Insulation Cheat Sheet Part 1

Selecting the right type of insulation is far more complicated that simply looking at a product’s R-value. It’s important to understand the entire long term impact of sourcing and using a particular insulation product. This means how and where the product is made, the ingredients, the waste generated during manufacturer and during installation, what happens at the end of its useful life, the R-value as tested, the R-value at extreme temperatures, the R-value long term as it ages, the vapor permeability, the air permeability, the resistance to water, the resistance to rodents and insects, the ease or difficulty in installation, the stability, the availability, and the cost. Rather than doing a deep dive, to make things easier we’ve summarized the most common insulation board products into this quick Insulation Cheat Sheet.

AVOID

XPS FOAM

         extruded polystyrene

         closed cell / vapor impermeable

         typical blue or pink under names “Styrofoam” and “Foamular”

         R-5 / inch but loses R value as it ages.  actual R-4 / inch.

         suitable for below grade / underslab / comes in different densities

         blowing agent (currently used in US) has very high GWP and therefore should be avoided.

         High Availability / Low Initial Cost / High GWP

3 Primary Types of Foam Insulation

USE SELECTIVELY BUT BEST TO AVOID

EPS FOAM

         expanded polystyrene

         semi closed cell / essentially vapor impermeable unless very thin

         typically white and made of tiny beads

         approx R-4 / inch

         suitable for below grade / underlab / comes in different densities

         blowing agent has fairly low GWP. 

         Readily Available / Low Initial Cost / Medium Low GWP

GRAPHITE EPS FOAM

         expanded polystyrene with embedded graphite particles

         semi closed cell / essentially vapor impermeable unless very thin

         typically white and made of tiny beads

         approx R-4.5 / inch

         suitable for below grade / underlab / comes in different densities

         blowing agent has fairly low GWP. 

         Medium Availability / Low Medium Initial Cost / Medium Low GWP

POLYISOCYANURATE FOAM

         typically faced with foil or felt

         semi closed cell / vapor impermeable

         typically yellowish / off white with silver foil facing or black felt facing

         approx R-6 / inch but less R value at colder temps.  actual R-5 / inch.

         not suitable for below grade or underslab

         blowing agent has lowest GWP of rigid foams. 

most commonly use for commercial roof assemblies; used foam can sometimes be sourced.

         High Availability / Low Medium Initial Cost / Low GWP

 

GOOD

HIGH DENSITY MINERAL WOOL

         highly vapor permeable / hygrophobic (repels water)

         yellow gold color

         approx R-4 / inch.  maintains R value at cold temperatures

         now suitable for below grade or underslab

8lb per ft3 density / Roxul is most common manufacturer

         low GWP but uses steel mill byproduct / energy intensive

         Readily Available / Medium Cost / Low GWP

BEST

CORK

         highly vapor permeable / hygrophobic (repels water)

         can be used as exterior finish material if well protected

         approx R-4 / inch.  maintains R value at cold temperatures

         not suitable for below grade or underslab

         low GWP, from rapidly renewable resource,

imported from Portugal

         Medium Availability / Medium to High Cost / Low GWP

WOOD FIBER BOARD

         highly vapor permeable / paraffin wax provides weather resistance

         doubles as WRB when used on walls

         approx R-3.5 / inch.  maintains R value at cold temperatures

         not suitable for below grade or underslab

         very low GWP but currently imported from Europe

         Medium Availability / Medium to High Cost / Very Low GWP

More Cheat Sheets coming. Check back soon or subscribe for updates.

thermal bridge free exterior

next up on skidmore passivhaus is installing the outsulation on the walls along with the rainscreen furring.

the plywood sheathing was first covered by a weather resistive barrier with metal head flashings at the windows and doors.

most walls get a layer of 3" poly-iso, while the south wall will get 4" to match the recessed pocket for the exterior shades.

2 screws (with plastic washer) per 4x8 sheet hold it in place until the furring strips are installed.

all seams and fasteners are taped.  the face of the insulation is treated as a second weather resistive barrier.

additional flashings at all doors and windows will be taped to the insulation as the wood trim is installed.

1/2" x 2" pt plywood furring strips run vertically to create the drainage plane.  they are held in place by just a few fasteners until the next layer is installed.

since we are using vertical siding, a second layer of furring runs horizontally.  we used pt 1x4 as a solid nailing base for the siding.

long fasteners secure the second layer of furring strips running horizontally through the foam to the studs.  the straightforward framing layout makes the studs much easier to locate.

keep in mind that long fasteners get expensive.  we settled on grabber #10 x 6" square drive coated screws (from nw staple).

next up on the exterior is trimming windows and installing siding.

stop by again soon.