At Roundtower Lime, we supply a natural, breathable warm roof insulation system that combines Steico Flex 036 flexible wood fibre with Steico Special Dry sarking boards. This intelligent system delivers superior thermal performance, airtightness, and vapour permeability—ideal for both new-builds and sustainable retrofits.
Designed for use above and between rafters, this warm roof build-up helps minimise thermal bridging, regulate moisture, and reduce energy consumption, while maintaining the breathability critical for traditional and ecological buildings.
System Components
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Steico Flex 036
A highly flexible wood fibre insulation for between-rafter installation, with an exceptional lambda value of 0.036 W/m·K. Offers excellent thermal and acoustic insulation while maintaining breathability. -
Steico Special Dry
A dense, rigid sarking board with built-in weather resistance and vapour permeability, installed over the rafters to create a continuous insulation layer and external wind-tightness. Functions as a secondary rain barrier.
Key Features & Benefits
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High Thermal Efficiency – Significantly reduces heat loss through the roof structure
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Vapour Open System – Allows moisture to diffuse outwards, reducing condensation risk
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Natural & Sustainable – Made from FSC-certified wood, with low embodied energy
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Acoustic Comfort – Excellent sound insulation properties
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Wind and Rain Resistant – Steico Special Dry provides short-term rainproofing during construction
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Robust Airtightness – Reduces uncontrolled air leakage, improving indoor comfort and energy efficiency
Typical Applications
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Pitched roof constructions in both new-build and retrofit projects
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Heritage buildings requiring breathable, reversible roof insulation systems
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Timber frame or masonry buildings where warm roof detailing is preferred
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Deep retrofit schemes seeking NZEB-level performance
Warm Roof Insulation FAQs
Is this system compatible with breathable roofing membranes?
Yes. The system should include a vapour-open roofing membrane (e.g., Steico Multi UDB or Pro Clima Solitex) to ensure full moisture management while protecting against wind and rain.
Can this system be used in Irish weather conditions?
Absolutely. Steico Special Dry is certified for short-term exposure to Irish rainfall during the build phase and provides excellent resistance to wind-driven rain once installed.
How thick should the insulation layers be?
Typical depths include 100–200mm between rafters (Steico Flex 036) and 35–80mm over rafters (Steico Special Dry), depending on performance targets.
Do I still need a vapour control layer internally?
Not necessarily. In most roof types, a variable vapour control membrane (e.g., Pro Clima Intello) is recommended on the warm side of the insulation, especially in high-moisture environments like kitchens or bathrooms.
Is this system suitable for conservation projects?
Yes. The system is fully vapour open, reversible, and uses natural materials—ideal for historic or protected structures.
