how roof insulation works

So How Roof Insulation Works is very simple. Roof Insulation products all have R-value rating. This R-value if Roof Insulation is the ability of the Roof Insulation to restrict the heat flow in the home. In fact the higher the R-value, the more efficient the Roof Insulation.

So how does your roof accomplish being this energy efficient barrier? Materials are one thing another is knowing how roof insulation works. Asphalt shingles are going to absorb the majority of the Sun’s UV rays whereas a metal roof will reflect more. That fibres you don’t want to replace a roof that’s only 2-3 years old just for the sake of efficiency. The answer to cold retention and dispelling heat then is your roof insulation.

What is Roof Insulation?

The reason your house is either warm or cold when it’s supposed to be is as a result of insulation in the walls. Sure your siding and sheathing offer some R-value properties, but it’s the insulation that makes the most significant difference. Put your hand near a light switch on an exterior wall on a cold day. You’ll instantly be able to determine if insulation surrounds it or if you feel a draft meaning it’s not.

How Roof Insulation works in much of the same way as it does on the wall. Roof insulation is especially important in the Winter. Since warm air rises, you could be losing essential heat out the top of your home. Insulating your attic combined with a ceiling fan pushing the air downward helps retain that heat and keep your utility bills low.

Speaking of the attic, that’s where the insulation is installed and not necessarily on top of the roof itself. If your home has no loft the insulation is placed in the roof space created by the trusses. Knowing how roof insulation works will go a long way to help you make the right choice.

In fact, if you have no idea how roof insulation works you will never be able to make the right choice.

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Cold Roofs and Warm Roofs How Roof Insulation Works

To determine what type of insulation is installed in the roof, a few things need to be evaluated. A “cold” roof is an unused attic or open roof truss space. You don’t want any heat to escape into this space, so insulation is installed on top of the floor joists. A warm roof is an attic that is used as a living space or for storage. You want warmth in this area, so insulation is installed under the roof rafters.

How Roof insulation works are that it creates a barrier between the ceiling space and the roof. In fact how the roof insulation works are that it reduced the heat flow into the home and reduced the warm air in the house being lost into the ceiling.

How the attic is used determines where the insulation is installed but also what type to use. Installing on an attic floor joist (cold) gives much more space. Insulation placed between ceiling drywall and roof rafters needs to be a bit more creative.

Roof Insulation How Much is Enough?

If you’ve got a cold attic with three or four feet of space is it best to fill it to the rafters with insulation? The answer is no because remember roof insulation is not only for cold weather but also cold. Your roof space needs to have air circulation so it can breathe when the temperatures rise. Inadequate airflow will spike temps inside the home and possibly cause the roofing materials to deteriorate. Hot temperatures also harbour moisture which can lead to mould growth in the house and on the roof. When you know how roof insulation works it is far easier to make the right choice.

While you need to maintain attention to the maximum amounts of recommended insulation, there are minimums as well. In an unused space, the building recommendations call for a minimum of 145 mm in thickness. One thing to note is that even a home with existing insulation may need to have some added to meet code. This is because previously recommended depths ranged from 100 mm to as low as 50 mm. Knowing how roof insulation works you can see that this will give you almost no benefit. The reason for this back in the day has consumers had no idea on how roof insulation works so whatever was offered is what they installed.

Warm roof recommended insulation depths are a bit different. There may not even be 250-300mm of space available between the attic ceiling and the underside of the roof sheathing. Insulation with a lower thermal conductivity is used to obtain the desired U-value of 0.16W/m2K. U-value is essentially the rate at which a wall will lose heat so in this instance a lower number is better.

Insulating a Flat Roof

Of course, there are some building designs which 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. 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 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 its effectiveness.

Loose Fill (Blown-In) – the best choice for retrofits because loose insulation can be blown into vast spaces via a small opening. Gives a very thorough fill as the loose fibers 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 approve.
  • 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 were 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. 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.