Fiberglass batts are one of the most common insulation types for exterior walls, especially in residential construction. R-value: Typically R-13 for 2x4 walls and R-19 for 2x6 walls. Installation: Fiberglass batts are designed to fit snugly between wall studs.
In cold climates, closed-cell spray foam is often considered the best insulation for exterior walls due to its high R-value per inch, which makes it very effective at resisting heat flow. Additionally, it serves as both an air barrier and moisture barrier, crucial for preventing condensation and mold growth.
It is recommended to use at least R-12 for exterior insulation with a breathable cavity insulation like fiberglass, mineral wool or blown in cellulose (dries to inside) but with closed cell foam in the cavities, I'll have no worries of moisture condensing in the 2×4 cavities by using closed cell spray foam.
EPS is most commonly used. This is the main insulation - it is normally made of either expanding polystyrene or mineral wool. Technologies such as phenolic resin insulation are also available. All of these materials are used to prevent heat escaping through walls.
R-Value and Exterior Walls
According to the U.S. Department of Energy, R-values for exterior walls in colder climates should be at least R-13 to R-23. In milder climates, a lower R-value may be sufficient. For example, in a moderate climate, an R-value of R-13 to R-15 is typically recommended.
It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That's when mold starts to grow.
R-value is used to judge thermal insulation performance and the higher the number, the better the product's insulating ability. So R19 has better insulating ability than R13. Now R-Value ranges widely across products and home applications.
The cheapest way to insulate exterior walls is by using Expanded Polystyrene (EPS) boards, which are easy to install. Additionally, you can reduce costs by applying for UK government grants to help offset the expenses.
If you live in a mixed climate – hot and humid with several heating months in the winter, you probably need a vapor retarder. Specifically, if you live in climate zones 4C (marine), 5, 6, 7 and 8. Not sure your climate zone? You can check here.
The most effective thermal insulator on the market is likely polyurethane spray foam, followed closely by rigid insulation boards such as polyisocyanurate (PIR) boards. These materials boast some of the highest r values of all insulation materials on the market.
Thermablok® Aerogel is a revolutionary advancement in thermal technology offering the thinnest insulation available to prevent thermal and cold bridging. Classed as a Super Insulation, Aerogel has the highest insulation value of any known material with the lowest thermal conductivity value of any solid (0.015W/mK).
Fiberglass: Fiberglass is the most common insulation material. It's made from fine glass fibers and is most often used in batts, rolls and loose-fill insulation.
The DOE Insulation Fact Sheet (DOE/CE-0180) can be ordered from the Energy Efficiency and Renewable Energy Clearinghouse or accessed from the Internet at www.ornl.gov/ roofs+walls. Fiberglass and rock wool batts—2x4 walls can hold R-13 or R-15 batts; 2x6 walls can have R-19 or R-21 products.
Fiberglass Batt Insulation
Fiberglass batt insulation is one of the most common and affordable options for exterior wall insulation. It comes in pre-cut panels, making it easy to install between studs. R-Value: Around R-2.9 to R-4.3 per inch. Benefits: Affordable, easy to install, and widely available.
External Wall Insulation (EWI) reduces heat loss through the walls by adding an insulating layer that prevents the transfer of heat. This layer can be made of materials like expanded polystyrene (EPS), mineral wool, or phenolic foam.
The minimum thickness of exterior walls in one-story buildings shall be 10 inches (254 mm). The walls shall be laterally supported at intervals not exceeding 24 feet (7315 mm). The minimum thickness of interior load-bearing walls shall be 8 inches (203 mm).
Insulation for 2x4 Walls
In most wall applications, you will use R-13 or R-15 kraft-faced fiberglass insulation rolls for these two-by-four stud walls. While rated differently, these two types of insulation are close enough in thickness that they can both fit into modern two-by-four wall systems.
External wall insulation typically lasts 30–40 years or more when installed by professionals and maintained properly. Its long lifespan makes it a cost-effective solution for councils and housing providers. Regular inspections and cleaning can further extend its performance, reducing the need for frequent replacements.
Exterior Wall Insulation
This is more expensive and usually requires a contractor, but it may be worth the cost—especially if you live in a very cold climate. If you replace the exterior siding on your home, consider adding insulation at the same time.
External wall insulation does not usually require planning permission unless: The house is located within a Conservation Area. The house is located in an Area of Outstanding Natural Beauty. The house is a Listed Building.
Depending on where you live and the part of your home you're insulating (walls, crawlspace, attic, etc.), you'll need a different R-Value. Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38 and R-49 are common for ceilings and attic spaces.
Exterior walls: R13 insulation is often used in exterior walls in moderate climates. It provides a good balance of cost and performance and can help to reduce energy consumption.
While both types provide insulation, R30 is the better option for maximizing energy savings in areas where heat loss or gain is a major concern. For example, R19 may suffice for interior walls, but R30 is more appropriate for exterior-facing attics or floors.