Shrinkage is not always the cause of gaps

MIDLAND, Mich. - September 28, 2017

During remodeling projects where wall frames are exposed, it’s sometimes discovered that gaps exist between foam insulation boards. While it’s typically assumed the cause of gaps is believed to be shrinkage of the foam, there is mounting evidence that shrinkage is not necessarily the cause of gaps.

Testing for shrinkage

Dow conducted a 5-year in-use study at the Wall Assembly Research Lab in Midland, Michigan to analyze STYROFOAM™ Brand Insulation joint dimensional stability. Wood framed wall assemblies sheathed with a one-inch layer STYROFOAM™ Brand Insulation were included as experimental, long-term wall exposure samples installed on the building. During late 2015, four wall assemblies installed on each cardinal direction were available for inspection. The wall specimens were constructed in a lab environment in late 2010 and installed shortly after into the research building.

The wall cladding consists of manufactured stone installed on the lower half of the wall sample and vinyl siding on the upper half. Several board joints were included in each sample to measure the performance of the taped joints used as a weather resistive barrier (WRB). The vinyl siding was removed for the inspection of board gaps and the condition of the construction tape used to seal the joints creating the WRB. Normally, when gaps are found, even small gaps such as those observed in these wall samples, foam shrinkage is claimed as the root cause.

Rigorous photo documentation of starting and ending conditions found showed similar spacing to the original installation – meaning that no opening of board joints occurred during this test exposure period. The construction tape was still strongly adhered to the foam boards with no evidence of loss of adhesion performance through this five-year period.

External evidence

Using scientific data to get to the bottom of this, Dow conducted three case studies where initial conditions of installation are generally well known. The first case is an examination of test wall assemblies after five years of test exposure in a climate research laboratory. The second case is an instrumented multi-story building in the Pacific Northwest where foam movement was monitored over several years. The third and final case study is an examination of a 10-year old single-family residential home in Midland, Michigan.

A housing complex in Vancouver

During a multi-story cladding rehabilitation project in Vancouver, British Columbia, there was an opportunity to install instrumentation to monitor movement within the retrofit wall system. The building is a 64-unit social housing complex in a seven-story reinforced concrete structure, with steel stud infill walls and commercial space on the first floor. The original envelope assemblies included cement stucco on steel-stud-infill walls, exposed mass concrete, brick at the first floor front elevation, and built-up roof systems on main and terrace-level roofs. The new wall assembly includes three inches of STYROFOAM™ Brand insulation with a nominal R-value of R15. The rain screen cavity is achieved by fastening the paperback lath on the outside face of the metal Z girt over which a three coat stucco is traditionally applied

Using sophisticated sensors placed on different floors, building position on the south and north facades of the building were measured. The study concluded that there was no evidence of foam insulation board shrinking.

Measuring a single-family home in Midland

In early summer 2016, Dow conducted an inspection of foam condition in a single-family residential dwelling located in Midland, Michigan prior to the addition of a room. The house had been built 10 years earlier by Midland County Habitat for Humanity. The one-inch foam layer was applied direct to studs using cap nails with construction tape on seams as the WRB.

Current dimension in the width direction on three of the boards where the factory edges were still intact were measured. It was noted that each board remains at the manufacturing design dimension – and actually are slightly wider. Again, this shows that boards have not shrunk in the width dimension.

Since no wood sheathing was used in construction of the wall system, it was possible to inspect cavity conditions for signs of deterioration and water intrusion. One removed piece of STYROFOAM™ Brand Insulation showed it remained in clean condition with no signs of water anywhere on the board, including around fasteners and board edges. No signs of moisture or deterioration within the cavity, including the bottom plate and subfloor below the bathtub at the interior of the inspected cavity were identified.

Click here for a full overview of these case studies.