Don't Staple Tyvek

For an air barrier to be effective, an airtight seal must be maintained between all of its elements--between the individual sheets of gypsum board, for example. This seal must remain intact under all temperature and pressure conditions that the air barrier will encounter. But do common air barrier assemblies withstand the tests of temperature and pressure over time? That's the question Canada Mortgage and Housing Corporation (CMHC) set out to answer when it commissioned a study of the behavior of various air barrier connection techniques over a prolonged period. Their conclusions: Tyvek and staples do not a winning combination make, and both Tyvek and caulk wilt when the temperature rises.

Researchers, led by project manager Jacques Rousseau, exposed 23 assemblies to a pressure differential of 150 Pa over five months. Testing took place at -20°C (-4°F), 20°C (68°F), or 65°C (150°F), depending on where the air barrier was likely to be located in the wall. The conditions that an air barrier is exposed to depend on its location. lf the air barrier is located on the room side of the insulating material, the temperature remains fairly constant at around 68°F. However, if the air barrier is located on the exterior side, the temperature may vary from -4°F in winter to 150°F in summer. Since temperature has a direct effect on strength, adherence, and connection creep, it is essential to consider temperature extremes in selecting air barrier materials.

For each assembly, CMHC measured air leakage under a pressure differential of 75 Pa at the beginning of the test and at the end (see Table 1). The increase in air leakage from beginning to end indicates the extent to which each of the assemblies deteriorated.

None of the samples tested at a frigid -4°F suffered damage or lost airtightness. At room temperature (68°F), test samples with open-cell gaskets, sheet-type air barriers, or mineral wool actually gained airtightness, because dust accumulated on or within the joints. Test samples with closed-cell backer joints and EPDM gap gaskets lost airtightness at the joint ends from shrinkage.

At 150°F--a temperature that many attics reach in the summer--the spun bonded olefin paper, better known as Tyvek, was completely torn off its staples, causing it to totally lose its airtightness. The acrylic sealing joint samples were extensively damaged. All the joints cracked, and one of the 1/2 inch joints popped out completely over several centimeters. It was not possible to take a final airtightness measurement on this sample.

Silicone base sealant and adhesive tape showed perfect adherence qualities under all conditions. In contrast, open-cell gaskets, mineral wool, and perforated polyethylene air barrier joints should not be used as air barriers, given their high permeability.

Considering these results, spun bonded olefin paper and acrylic base sealant or caulk should not be used at connections that may be exposed to high temperatures. And Tyvek should not be attached with staples if it is expected to act as an air barrier.

--Mary James

Mary James is editor/publisher of Home Energy.

For more information: The research report, Air Tightness Tests on Components Used to Join Different or Similar Materials of the Building Envelope, is available from the Canadian Housing Information Centre, Canada Mortgage andHousing Corporation, 700 Montreal Road, Ottawa, Ontario K1A 0P7. Tel:(613)748-2367; Fax:(613)748-2098.

Table 1. Materials or Assemblies Tested
Material Description	Air Leakage Before Testing (m3/h-m @ 75 Pa)	Air Leakage After Testing (m3/h-m @ 75 Pa)	Change in Air Leakage
Closed-cell backer rod (initial compression = 50%)	0.074 (68°F)	0.075	+1%
Open-cell backer rod (initial compression = 50%); open-cell gasket (compression = 20%)	24 (68°F)	22	-8.5%
Mineral wool; width = 12.7mm (1/21); low compaction density	14 (68°F)	14	No difference
Wood - urethane (12.7 mm (1/21);- aluminium	0.060 (68°F)	0.06	-0.5%
Adhesive tape on water-resistant drywall joints; Spacing = 12.7 mm (1/21)	0 (-4°F)	0	No difference
	0 (150°F)	0	No difference
Adhesive tape on water-resistant drywall joints; Spacing = 6.35 mm (1/41)	0 (-4°F)	0	No difference
	0 (150°F)	0	No difference
Adhesive tape on spun bonded olefin paper joints (Tyvec)	0.03 (68°F)	0.025	-9%;
	0.03 (-4°F)	0.026; 0.03	-2%
	0.026 (00šF)	no measurable tightness	N/A
Adhesive tape on perforated polyethylene air barrier joints (Typar or Barricade)	0.77 (68°F)	0.53	-32%
	1.545 (-4°F)	0.53	-66%
	3.17 (150°F)	0.53	-23%
Interior sealant joints (silicone); width = 12.7 mm (1/2-in.); wood-sealant-aluminium - backer rod	0 (68°F)	0	No difference
Exterior sealant joints (acrylic); width = 12.7 mm (1/2-in.); wood-sealant-aluminium - backer rod	0 (-4°F)	0	No difference
	0 (150°F)	no measurable tightness	N/A
Exterior sealant joints (silicone); width = 6.35 mm (1/4-in.); wood-sealant-aluminium - backer rod	0 (-4°F)	0	No difference
	0 (150°F)	0	No difference

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