How do you Seal Your Building Envelope?

by David Lindholm, illbruck Sealant Systems

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Alright - so building joints are not the most exciting topic to plan and engineer in building development, but details as mundane as construction joints can be a big contributor to the well-being of a new (or renovated) building.

A Star-Tribune newspaper cover story dated June 19, 2000 detailed the deterioration of some new homes that were literally rotting invisibly from inside the walls. That is, the deterioration was invisible until mushroom “gardens” took on full bloom on the interior finish of the walls around some window frames. The problem was not in creating tight building joints, instead, a big contributor to the problem was a building envelope that was too tight, and never allowed moisture that developed within the walls to dry out.

European Building Construction

Despite our recent spike in energy costs, energy is still inexpensive here relative to what most Europeans pay for power. The result is that many building codes and general building practices in Europe have for years been designed to create energy efficient dwellings, yet breathable building structures and joints in the building envelope.

In general, European commercial construction principles identify a two-part wall system; an outer wall and an inner wall. A systems approach to fenestration joints is then applied to connect door and window frames to the outer wall using specific characteristic products, and the inner wall connection with complimentary characteristic products. The principles of the system are widely used in all types of construction projects, including commercial offices, industrial warehouses, and residential condominiums and homes. The joint sealant system can also be very easily implemented into American construction as well.

The System: Breathe Out and Close In

In general terms, the joint system is designed to allow air pressures and moisture vapor from within the building envelope to pass through the exterior of the joint system. The inside of the joint is sealed with vapor barrier products so the same moisture and vapors that may develop within the building envelope will not pass into the interior of the building, and can instead balance and dry to the outside.

Breathe Out

Breathable joint materials that repel wind, rain, and combinations thereof have been developed for use on the exterior joint connections between the fenestration frame and the outer wall. Products have been tested to withstand up to 600 pascals (12.5 psf) pressure of simulated driving rain onto the upright joints, and not allow water to pass through the joint material. This same material will allow air and moisture vapor to permeate through to enable the building wall cavity to dry. Application of the exterior, breathable joint sealant product in this system directly connects the fenestration framing to the outer wall of the building envelope. Decorative trimwork may be attached over the top of the joint, or the breathable sealant may be left exposed as a shadow joint.

Close In

The inside joint sealant in this system makes a direct, air tight, (vapor barrier) connection between the fenestration frame and the inner wall (or the fenestration frame and the framing of the punched opening). Custom engineered foil/film and butyl tapes have all been effectively used as the inside joint sealant material in this system. Condensation and moisture vapor from within the building envelope is not able to pass into the interior of the building at the fenestration joints, even in negative pressure conditions.

The joint sealant system introduced above is not a cure-all for the bigger issues in the building industry (i.e. Sick Building Syndrome, Building Related Illness, etc.), but it can be a contributing part of overcoming some of difficulties associated with our continuing trend towards tighter building envelopes.

David Lindholm is a Sealant Systems Manager for illbruck Sealant Systems, inc. illbruck is a European headquartered manufacturer of joint sealant products and systems since 1952. David can be reached at 612-521-3555, or email at dlindhol@illbruck.com.

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© 2000 David Lindholm

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