Breathing Airtightness with Tapes in Lightweight Construction

Airtightness in buildings refers to the ability of the building envelope to prevent uncontrolled air leakage through gaps, cracks, or other penetrations. By strengthening walls, roofs, doors, windows and other building envelope elements with a combination of insulation materials, airtight membranes, sealing tapes or silicone sealants, a continuous barrier between the indoor and outdoor environments can be created.

Richard, what are the effects of airtightness in buildings?

By preventing uncontrolled air exchange and leaks, energy loss can be minimised, making buildings more efficient and therefore saving costs and energy. Airtightness also helps to improve the quality of air inside by enabling controlled air exchange through ventilation systems that filter particles and other substances for better living comfort.

Where do air leaks usually occur?

Wherever the building envelope is interrupted or penetrated, there is a high potential for air leakage. Window and door frames, electrical outlets and switches, ducts and pipes, or gaps between structures or cracks are common examples where air leakage occurs.  

We have seen that airtightness is a common issue in traditional buildings. Now let us delve deeper into the specifics of lightweight construction and why it could be even more challenging yet beneficial in such buildings.

Richard, what are the challenges of achieving airtightness, especially in lightweight construction?

At Saint-Gobain, we live and breathe lightweight construction. These building technologies offer various advantages, such as the use of thin and flexible materials. However, because the lightweight construction materials used in these buildings can be more prone to air leakage, achieving airtightness with sealants, foams, and tapes becomes even more critical.

In addition to adding sealants and tapes as airtight gasketing materials, airtightness is achieved through a process where the building envelope is tested to quantify the leakage of air. The test measures air leakage rates through a building envelope under controlled pressurisation and depressurisation.

Building testing is not a mandatory test prescribed in building regulations, but a performance-based option that many designers require.

Some of the testing procedures for airtightness include:

• The United States Army Corps of Engineers Air Leakage Test Protocol for Building Envelopes
• ISO 9972:2006 – Thermal performance of buildings – Determination of air permeability of buildings – Fan pressurisation method
• ASTM E779 – Standard Test Method for Determining Air Leakage Rate by Fan Pressurisation
• ASTM E1827 – Standard Test Methods for Determining Airtightness of Buildings Using an Orifice Blower Door
• ASTM E3158 – Standard Test Method for Measuring the Air Leakage Rate of a Large or Multizone Building
• ATTMA – Measuring Air Permeance of Building Envelopes (Dwellings)
• ATTMA – Measuring Air Permeance of Building Envelopes (Non-Dwellings)

How can special tapes help address these challenges?

Tapes are often used as a premium product to achieve airtightness because they do not crack over time. They allow for swelling and shrinkage, have more consistent thickness than liquid solutions for thick layers, can be installed or applied in a shorter timeframe without creating mess, and do not need a curing cycle. In addition to airtightness, tapes do an excellent job of achieving watertightness. Some tapes can also allow wet areas to dry instead of trapping in the moisture. Trapped moisture is dangerous because it leads to mould growth and can cause natural materials to decompose.

Tapes used for air tightness include PVC foam, polyurethane foam, acrylic foam, EPDM foam, polyethylene (PE) foam, and butyl-coated foam adhesive tapes. PVC foam tapes provide sealing and insulation against air, dust, moisture, impact, and vibration. These compressible, flexible tapes are available in low, medium, and high densities and conform to tight curves and irregular surfaces. PVC foam strikes a good balance between cost and performance and offers good fire resistance, even though it is a lower-temperature sealing tape.

Polyurethane tapes are long-lasting and can withstand extreme temperatures. They conform to indoor or outdoor surfaces to provide an effective seal with only 30% compression. Low-density polyurethane foam tapes also offer effective insulation. Polyurethane foam maintains its sealing properties at high temperatures and can provide a seal with minimal compression. This means less tape is required to seal the same gap.

Acrylic foam tape is a highly durable bonding adhesive for high-temperature and long-term applications. Acrylic foam is used to bond insulation materials such as ACM (Aluminium Composite Material) panels, sandwich panels, and insulated wall panels.

EPDM (Ethylene Propylene Diene Monomer) closed-cell foam is a versatile material resistant to weathering, ozone, and UV. Its closed-cell structure makes it impermeable to air and provides a quality seal with higher compression of about 50%. EPDM foam is used for sealing when high temperatures and larger gaps need to be filled. EPDM doesn’t seal as effectively as polyurethane, but it is available in greater thicknesses to seal and fill the space.

Butyl tapes have good temperature resistance and maintain their stickiness at much lower temperatures than natural rubber. Butyl rubber tape adheres instantly to most surfaces and has a high level of adhesion. Butyl tapes have higher adhesion than butyl-coated foam because they contain a thicker layer of adhesive. Butyl-coated foam and butyl sealant tapes are used around windows and doors, between insulated wall panels, behind electrical boxes, and on seal plates.

PE foam is not soft at all, so it is not generally used for sealing. Instead, it is used for thermal insulation and in areas where space needs to be filled, but it cannot withstand high temperatures like polyurethane and EPDM.

What are silicone sealants and what are they used for?

TEKBond Silicone Construction is a non-corrosive silicone sealant for indoor and outdoor use. It exhibits outstanding adhesion to key building materials such as glass, ceramics, steel, aluminium, brick, concrete, wood, and most plastics. Applied with a gun, it offers excellent durability and is also resistant to ozone, UV, humidity, and elevated temperatures. It can withstand peak temperatures of up to +150°C.

The neutral cure silicone is non-corrosive, meaning it will not damage metals or other materials over time. This non-corrosive property allows it to be used in areas where metal surfaces are present, such as around doors and windows, where other types of silicone sealants may cause corrosion over time. Neutral cure silicone is less likely to crack or shrink over time, which can be an issue with other types of silicone sealants. Crack and shrink resistance is critical to maintaining the air tightness of the structure.

How can a combination of the right tapes and sealants maximise value in airtight lightweight buildings?

Often, both sealants and tapes are used around windows and doors. Tapes are paintable, whereas silicone sealants are not. Therefore, if the final product needs to be painted, tape can be applied over the entire structure to create a neat aesthetic line. Additionally, around corners, edges, and tops, tape can be much easier and faster to apply, providing a more robust seal. Once the tapes are in place in the most challenging areas to seal, silicone sealant can be used in the straight areas and narrower gaps, while foam tapes can be used to fill wider gaps. Finally, narrow gaps can be sealed with a liquid silicone sealant, and the finishing touches can be applied.

Now we can better understand why airtightness is important in modern buildings and what the special requirements in lightweight construction are. If you aim to optimise living comfort and energy consumption in buildings, we hope this article helped you find out how specialised tape and silicone sealant solutions can solve your problems and breathe life into your projects.