Air sealing failure stories........

[BoilerMan]

Just wanted to share something I learned today so that someone else does not make the same mistake.

I was in the attic today to run some wire for a sodium flood light and I noticed frost on top of the insulation. It was in a straight line about 6" wide. When I built the house 4 years ago I used 1.5" foil-faced Dow Tuff-R attached to the bottom cord of the trusses with button cap nails. I was EXTREMLY meticulous about sealing up EVERY crack/seam with foil-faced tape. I wiped down all the seams with solvent before applying the tape...........and man did it stick!

Well this frost was only in a few places and I lifted up the 12" fiberglass insulation (Roxul next time!) and low and behold a seam in the tuff-R, slightly darkened insulation above the seam and frost............ Got out the spray foam and sealed up and cracks I could find by lifting up the fiberglass.

The leakage was fairly local to just a few 8' seams as indicated by the frost. Next house I build (my wife hates it when I say that) I will use either spray foam to seal seams or better yet do two layers of foam and stagger the seams 4'.

BOTTOM LINE: Don't rely on any type of tape as a long lasting seal for anything. No matter how well it seems to work at first in a few years/decades it will fall off and be rendered useless!

TS

 

[BrotherBart]

Eeek! I sealed my biggest attic air leak last Spring with, uh, tape.

 

[EatenByLimestone]

The moisture came from below?

 

[BoilerMan]

The moisture came from below?

Yes. Warm moist air drafted through the seam between the two sheets of foam, as it rose through the fiberglass it cooled, condenced, and froze once it got to the surface (attic side) where it was 15F. This is a common source of frost in an attic rotting things out. Even in a well vented attic, which mine is, the moisture condenses on the cold wood and freezes. Once things warm up, or the sun hits the roof surface, this frozen moisture turns to water and soaks into the wood, re-freezes, and more moisture takes it's place.............rinse and repeat. Leads to rotted attic lumber over time.

TS

 

[BoilerMan]

Eeek! I sealed my biggest attic air leak last Spring with, uh, tape.

I think spray foam is the best choice for most air sealing.

TS

 

[EatenByLimestone]

I've been using foam and caulk, but between foam sheets that have foam sprayed in the cracks, I've been using metal tape. I'm hoping it holds now.

 

[mole]

Just wanted to share something I learned today so that someone else does not make the same mistake.

I was in the attic today to run some wire for a sodium flood light and I noticed frost on top of the insulation. It was in a straight line about 6" wide. When I built the house 4 years ago I used 1.5" foil-faced Dow Tuff-R attached to the bottom cord of the trusses with button cap nails. I was EXTREMLY meticulous about sealing up EVERY crack/seam with foil-faced tape. I wiped down all the seams with solvent before applying the tape...........and man did it stick!

Well this frost was only in a few places and I lifted up the 12" fiberglass insulation (Roxul next time!) and low and behold a seam in the tuff-R, slightly darkened insulation above the seam and frost............ Got out the spray foam and sealed up and cracks I could find by lifting up the fiberglass.

The leakage was fairly local to just a few 8' seams as indicated by the frost. Next house I build (my wife hates it when I say that) I will use either spray foam to seal seams or better yet do two layers of foam and stagger the seams 4'.

BOTTOM LINE: Don't rely on any type of tape as a long lasting seal for anything. No matter how well it seems to work at first in a few years/decades it will fall off and be rendered useless!

TS

Thanks for sharing that, boilerman. I'm going to start my airsealing in March. I'm sure I would have ended up using some of that foil faced tape!

 

[BoilerMan]

Thanks for sharing that, boilerman. I'm going to start my airsealing in March. I'm sure I would have ended up using some of that foil faced tape!

FWIW, it was SureTape brand. I don't know but 3M or Venture brand may hold up better. It's just one of those things that is seems to work really well at first, but only time will tell.........like so many things in life.

TS

 

[EatenByLimestone]

When I was in HS I helped an AC company make ductwork. We used the metal tape to assemble pieces. We also used a piece of plastic like a credit card to press the pieces down. It might make a difference in adhesion. I'm not sure. When I was airsealing my 2nd floor I didn't do anything but press it down with my hands.

 

[Frozen Canuck]

Acoustical sealant is intended for sealing seams on poly VB. The stuff never dries. Tuck tape is handy for taping over ooze out so it doesn't get on everything. Right tool for the job issue.

 

[DickRussell]

Proper selection of the tape is important. A decent rundown on tape testing is found here: http://www.greenbuildingadvisor.com/blogs/dept/musings/air-sealing-tapes-and-gaskets

 

[BoilerMan]

Great read Dick! I'm always in a state of learning..........

TS

 

[semipro]

There seems to be quite a debate out there about the best way to create long lasting seals.
In Europe, gasket materials are commonly used where we tend to use expanding foam here.
Many who sprayed expanding foam are finding cracks and leaks later when things shift.
Tapes have obviously issues with long term adhesion and pressure sensitive adhesives don't stick well if adequate pressure is not applied. Pressure basically "activates" the adhesive.
A recent contributor to JLC tested the best seals for wires passing through wood (as is typical in top plates into attic space) and found that some caulks worked best.
I wonder how mastics applied over something like fiberglass tape hold up?
I've also wondered how to best seal the overlap of roofing felt when its used as an weather barrier on exterior walls under cedar. (the tannins in wood supposedly damage Tyvek).