As building codes change and insulation options diversify, designers are left with big decisions when it comes to choosing the right building materials for maximum thermal performance. In this article, we compare two exterior insulation options: polyiso andvs Rockwool.
Exterior Insulation Options
Exterior insulation comes in many forms, but for this article, we’ll focus on those that are available in board form since it is a common application. Board insulation typically comes in modular sizes such as:
2’ x 4’
4’ x 4’
4’ x 6’
4’ x 8’
The thickness of the boards can range between one and five inches in order to achieve the design’s desired R- value (thermal performance). Common board insulation types available today include: mineral wool, polyiso, and polystyrene.
Mineral Wool Insulation
Mineral wool insulation is a broad category of insulation that is made from spinning mineral fibers together. The mineral fibers can include various types of rocks, minerals, and slag waste. Stone wool is one type of mineral wool insulation (made from volcanic rock like basalt). Rockwool is a brand name for one type of stone wool insulation.
Polyiso Insulation
Polyiso insulation is a thermoset, closed-cell foam insulation made from polyisocyanurate foam core that is bonded to various facer materials. Facers can range from cellulose-based paper to aluminum foil facers. Facer material can enhance the properties of the insulation.
Comparing Rockwool and Polyiso
When comparing polyiso to Rockwool, there are pros and cons to each type of building insulation. Let’s do a side-by-side comparison of polyiso and Rockwool.
Similarities
The installation methods and applications for polyiso and mineral wool insulation are similar. Both are available in board form and are installed in a modular fashion by securing boards to the substrate with fasteners and oversized washers. Both materials require finishing, such as exterior cladding or interior drywall. Rockwool and polyiso are both fire-resistant.
Installation
While the installation methods for polyiso and Rockwool boards are similar, the handling of each material differs. Polyiso can be scored and snapped to cut pieces to fit, while mineral wool requires a serrated knife to cut through the entire length of boards.
Thermal Performance
Mineral wool carries a lower R-value than polyiso. That means to achieve an R13, you’ll need at least 3-½” of Rockwool, while just 2-¼” of polyiso can achieve the same thermal performance. Polyiso’s higher R-value per inch can reduce labor and material costs for large projects.
Air Barrier
Rockwool is a permeable material, meaning air and vapor can travel through it. If an air barrier is required, it must be installed as a completely separate product. Polyiso, on the other hand, is available in versions with varying permeability. For example, Rmax’s EcoMAXci® FR Air Barrier is a foil-faced polyiso that can be installed as an air barrier when joints are sealed.
Weight
Mineral wool is four times heavier than polyiso. Mineral wool insulation adds significant dead loads to your structure. The added weight also slows down installation, and requiresrequiring multiple workers instead of one to install each board.
Acoustic Performance
Acoustic performance is an unexpected benefit of using mineral wool insulation. It is one of the best products to use for sound dampening and sound absorption.
Applications
Mineral wool is typically only installed on walls because of its weight, while polyiso can be used for the entire building envelope, from foundations up to the rooftops.
Environmental Impact
Mineral wool can’t be recycled or reused on future projects, while it’s very common to repurpose polyiso insulation for use inside future buildings. The manufacturing process of mineral wool also requires significantly more energy to produce than polyiso.
Cost
Mineral wool is more expensive per board foot than polyiso. On top of that, it requires thicker layers of mineral wool to achieve the same R-value since it has a lower R-value per inch than polyiso. This drives the price up even further, along with increased labor costs due to the heavier weight of Rockwool.
Polyiso: The Superior Choice
Unless you’re looking for sound dampening, polyiso is the clear winner when comparing polyiso to Rockwool. Polyiso costs less, weighs less, has better thermal performance, and is more versatile than mineral wool. Whether insulating concrete slabs, foundations, crawl spaces, walls, or roofs, polyiso is a superior building insulation suitable for many applications.
Use Rmax Polyiso For the Job
When it comes to making the call on your building materials, it helps to get a second opinion from those who have been in the industry for decades. Rmax has been perfecting polyiso since 1978 and has experts on staff to help you make the right call.
Reach out to your local Rmax representative to see how they can help you today!