Passive Slab (Izodom) vs ISOQUICK
Two insulated foundation systems for low-energy builds, compared using what each supplier publishes.
Who wrote this: ISOQUICK, so we have a stake in the answer. Every Passive Slab statement below comes from its own website, and every ISOQUICK statement comes from our Kiwa certificate, our published U-value tables, or is marked as ISOQUICK's own. We could not find Izodom's own technical data for its foundation slabs, so where the Passive Slab pages are silent we say "not stated". We have not tested either product. Check current details with each supplier. Part of a wider comparison of UK insulated foundation systems.
Which "Passive Slab"?
Two different suppliers use this name. Passive Slab (passiveslab.co.uk, Clydebank, Scotland) describes itself as the exclusive UK partner for Izodom 2000 products and supplies Izodom insulating panels for foundation slabs. Viking House in Ireland also sells a product it calls "Passive Slab", which is a different system. This page is about the Clydebank Passive Slab, and searches for "Izodom 2000 foundation" lead here.
At a glance
| Passive Slab (Izodom panels) | ISOQUICK | |
|---|---|---|
| Insulation | "High-quality, high density interlocking insulation panels from Izodom" (EPS grade and compressive strength not stated on its pages) | EPS in three grades: IQ-60e (200 kPa, λD 0.031), IQ-90 (300 kPa, λD 0.033) and IQ-210 (700 kPa, λD 0.034), per the Kiwa certificate. |
| Design | Panels join with tongue-and-groove and dovetail joints around an in-situ reinforced concrete slab. The slab profile (flat or with edge beams) is not described on the pages reviewed. | ISOQUICK describes its system as a flat raft, where wall loads are spread across the slab. |
| Certification | Not stated for the foundation system on the pages reviewed. Econekt, which also distributes Izodom products in the UK, describes Izodom's ICF wall products as Passivhaus certified; that statement is about the walls, not the foundation slab. | Kiwa BDA Agrément BAF-20-179-S-A-UK, for new dwellings (first issued February 2022, reissued July 2025). Also a Certified Passive House Institute component (certificate 0379fs03) for ICF, external-insulation and lightweight-timber connection details. |
| Published U-value | 0.09–0.14 W/m²K, "p/a ratio dependant". Build-up not stated. | 0.07–0.18 W/m²K across grades, depending on under-slab insulation (150–300 mm) and P/A ratio, with a 250 mm slab assumed. For example, IQ-60e with 200 mm under-slab insulation gives 0.09 at P/A 0.1 rising to 0.13 at P/A 0.6 and above. |
| Published Psi-value | Not stated. It says the system "completely isolates the building from the ground" and removes thermal bridging at the slab-to-wall junction. | ISOQUICK states a PHPP Psi-value below 0.1 W/mK for a typical 200 mm build-up. The Passive House certification criterion for certified details is Ψe ≤ 0.01 W/mK. |
| Service model | Supply only, on-site assistance at key stages, or a full supply and install service. Includes thermal modelling and U-value calculations, point-load assessments, reinforcement layouts and installer training workshops. | Design support and supply. |
| Where | Clydebank, Scotland; says it provides services nationwide across the UK. | UK-wide. |
Sources: passiveslab.co.uk (home, About and Services pages); Econekt product listing for Izodom 2000; ISOQUICK Kiwa certificate BAF-20-179-S-A-UK, U-value tables TD-0002 and TD-0004 (May 2025) and Passive House Institute certificate 0379fs03.
What the comparison can and can't tell you
Certification is the clearest difference on paper. ISOQUICK publishes a third-party certificate number for its foundation system. Passive Slab's pages do not name one for its foundation slabs, so if you are considering it, ask which certificate or assessment covers the foundation system, what it covers and when it expires. Izodom may hold documentation we could not find, and a supplier not stating something is not the same as not having it.
The U-values are not like-for-like. Passive Slab gives a range with no build-up. ISOQUICK's tables state the slab thickness they assume and the insulation depth for each figure. Ask both for a calculation at your own P/A ratio.
The service models differ. Passive Slab offers a wider range of involvement, including full installation and training. If you want the foundation designed, supplied and installed by one team, that matters as much as the thermal figures. Ask each supplier what is included in the price and who carries design responsibility.
Questions to ask both suppliers
- Which certificate covers the foundation system, what wall types does it cover, and when does it expire?
- What is the EPS grade and compressive strength, and what permanent load can it carry?
- What is the U-value for my P/A ratio, with slab thickness and insulation depth written out?
- What is the Psi-value at the wall-floor junction for my wall type, and who calculated it?
- Is the slab a flat raft or does it have edge beams, and who takes design responsibility?
- What ground conditions is the design suitable for, and what does the engineer need from me?
Get ISOQUICK figures for your project
Send us your plans and wall type and we will give you the U-value, the junction detail and the certification that applies.
Get a Quote All systems comparedSources
- Passive Slab — Home, About and Services
- Econekt — Izodom 2000 ICF product listing and Passivhaus page
- Viking House — Passive Slab (Ireland)
- ISOQUICK — Kiwa BDA Agrément BAF-20-179-S-A-UK; U-value tables TD-0002 and TD-0004; Passive House Institute certificate 0379fs03
Spotted something out of date or wrong? Suppliers and readers can tell us through the callback form and we will correct it.