Same product: More uses!



The most common solution for insulating a pitched roof, is to install one or more layers of fibrous, mineral wool insulation between and/or over the ceiling joists in the loft.  This is an example of a ‘cold pitched roof’, and it has some fantastic advantages, for example it is easy to achieve low U-values for the roof.  However, the biggest drawback is that this means the loft space cannot be used as habitable space; and unless boards are put down over the insulation, it cannot easily be used for storage.

The alternative is a ‘warm pitched roof’ system. This is where the roof insulation is installed along the rafters of the roof, and provides the benefit of keeping the loft within the heated envelope so that it can be used to provide a ‘room-in-roof’ storey.  Typically, most warm pitched roof insulation systems have a U-value between 0.15 and 0.18 W∙m‑2∙K‑1, although the U-value through an uninsulated, horizontal ceiling to lofts space above the room-in-roof storey will be significantly greater than this.

Thermal Economics’ Raftertherm boards have been an LABC Assured product for over six years as an LABC Registered Detail.  LABC Assured status means that Raftertherm has been assessed for compliance in buildings by the LABC, and doesn’t need to be substantially re-assessed for future use on other sites.

However, Alreflex Raftertherm how has a new LABC Registered Details certificate with new and improved applications for its use in ventilated and non-ventilated pitched roofs to accommodate thinner constructions and greater room heights in room-in-roof storeys.

 

What’s different?

The product itself has not changed, and Raftertherm is available in two different board types:

  • Raftertherm S – our standard, graphite-enhanced EPS board;
  • Raftertherm A – our unique, graphite-enhanced EPS board laminated with reflective foil-and-bubble membrane.

Depending upon your cost and design constraints, Raftertherm can be used in various build ups.

In our previous LABC Registered Detail, Raftertherm had been assessed for use in non-ventilated pitched roof systems, with a Type LR breather membrane; and with the use of the Raftertherm fixing brackets and battens to create a service cavity.  However, our registration now includes installation between and beneath the roof rafters; or in combination with fibrous mineral wool insulation or with an insulated plasterboard.  Although, we obviously think that the combination of Raftertherm beneath and in between the rafters is best!

 

What is a non-ventilated pitched roof and how does it work?

Often warm roof constructions tend to be ventilated through the rafters between the top of the insulation and the bottom of the roofing membrane or sarking board.  This makes it easy to prevent interstitial condensation, but limits the thickness of insulation that can be installed between the rafters; and more importantly the thermal performance of the pitched roof unless a thick, insulating plasterboard is installed beneath the rafters.

For example: The insulated plasterboard would typically be 80 mm thick for a U-value of 0.16 W/m2K in a ventilated warm roof; but the same U-value could be achieved in a non-ventilated pitched roof with only a 50 mm insulated plasterboard; saving costs and increasing room heights!

Non-ventilated warm roofs rely on using a low-resistance roofing membrane to enable water vapour to permeate through the construction and prevent interstitial condensation.  We can show how Raftertherm can be used successfully in non-ventilated pitched roofs: Ask us about our condensation risk assessments!

 

Sounds great!

You can view the certificate and fact sheet for Raftertherm on the LABC website, but you can also speak to our technical department at Thermal Economics for more information including U-value calculations and interstitial condensation risk assessments:

Tel:      01582 544255

E-mail: [email protected]

Chat:   www.thermal-economics.co.uk

In addition, we can also provide you with thermal bridging calculations of the linear thermal transmittance for use in SAP energy assessments.  In particular, calculated Ψ-values for the E11 and E13 Junctions with Raftertherm could mean a better SAP band on the EPC.