Closed-cell spray foam, while effective at sealing and insulating, has raised concerns for its potential to place undue stress on roof timbers. For homeowners considering this type of insulation—or dealing with its aftereffects—understanding the risks is crucial.​

How Closed-Cell Foam Stresses Roof Timbers​

Rigid Nature
Once set, the closed-cell foam becomes rigid, adhering tightly to roof timbers and other surfaces. This rigidity can create stress points as the building naturally shifts or settles over time. Unlike flexible materials, the foam doesn't accommodate these movements, potentially leading to cracking or damage to the timbers.

Restricted Air Circulation
Proper ventilation is essential for maintaining the health of roof timbers. Closed-cell foam forms an impermeable barrier, which can trap moisture. Over time, this trapped moisture can lead to timber decay, rot, or even structural failure.

Weight and Pressure
Closed-cell foam is heavier than open-cell alternatives. This additional weight, particularly if applied excessively, can strain the roof structure, especially in older properties not designed to bear such loads.

Hidden Damage
Once the closed-cell foam is applied, it becomes difficult to inspect the condition of the roof timbers. Any pre-existing issues, such as dampness or decay, can go unnoticed and worsen over time, potentially leading to costly repairs.

Inappropriate Application
In some cases, closed-cell foam has been used as a "quick fix" to stabilize failing roofs. While this might provide temporary relief, it can exacerbate long-term problems by masking underlying structural issues rather than addressing them.

Why Proper Installation Matters

When installed correctly, closed-cell spray foam can be a valuable insulation material. However, issues often arise from:

• Poorly trained installers: Improper application can result in uneven coverage or excessive foam, increasing stress on timbers.
• Use on unsuitable structures: Older roofs or those with existing ventilation issues may not be ideal candidates for closed-cell foam.
• Lack of pre-installation assessments: Skipping a structural inspection can lead to undetected problems being sealed in.