800-255-0776

Performance

Technical Information / Performance

Problems with Traditional Methods

Assembly overview

Over the Purlin is a term that is appropriately used when the insulation and vapor retarder are pulled over the purlin (on top, perpendicular) and compressed when the roof sheets are attached.

Behind the Girt is a term that is used when the insulation and vapor retarder are hung from the eave and installed behind the girt (outside, perpendicular) and compressed when the wall panels are attached.


3 Major Design Defects

1. Vapor Retarder Placement - Defective
Traditional metal building insulation methods do not isolate the highly conductive steel purlins and girts from the conditioned space. Improper placement outside the dew point line commonly results in condensation and corrosion problems.

Illustration of corrosion caused by condensation on exposed steel purlins

2. Insulation Compression - Extreme
Traditional installation techniques compress the insulation throughout the entire structural cavity and is dramatically compressed directly above the purlins and outside the girts; minimizing actual installed thermal performance.

 

Insulation compression is not just above the purlin and behind girt flanges;
the tensioned facing (vapor retarder) limits the amount of recovery/thickness
throughout the cavity, as typically installed
.

 

3. Infiltration / Seams - Multiple
Traditional installation techniques requires the installer to “seal” consecutive runs of laminated fiber glass rolls of insulation. This is commonly done by tape or by aligning, rolling and stapling the tabs of each roll together. It is not uncommon for the staples and joints to deteriorate over time, increasing the opportunity for heat transfer.

Related Problems

Energy Waste
There is a large amount of effective insulation essentially wasted when it is compressed, resulting in higher monthly costs to condition the building.

Condensation
Causes dripping, damage to ceilings and building contents, deterioration of laminated vapor retarder facings, and wet insulation. Condensation in metal building roofs are often mistakenly perceived to be caused by roof leaks.

Corrosion
Structural deterioration, roof panel deterioration, shortened roof life, high repair costs. Also causes loosening of roof fasteners and standing seam clip fasteners.


Roof : Single Layer

Method
A single layer of laminated insulation is draped over and installed perpendicular to the purlins and compressed when the metal roof panels are attached.

Vapor Retarder
The laminated facing serves as the vapor retarder and is placed towards the interior of the building, over the purlin flange and below the compressed insulation.

Seams
Consecutive runs of laminated insulation are sealed to one another by aligning, rolling and stapling the tabs. Other obsolete alternative methods include adhesive tape or lapped tabs.

R-value ASHRAE 90.1
U-factors
Overstated
Performance2
Pre-Installed  Installed  Revised1 Published
R-10 R-5.4 U-0.184 U-0.153 16.8%
R-11 R-5.5 U-0.182 U-0.139 23.6%
R-13 R-5.7 U-0.174 U-0.130 25.3%
R-16 R-6.4 U-0.157 U-0.106 32.5%
R-19 R-6.6 U-0.151 U-0.098 35.1%
1ASHRAE News Release (January 2010) and Standard 90.1-2013
2Percent based upon comparing differences in U-factors

Thru-fastened / Screw Down

Roof Configuration
Metal roof panels are fastened directly to the top of the purlin using self-drilling fasteners. The head of the fastener is exposed to the outside weather conditions and the bottom of the fastener is exposed to the conditioned space of the building. This insulation assembly and roof type combination does not utilize stand-off clips or thermal spacer blocks.


Standing Seam

R-value ASHRAE 90.1
U-factors
Overstated
Performance2
Pre-Installed  Installed  Revised1 Published
R-10 R-8.7 U-0.115 U-0.097 15.7%
R-11 R-9.3 U-0.107 U-0.092 14.0%
R-13 R-9.9 U-0.101 U-0.083 17.8%
R-16 R-10.4 U-0.096 U-0.072 25.0%
R-19 R-12.2 U-0.082 U-0.065 20.7%
1ASHRAE News Release (January 2010) and Standard 90.1-2013
2Percent based upon comparing differences in U-factors

Roof Configuration
Stand-off roof clips are fastened to the top of the purlins using self-drilling fasteners and the metal roof panels are attached to the stand-off clip, creating slightly more space above the purlin. A thermal spacer block is typically recommended depending on the stand-off distance and the amount of insulation draped over the purlins. Check with building manufacturer for limitations.


Roof : Double Layer

Standing Seam

R-value ASHRAE 90.1
U-factors
OverstateD
Performance2
Pre-Installed  Installed  Revised1 Published
R-10+R-10 R-11.4 U-0.088 U-0.063 28.4%
R-10+R-11 R-11.6 U-0.086 U-0.061 29.1%
R-11+R-11 R-11.8 U-0.085 U-0.060 29.4%
R-10+R-13 R-11.9 U-0.084 U-0.058 31.0%
R-11+R-13 R-12.2 U-0.082 U-0.057 30.5%
R-13+R-13 R-13.3 U-0.075 U-0.055 26.7%
R-10+R-19 R-13.5 U-0.074 U-0.052 29.7%
R-11+R-19 R-13.9 U-0.072 U-0.051 29.2%
R-13+R-19 R-14.7 U-0.068 U-0.049 27.9%
R-16+R-19 R-15.4 U-0.065 U-0.047 27.7%
R-19+R-19 R-16.7 U-0.065 U-0.046 23.3%
1ASHRAE News Release (January 2010) and Standard 90.1-2013
2Percent based upon comparing differences in U-factors

Method
The bottom layer of laminated insulation is draped over and installed perpendicular to the purlins. The top layer of unfaced insulation is installed parallel and between the purlins above the laminated layer of insulation. Both layers of insulation are compressed when the metal roof panels are attached.

Vapor Retarder
The laminated facing serves as the vapor retarder and is placed towards the interior of the building, over the purlin flange and below the compressed insulation.

Seams
Consecutive runs of laminated insulation are sealed to one another by aligning, rolling and stapling the tabs. Other obsolete alternative methods include adhesive tape or lapped tabs.

Roof Configuration
Stand-off roof clips are fastened to the top of the purlins using self-drilling fasteners and the metal roof panels are attached to the stand-off clip, creating slightly more space above the purlin. A thermal spacer block is typically recommended depending on the stand-off distance and the amount of insulation draped over the purlins. Check with building manufacturer for limitations.


Wall

R-value ashrae 90.1
U-factors
Overstated
Performance2
Pre-Installed  Installed  Revised1 Published
R-10 R-5.4 U-0.186 U-0.134 28.0%
R-11 R-5.4 U-0.185 U-0.123 33.5%
R-13 R-6.2 U-0.162 U-0.113 30.2%
R-16 R-6.5 U-0.155 U-0.093 40.0%
R-19 R-6.8 U-0.147 U-0.084 42.9%
1ASHRAE News Release (January 2010) and Standard 90.1-2013
2Percent based upon comparing differences in U-factors

Single Layer

Method
A single layer of laminated insulation is hung from the top outside of the eave, perpendicular to the girts and compressed when the metal wall panels are attached.

Vapor Retarder
The laminated facing serves as the vapor retarder and is placed towards the interior of the building, behind the girt flange and inside of  the compressed insulation.

Seams
Consecutive runs of laminated insulation are sealed to one another by aligning, rolling and stapling the tabs. Other obsolete alternative methods include adhesive tape or lapped tabs.

Wall Configuration
Metal wall panels are fastened directly to the girt flange using self-drilling fasteners. The head of the fastener is exposed to the outside weather conditions and the tip of the fastener is exposed to the conditioned space of the building. This insulation wall assembly typically does not include any additional thermal spacer block at the girts.

Join our mailing list