Housing and Community Development

I am posting this mesage on behalf of Detailing for Durability presenter, Paul Fisette.

Hello everyone. Wow this is a lot of questions and they are uniformly excellent. I simply don't have the time to provide long thoughtful answers to these great questions. However, I did try to provide some guidance on each and every question. I hope this is useful. - Paul Fisette

Your questions and Paul's answers can now be found with his presentation in the HKC Resource Library:
http://network.aia.org/AIA/Resources/ViewDocument/?DocumentKey=7820c63b-3dff-4b76-9ca2-277f5a451479

The recording of the webinar will be available at the same URL in the coming weeks. Thank you to the 500+ attendees from yesterday's webinar.

-------------------------------------------
Stephen Schreiber FAIA
Director and Professor
University of Massachusetts Amherst, Department of Art, Architecture & Art History
Amherst MA
-------------------------------------------

Hello Stephen and Paul,
On behalf of the AIA HKC, CRAN and other AIA forums, Thank You for the excellent online-real-time Webinar Monday.  I enjoyed it, as I am sure, others did as well.  I am a long time fan of Paul Fisette's and have quoted previous vapor barrier studies he has done on my website, to act as learning aides for clients, contractors and other architects and engineers.  This is not a particularly sexy area of architecture, but one that is fraught with peril for those ignoring wise counsel.  I noted Paul's apparent interest in the Huber zip system and restate my concerns about the long-term adhesion of the glues in the tape: can an architect and homeowner really rely on the tape, the most critical point in the system, to remain adhered to the coated building panels forever?  How long will the adhesion last?  10 years?  20? Then what happens?  I fear that the widespread use of this product may be creating an future tsunami of potential failures, similar to the EIFS debacle, by use of a system with inherent weaknesses that at first seems to be a clever way to save a few hundred bucks, but then comes back in a decade or so with a huge due bill for repairs.  In other words, I am concerned that the tape will eventually give way, then any moisture under the surfaces of the walls and roof can then leak through those joints and into the houses that they are supposed to protect.  I would appreciate being made aware of any accelerated aging tests on this matter that proves my fears unjustified, if that is the case.  For me, I think I'll stick with good old 15# asphaltic felt, which is, as Paul says (and as he has on his own house), a smart vapor/water barrier that has a Perm rating that changes according to the humidity, miraculously becoming what we need it to be during each season.  I have always had excellent performance with "tar paper" over wall sheathing and based on Paul's excellent studies, I think I'll probably stick with that.  No concerns about tape falling loose.  Thanks again for your interesting program; I look forward to more!

-------------------------------------------
Rand Soellner AIA
Architect/Owner/Principal
Rand Soellner Architect
Cashiers NC
-------------------------------------------

-------------------------------------------
Philip Burdick AIA
Philip D. Burdick, Architect
Springfield MA
-------------------------------------------
I was unable to attend the webinar, is there a possibility it can be re-broadcasr?

Here is a good link for information on house wrap
http://inspectapedia.com/BestPractices/Sheathing_Wrap.htm
This article states that 15 lb. felt isn't what it used to be.  Look it over.

My 1909 house has a thin black asphaltic coated paper under the red cedar shingles.  The west facing exposure was replaced a little over 20 years ago with red cedar shingles over Tyvek.  So far no problems, although I can't vouch for performance as a air barrier.  The sheathing is (full) 3/4" T&G boards.  Insulation (full 4" studs) is blown in cellulose (mostly).  The north elevation still has the original red cedar shingles form 1909 still onver the original building paper and still in very good shape.  The south wall is looking to need new shingle siding.  The east and portions of the south wall is a mixture new construction (red cedar over Tyvek) and original shingle work in varying condition.

The roof (replaced about the same time as the western wall shingles) was stripped to the 7/8" x 6' +/- spaced decking (to allow the original wood shingles to breath from the underside) which was then infilled with 1x2 & 1x3 stock and roofed with asphalt shingles over 30lb felt.  Asphalt shingles are starting to show signs of wear but no leaks.

The hole in the system is at the eaves where only the large crown moulding separates the outside from the space behind the knee walls of the finished attic.  Plenty of ventilation there as well as occasional squirrels, raccoons, etc.  I've been considering backing that from the inside with a combination of rigid and spray foam in the manner of a "hot" roof as I have never seen any evidence of condensation on the inside of the exerior sheathing despite having steam heat and relying on oil based primer over the existing wood lath and plaster walls  to serve as the interior vapor barrier.  I used a conventional vapor barrier when renovation a bathroom and will do so on the exterior wall of the next bathroom that needs to be gutted, perhaps this summer.

I'b be interested in hearing other building wrap stories,  This far I would agree that felt still works.





Original Message:
Sent: 03-07-2012 07:53
From: Rand Soellner
Subject: Detailing for Durability: Your Questions Answered

Hello Stephen and Paul,
On behalf of the AIA HKC, CRAN and other AIA forums, Thank You for the excellent online-real-time Webinar Monday.  I enjoyed it, as I am sure, others did as well.  I am a long time fan of Paul Fisette's and have quoted previous vapor barrier studies he has done on my website, to act as learning aides for clients, contractors and other architects and engineers.  This is not a particularly sexy area of architecture, but one that is fraught with peril for those ignoring wise counsel.  I noted Paul's apparent interest in the Huber zip system and restate my concerns about the long-term adhesion of the glues in the tape: can an architect and homeowner really rely on the tape, the most critical point in the system, to remain adhered to the coated building panels forever?  How long will the adhesion last?  10 years?  20? Then what happens?  I fear that the widespread use of this product may be creating an future tsunami of potential failures, similar to the EIFS debacle, by use of a system with inherent weaknesses that at first seems to be a clever way to save a few hundred bucks, but then comes back in a decade or so with a huge due bill for repairs.  In other words, I am concerned that the tape will eventually give way, then any moisture under the surfaces of the walls and roof can then leak through those joints and into the houses that they are supposed to protect.  I would appreciate being made aware of any accelerated aging tests on this matter that proves my fears unjustified, if that is the case.  For me, I think I'll stick with good old 15# asphaltic felt, which is, as Paul says (and as he has on his own house), a smart vapor/water barrier that has a Perm rating that changes according to the humidity, miraculously becoming what we need it to be during each season.  I have always had excellent performance with "tar paper" over wall sheathing and based on Paul's excellent studies, I think I'll probably stick with that.  No concerns about tape falling loose.  Thanks again for your interesting program; I look forward to more!

-------------------------------------------
Rand Soellner AIA
Architect/Owner/Principal
Rand Soellner Architect
Cashiers NC
-------------------------------------------

Sometimes it is hard to separate out what is doing what in a wall, when some materials provide dual functions, and designers have options in how to approach the problem. There are three things we are trying to stop at the wall- moisture, from precipitation; vapor, the water that is in air, which varies by temperature and humidity; and air, AKA drafts. Vapor moving across the building envelope is driven by temperature differential, not wind. Air moving across the building envelope is driven by pressure differential  across the building envelope.

To compare housewrap with tape to tar paper/15# felt is to compare apples and oranges. Both provide a vapor permeable moisture barrier, but the reason the housewrap is taped is so it forms an air barrier. The tar paper is not forming an air barrier.

If you use 15# felt, then the air barrier is usually formed on the inner side of the wall , by the poly and the drywall. In an old house, the air barrier , imperfect, yes,  but still the air barrier is the plaster. The same durability argument might be made for the tape sealing the joints of the poly, however as it is on the inner face of the wall it is not subject to the temperature variations that the taped housewrap is on the outside of the wall.
My distrust of the tape's durability leads me to attempt to use the drywall as the air barrier, caulking junctions to other materials, using gaskets and using spray foam insulation to make the air barrier continuous across the floor joist cavity.

Both housewrap and 15# felt are vapor permeable , so do not form a vapor barrier. The poly acts as the vapor barrier, without poly in place  the vapor barrier is the paint on the wall or the vapour is not stopped , just slowed down.

It is common practice here to use two layers of the 15# felt because as was said, it ain't what it used to be. It is placed on the building lapped shingle style to get two layers, as opposed to a gift wrapped twice method. This two layer felt method is what I prefer. I like tyvek letter envelopes, though.

-------------------------------------------
Maura Gatensby Intl. Assoc. AIA
Maura Gatensby Architect
Vancouver BC
-------------------------------------------







Original Message:
Sent: 03-08-2012 12:14
From: Philip Burdick
Subject: Detailing for Durability: Your Questions Answered



-------------------------------------------
Philip Burdick AIA
Philip D. Burdick, Architect
Springfield MA
-------------------------------------------
I was unable to attend the webinar, is there a possibility it can be re-broadcasr?

Here is a good link for information on house wrap
http://inspectapedia.com/BestPractices/Sheathing_Wrap.htm
This article states that 15 lb. felt isn't what it used to be.  Look it over.

My 1909 house has a thin black asphaltic coated paper under the red cedar shingles.  The west facing exposure was replaced a little over 20 years ago with red cedar shingles over Tyvek.  So far no problems, although I can't vouch for performance as a air barrier.  The sheathing is (full) 3/4" T&G boards.  Insulation (full 4" studs) is blown in cellulose (mostly).  The north elevation still has the original red cedar shingles form 1909 still onver the original building paper and still in very good shape.  The south wall is looking to need new shingle siding.  The east and portions of the south wall is a mixture new construction (red cedar over Tyvek) and original shingle work in varying condition.

The roof (replaced about the same time as the western wall shingles) was stripped to the 7/8" x 6' +/- spaced decking (to allow the original wood shingles to breath from the underside) which was then infilled with 1x2 & 1x3 stock and roofed with asphalt shingles over 30lb felt.  Asphalt shingles are starting to show signs of wear but no leaks.

The hole in the system is at the eaves where only the large crown moulding separates the outside from the space behind the knee walls of the finished attic.  Plenty of ventilation there as well as occasional squirrels, raccoons, etc.  I've been considering backing that from the inside with a combination of rigid and spray foam in the manner of a "hot" roof as I have never seen any evidence of condensation on the inside of the exerior sheathing despite having steam heat and relying on oil based primer over the existing wood lath and plaster walls  to serve as the interior vapor barrier.  I used a conventional vapor barrier when renovation a bathroom and will do so on the exterior wall of the next bathroom that needs to be gutted, perhaps this summer.

I'b be interested in hearing other building wrap stories,  This far I would agree that felt still works.

Whoa!  Maura, please re-examine the issues surrounding polyethylene, especially locating it on the inside face of an exterior wall.  Paul Fisette's own research and Building Science Corporation has research that indicates that this is not a good thing to do.  I am sure that the type of climate in which you are located drives decisions like this, but in my experience in the mid to lower USA, is that typically what happens is that polyethylene acts as a TOTAL water and moisture barrier and that this is Not a good thing, especially in a wood stud wall (if that is what is being used for the purposes of discussion here).  What I have seen happening with this is that during the summer, damp hot air penetrates the exterior face of the wall, travels through it, then condenses on the polyethylene, because it is chilled by the interior's air-conditioning.  The result is trapped moisture that then breeds mold. I have had to fix buildings that have used something similar to this (that I did not design) when they used vinyl wall covering over the interior face of exterior walls, which is a big no-no, from a healthy building viewpoint.  Everything I have seen from healthy building specialists indicates that "Smart" vapor barriers (like 15# asphaltic felt are superior in every way to fixed materials with static characteristics like polyethylene.  Hey Paul, if you are monitoring this, please chime in.

-------------------------------------------
Rand Soellner AIA
Architect/Owner/Principal
Rand Soellner Architect
Cashiers NC
-------------------------------------------







Original Message:
Sent: 03-10-2012 04:05
From: Maura Gatensby
Subject: Detailing for Durability: Your Questions Answered

Sometimes it is hard to separate out what is doing what in a wall, when some materials provide dual functions, and designers have options in how to approach the problem. There are three things we are trying to stop at the wall- moisture, from precipitation; vapor, the water that is in air, which varies by temperature and humidity; and air, AKA drafts. Vapor moving across the building envelope is driven by temperature differential, not wind. Air moving across the building envelope is driven by pressure differential  across the building envelope.

To compare housewrap with tape to tar paper/15# felt is to compare apples and oranges. Both provide a vapor permeable moisture barrier, but the reason the housewrap is taped is so it forms an air barrier. The tar paper is not forming an air barrier.

If you use 15# felt, then the air barrier is usually formed on the inner side of the wall , by the poly and the drywall. In an old house, the air barrier , imperfect, yes,  but still the air barrier is the plaster. The same durability argument might be made for the tape sealing the joints of the poly, however as it is on the inner face of the wall it is not subject to the temperature variations that the taped housewrap is on the outside of the wall.
My distrust of the tape's durability leads me to attempt to use the drywall as the air barrier, caulking junctions to other materials, using gaskets and using spray foam insulation to make the air barrier continuous across the floor joist cavity.

Both housewrap and 15# felt are vapor permeable , so do not form a vapor barrier. The poly acts as the vapor barrier, without poly in place  the vapor barrier is the paint on the wall or the vapour is not stopped , just slowed down.

It is common practice here to use two layers of the 15# felt because as was said, it ain't what it used to be. It is placed on the building lapped shingle style to get two layers, as opposed to a gift wrapped twice method. This two layer felt method is what I prefer. I like tyvek letter envelopes, though.

-------------------------------------------
Maura Gatensby Intl. Assoc. AIA
Maura Gatensby Architect
Vancouver BC
-------------------------------------------







Original Message:
Sent: 03-08-2012 12:14
From: Philip Burdick
Subject: Detailing for Durability: Your Questions Answered



-------------------------------------------
Philip Burdick AIA
Philip D. Burdick, Architect
Springfield MA
-------------------------------------------
I was unable to attend the webinar, is there a possibility it can be re-broadcasr?

Here is a good link for information on house wrap
http://inspectapedia.com/BestPractices/Sheathing_Wrap.htm
This article states that 15 lb. felt isn't what it used to be.  Look it over.

My 1909 house has a thin black asphaltic coated paper under the red cedar shingles.  The west facing exposure was replaced a little over 20 years ago with red cedar shingles over Tyvek.  So far no problems, although I can't vouch for performance as a air barrier.  The sheathing is (full) 3/4" T&G boards.  Insulation (full 4" studs) is blown in cellulose (mostly).  The north elevation still has the original red cedar shingles form 1909 still onver the original building paper and still in very good shape.  The south wall is looking to need new shingle siding.  The east and portions of the south wall is a mixture new construction (red cedar over Tyvek) and original shingle work in varying condition.

The roof (replaced about the same time as the western wall shingles) was stripped to the 7/8" x 6' +/- spaced decking (to allow the original wood shingles to breath from the underside) which was then infilled with 1x2 & 1x3 stock and roofed with asphalt shingles over 30lb felt.  Asphalt shingles are starting to show signs of wear but no leaks.

The hole in the system is at the eaves where only the large crown moulding separates the outside from the space behind the knee walls of the finished attic.  Plenty of ventilation there as well as occasional squirrels, raccoons, etc.  I've been considering backing that from the inside with a combination of rigid and spray foam in the manner of a "hot" roof as I have never seen any evidence of condensation on the inside of the exerior sheathing despite having steam heat and relying on oil based primer over the existing wood lath and plaster walls  to serve as the interior vapor barrier.  I used a conventional vapor barrier when renovation a bathroom and will do so on the exterior wall of the next bathroom that needs to be gutted, perhaps this summer.

I'b be interested in hearing other building wrap stories,  This far I would agree that felt still works.

Thank you Rand , you are absolutely right, I appreciate you pointing out the critical element that I missed- any wall must be designed for the local climate, and the 'climate' we are creating within the building.  There is no one frame wall assembly that works throughout North America, and many many problems are caused by placing a wall design excellent for one place in another place where it is a disaster. My comments related to my local climate, cold winters, and summer such that we rarely install AC in homes. In a place with hot humid summers, poly on the inside , be it a layer of poly or applied vinyl wall coverings, is exactly one of those disasters, as you have noted. That would not be the case in the climate found here.

I will try my point again- each element in a wall design must be examined and it must be determined what its function is, and whenever we place in element in a wall, we must know how it will respond to what the conditions-either natural climate or conditioned interior space, it will be subject to.

-------------------------------------------
Maura Gatensby Intl. Assoc. AIA
Maura Gatensby Architect
Vancouver BC
-------------------------------------------







Original Message:
Sent: 03-12-2012 07:49
From: Rand Soellner
Subject: Detailing for Durability: Your Questions Answered

Whoa!  Maura, please re-examine the issues surrounding polyethylene, especially locating it on the inside face of an exterior wall.  Paul Fisette's own research and Building Science Corporation has research that indicates that this is not a good thing to do.  I am sure that the type of climate in which you are located drives decisions like this, but in my experience in the mid to lower USA, is that typically what happens is that polyethylene acts as a TOTAL water and moisture barrier and that this is Not a good thing, especially in a wood stud wall (if that is what is being used for the purposes of discussion here).  What I have seen happening with this is that during the summer, damp hot air penetrates the exterior face of the wall, travels through it, then condenses on the polyethylene, because it is chilled by the interior's air-conditioning.  The result is trapped moisture that then breeds mold. I have had to fix buildings that have used something similar to this (that I did not design) when they used vinyl wall covering over the interior face of exterior walls, which is a big no-no, from a healthy building viewpoint.  Everything I have seen from healthy building specialists indicates that "Smart" vapor barriers (like 15# asphaltic felt are superior in every way to fixed materials with static characteristics like polyethylene.  Hey Paul, if you are monitoring this, please chime in.

-------------------------------------------
Rand Soellner AIA
Architect/Owner/Principal
Rand Soellner Architect
Cashiers NC
-------------------------------------------







Original Message:
Sent: 03-10-2012 04:05
From: Maura Gatensby
Subject: Detailing for Durability: Your Questions Answered

Sometimes it is hard to separate out what is doing what in a wall, when some materials provide dual functions, and designers have options in how to approach the problem. There are three things we are trying to stop at the wall- moisture, from precipitation; vapor, the water that is in air, which varies by temperature and humidity; and air, AKA drafts. Vapor moving across the building envelope is driven by temperature differential, not wind. Air moving across the building envelope is driven by pressure differential  across the building envelope.

To compare housewrap with tape to tar paper/15# felt is to compare apples and oranges. Both provide a vapor permeable moisture barrier, but the reason the housewrap is taped is so it forms an air barrier. The tar paper is not forming an air barrier.

If you use 15# felt, then the air barrier is usually formed on the inner side of the wall , by the poly and the drywall. In an old house, the air barrier , imperfect, yes,  but still the air barrier is the plaster. The same durability argument might be made for the tape sealing the joints of the poly, however as it is on the inner face of the wall it is not subject to the temperature variations that the taped housewrap is on the outside of the wall.
My distrust of the tape's durability leads me to attempt to use the drywall as the air barrier, caulking junctions to other materials, using gaskets and using spray foam insulation to make the air barrier continuous across the floor joist cavity.

Both housewrap and 15# felt are vapor permeable , so do not form a vapor barrier. The poly acts as the vapor barrier, without poly in place  the vapor barrier is the paint on the wall or the vapour is not stopped , just slowed down.

It is common practice here to use two layers of the 15# felt because as was said, it ain't what it used to be. It is placed on the building lapped shingle style to get two layers, as opposed to a gift wrapped twice method. This two layer felt method is what I prefer. I like tyvek letter envelopes, though.

-------------------------------------------
Maura Gatensby Intl. Assoc. AIA
Maura Gatensby Architect
Vancouver BC
-------------------------------------------

-------------------------------------------
Daniel Ocasio AIA
Architect Project Manager
Urban Access, Inc.
Boston MA
-------------------------------------------
I worked with a design build firm for several years building some fairly large houses in Massachusetts. We went back to using 15# felt underlayment behind the shingles or clapboards because it is water resistant. The  firm did both additions and new construction and whenever a wall was taken apart where the Tyvek was used, the studs and wood sheathing were found to be wet and rotting. Not true whenever an older, sometimes hundred year old building, was opened up and the side wall was exposed to add a new addition. I continue to design houses and additions using the 15# felt underlayment, Batt insulation, and poly as the vapor barrier on the inside face of wall with drywall finish. When we use foam insulation (3 x the cost of Batt insulation) we do not use a vapor barrier.







Original Message:
Sent: 03-13-2012 03:46
From: Maura Gatensby
Subject: Detailing for Durability: Your Questions Answered

Thank you Rand , you are absolutely right, I appreciate you pointing out the critical element that I missed- any wall must be designed for the local climate, and the 'climate' we are creating within the building.  There is no one frame wall assembly that works throughout North America, and many many problems are caused by placing a wall design excellent for one place in another place where it is a disaster. My comments related to my local climate, cold winters, and summer such that we rarely install AC in homes. In a place with hot humid summers, poly on the inside , be it a layer of poly or applied vinyl wall coverings, is exactly one of those disasters, as you have noted. That would not be the case in the climate found here.

I will try my point again- each element in a wall design must be examined and it must be determined what its function is, and whenever we place in element in a wall, we must know how it will respond to what the conditions-either natural climate or conditioned interior space, it will be subject to.

-------------------------------------------
Maura Gatensby Intl. Assoc. AIA
Maura Gatensby Architect
Vancouver BC
-------------------------------------------







Original Message:
Sent: 03-12-2012 07:49
From: Rand Soellner
Subject: Detailing for Durability: Your Questions Answered

Whoa!  Maura, please re-examine the issues surrounding polyethylene, especially locating it on the inside face of an exterior wall.  Paul Fisette's own research and Building Science Corporation has research that indicates that this is not a good thing to do.  I am sure that the type of climate in which you are located drives decisions like this, but in my experience in the mid to lower USA, is that typically what happens is that polyethylene acts as a TOTAL water and moisture barrier and that this is Not a good thing, especially in a wood stud wall (if that is what is being used for the purposes of discussion here).  What I have seen happening with this is that during the summer, damp hot air penetrates the exterior face of the wall, travels through it, then condenses on the polyethylene, because it is chilled by the interior's air-conditioning.  The result is trapped moisture that then breeds mold. I have had to fix buildings that have used something similar to this (that I did not design) when they used vinyl wall covering over the interior face of exterior walls, which is a big no-no, from a healthy building viewpoint.  Everything I have seen from healthy building specialists indicates that "Smart" vapor barriers (like 15# asphaltic felt are superior in every way to fixed materials with static characteristics like polyethylene.  Hey Paul, if you are monitoring this, please chime in.

-------------------------------------------
Rand Soellner AIA
Architect/Owner/Principal
Rand Soellner Architect
Cashiers NC
-------------------------------------------







Original Message:
Sent: 03-10-2012 04:05
From: Maura Gatensby
Subject: Detailing for Durability: Your Questions Answered

Sometimes it is hard to separate out what is doing what in a wall, when some materials provide dual functions, and designers have options in how to approach the problem. There are three things we are trying to stop at the wall- moisture, from precipitation; vapor, the water that is in air, which varies by temperature and humidity; and air, AKA drafts. Vapor moving across the building envelope is driven by temperature differential, not wind. Air moving across the building envelope is driven by pressure differential  across the building envelope.

To compare housewrap with tape to tar paper/15# felt is to compare apples and oranges. Both provide a vapor permeable moisture barrier, but the reason the housewrap is taped is so it forms an air barrier. The tar paper is not forming an air barrier.

If you use 15# felt, then the air barrier is usually formed on the inner side of the wall , by the poly and the drywall. In an old house, the air barrier , imperfect, yes,  but still the air barrier is the plaster. The same durability argument might be made for the tape sealing the joints of the poly, however as it is on the inner face of the wall it is not subject to the temperature variations that the taped housewrap is on the outside of the wall.
My distrust of the tape's durability leads me to attempt to use the drywall as the air barrier, caulking junctions to other materials, using gaskets and using spray foam insulation to make the air barrier continuous across the floor joist cavity.

Both housewrap and 15# felt are vapor permeable , so do not form a vapor barrier. The poly acts as the vapor barrier, without poly in place  the vapor barrier is the paint on the wall or the vapour is not stopped , just slowed down.

It is common practice here to use two layers of the 15# felt because as was said, it ain't what it used to be. It is placed on the building lapped shingle style to get two layers, as opposed to a gift wrapped twice method. This two layer felt method is what I prefer. I like tyvek letter envelopes, though.

-------------------------------------------
Maura Gatensby Intl. Assoc. AIA
Maura Gatensby Architect
Vancouver BC
-------------------------------------------

Daniel, your finding parallel Paul Fisette's research and the University of Massachusetts at Amherst.  Paul has said that the problem with housewraps like Tyvek is that water vapor can pass through them, but then when than vapor condenses on sheathing (after passing through the housewrap) that the now actual water state of the moisture cannot pass back through the housewrap, resulting in the conditions that you have found.  Fisette's and the U of M research has found that 15# asphaltic felt has a perm rating that changes with relative humidity.  The asphaltic felt was found to be a Smart vapor barrier that blocks vapor from coming in during hot humid exterior conditions, but lets vapor pass through (when driven from the interior toward the exterior) in cooler months, to avoid moisture being trapped within the wall.  And Fisette's research, along with the U of M found that batt insulation manufacturer's integral kraft paper backing was another Smart vapor barrier, operating most effectively on the interior side of the wall to handle conditions there.  What is interesting about this is that this is a fairly typical wall section for frame building construction throughout the USA for much of the last hundred years.  Insulation manufacturers must have been aware of this, hence its widespread and effective use.  Beware of using plastic vapor barriers, which has been frowned upon in the central to lower USA due to its total blockage of vapor movement, allowing condensation and mold growth inside the wall section.  And my research agrees with yours, Daniel, in regards to using foam, particularly closed cell: it acts a vapor barrier in and of itself (e.g.: polyurethane) and needs no additional vapor barrier. 

Regarding Maura's issue about establishing an infiltration barrier, I actually have a different method: I have the insulation crew spend one day with 3 laborers using expanding foam canisters seal all the cracks from the inside face of the framing, also using fireproof expanding sealant between framing holes between floor/ceiling levels (which is required by code anyway).  Air does not come through solid materials like OSB.  Unwanted air intrusion comes through cracks in the construction, where these materials join together.  So, if we seal these cracks, the infiltration should be reduced substantially.  Also, specifying and using plastic air sealed containment cases behind any electrical outlets and switches helps avoid infiltration at these locations.  This is a little different approach to using polyethylene sheets, but proves even more effective, in my opinion, because you are stopping the outside air before it can get into your walls.

I keep seeing Mike Holmes using poly up in Canada on the inside face of exterior walls as a vapor barrier and I squirm each time I see that going up.  Has any architect in Canada actually looked into 20+ year old walls with poly to see if there is any mold growth?  What have you found?  I'd really like to know...

-------------------------------------------
Rand Soellner AIA
Architect/Owner/Principal
Rand Soellner Architect
Cashiers NC
-------------------------------------------







Original Message:
Sent: 03-15-2012 17:34
From: Daniel Ocasio
Subject: Detailing for Durability: Your Questions Answered



-------------------------------------------
Daniel Ocasio AIA
Architect Project Manager
Urban Access, Inc.
Boston MA
-------------------------------------------
I worked with a design build firm for several years building some fairly large houses in Massachusetts. We went back to using 15# felt underlayment behind the shingles or clapboards because it is water resistant. The  firm did both additions and new construction and whenever a wall was taken apart where the Tyvek was used, the studs and wood sheathing were found to be wet and rotting. Not true whenever an older, sometimes hundred year old building, was opened up and the side wall was exposed to add a new addition. I continue to design houses and additions using the 15# felt underlayment, Batt insulation, and poly as the vapor barrier on the inside face of wall with drywall finish. When we use foam insulation (3 x the cost of Batt insulation) we do not use a vapor barrier.







Original Message:
Sent: 03-13-2012 03:46
From: Maura Gatensby
Subject: Detailing for Durability: Your Questions Answered

Thank you Rand , you are absolutely right, I appreciate you pointing out the critical element that I missed- any wall must be designed for the local climate, and the 'climate' we are creating within the building.  There is no one frame wall assembly that works throughout North America, and many many problems are caused by placing a wall design excellent for one place in another place where it is a disaster. My comments related to my local climate, cold winters, and summer such that we rarely install AC in homes. In a place with hot humid summers, poly on the inside , be it a layer of poly or applied vinyl wall coverings, is exactly one of those disasters, as you have noted. That would not be the case in the climate found here.

I will try my point again- each element in a wall design must be examined and it must be determined what its function is, and whenever we place in element in a wall, we must know how it will respond to what the conditions-either natural climate or conditioned interior space, it will be subject to.

-------------------------------------------
Maura Gatensby Intl. Assoc. AIA
Maura Gatensby Architect
Vancouver BC
-------------------------------------------







Original Message:
Sent: 03-12-2012 07:49
From: Rand Soellner
Subject: Detailing for Durability: Your Questions Answered

Whoa!  Maura, please re-examine the issues surrounding polyethylene, especially locating it on the inside face of an exterior wall.  Paul Fisette's own research and Building Science Corporation has research that indicates that this is not a good thing to do.  I am sure that the type of climate in which you are located drives decisions like this, but in my experience in the mid to lower USA, is that typically what happens is that polyethylene acts as a TOTAL water and moisture barrier and that this is Not a good thing, especially in a wood stud wall (if that is what is being used for the purposes of discussion here).  What I have seen happening with this is that during the summer, damp hot air penetrates the exterior face of the wall, travels through it, then condenses on the polyethylene, because it is chilled by the interior's air-conditioning.  The result is trapped moisture that then breeds mold. I have had to fix buildings that have used something similar to this (that I did not design) when they used vinyl wall covering over the interior face of exterior walls, which is a big no-no, from a healthy building viewpoint.  Everything I have seen from healthy building specialists indicates that "Smart" vapor barriers (like 15# asphaltic felt are superior in every way to fixed materials with static characteristics like polyethylene.  Hey Paul, if you are monitoring this, please chime in.

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Rand Soellner AIA
Architect/Owner/Principal
Rand Soellner Architect
Cashiers NC
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This is a regional climatic subject, especially as it concerns the poly barrier behind the sheetrock. I work in the hot and humid South, where such an application would have terrible results. After our major hurricane in 1989, Hurricane Hugo, several contractors "breezed" into town to do repair work. Some of these folks evidently came from cool climates, because some houses were repaired (and some even newly constructed) using the poly barrier immediately behind the sheetrock. I have personally witnessed the effect of this application on two properties that I was asked to inspect 20 and 25 years after the application. The result was that moisture was trapped in the wall cavity, mold growth was evident, and worse - the studs had rotted compromising the structure.

In warm, humid climates the system we use is pre-primed wood or cementitious siding, a drainage plane separator (treated furring strips or a cedar breather type product), 30# felt, CDX plywood sheathing (treated bottom course). The insulation is either batt, spray in, or foam. Positive pressure from the HVAC is required.

I can see the opposite being applicable in cooler climates.

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William Huey
Bill Huey + Associates
Charleston SC
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Original Message:
Sent: 03-15-2012 17:34
From: Daniel Ocasio
Subject: Detailing for Durability: Your Questions Answered



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Daniel Ocasio AIA
Architect Project Manager
Urban Access, Inc.
Boston MA
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I worked with a design build firm for several years building some fairly large houses in Massachusetts. We went back to using 15# felt underlayment behind the shingles or clapboards because it is water resistant. The  firm did both additions and new construction and whenever a wall was taken apart where the Tyvek was used, the studs and wood sheathing were found to be wet and rotting. Not true whenever an older, sometimes hundred year old building, was opened up and the side wall was exposed to add a new addition. I continue to design houses and additions using the 15# felt underlayment, Batt insulation, and poly as the vapor barrier on the inside face of wall with drywall finish. When we use foam insulation (3 x the cost of Batt insulation) we do not use a vapor barrier.







Original Message:
Sent: 03-13-2012 03:46
From: Maura Gatensby
Subject: Detailing for Durability: Your Questions Answered

Thank you Rand , you are absolutely right, I appreciate you pointing out the critical element that I missed- any wall must be designed for the local climate, and the 'climate' we are creating within the building.  There is no one frame wall assembly that works throughout North America, and many many problems are caused by placing a wall design excellent for one place in another place where it is a disaster. My comments related to my local climate, cold winters, and summer such that we rarely install AC in homes. In a place with hot humid summers, poly on the inside , be it a layer of poly or applied vinyl wall coverings, is exactly one of those disasters, as you have noted. That would not be the case in the climate found here.

I will try my point again- each element in a wall design must be examined and it must be determined what its function is, and whenever we place in element in a wall, we must know how it will respond to what the conditions-either natural climate or conditioned interior space, it will be subject to.

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Maura Gatensby Intl. Assoc. AIA
Maura Gatensby Architect
Vancouver BC
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Original Message:
Sent: 03-12-2012 07:49
From: Rand Soellner
Subject: Detailing for Durability: Your Questions Answered

Whoa!  Maura, please re-examine the issues surrounding polyethylene, especially locating it on the inside face of an exterior wall.  Paul Fisette's own research and Building Science Corporation has research that indicates that this is not a good thing to do.  I am sure that the type of climate in which you are located drives decisions like this, but in my experience in the mid to lower USA, is that typically what happens is that polyethylene acts as a TOTAL water and moisture barrier and that this is Not a good thing, especially in a wood stud wall (if that is what is being used for the purposes of discussion here).  What I have seen happening with this is that during the summer, damp hot air penetrates the exterior face of the wall, travels through it, then condenses on the polyethylene, because it is chilled by the interior's air-conditioning.  The result is trapped moisture that then breeds mold. I have had to fix buildings that have used something similar to this (that I did not design) when they used vinyl wall covering over the interior face of exterior walls, which is a big no-no, from a healthy building viewpoint.  Everything I have seen from healthy building specialists indicates that "Smart" vapor barriers (like 15# asphaltic felt are superior in every way to fixed materials with static characteristics like polyethylene.  Hey Paul, if you are monitoring this, please chime in.

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Rand Soellner AIA
Architect/Owner/Principal
Rand Soellner Architect
Cashiers NC
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Maura, I know Vancouver and south Louisiana are very different, but your statement "There are three things we are trying to stop at the wall- moisture, from precipitation; vapor, the water that is in air, which varies by temperature and humidity; and air, AKA drafts." do not apply here.  And you can add heat gain and loss to that formula.  I have seen many problems with putting a vapor barrier in the wall configuration.  Here, if the wall can dry to both the interior and exterior the better off it is.  The warm side switches with the seasons, and this just confuses the vapor barrier.
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Edward Cazayoux FAIA
Principal/architect
EnvironMental Design
Breaux Bridge LA
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Original Message:
Sent: 03-12-2012 07:49
From: Rand Soellner
Subject: Detailing for Durability: Your Questions Answered

Whoa!  Maura, please re-examine the issues surrounding polyethylene, especially locating it on the inside face of an exterior wall.  Paul Fisette's own research and Building Science Corporation has research that indicates that this is not a good thing to do.  I am sure that the type of climate in which you are located drives decisions like this, but in my experience in the mid to lower USA, is that typically what happens is that polyethylene acts as a TOTAL water and moisture barrier and that this is Not a good thing, especially in a wood stud wall (if that is what is being used for the purposes of discussion here).  What I have seen happening with this is that during the summer, damp hot air penetrates the exterior face of the wall, travels through it, then condenses on the polyethylene, because it is chilled by the interior's air-conditioning.  The result is trapped moisture that then breeds mold. I have had to fix buildings that have used something similar to this (that I did not design) when they used vinyl wall covering over the interior face of exterior walls, which is a big no-no, from a healthy building viewpoint.  Everything I have seen from healthy building specialists indicates that "Smart" vapor barriers (like 15# asphaltic felt are superior in every way to fixed materials with static characteristics like polyethylene.  Hey Paul, if you are monitoring this, please chime in.

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Rand Soellner AIA
Architect/Owner/Principal
Rand Soellner Architect
Cashiers NC
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Original Message:
Sent: 03-10-2012 04:05
From: Maura Gatensby
Subject: Detailing for Durability: Your Questions Answered

Sometimes it is hard to separate out what is doing what in a wall, when some materials provide dual functions, and designers have options in how to approach the problem. There are three things we are trying to stop at the wall- moisture, from precipitation; vapor, the water that is in air, which varies by temperature and humidity; and air, AKA drafts. Vapor moving across the building envelope is driven by temperature differential, not wind. Air moving across the building envelope is driven by pressure differential  across the building envelope.

To compare housewrap with tape to tar paper/15# felt is to compare apples and oranges. Both provide a vapor permeable moisture barrier, but the reason the housewrap is taped is so it forms an air barrier. The tar paper is not forming an air barrier.

If you use 15# felt, then the air barrier is usually formed on the inner side of the wall , by the poly and the drywall. In an old house, the air barrier , imperfect, yes,  but still the air barrier is the plaster. The same durability argument might be made for the tape sealing the joints of the poly, however as it is on the inner face of the wall it is not subject to the temperature variations that the taped housewrap is on the outside of the wall.
My distrust of the tape's durability leads me to attempt to use the drywall as the air barrier, caulking junctions to other materials, using gaskets and using spray foam insulation to make the air barrier continuous across the floor joist cavity.

Both housewrap and 15# felt are vapor permeable , so do not form a vapor barrier. The poly acts as the vapor barrier, without poly in place  the vapor barrier is the paint on the wall or the vapour is not stopped , just slowed down.

It is common practice here to use two layers of the 15# felt because as was said, it ain't what it used to be. It is placed on the building lapped shingle style to get two layers, as opposed to a gift wrapped twice method. This two layer felt method is what I prefer. I like tyvek letter envelopes, though.

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Maura Gatensby Intl. Assoc. AIA
Maura Gatensby Architect
Vancouver BC
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Philip,

Yes. The recording will be posted to YouTube and embedded on the library entry page in the next few weeks. Please bookmark the page:

http://network.aia.org/AIA/Resources/ViewDocument/?DocumentKey=7820c63b-3dff-4b76-9ca2-277f5a451479  

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Kathleen Simpson
Manager, Knowledge Communities
The American Institute of Architects
Washington DC
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Original Message:
Sent: 03-08-2012 12:14
From: Philip Burdick
Subject: Detailing for Durability: Your Questions Answered



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Philip Burdick AIA
Philip D. Burdick, Architect
Springfield MA
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I was unable to attend the webinar, is there a possibility it can be re-broadcasr?

Here is a good link for information on house wrap
http://inspectapedia.com/BestPractices/Sheathing_Wrap.htm
This article states that 15 lb. felt isn't what it used to be.  Look it over.

My 1909 house has a thin black asphaltic coated paper under the red cedar shingles.  The west facing exposure was replaced a little over 20 years ago with red cedar shingles over Tyvek.  So far no problems, although I can't vouch for performance as a air barrier.  The sheathing is (full) 3/4" T&G boards.  Insulation (full 4" studs) is blown in cellulose (mostly).  The north elevation still has the original red cedar shingles form 1909 still onver the original building paper and still in very good shape.  The south wall is looking to need new shingle siding.  The east and portions of the south wall is a mixture new construction (red cedar over Tyvek) and original shingle work in varying condition.

The roof (replaced about the same time as the western wall shingles) was stripped to the 7/8" x 6' +/- spaced decking (to allow the original wood shingles to breath from the underside) which was then infilled with 1x2 & 1x3 stock and roofed with asphalt shingles over 30lb felt.  Asphalt shingles are starting to show signs of wear but no leaks.

The hole in the system is at the eaves where only the large crown moulding separates the outside from the space behind the knee walls of the finished attic.  Plenty of ventilation there as well as occasional squirrels, raccoons, etc.  I've been considering backing that from the inside with a combination of rigid and spray foam in the manner of a "hot" roof as I have never seen any evidence of condensation on the inside of the exerior sheathing despite having steam heat and relying on oil based primer over the existing wood lath and plaster walls  to serve as the interior vapor barrier.  I used a conventional vapor barrier when renovation a bathroom and will do so on the exterior wall of the next bathroom that needs to be gutted, perhaps this summer.

I'b be interested in hearing other building wrap stories,  This far I would agree that felt still works.