Common Air Barrier Failures and How to Avoid Them

Common Air Barrier Failures and How to Avoid Them

Top Ten *NO* Eleven Air Barrier Failures

1. It's not continuous!

airtight gap
Mind the gap!

The mother of all failures. You don't have an air barrier if it's not continuous- it won't be air tight. Many of the items that follow below are all causes of discontinuity. Like a balloon or a submarine - the continuity of the airtight layer must be sacrosanct. While discontinuity can happen anywhere it is at the junctures (floor to wall, wall to wall, and wall to roof to name a few) and penetrations where efforts often fall short.

2. Forgot to plan ahead

airtight sequencing
Think about airtightness before you frame! A great example of doing it right by Ed May and Bldg typ.

So you've got great details and materials specified - and you've got it under control. WRONG. Best intentions can run amuck fast. Were the components ordered on time and are on the job site when needed? Is the sequencing spelled out? The GC may be responsible for means and methods - but you better sure as hell give them a heads-up on how out of sequence work can make a straight-forward airtightness plan a nightmare of chasing unsealable rabbit holes.

Instead be sure the plans, details and specifications address sequencing in a coordinated manner. And insist on tradesperson training, so that the trades can more readily understand and anticipate next steps - often making the difference between failure and success. See planning done right: Ashfield MA: Deep Energy Retrofit (DER) by Quigley Builders

3. Not a systematic approach

Too often we see incompatible products cobbled together - some free tape is attaching to a liquid membrane left over from another job with caulk from the corner hardware store. We provide whole systems solutions by Pro Clima for airtightness and moisture control. The Pro Clima membranes work with the Airtight tapes, work with the adhesives, the primers, the gaskets. Systems continuity ensures durable systematic airtightness.

4. Poor and untested materials and assemblies used

The construction industry is in the habit of making disposable buildings - like the auto industry of the 1970s, components and materials too often lack basic durability, not even able to make it to trade-in. The car industry, at the insistence of Japanese know-how, figured out how to make durable cars. Today it's the Germans demonstrating that buildings too, can be made to last. Foams fail, gwb is a sacrificial material, adhesives can embrittle and fail, membranes are be affected by exposure to UV exposure or contaminants. Durability testing of 15 and 20 years is not good enough. Today we have our TESCON VANA tape which adhesion has been confirmed with 100-year testing. The materials we use should be built to last.

airtight foam leak
Foam leaks.

The materials should also be less toxic and more sustainable. (See Make Better Choices: Toward a Less Toxic World)

Would you use a drug or airbag that hasn't been tested for its specific use? Too often materials that may be airtight are used as components of airtight systems BUT MIGHT NOT ACTUALLY BE AIRTIGHT when used in assemblies. OSB is the great example of this. Drywall and spray foam are more examples - where the material itself may specified or tested as being airtight in ideal/lab conditions, but the assembly most assuredly is not or not in a lasting manner. (see 5 Reasons Airtight Drywall is Obsolete)

5. There's only one air barrier

We like fibrous insulations: cellulose, wood, mineral wool, sheepwool and fiberglass. (And again, while foam itself is airtight it is not an air barrier as connection failures, shrinkage, cracking are inevitable.) With fibrous insulation like your sweater on a cold windy day, we want to surround the insulation with airtightness. If we don't, the insulation's value can be substantially subjecting the insulation to convective loops and wind washing.

6. Assuming the air barrier should be a vapor BARRIER* too

Airtightness can be very confusing and vapor control can be even more confusing! A misplaced vapor barrier can dam moisture in the assembly and cause damages. Generally speaking the air barrier should NOT be a vapor barrier (note: *barrier≠retarder). Always think about how to build drying reserves of the assembly - make a safety buffer. An increasingly common way to do this is to use an air barrier that is also a smart vapor variable retarder. The best vapor variable retarder is INTELLO Plus. (See Why the Vapor Curve Matters)INTELLO Plus retards vapor diffusion and wetting of enclosure in the winter and promotes vapor diffusion and drying in the summer.

7. Air barrier placed at cold side of assembly

We see airtightness outboard of insulation in cold climates. It is bewildering. It's like seeing someone wearing their underwear on top of their pants! The primary air barrier must be inboard of the insulation layers to keep moist conditioned air away from cold components. (See An Interior Air Barrier Does It Better)This is common sense.

8.Poor windows & doors (& other penetration components) with poor installations

airtight window install
Fully integrate your windows and other penetration components into your airtight control layers.

Too often professionals forget that the windows and doors must be as airtight as the rest of the enclosure. Industry standards no longer suffice. Airtightness isn't only about moisture damage control, it's also about comfort, health, and efficiency.

And not only do the windows and doors themselves need to be airtight, all is lost if their installation is not completed in a fully integrated, insulated and airtight manner. Remember the CONTINUITY! See our window install blog post.

The continuity is not only critical at window and door penetrations but at all penetrations: ducts, pipes and wires. Too often some crappy caulk or Great Stuff foam is applied to attempt an air seal. They fail. ROFLEX and KAFLEX flexible gaskets, and flexible Pro Clima tapes provide robust penetration air sealing.

airtight service cavity
A service cavity reduces penetrations and make airtightness easy.

Finally, a service cavity is a great way to minimize the number of penetrations - dramatically reducing the number of potential failure points and protecting the air barrier for the life of the installation. If you can't provide a service cavity we have recommendations for that too.

9. No built-in flexibility for building movement

Buildings move - they settle, sway, deflect, material like wood expand and contract. As a result embrittled, stressed or overly tight connections deteriorate, separate, crack and fail. What might have been airtight on day one by year three is leaking like a sieve due to a lack of juncture flexibility. By building in room for movement in membrane connections, and using tapes that can stretch and move we make sure the airtightness lasts.

10. Blower door testing - too late or not at all

Builders are not doing blower door testing or not doing it as needed by the progress of their work. It's like trying to fix broken bones without taking an x-ray. If you're not doing blower door it's most likely that your continuity is

airtight test
Blower doors have been around for decades - don't wait any longer to start measuring your airtightness.

broken. Blower doors are a diagnostic tool that identifies leaks, allows for timely repairs to the air barrier. To repair the leaks, the air barrier must be accessible at the time of testing! Otherwise, the only thing the test result will tell you, is that you have failed and you no longer have a chance to fix your mistakes. Finally, it's not good enough to just depressurize or pressurize - you should do both. This is because components like windows or dampers or connections can be pushed closed or open depending on the direction of pressure applied - airtight enclosures need to work in both directions - because they will be exposed in real life to negative and positive pressure as well throughout the year.

The blower door testing protocol should be called out in the plans, details and specifications as required.

11. Insufficient training or experience

Airtightness is a team sport. Too often basic training is perfunctory or non-existent handicapping the effort from the start. Everyone on the team should have some basic competence in airtightness and that means training or building a few airtight buildings. The best training is our own Make it Tight training - a 4 hour exhaustive look at the science, materials and methods for complete airtightness. The next best is Passive House training: for professionals that's CPHD training for architects and engineers or Tradesperson training for contractors. And there is PHIUS training for CPHCs and Builders. For additional training resources, there is also Peel Passive House and EMU Systems.


This is not rocket science - you can do this! But it does require a comprehensive effort - of design, components, sequencing and execution. Avoid these 11 common failures and make enclosure airtightness a core competency of your project delivery.