how roof insulation works


So How Roof Insulation Works is simple. Roof Insulation products all have an R-value rating. Insulation’s R-value rating is the Roof Insulation’s ability to restrict the heat flow in the home. The higher the R-value, the more efficient the Roof Insulation.

So how does your roof accomplish being this energy-efficient barrier?

When we Insulate your roof space with good quality roof insulation to block the heat flow up or down, we are creating a barrier between the home and the ceiling, and roof insulation blocks the heat flow down in summer and up in winter. For this reason, insulated homes are as much as 4 – 8 degrees better in summer and winter.

What is Roof Insulation?

Roof insulation is specially designed for homes and offices. Also, roof insulation is available in many forms. Mostly, the roll insulation types are the most popular and cost-effective insulation.

Do all roof insulation products have R-value? All roof insulation products have an R-value, and the higher the R-value, the better the performance of the insulation.


Cold Roofs and Warm Roofs How Roof Insulation Works

In most cases, we find that a hot home summer is a chilly home in winter. However, one must remember that this is not always the case as houses in a moderate summer climate are cold.

On hot summer days, the heat build-up in the roof space builds up rapidly. The result would be an increase in internal temperature as the heat penetrates the home via the ceiling. For this reason, insulated homes will block 90% of the heat flow down into the house. Thus, it is resulting in a fresher, more energy-efficient home.

In winter, we lose the warm air in the home to the cold ceiling. But, remember that warm air rises. To reduce heat flow out of the house, good quality roof insulation will reduce heat loss by 90%. Because of roof insulation fitted to the ceiling, the insulation blocks heat loss as much as 90%.

Roof Insulation acts as a barrier between the hot air and the cold air.

How Much Is Roof Insulation Enough?

For roof insulation, thickness and R-value of insulation are the most important factors. All roofing insulation products must have an R-value. The insulation R-value is based on the specific thickness of the insulation. Importantly never compress the insulation in the roof space. For example, compressing insulation by 50% will cause a 50% reduction in R-value and efficiency.

The climate conditions in South Africa require an insulation R-value of 3.70. However, increasing the R-value will mean we are increasing the insulation benefits. Importantly we can’t expect to double our insulation efficiency by increasing the thickness. We will, however, improve the insulation benefits marginally.

A single layer of 135mm Aerolite Insulation will reduce heat flow by as much as 88%. Above all, adding a second layer of 135mm Aerolite will only improve the heat flow by as much as 92%. For this reason, the second layer of insulation has only improved heat flow by 4%. However, additional benefits include soundproofing improve substantially.

Finally, ceiling insulation exceeding R-value 3.70 is perfect. In addition, be sure the insulation that has been selected does not collapse over time. As ceiling insulation that has collapsed will have the R-value of the collapsed thickness.

Insulating a Flat Roof

Of course, there are some building designs that have no roof trusses at all. Commercial and industrial buildings, for example, are frequently built with a flat roof, mostly for the ability to place the HVAC system and other components up there. However, these types of buildings will still suffer from retaining heat in warm weather and losing it in the cold.

The most significant component of flat roof insulation is a vapour membrane. This feature stops warm air from condensing as it rises and Winter elements from melting when exposed to warmth. In addition to the vapour membrane, however, flat roofs are still insulated. In fact, flat roofs can be covered in any of three spots:

Insulation on top of the roof deck and between the weather membrane.

Insulated beneath the roof deck towards the innermost part of the building.

Insulated on top of the weather membrane with an additional layer of gravel or tar installed over the top.

Individual analysis of the buildings needs to be taken into account to determine which solution is best. Plus, some flat roof insulation types are best installed when a new roof is being laid compared to a retrofit.

What Materials are Used for the Insulation?

The choice of what material to use for the roof insulation depends on three main factors:

  • Feasibility of Installation
  • Desired R-Value
  • Cost
  • Health issues
  • Saving energy

A homeowner can dig a bit deeper and help choose their insulation based on the square footage of their home, heating source, what direction their property faces and more. The above, however, are the five main factors to consider now that you know how roof insulation works.

Feasibility of Installation

How well a material installs essentially comes down to access. In a new home build, virtually every type of roof insulation is at your disposal. Often with a retrofit, however, access to the attic or roof panels is hindered. Here are the three main types of “shapes” that roof insulation is available in:

Batts and Blankets – very similar to the wall insulation that many people are familiar with. Batts and blankets unroll to quickly fill in the spaces between floor joists or roof rafters. Multiple layers are often installed to meet depth requirements. Unfortunately, the batts must be cut around pipes, outlets, and wires, which can lose some of their effectiveness.

Loose Fill (Blown-In) – the best choice for retrofits because loose insulation can be blown into vast spaces via a small opening. It gives a very thorough fill as the loose fibres pack into small gaps.

Structural Insulated Panels (SIP) / Rigid Foam– 4X8 sheets or larger with immense energy-saving capabilities. Installed over the frame but under the sheathing to eliminate any cold gaps around studs. Great for use in warm roofs and is also the least messy of insulating shapes.

Once you’ve determined how you want to install the roof insulation, the next things to consider are the R-value you want to achieve per the cost.

R-Value and Cost of Roof Insulation

There are some roof insulation products on the market in South Africa. We will cover a few of the leading contenders in a brief description with our opinion on the product considering R-value and lifespan of insulation.

Aerolite Insulation

  • Aerolite Roof Insulation a fibreglass
  • insulation type.
  • This Aerolite insulation is very popular in Europe and the UK as well as the USA.
  • Aerolite manufactured to international standard as well as SABS approval.
  • The Aerolite  135mm thickness is SANS compliant. And should be installed in all homes in the Western Cape. In fact, Johannesburg and Pretoria must also fit the Aerolite 135 mm thickness.
  • The correct R-value of insulation for these regions is R-value 3.70 and is achieved on the Aerolite 135 mm.
  • Read the Aerolite Specifications page for more info

Isotherm Insulation

  • Isotherm Roof Insulation is a polyester type insulation. Manufactured from recycled plastic bottle pollution PET.
  • Isotherm Polyester types of roof insulation have become very popular worldwide as they are dust-free and allergy-free.
  • The long lifespan of Polyester Isotherm insulation types like Isotherm will outlast most homes.
  • In fact, the price of Isotherm Insulation is very economical when one considers the lifelong energy-saving benefits.
  • The correct thickness Isotherm Insulation is the Isotherm 145 mm thick insulation SANS compliant for the Western Cape region. As well as Johannesburg and Pretoria.
  • The correct R-value of installed insulation in these regions should be R-VALUE 3.70 achieved with the Isotherm 145 mm.

 Rock Wool Insulation

  • Rock wool insulation is a very high-density product made from molten rock. This insulation can withstand temperatures of 650 degrees c.
  • All rock wool insulation is primarily used in the industrial sector, where extreme temperatures need to be controlled for energy saving. This would be mostly for furnaces and industrial manufacturing plants.
  • In fact, rock wool insulation is not suitable for residential homes as it is a very high density. In addition, the weight of the product would not be ideal for roofs.
  • The cost of Rock Wool insulation is also more than 5 times the price of standard roof insulation.