I believe gaskets are preferable to caulk wherever both could be used. I believe every penetration of or interruption of exterior wall and ceiling needs to be gasket-ed or caulked. Similarly every penetration of the outer sheathing/house-wrap needs to be gasket-ed if possible or caulked. In addition basement/crawlspace wall to sub floor needs to be sealed, this is probably best done with spray foam.

Lots of details to attend to! I like the EDPM gaskets from Conservation Technology and plan on using them around all my windows and doors both on the inner stud wall and the outer.

Dana,
My solution to the dryer vent problem is a condensing dryer (un-vented). The only one available in the US are in washer dryer combos & the largest is by LG.

Bob, did you gasket all the interior, as well as exterior walls at the top plate? How about the stud next to an exterior wall on all interior walls? (I'm trying to estimate how much gasket to buy) How do you seal pluming vents where they go through an interior wall's top plate? I'm thinking this is another place for an EDPM 'boot'.

Dryer vent - this one seems to work well in my house -
Heartland SPV21000789
http://www.amazon.com/HEARTLAND-Heartland-Dryer-Vent-SPV21000789/dp/B004HDXMH4

A few suggestions:
Lots of polyurethane caulk in the exterior sheathing seams, windowpaning wherever sheathing meets framing on the interior, every penetration of the sheathing by nails or screws. Foam all the electrical boxes and where the holes are cut in framing for electrical wires. Stagger joints and taping the exterior foam.

-Rosalinda

"did you gasket all the interior, as well as exterior walls at the top plate"
Yes; that is an energy star requirement.
EDPM boots are the best way to seal the pipes.
I agree with you on the gaskets vs caulk. Caulk lasts until the wood moves; the gaskets will last indefinitely.

It seems to me that a gasket on the top plate isn't as important as a gasket on the bottom plate. The top plate to wall corner seam at the top is sealed by the drywall tape etc. The bottom plate to sub floor is, or should be, sealed with a gasket So the bottom of the drywall needs to be either gasket-ed or caulked to the bottom plate of exterior walls. I'd prefer to NOT depend on spray foam as well as caulk. So I have devised the following: After the basement walls are up and ready for the PT sill plates I'll put a strip of "Celotex" asphalt impregnated fiberboard atop the basement walls. Then I'll put a 4 ft wide piece of plastic sheet (say 8 mill polyethylene) a-top the wall with about 2" overlap of the outside piercing the plastic for the sill attach bolts. Next attach the outer sill plate. then fold the sheet so about 2" is inside the basement wall line. Pierce the top layer of plastic with the inner sill plate's attach bolts and attach the inner sill plate proceed with floor framing till the sub floor is on (sub-floor covers inside wall area only). Wrap plastic over rim joist & staple to sub floor, do this on all sides note sides parallel to the joist have sheat-ed stub walls instead of rim joist. Make and "pre-plumb" any necessary penetrations of the rim joist using EDPM boots on the outside of the plastic. Tape the corners of the plastic where rim joist join stub walls. Now build and erect outer exterior walls then inner exterior walls that have a gasket on their bottom plates. After exterior walls are up remove staples from subfloor & staple plastic to the inside of the inner exterior wall & install "drywall gasket" on bottom plates. After all exterior walls are up but before roof trusses are set place another plastic sheet over the tops of both exterior walls stapled to the inner face of the inner wall's top plate and over lapping the exterior sheating by a few inches tape to the exterior sheating. Set trusses & proceed.

Posted By Rosalinda on 25 Jan 2012 11:13 PM
Dryer vent - this one seems to work well in my house -
Heartland SPV21000789
http://www.amazon.com/HEARTLAND-Heartland-Dryer-Vent-SPV21000789/dp/B004HDXMH4

A few suggestions:
Lots of polyurethane caulk in the exterior sheathing seams, windowpaning wherever sheathing meets framing on the interior, every penetration of the sheathing by nails or screws. Foam all the electrical boxes and where the holes are cut in framing for electrical wires. Stagger joints and taping the exterior foam.

-Rosalinda

I have a similar version at my house, and yes, it does improve the basement or first-floor infiltration aspects. It may be less effective if your dryer vent is on the second or third floor, but I haven't seen a good solution for that scenario. 

But by inserting first a relatively tight 90 degree turn followed a uber-short radius 180, it increases the effective duct length by ~15'.  They are  best used with the shortest & straightest ducting to the dryer as possible, as the additional duct impedance cuts into dryer efficiency, even if the total effective length still meets code.

You'd have to be doing a LOT of laundry for the lowered drying efficiency to match or exceed the heating/cooling savings of the lowered infiltration though.

How does one handle the bathroom vents? They are mandatory but once again, they are a source of energy loss.
Having an attic that is not vented, I assume you would have to utilize a SIP or concrete roof? Don't most codes frown on un-vented attics?
What about kitchen exhaust vents? That is another sore spot.

I'm planning to exhaust 50 CFM from each bathroom and 50 CFM from the kitchen through a central ERV and distribute the returning fresh air to the bedrooms, family room, living room & dining room. It's my understanding this is code accepted and eliminates individual bathroom fans. The ERV should recapture 60% to 80% of the energy for about 75 watts of elctricity. My attic will be vented with sofffit vents and ridge vent. The "attic" is above the 20"+ of loose cellulose. I'm still debating with myself whether to use a recirculating range food or provide for a range hood exhaust. Another option is the Panasonic ERV bathroom fan (FV-04VE1).

Posted By Liebler on 26 Jan 2012 08:51 PM
I'm planning to exhaust 50 CFM from each bathroom and 50 CFM from the kitchen through a central ERV and distribute the returning fresh air to the bedrooms, family room, living room & dining room. It's my understanding this is code accepted and eliminates individual bathroom fans. The ERV should recapture 60% to 80% of the energy for about 75 watts of elctricity. My attic will be vented with sofffit vents and ridge vent. The "attic" is above the 20"+ of loose cellulose. I'm still debating with myself whether to use a recirculating range food or provide for a range hood exhaust. Another option is the Panasonic ERV bathroom fan (FV-04VE1).

What about the plumbing vent stacks and vent pipes? Those CANNOT be recirculated into the homes air, not only is that smelly but dangerous. They have to vent outside.

How does one handle the bathroom vents? They are mandatory but once again, they are a source of energy loss.

You can integrate the run-time for the bathroom fans into the minimum necessary ventilation for the home. I like those electronic timers that the user can punch to select the amount of run time until they gturn off automatically.

You can also go wild and use the Panasonic ERV that Liebler mentioned above for each bathroom if you can't stand losing the heat, or you can use a whole-house HRV that runs 20 min each hour or so with an over ride switch in each bathroom to make sure a user can start the venting when needed.

I have a toilet room in each bathroom on the theory that it makes the bathroom usable by two people at the same time. The toilet rooms are vented by plain old-fashioned vent fans on timers.

What about the plumbing vent stacks and vent pipes?

There is a water trap on those pipes. They exist to allow a small amount of air to enter the drainpipes to equal the water going down the drains. It doesn't represent much volume and the water traps help seal them from free air exchange

Posted By Lbear on 26 Jan 2012 08:02 PM
How does one handle the bathroom vents? They are mandatory but once again, they are a source of energy loss.
Having an attic that is not vented, I assume you would have to utilize a SIP or concrete roof? Don't most codes frown on un-vented attics?
What about kitchen exhaust vents? That is another sore spot.

Kitchen exhausts can be ventless and in some instances not required at all

Posted By Liebler on 26 Jan 2012 09:33 AM
It seems to me that a gasket on the top plate isn't as important as a gasket on the bottom plate. The top plate to wall corner seam at the top is sealed by the drywall tape etc. The bottom plate to sub floor is, or should be, sealed with a gasket So the bottom of the drywall needs to be either gasket-ed or caulked to the bottom plate of exterior walls. I'd prefer to NOT depend on spray foam as well as caulk. So I have devised the following: After the basement walls are up and ready for the PT sill plates I'll put a strip of "Celotex" asphalt impregnated fiberboard atop the basement walls. Then I'll put a 4 ft wide piece of plastic sheet (say 8 mill polyethylene) a-top the wall with about 2" overlap of the outside piercing the plastic for the sill attach bolts. Next attach the outer sill plate. then fold the sheet so about 2" is inside the basement wall line. Pierce the top layer of plastic with the inner sill plate's attach bolts and attach the inner sill plate proceed with floor framing till the sub floor is on (sub-floor covers inside wall area only). Wrap plastic over rim joist & staple to sub floor, do this on all sides note sides parallel to the joist have sheat-ed stub walls instead of rim joist. Make and "pre-plumb" any necessary penetrations of the rim joist using EDPM boots on the outside of the plastic. Tape the corners of the plastic where rim joist join stub walls. Now build and erect outer exterior walls then inner exterior walls that have a gasket on their bottom plates. After exterior walls are up remove staples from subfloor & staple plastic to the inside of the inner exterior wall & install "drywall gasket" on bottom plates. After all exterior walls are up but before roof trusses are set place another plastic sheet over the tops of both exterior walls stapled to the inner face of the inner wall's top plate and over lapping the exterior sheating by a few inches tape to the exterior sheating. Set trusses & proceed.

When we test houses we usually find lots of air leakage at the upper corner joints behind the drywall.  It comes from the wall cavities, not the inside of a room, so your upper gasket is indeed very important.

Your poly plan sounds like an old article in JLC from many years ago that a builder from WI was doing? I don't think poly is very reliable to air seal, it does good until puntured and that likelyhood is quite high.

Yes plumbing vents are required. Their penetrations of the airtight "envelope" are best handled with EDPM 'flashing' boots. Plumbing vents should not, however, contribute to air leakage as they all have water filled traps to stop air under normal pressure differences. On the topic of pluming, exterior faucets, are typically 'frost free' and penetrate the air barriers in the rim joist area. I'm planning to use a pipe within a pipe for these with a piece of 2" pvc as the outer pipe that's "booted" to the air barriers and ends flush on the outside, the actual plumbing will be inside that pipe and the space between filled with spray foam. Regarding the reliability of poly as an air barrier, I don't see an alternative that is self sealing if punctured. Booting the necessary penetrations is a price of air tightness.

Poly is a double-edged sword due to it's extremely high vapor retardency. If it CAN be designed out of the assembly, it SHOULD be, especially in areas where masonry meets wood. As greentree correctly points out, it's easily damaged and not the greatest air-barrier, but even when ripped an riddled with holes it's still a powerful vapor barrier, and defines the direction in which the materials MUST dry. It's usually possible to come up with local-climate appropriate stackups that allow reasonable drying rates toward both the exterior and interior, making the assembly much more robust & fault-tolerant. In the 1980s, even into the '90s poly sheeting was often viewed as "the solution" to moisture management but being commonly mis-applied and so susceptible to damage it seems to cause as many moisture problems as it avoids, in the real world.

Using rigid & rugged structural sheathing as the primary air barrier is preferable. Air tight wallboard techniques work in the short & intermediate term, but are still susceptible to a "death of a thousand cuts" over decades of occupancy. Poured concrete/ICF has the best long-term prospects for air tightness, but how it's detailed at the windows/doors and top interfaces with the roof/ceiling makes it or breaks it.

Dana,
Would a strip of poly under the sill plates atop a concrete block basement be desirable? Then a strip of moisture permeable house wrap, under the inner sill plate wrapped over the band joist, or stub wall, under the bottom plate, gasket-ed, inner exterior wall & over the bottom plate but under the drywall gasket, be better?

Putting poly on the top of the masonry as a capillary break separate the masonry from the wood is fine, but it's not a good air-barrier for the crack.

The EPDM sill gaskets recommended by BobI are a much better solution.

Detailing the rigid foam as part of the air barrier system is also good, and can be part of the primary continuous overall air-barrier for the building. (You have to work a lot harder to punch holes through a few inches of foam than through 8 mils of poly, eh? :-) )