Warm roof insulation*
There are lots of important factors to consider when installing a flat roof. Whether it’s a new build or refurbishment, what waterproofing system you will use, what your budget is and much more. This article explores the warm roof insulation details.
What is the warm roof?
In a warm roof construction insulation layer is placed above the rafters, resulting in the structural deck and support structure being at a temperature similar to that of the building interior.
A vapour control layer beneath the insulation is required to prevent moisture vapour being driven into the insulation through thermal pressure from within the building.
The waterproofing system is placed over the insulation.
Warm roof build ups can be installed on construction material types such as concrete and timber. The process of installing a warm roof simply offers a greater level of thermal insulation.
It is economical to install as all the work is carried out above the roof joists.
Disadvantages of a warm flat roof?
When ‘cold roof’ does not add any extra height to the roof, ‘warm roof’ does.
It has a higher depth which means it may not be suitable in certain situations where there a limits on height.
The finish of roof is soft. This is where Plydeck takes its place. To avoid a soft finish, decking must be laid above the insulation.
Advantages of a warm flat roof?
‘Warm roof’ is one continuous quilt on insulation. Whereas with a ‘cold roof’ the insulation is placed in between the joists. Warm roof construction will stops thermal bridging. Whereas, cold roof construction will have some degree of thermal bridging. Warm roof takes away the need for cutting in between joists and removes the problem of mistakes happening when cutting the insulation.
Whichever build up you choose, it’s vital to ensure that you adhere to building regulations and that the fall in your flat roof provides efficient drainage. When building a flat roof, it is vital that insulating layer is located above the roof rafters and between the structural supports, a warm deck roof results in a temperature for the roof and loft area that is consistent with the rest of the property.
What material should I be using for warm roof?
There are a variety of types of insulation available for flat roofs including PIR. Insulating a flat roof in the first instance is the best way to achieve a well-insulated, competent and good-looking structure.
When it comes to best thermal performance of a flat roof, warm deck construction should be used.
A warm roof deck is the most common and most preferred type of flat roof build up in the UK. This ‘3 in 1’ solution removes the risk of condensation forming and resulting damp. This type of system significantly reduces the heat loss which can occur with cold deck construction.
Whether the flat roof being installed will be walked on or not, flat roof insulation board typically has a hard-faced surface.
What are the options of flat roof build ups?
Kingspan, Celotex, Recticel and Xtartherm are most well-known flat roof insulation brands. All of theirs products are simple and quick to install.
Ply-Deck Xtratherm FR/TP insulation boards are recommended for insulating a flat roof. Plydeck is very useful when applying hot bitumen on a flat roof without damaging the insulation. Xtratherm PlyDeck is a laminated sandwich construction comprising a PIR foam core with an aluminium foil inner face and timber 6mm plywood on top. There are a number of insulation thicknesses to choose from. All of these PIR insulation boards can help achieve excellent U-Values. Xtratherm FR/TP is suitable for use with mechanically fixed single-ply waterproofing membranes, mastic asphalt, roll and pour and adhered systems.
The thermal conductivity of the PIR insulation board is 0.022 W/mK (Lambda value).
The thermal conductivity of the 6mm WBP Plywood is 0.14 W/mK (Lambda value).
Thickness range 21-171mm
21mm ǀ 26mm ǀ 31mm ǀ 36mm ǀ 41mm ǀ 46mm ǀ 51mm ǀ 56mm ǀ 61mm ǀ 66mm ǀ 71mm ǀ 76mm ǀ 81mm ǀ 86mm ǀ 96mm ǀ 106mm ǀ 116mm ǀ 126mm ǀ 136mm ǀ 146mm ǀ 156mm ǀ 171mm
Kingspan Thermaroof TR31 is a high - quality PIR insulation board bonded to 6mm FSC certified plywood on one side and multilayer foil on reverse side.Thermaroof TR31 is suitable for use with mechanically fixed single-ply waterproofing membranes, mastic asphalt, roll & pour and adhered systems. It provides a cost effective means of reducing CO2 emissions and for compliance with Building Regulations and Standards.
Kingspan TR31 achieves high performance insulation for warm flat roof structures. The insulation core and facings resist attack by mould and microbial growth.
The thermal conductivity (λ-value) of the insulation is 0.022 W/mK.
The thermal conductivity (λ-value) of the plywood is 0.14 W/mK.
Thickness range 56-126mm
Celotex TD4000 (TD4126) Insulated Plywood Board is a '3 in 1' product designed to provide decking, vapour control layer and insulation for new and refurbishment flat roof applications.
Celotex TD4000 provides a quick and easy way to achieve effective thermally insulated flat roof decks for building structures such as small extensions or garage roofs where there will only be occasional trafficking.
Is ideal for use in occasionally trafficked applications. Provides warm roof construction due to over joist installation. Is rapidly installed and weatherproofed. Accepts a wide variety of weathering systems.
Is available in a standard board size of 1200mm x 2400mm.
Thickness range 96-126mm
Recticel Plylok Thermal Laminate Plywood - this board is faced with a gas diffusion tight multilayer foil on both sides and post laminated to plywood on one side.
Thickness range 96 - 126mm
Which is the better choice for your flat roof will depend on your own situation.
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