Pitched Roof Insulation

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Pitched roofs are a prevalent type of roof in the UK as they are highly versatile and generally don't require as much upkeep as other roof types. At Materials Market, we not only stock glass mineral wool slabs and rolls but also rigid polyisocyanurate (PIR) boards that can be used within a variety of pitched roof applications. This includes insulating at either joist or rafter level in your pitched roof construction.

Find Out More About Our Types of Pitched Roof Insulation
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What Is Pitched Roof Insulation? 

Pitched roofs are generally insulated by laying insulation boards, polystyrene insulation panels (backed with foil) or rolls at rafter level.

When installing insulation within a pitched roof you have a couple of options; you can either install standard loft insulation that sits on top of the joists (a method which can limit overall roof space) or warm-roof insulation, which insulates the entire loft area.

When tackling warm pitched roof construction, we recommend investing in a rigid insulation board such as 100mm Celotex GA4100 PIR Insulation Board, which is suitable for application between and over the rafters.

If you're looking for a more cost-effective solution, Loft Roll can be used between the rafters, with the option of installing PIR Insulation or Insulated Plasterboard over the rafters for thermal enhancement.

Please note pitched roof insulation costs will vary depending on the material and method you use. 

Benefits of Pitched Roof Insulation

  • Improves thermal performance/thermal efficiency in pitched roof spaces
  • Prevents heat loss 
  • Reduces energy bills
  • Reduces your carbon footprint
  • Increases a structure's overall value
  • Installing roof insulation is a preventative measure to ensure the durability of your build
  • Depending on the insulation used, other benefits of insulating your roof could include an improvement in acoustic performance

Warm Pitched Roof 

Opt for a warm-pitched roof construction if you plan on making your loft space into a usable space. The insulation is placed over, under, or between the roof rafters in this type of construction.

Warm roof construction/built-up roof (BUR) is one where all the insulation is above the joists/roof deck and below the waterproofing layer, making it part of the warm fabric of the building. 

In a warm roof space, the insulation layer is positioned immediately below the waterproof membrane. The vapour barrier rests on top of the decking but underneath the insulation material; insulation can be adhered, mechanically fixed or loose-laid.

We recommend using a PIR insulation board primed towards pitched roof applications such as the Kingspan Kooltherm K107 Pitched Roof Insulation Boards. These boards have an impressive 0.018 W/mK thermal conductivity. 

Cold Pitched Roof 

Cold roof insulation sees thermal insulation placed beneath the structural deck and roof joists, allowing it to remain cold. Cold flat roofs require a vapour control layer to function effectively, in conjunction with adequate ventilation to allow water vapour to escape before it condenses on the cold deck.

In this case, we recommend installing a thermally efficient solution such as Kooltherm K107 between the rafters and Kooltherm K118 Insulated Plasterboard to the inside face of the roof rafters.

In this system, a cavity should be left between the insulation and the waterproofing layer to assist in ventilating. Cold flat roofs are typically a less popular method than warm flat roofs because of this need for proper ventilation and for reasons relating to space, labour costs, etc.

Frequently Asked Pitched Roof Insulation Questions

What Is The Difference Between A Flat Roof & A Pitched Roof? 

Although they are called flat roofs, they aren't actually entirely flat. They have a very slight slope to stop water from pooling on your roof. Pitched roofs have a much sharper incline that then pushes water away from and out of a structure.

What Is a Ventilated Roof? 

Most pitched roofs that feature habitable space are of the ventilated construction type, which is also often preferred for loft conversions or in cases where replacing the roof covering is not possible or desirable.

A ventilated roof features a space between the insulation and the bottom of the sarking felt. This ventilated space ultimately allows air to flow and the structure to breathe.

When tackling an unventilated roof construction, a vapour-open underlay/breather membrane should be utilised. 

What's More Important - Roof or Wall Insulation? 

When it comes to insulation, you really can't go wrong with either option. Insulation is a one-time cost that will make your house more energy-efficient in the long run, without the need for any additional spending. 

However, we don't always have the budget to afford both at once. If you're working with a tight budget and have to make a choice, prioritise insulating your roof first. Doing so could save you around 35% on heating and cooling energy expenses down the line.

Do Building Regulations Apply To Pitched Roofing?

Yes, however, you won't need building regulations approval if you are simply repairing less than 25% of your roof – you can just dive in and get to it without hold-up.

On the other hand, the following procedures will call for building regulations approval:

  • Repair or re-cover more than 25% of your roof
  • If you're looking at re-covering your roof with a materially heavier or a greater/lesser fire retardant material than the existing material
  • To perform structural alterations
  • To install one or more windows within the roof itself (roof lights)
  • To upheave and create an entirely new roof

What Are The Four Main Materials Used in Roof Insulation? 

  • Fibreglass insulation
  • Insulation boards/insulation panels
  • Glass mineral wool insulation
  • Spray foam insulation (PUR)

What Is Rafter Level? 

When we mention 'rafter level' we are referring to the structural timbers that support the pitched roof. Joists are the flat horizontal beams at ceiling level.

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