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There has been a long standing debate about home construction and how to build good, sound, safe, healthy homes.  Over the last half century, homes have become increasingly air tight as mandated by changes to building codes.  This has caused a number of issues in building envelope performance and has stoked the ongoing debate.

Long standing, experienced home builders advocate a home that naturally breathes as being healthier.  Allowing a home to naturally breathe allows any moisture that accumulates inside the walls or attic space to naturally exit as it evaporates over time back into the air column around it and is then carried out through soffets, transitions or simply through a semi permeable wall assembly.

With increasing energy costs and consumer awareness of energy efficiency, homeowners are calling for more efficient homes and builders and code officials have responded with tighter envelopes.  In an increasingly energy conscious world, it makes no sense to simply allow a building to leak air naturally when we have to spend an ever increasing amount of money to heat and cool our homes.  Since we have the technology to make homes more efficient, we should.  Any concerns about moisture accumulation can be handled by mechanical equipment and maintaining humidity in an acceptable range.

With the increasing tightness of code required buildings, there have been situations where trapped moisture in wall cavities, unable to exit to the exterior of the wall has collected and resulted in rot, mildew, mold, or structural damage and in extreme cases caused health related concerns and significant financial hardship.

The core of the issue though is moisture accumulation.  Moisture does cause damage and needs to be addressed.  99% of modern newly built homes continue to use a fibrous material to thermally insulate them.  This is the core of the problem.  Because fiberglass, Roxol, cellulose or any other fiber based product is permeable to moisture laden air, and because a vapor barrier is only placed on one side of the wall or the other (In Canada, this is on the warm, indoor side of the wall), moisture does enter wall cavities, where it does come into contact with condensing surfaces and can accumulate to cause damage in tightly sealed homes.

While tight homes are energy efficient, they risk becoming health risks, while freely breathing homes have healthy indoor air quality because of the natural air exchanges that take place each day, they are costly to heat and uncomfortable to live in.  What is the answer?

Fibrous insulation IS at the core of the problem and the reason moisture enters wall cavities.  What if the insulation used in homes was impermeable to air & moisture – it would not matter where the vapor pressure was coming from, moisture could not enter the wall cavity.  What if the insulation was also able to perfectly seal the wall cavity so that no air could move around it either?  Such a wall assembly would by design be vastly more resilient to moisture damage and its resultant health concerns.

Spray foam insulation is the solution.  Spray foam insulation has a higher R Value than any other insulation product on the market.  Spray foam insulation is a recognized air barrier and vapor barrier, meaning it is impervious to moisture and prevents the damage water can cause.  Spray foam insulation is custom fit to the walls of your home because as it expands it wraps itself around every element in your walls and seals them entirely.  Unlike fibrous products which will settle or sag over time, spray foam will never move, never deform – it is elastic enough to allow for settling of new homes and moves with the framing members.

With spray foam insulation, the modern mantra “Build it tight, ventilate it right.” results in not only energy efficient homes, but healthy indoor living environments and durable buildings by preventing moisture and its resultant damage from entry.

Tags : air quality, building envelope, Environment, moisture, spray foam insulation
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An Air Barrier systems should:

Air Barrier

- eliminate air movement through the building envelope

- be continuous over the entire building enclosure

- be robust enough to withstand its environment and forces applied

- be durable

Air barrier systems are created in numerous ways:

- exterior air barrier membranes – blueskin used on commercial applications

The advantage to the blueskin membrane is that it self adheres, does not release and is continuous when properly installed.  Its disadvantages include its cost.  It is therefore generally used only in Commercial applications.   Being installed on the exterior of the wall, it does nothing to prevent differential pressure from moving moisture laden air into the wall from the interior of the building.

- Exterior applied rigid foam panels

Exterior rigid foam panels form a continuous insulating layer which when newly and properly installed form an air barrier system that is impenetrable to the effects of wind pressure and resultant heat loss.  The main disadvantage is that the system relies on the resilience of adhesives and sealant caulking which yield over time allowing air movement around the panels.  Rigid Foam Panels do not prevent moisture laden interior air from moving into the wall cavity.

- interior air barrier membranes – 6 mil polyethylene

The main advantage to 6 mil polyethylene sheet is that it is widely accepted and inexpensive.  It also prevents moisture laden air from entering the wall cavity through the interior side of the wall assembly.  The disadvantages is that it is dependant on adhesives and sealants which fail in time and it is subject to penetrations at time of construction and by occupants who hang paintings, or make changes to their interiors.  Because it is applied to the warm side fo the wall assembly in Canada, it does nothing to prevent wind pressure or vapor pressure from moving moisture laden air into the wall cavity from the exterior side of the wall.  Ove rthe life of a building, it performs as a poor air barrier.

- interior air barrier through gypsum board

Gypsum board as an air barrier is a difficult assembly to create because it requires a level of attention to detail that most contractors and tradesmen fail to provide.  Top and bottom plates, rim joists and sub floor, ceiling board, sill plates must all be caulked, glued, taped, or sealed with gaskets prior to installation.  This is an air barrier system which will only perform with extreme attention to detailing as it is installed and therefore generally fails to meet its performance criteria even when just installed.   In time, these sealants release causing drywall to perform as a poor air barrier.

- cavity filled spray foam insulation air barrier

Spray Foam insulation is an effective air barrier system, surpassing the National Building Code of Canada’s specification (the most stringent in the world) with an air permeance of less than 0.02 l/(s-m2) @ 75 Pa.  Acting as an air barrier, vapor barrier and insulation layer in a single application, drying is not a factor as the materials itself is impermeable to moisture.  The main advantage to spray foam is that it is ‘custom fit’ – adhering to and formed specifically for the space into which it is applied.  It requires no detailing or other special care, it never settles, sags, or degrades in performance.

Unlike other air barriers which are designed to protect a fibrous insulating material, insulating foam is not subject to moisture ingress from either the warm or cold side of the wall and thus moisture accumulation and damage is not an issue.  This is a very significant benefit to using foam.  Spray foams main disadvantage is its perceived cost.  While up front it is more expensive, the long term impact on ownership costs result in savings to homeowners who choose spray foam insulation.

Air Barriers are key to the building Envelope, see our next article….. moisture control and the building envelope.

Tags : building envelope, energy efficient, Environment, moisture, spray foam insulation
Posted in : building envelope | 39 Comments »

Your Building Envelope

The Building Envelope: your first

line of defence

The first article in this series identified the importance of a tight building envelope in creating green homes.  Structural Insulated Panels and Insulated Concrete forms create an excellent air tight wall Assembly and building envelope because they do no breathe, have a high resistance to heat loss and create healthy indoor living environments by controlling the flow of moisture and eliminating condensing surfaces on the internal wall surfaces.  However 99% of all homes are built with conventional 2×6 framing.  This article looks at the design of conventional building envelope, the advantages of sealing homes with spray foam insulation and the importance of effective air barrier and vapor barrier control layers.

The building envelope is made up of the roof, above grade walls, below grade walls, and the basement floor.  These building envelope components should be thought of as systems for each is made of an assembly of individual products, working together.  These products include exterior cladding, control layers (moisture barrier, air barrier, thermal barrier) and the structural members (framing).  Each of these components plays an integral role in how a building envelope and the house it encloses performs – the failure of any of them can result in the failure of the building envelope.

Are conventionally built homes satisfactory?  Modern homes are code required to be built with 2×6 structural framing, a minimum of R-20 insulation (thermal barrier) and a layer of 6 mil polyethylene sheet (vapor barrier & air barrier).  There are additional layers to the wall assembly including gypsum wall board, and paint on the interior and OSB, house wrap and cladding on the exterior.

Traditional Building Envelope design: Deficient

The problem with the above building envelope is this:  The entire system relies on the 6 mil polyethylene membrane to stop air movement, vapor movement and to permit the fiberglass batt to perform as designed!  In Canada, the polyethylene layer goes on the warm side of the wall because we are in a climate which predominantly requires heating meaning it is subject to dozens of penetrations at the time of installation (electrical outlets, light switches, window frames and doors, recessed lighting enclosures, seams – top, bottom and where the layer must be installed around framing members.)  This says nothing of the penetrations added with decorative wall hangings, nail holes and modifications done after the fact.  Unless these seams and penetrations are sealed in such a way as they never release, plenty of opportunity for air movement and with it moisture movement is created.  Worse, because fiberglass batt insulation allows air and moisture to move through it, penetrations and deficiencies in the 6 mil poly layer allow for air pressure differences across the wall assembly to degrade the performance of the insulating layer over time resulting in effective R-Values of half (or less) the advertised value.

Spray Foam Insulation creates a lasting high performance building envelope.

If this same building envelope were insulated and sealed with a  single application of spray foam insulation, the result would be significantly different.  Because spray foam is manufactured on site, it conforms to every minute variance, nook and cranny in the building envelope.  It is a perfect, custom made fit.  Made up of billions of tiny, microscopic bubbles, it will never settle, sag, or move, it absolutely and completely seals a wall without any penetrations.  It conforms to electrical boxes, outlets, and recessed light cans, wrapping itself around and behind them to completely enclose them.  It is inches thick and not subject to any of the potential problems of a layer only 6 mil thick.  Spray Foam is not dependant on caulking, glue or sealants to act as an air barrier or vapor barrier and results in a building envelope that is air tight, impenetrable to moisture, and has a stable R-Value much higher than fiberglass.  At an R value of 6 per inch, there is potentially R-33 available in a 2×6 cavity wall if super insulating is required.

Conclusion:

A robust building envelope is designed to endure and separate two different environments.  The modern, conventional building envelope does not do this adequately because it is constructed using an air barrier and vapor barrier subject to degradation over time.  The system created to accomplish this is too heavily dependant on a single layer of thin plastic (6 mil polyethylene), and any penetrations or deficiencies in its installation, or subsequent use degrades building envelope performance allowing moisture into the building envelope and heat loss from it resulting in higher expense and shorter useful life span.  Spray Foam, though more costly at time of installation addresses this in a single, simple application and is required in new homes by informed homeowners.

Our next article will look at the importance, function, design and performance of the air barrier layer and materials used to create air barriers in the building envelope.

Tags : air tight, benifits, building envelope, Environment
Posted in : building envelope | 12 Comments »