SIPit 245 mm SIP Panels: A Simple system for Passivhaus Performance

Achieving Passivhaus performance doesn’t need to involve complex assemblies, deep build‑ups, or multiple insulation layers. SIPit’s 245 mm OSB‑PU structural insulated panels provide a simple, predictable, and certifier‑friendly route to ultra‑low energy construction — delivering both thermal performance and airtightness with minimal detailing.

With a U‑value of 0.09 W/m²K, the 245 mm SIPit panel meets and exceeds the fabric requirements for Passivhaus envelopes. Combined with insulated splines and reduced joint frequency, the system is engineered to achieve airtightness comfortably below 0.6 ACH @ 50 Pa when installed correctly — the critical threshold for Passivhaus certification.

Passivhaus Airtightness

Airtightness is one of the most demanding aspects of Passivhaus construction. The standard requires:

• ≤0.6 air changes per hour (ACH)

• Measured at 50 Pascals using a blower door test

• Verified during construction and at completion

SIPit’s large‑format OSB‑PU panels, insulated splines, and minimal timber content create an envelope with very few joints, making airtightness detailing significantly simpler than traditional timber frame or masonry systems.

With correct installation — continuous VCL, sealed service void, taped junctions, and controlled penetrations — SIP envelopes routinely achieve results well below 0.6 ACH, providing:

• Lower heating demand

• Improved comfort

• Reduced risk of moisture ingress

• Predictable certification outcomes

This makes SIPit an ideal choice for designers targeting Passivhaus Classic, Plus, or Premium.

Passivhaus Wall Build‑Up (Internal → External)

A clean, minimal build‑up that delivers high performance without complexity:

• 12.5 mm plasterboard

• 25 mm service void (keeps penetrations out of the airtight layer)

• Vapour Control Layer (VCL)

• 245 mm SIPit panel

• Breather paper

• 50 mm ventilated cavity

• External cladding, render board, or stone facing

Why This Works for Passivhaus

• 0.09 W/m²K centre‑panel U‑value

• Insulated splines minimise cold bridging

• Low timber fraction improves whole‑wall performance

• Ventilated cavity ensures moisture safety

• Simple airtightness detailing with predictable junctions

This is a wall build‑up that meets Passivhaus fabric targets without secondary insulation — reducing cost, depth, and complexity.

Openings and Structural Logic

Passivhaus design often involves careful control of thermal bridges around openings. SIPit simplifies this:

• Small openings: SIP lintels

• Medium spans: 195×45 mm timber lintels (Insulated on the internal face)

• Large spans (2.5 m+): flitch beams or steel I‑beams with posts (Insulated on the internal face)

Insulated splines and minimal timber content ensure thermal continuity around openings, supporting PHPP modelling and certification.

Passivhaus Roof Build‑Up (Internal → External)

The SIPit roof panel mirrors the simplicity of the wall system:

• 12.5 mm plasterboard

• 45 mm service void

• VCL

• 245 mm SIP roof panel

• Breather paper

• 50 mm ventilated void (essential for timber‑based systems)

• Furring pieces / battens / counter‑battens

• Roof finish

Structural Capability

• Typical span for a 245 panel: 5–6 m

• Increased spans possible with:

  • Load‑bearing partitions, or

  • Mid‑span purlins

The ventilated void above the OSB ensures long‑term moisture safety — a critical factor in Passivhaus roof design.

Intermediate Floors: MVHR‑Friendly Solutions

Passivhaus buildings rely on efficient MVHR systems. SIPit recommends metal web joists at intermediate floors to allow:

• MVHR ducting to pass through the floor zone

• Clean service runs without compromising airtightness

• Faster installation and reduced penetrations

This supports both airtightness and serviceability — two key Passivhaus principles.

Why SIPit Works So Well for Passivhaus Projects

• Ultra‑low U‑values with a single panel

• Airtightness below 0.6 ACH with correct detailing

• Minimal cold bridging through insulated splines

• Low timber fraction improves PHPP results

• Predictable moisture behaviour

• Straightforward junctions for certifier approval

• Fast installation reduces site exposure and risk

SIPit’s 245 mm OSB‑PU system offers and easier route to Passivhaus performance — without the complexity often associated with ultra‑low‑energy construction. Simple construction means less figuring out onsite, therefore less time onsite, with more cost efficiency, less margin for error, and it also makes it easier to achieve a higher standard of finish.

If you have a project you would like to build with SIP, Contact us for more information and we can provide you with everything you need to start your SIP journey. info@sipit.uk T: 01224 531947