Air Sealing, Insulation, & Thermal Bypass

How heat flows in a building:

Air Leakage - need an air barrier to stop flow.

Transmission - need insulation to stop flow

What is a Building Envelope?

The pressure boundary (air barrier) AND

The thermal boundary of the house (insulation)

These must be continuous around the entire conditioned space

What is a Thermal Bypass?

When heat, air and moisture “bypass” the thermal envelope of a building due to missing insulation or air barriers.

Insulation must have an air barrier

touching it on all sides. The exception is at vented ceilings where only a barrier between the attic and conditioned space is required.

Where is the Building Envelope?

• Basement?• Enclosed porch?• Attic?• Where are the ducts?• Where is the heating system?• Potential health and safety

concerns• NEVER the garage• Designers should examine the drawings and

determine the location of the envelope.

Air BarrierThe Air Barrier:• Limits air flow between inside and outside

• More difficult to identify

• Not always where you think it is

• Blower door is used to measure how tight the air barrier is.

7

BUILDING SCIENCE BASICS

The Thermal Boundary:• Limits heat flow between inside and outside• Easy to identify by presence of insulation• The location of insulation in relation to other

building components is critical to its effectiveness

• Even small areas of missing insulation are very important

• Voids of 7% can reduce effective R-value by almost 50%

What Insulation DoesPrimary:

Slows down heat flowmeasured by R-value

Secondary:Control air leakageControl convective loops

(which is a function of it’s density)

Control water vapor(measured in perm rating)

Cavity Mineral Fiber Batts

Reduce Heat Flow: fairControl Air Leakage: poorControl Convective Loops: poorControl Water Vapor: poor

Dirty insulation is evidence of air movement.

Blown / Spray Mineral Fiber

Reduce Heat Flow: goodControl Air Leakage: fairControl Convective Loops: fairControl Water Vapor: poor

Blown / Spray Cellulose and Cotton

Reduce Heat Flow: goodControl Air Leakage: goodControl Convective Loops: goodControl Water Vapor: poor

Open Cell (1/2 lb.) Spray Polyurethane

Reduce Heat Flow: goodControl Air Leakage: goodControl Convective Loops: greatControl Water Vapor: depends

Closed Cell (2 lb.) Spray Polyurethane

Reduce Heat Flow: greatControl Air Leakage: greatControl Convective Loops: greatControl Water Vapor: great

Expanded Polystyrene Boards

Reduce Heat Flow: goodControl Air Leakage: greatControl Convective Loops: greatControl Water Vapor: great

Extruded Polystyrene

Reduce Heat Flow: goodControl Air Leakage: greatControl Convective Loops: greatControl Water Vapor: great

Polyisocyanurate

Reduce Heat Flow: greatControl Air Leakage: greatControl Convective Loops: greatControl Water Vapor: great

R-value is the resistance a material shows to heat flow across it. Larger numbers show better insulation values.

It must be a tested value from a government lab, NOT a claimed “effective” value by the manufacturer.

How Is Insulation Measured?

R-value Radiant barrier products claim that R-value only measures conductive heat flow and ignores convection and radiation. In fact, R-values include all three.

Making it a useful way to compare products.

How Is Insulation Measured?

Typical R-Values

Open Cell Foam R- value 3.6/inchClosed cell Foam R-value 6.5/inch

What Influences the Performance of Insulation

R value - higher is better

How much air can flow through it (air impermeability)

Installation - 4% gaps can lead to 30% less effectiveness

Convection heat loss

Insulation ProblemsCaused By Poor Installation

Vented vs. non-vented roofs• 2006 IRC (not the IECC) section

R806.4• Allows for unvented roofs if “air-

impermeable” insulation can be used in contact with the roof sheathing.

• “air-impermeable” is defined – but basically it meets the requirements for an air barrier.

• Spray foam and rigid foam meet the standard, but cellulose does not.

Vented vs. non-vented roofs• Section R806.4 allows for a combination

of air-impermeable insulation and air-permeable insulation as follows:

In climate zones, 5,6, 7 and 8 any air-impermeable insulation shall be a vapor retarder, or shall have a vapor retarder coating or covering in direct contact with the underside of the insulation.

Vented vs. non-vented roofs Either items 5.1, 5.2 or 5.3 are met

depending on the air impermeability of the insulation directly under the structural roof sheating.

5.1 Air-impermeable insulation only (rigid or spray foam) shall be applied in direct contact with the underside of the structural roof sheathing to the value in table R806.4

Vented vs. non-vented roofs5.2. Air-permeable insulation only must also include air-impermeable insulation (rigid board or spray foam) shall be installed directly ABOVE the structural roof sheathing as specified in Table R806.45.3. Air-impermeable and air-permeable insulation. The Air-impermeable shall be applied in direct contact with the underside of the structural roof sheathing

Vented vs. non-vented roofs3. cont….as specified in Table R806.4 for condensation control. The air-permeable insulation shall be installed directly under the air-impermeable insulation.

Vented vs. non-vented roofs

If you insulate with certain types of foam, thick insulation puts the planet at greater risk than thin insulation!Download from www.greenbuildingadvisor.com

Choose Palo Santo Designs for your Custom Home Project

Palo Santo Designs LLC is an Award Winning General Contractor in Santa Fe, specializing in the design and construction of Fine Custom Homes, Renovations and Distinctive Commercial Spaces. Our experience is unsurpassed in the design and construction of high performance buildings, utilizing the most effective methods for energy and water efficiency, sustainability and comfort. Contact us at palosantodesigns.com.