Why Think Twice About Sandwich Panels for Your Roof Renovation

If you are planning your next home renovation, you may be exploring a sandwich panel roof as an affordable option to help get your project on its way. However, there are a number of potential disadvantages to sandwich panels that might make you pause for thought.

Here at Simplicity Planet, we tend to advise our clients against this roofing material, and today, we’ll walk you through exactly why that is. But first, let’s begin by covering what sandwich panels are—and then we’ll dive into the details of why they are sometimes so problematic.

What Are Sandwich Panels?

Sandwich panels are rigid construction panels that can be used in roofing as well as for interior or exterior walls and floors. They are made from two inflexible external layers with a third, insulating layer in between.

As you can imagine, this sandwich-like structure is where these distinctive panels get their common name, however, you may also hear sandwich panels referred to as structural insulated panels, insulated building panels, foam-core panels, stress-skin panels, or structural foam panels.

When first popularised in the United States in the mid-twentieth century, the sandwich panel was considered hugely innovative as it provided an alternative to wood-framed buildings during a time of growing concern about energy efficiency and deforestation.

Today, the insulating core of sandwich panels can be made from several different materials, including fibreglass, plastic-based materials like Polyurethane (PUR) or Expanded polystyrene (EPS), and rock wool. While these choices boost the potential versatility of this construction resource, many contemporary architects still approach its use with caution.

What’s the Problem With Sandwich Panels?

Fire Hazard

The various synthetic foams used in the creation of sandwich panels are each highly flammable, which means that homes featuring this construction material are often at greater risk of fire. What’s more, arranging insurance for a home with a sandwich panel roof may be more challenging.

According to Allianz Risk Consulting, “Sandwich panels with combustible insulation have been involved in a number of serious fire losses globally. It is very difficult for firefighters to extinguish a fire involving sandwich panels containing a combustible core. These fires often result in a total loss of the building.”

This danger can be somewhat reduced by ensuring that anything combustible is kept away from the panels, that they are sealed and surrounded by fire-safe materials, and that heat-generating equipment is also installed at a safe distance.

However, factors beyond our control such as the elevated risk of wildfires here in Portugal are not something that we can plan for, making the use of synthetic-core sandwich panels a prospect with some inherent risk.

Moisture Issues

While the waterproof exterior sheathing of most sandwich panel types might have you imagining an end to moisture-related issues in your home, this unfortunately isn’t always the case. In fact, there are a couple of different ways in which water and sandwich panels can strike up an unwelcome friendship.

Because sandwich panelling is not breathable and often serves as a barrier between variable outdoor and indoor temperatures, in some circumstances, moisture can collect on the underside of panel roofing leading to indoor condensation, dampness, and dripping.

Adding yet another layer of possible complication, when sandwich panels are not adequately sealed during installation, moisture can begin to accumulate within their core. This can compromise the thermic insulating properties of the panels, increase their structural weight, and lead to mould formation.

Structural Vulnerability

While the relative strength-to-weight ratio of sandwich panels is certainly impressive, it is important to understand how those mighty tensile capabilities are achieved so that structural compromise can be avoided.

Essentially, the strength of sandwich panels is rooted in the consistency of both the distance between the two exterior faces and the density of the core in between. This means that when sandwich panels are poorly cut, strained, or bent during installation, they can lose vital integrity. Cutting into sandwich panel surfaces to install wiring or plumbing can often contribute to this issue.

Because of these factors, damage to sandwich panel roofing can lead to long-term structural challenges. This makes these types of roofs particularly vulnerable to strong winds, which must always be considered during the project design phase.

In addition, when sandwich panels are installed in a home renovation, their inability to flex with the timber frame of a house may also lead to the formation of air gaps and sounds emitted as different materials struggle to accommodate each other during changeable weather and temperatures.

Other Potential Sandwich Panel Pests

While the above three areas of concern are certainly the big trio when it comes to potential problems with sandwich panels, there are a couple of other things to keep in mind.

We’ve covered the importance of proper sealing during the installation of sandwich panels, both for fire safety and the avoidance of moisture accumulation. However, it’s also worth noting that pests like insects or rodents can also move into your home via sandwich panelling.

This is because the core layer of many sandwich panel types, whether synthetic foam or rock wool, makes for great nesting material and can easily be burrowed into. For this reason, manufacturers often suggest applying insecticide to sandwich panel joins and sidings. Although this may not be an adequate long-term solution.

The Bottom Line: Sandwich Panels are Not Always Cost-Effective

Sandwich panels are an understandably tempting option for those looking to re-roof their house on a budget, and for some homeowners, they might be a reasonable choice. However, at the end of the day, their installation can sometimes prove a false economy, causing problems in the long term that offset any initial cost benefits.

Choosing high-quality panels, bespoke-made for your project rather than off-the-rack, and with an inflammable core may mitigate some of these issues. However, this route will likely come with a much larger price tag, levelling the playing field with other roofing materials.

For these reasons, we at Simplicity Planet prefer to install either traditional tile roofs on a wood frame or concrete structure, or EPDM flat roofs for our clients here in Portugal. Whether your dream home is a characterful renovation or an ultra-modern new build, we can provide the right roofing solution for your needs. To find out more, contact our team today.