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Ultratherm board showing "tongue" profile
Ultratherm board showing "groove" profile
The tight fitting "tongue & groove" connection prevents rainwater penetration into the structure
Gutex whole house insulation systems

Gutex Ultratherm

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  • Product Overview
  • Technical Details
  • Installation guide

Main purpose

Weather and rain-proof insulated sarking board. Provides a thermal insulation and robust outer layer for timber frame or Cross Laminated Timber walls and roofs. It can be used on top of other, less-dense, wood fibre insulation boards to provide weatherproofing and additional insulation.

Use it on

Above rafters on pitched roofs and over studs on the external side of timber frame walls.


Gutex Ultratherm is a robust wood fibre insulation board used as weatherproof and rain-proof sarking. It provides excellent thermal insulation in the winter, protects against overheating in summer and eliminates thermal bridges through timbers. Ultratherm has a special tongue and groove profile, which prevents rainwater penetrating the joints between each board. This ensures Ultratherm can be left uncovered on roofs (over 15° pitch), for up to 3 months before cladding or tiles are fitted. Ultratherm is resistant to extreme weather conditions like hail, wind and rain. It also features exceptional acoustic performance.

Where to use it

Gutex Ultratherm can be used externally as an insulated weatherproof sarking board installed on top of the timber or steel rafters and can also be used on the external face of timber stud walls or solid Cross Laminated Timber (CLT) walls.

What it does

Gutex Ultratherm sarking board provides excellent thermal performance in the winter and significantly contributes to a reduction of overheating in the summer due to its high thermal mass. As the board is fixed onto the external face of timbers, it also eliminates thermal bridging though the timbers and can provide significant reductions in heat loss where walls meet floors and roofs and around windows and doors (these are known as non-repeating thermal bridges). 

Why we love it

Gutex Ultratherm insulation board is extremely robust and has a special tongue and groove profile that locks each board together. The profile gives excellent resistance to rainwater penetration (on roofs steeper than 15°) and provides a high degree of wind tightness. The product is also extremely robust and resistant to hailstones. Gutex Ultratherm can be left exposed as the only roof covering for up to three months prior to it being covered with the final roof covering. 

Gutex Ultratherm is made from recycled wood chips generated from the production of other timber products. This means that it has a large amount of stored carbon, which is locked into the building when installed. The stored carbon is more than that emitted during manufacture, meaning Ultratherm is a carbon negative product.


  • Excellent winter thermal performance
  • Summer overheating reduction
  • Weatherproof tongue and groove profile
  • Exceptional acoustic performance
  • Robust and waterproof
  • Breathable
  • Temporarily protects building a construction phase
  • Elimination of thermal bridges


  • A robust connection ensures continuous insulation which prevents wind penetrating into the building.
  • The unique profile allows rainwater to run off the surface.
  • Can be used without an external breathable membrane on roofs over 15° pitch and can be used as a temporary roof cover (exposed to weather) for up to 3 months.
  • Extremely effective, it can achieve overall SAP targets or BER targets with reduced insulation thicknesses (lower psi values).
  • Creates a cosy, comfortable indoor environment and helps reduce heating bills.
  • Rooms in the roof are prone to overheating; this is significantly reduced with Ultratherm’s ability to absorb and slow heat penetration.
  • Allows moisture vapour to move through the insulation eliminating the build-up of damaging condensation. This prevents mould growth and results in good indoor air quality in the living space.
  • Exceptional acoustic performance due to its fibrous nature, high density and inherent windtightness. 


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Technical Details

Key Technical Data

Technical Datasheet

Material Safety Datasheet (MSDS)


Environmental Product Declaration (EPD)

Declaration of Performance (DOP)

System Brochure

Brand/Manufacturer Brochure

Installation Guide

How to Install

The boards should be temporarily fixed into place using thermally broken mushroom headed screws. The boards are then permanently fixed by screwing through the counter battens into the Gutex Ultratherm and then into the timber underneath. 

Fixing patterns for locations and directions of screws can be obtained by contacting our technical team.

Ultratherm boards being connected together on a roof
An example of how to connect Ultratherm boards
Roof completley fitted with Ultratherm panels with an installer working on the finishing touches
An entire roof of fitted Ultratherm panels
Valleys should be primed with Tescon Sprimer and covered with an airtight tape such as Tescon Vana 150mm wide
Valleys should be primed with Tescon Sprimer and covered with an airtight tape such as Tescon Vana 150mm wide

Hints and Tips

If the roof slope (pitch) is less than 15°, the Gutex Ultratherm needs to be covered with a breathable membrane such as Pro Clima Solitex Plus or  Solitex Plus Connect.  

In the case that no membrane is applied over the Ultratherm a number of important details must be addressed. All butt joints and service penetrations of the boards must be primed and securely sealed at the ridge of the roof, use Tescon RP Primer or Tescon Sprimer to prime the wood fibre then tape over with 150mm Tescon Vana airtight tape.

The pitch of a roof which has been fitted with Ultratherm primed and sealed with Tescon Vana airtight tape.
Prime the pitch of the roof and apply Tescon Vana airtight tape to seal the gap.

Rain protection with Gutex Ultratherm

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