Description
Within the XPS insulation boards range, Atlas Fundament 80 mm is the standard specification for foundation and basement walls — the depth most domestic new-builds and EWI retrofits actually order. The board delivers a thermal conductivity of λ 0.038 W/mK in a closed-cell foundation-grade structure, measuring 600 × 1250 mm with rebated edges and covering 0.75 m² per board.
What Atlas Fundament 80 mm Does in a UK EWI System
Atlas Fundament 80 mm delivers R 2.11 m²K/W — the thermal resistance most UK foundation specifications actually require to meet current Part L 2021 calculation targets (current at time of writing) on a typical domestic new-build or solid-wall retrofit. At λ 0.038 W/mK in a closed-cell foundation board, the 80 mm depth handles full foundation wraps, basement perimeter insulation up to 2 m below ground level, and standard plinth-to-DPC build-ups without venturing into the deeper, more cost-sensitive 100 mm-plus territory.
Each board measures 600 × 1250 mm with rebated edges that lock together to form a continuous insulation plane without thermal bridging at the joints — so the moisture-resistant layer reads as a single membrane from one course to the next.
Why Specifiers Choose Atlas Fundament 80 mm for UK Walls
- The default foundation specification: R 2.11 m²K/W sits at the depth most UK domestic projects converge on for Part L calculations — neither under-specified nor over-specified for typical foundation U-value targets.
- Closed-cell moisture protection: Permanent resistance to ground moisture and hydrostatic pressure keeps thermal performance constant for the life of the foundation up to 2 m below grade.
- Rebated edges for joint integrity: Tight overlapping joints reduce the cold-bridge risk that flat-edge boards leave at every horizontal course.
- Freeze-thaw stable: Holds full R-value through repeated UK winter cycles in exposed ground-contact and splash-zone positions.
- Volume-friendly take-off: 600 × 1250 mm covers 0.75 m² per board, so 1.33 boards per m² makes coverage calculations straightforward across long foundation runs and full basement perimeters.
Thermal Specifications — Atlas Fundament 80 mm
| Parameter | Value | Notes |
|---|---|---|
| Thermal conductivity (λ) | 0.038 W/mK | Declared value for foundation board |
| Thickness | 80 mm | Standard Atlas Fundament thickness |
| Thermal resistance (R) | 2.11 m²K/W | At declared λ × thickness |
| Reaction to fire | Per EN 13501-1 | Confirm via current DoP at order |
| Water absorption | Low (closed-cell) | Suitable for permanent ground contact |
Physical Specifications — Atlas Fundament 80 mm
| Parameter | Value |
|---|---|
| Board dimensions | 600 × 1250 mm |
| Coverage per board | 0.75 m² |
| Edge profile | Rebated (lap joint) |
| Compressive strength | Foundation-grade (confirm via TDS at order) |
| Boards per m² | 1.33 (add 5–10% cutting waste) |
Where Atlas Fundament 80 mm Performs Best — Wall Types & Build-Up
The 80 mm thickness is where Atlas Fundament earns its place as the default foundation board across UK domestic projects. The depth balances thermal performance, build-up height, and cost in the range that most Part L calculations land on — deep enough to deliver a meaningful R-value contribution to the overall foundation U-value, shallow enough to avoid the diminishing returns and detailing complications that come with 100 mm-plus boards.
- Full foundation wraps: Apply vertically against the external face of the foundation wall from footing level up to the damp-proof course on standard domestic new-builds. Backfill provides permanent mechanical restraint.
- Basement perimeter insulation: Use across basement and cellar perimeters up to 2 m below ground level, where ground moisture and hydrostatic pressure rule out open-cell alternatives.
- Plinth zones on EWI retrofits: Position from ground level up to the DPC line on solid-wall retrofit projects where the facade above is being insulated and rendered fresh.
- Standard floor build-ups with deeper screeds: Lay horizontally over a level slab in ground-floor extensions and heated utility spaces where the floor build-up can absorb 80 mm of insulation plus a finishing screed.
How Atlas Fundament 80 mm Fits Into a Full EWI System
In a full external wall insulation build-up, Atlas Fundament 80 mm handles the plinth and foundation zone below DPC, while the main facade above is finished with graphite EPS boards bonded with adhesive-and-basecoat and finished with mesh-reinforced render. Bond the 80 mm board with a specialist polyurethane adhesive such as Ceresit CT84 XPS Foam, which cures fast in the cool, damp conditions typical of UK ground-level work.
Above ground level — particularly on plinth zones exposed to wind uplift — add mechanical fixings from the EWI fixing accessories range at 6–8 plugs per m² to lock long-term bond security. The 80 mm board's increased face area catches more wind load than thinner variants, so mechanical fixings are standard practice on any exposed elevation above grade.
How Atlas Fundament 80 mm Compares to Sibling Foundation Boards
| Board | Thickness | R-Value (m²K/W) | Best For |
|---|---|---|---|
| Atlas Fundament 30 mm | 30 mm | 0.79 | Screed underlay, thin plinth, reveal zones |
| Atlas Fundament 50 mm | 50 mm | 1.32 | Floor insulation, shallow foundation wrap |
| Atlas Fundament 80 mm | 80 mm | 2.11 | Standard foundation, basement walls, Part L target |
| Atlas Fundament 100 mm | 100 mm | 2.63 | Deep foundation wrap, highest thermal target |
For projects weighing closed-cell foundation insulation against graphite EPS for the main facade, the XPS vs EPS comparison guide walks through where each material wins across the build-up.
How Atlas Fundament 80 mm Performs in UK Weather — Moisture, Frost, Wind Loads
The closed-cell structure keeps long-term water absorption at near-zero, so freeze-thaw cycling across a typical UK winter does not progressively reduce R-value the way it can on open-cell boards exposed to ground moisture. At 2 m below grade, the 80 mm board holds its thermal performance through saturation, drying, and re-saturation cycles for decades — the thermal envelope around the foundation stays continuous regardless of season.
Wind-load exposure is a meaningful factor above grade at this thickness. The 80 mm face area catches uplift on exposed plinth runs more readily than 30 mm or 50 mm boards do, and on tall facades or coastal sites the mechanical fixing pattern should be set to the project-specific fixing layout rather than a generic 6 plugs per m² — typical layouts run 8 plugs per m² on exposed corners and edges.
Handling & Storage on Site
- Keep dry and shaded: Stack boards flat on a clean, level surface. Cover with sheeting if outdoor storage exceeds a few weeks — prolonged UV softens the closed-cell surface.
- Score, don't snap: Cut with a fine-tooth saw or sharp blade rather than snapping the rebated edge. A clean cut keeps the bonding face true and protects the closed-cell surface.
- Brush the rebate before adhesive: Dust on the lap joint breaks the foam adhesive seal; a quick brush gives a full-face bond.
- Plan deliveries against pour schedule: The 80 mm board is the volume-runner of the range, so foundation-wrap orders typically arrive on full pallets. Stage delivery to match the bonding sequence so boards do not sit exposed on site longer than necessary.
Certifications & Compliance — Atlas Fundament 80 mm
Atlas Fundament boards are manufactured to recognised European foundation insulation standards. Reaction to fire is classified under EN 13501-1, and the declared thermal conductivity (λ 0.038 W/mK) appears on the manufacturer's current Declaration of Performance. For projects requiring specific compressive strength values, water absorption test results, or Approved Document L 2021 calculation inputs (current at time of writing), request the latest DoP at order — exact certified values can vary between production batches and the current Atlas Fundament datasheet is the authoritative reference for compliance submissions.
Is Atlas Fundament 80 mm Right for Your Project?
- Choose this thickness if your project targets standard Part L 2021 foundation U-values on a domestic new-build, EWI retrofit, or basement perimeter — 80 mm is the depth most UK calculations land on without over-specifying or under-delivering.
- Build-up height restricted? The Atlas Fundament 50 mm at R 1.32 m²K/W handles floor insulation under screed and shallow foundation wraps where the slab build-up cannot absorb 80 mm.
- Targeting deeper thermal performance? The Atlas Fundament 100 mm at R 2.63 m²K/W is the thickness for Passive-leaning new-builds and projects pushing well past current Part L thresholds.
- Detailing the plinth-to-facade transition? The plinth thermal-bridge guide walks through the 100 mm overlap detail that keeps the DPC line condensation-free.
What to Order Next — Pack Sizes, Lead Times, Compatible Components
Atlas Fundament 80 mm is supplied as a single board (0.75 m² coverage) and is the volume-runner of the foundation range — typical full-foundation orders ship on pallets from the Southampton warehouse. For project calculations, allow 1.33 boards per m² plus 5–10% cutting waste. To complete the foundation build-up, order Ceresit CT84 XPS Foam for bonding and a fixing pattern of 6–8 plugs per m² above grade for wind-uplift resistance, with 8 plugs per m² on exposed corners and edges.
FAQ — Atlas Fundament 80 mm Coverage, Compatibility, Installation
How many 80 mm Atlas Fundament boards do I need per square metre?
Each board covers 0.75 m² (600 × 1250 mm), so 1.33 boards per m² is the base figure. For typical foundation-wrap and basement-perimeter runs, add 5–10% cutting waste for corners, openings, and rebated overlaps, then round up to the nearest full board. On large projects, ordering in full pallets simplifies delivery and pricing.
Is 80 mm enough to meet Part L foundation targets?
For most standard domestic configurations, 80 mm of Atlas Fundament (R 2.11 m²K/W) brings a foundation wall or basement perimeter within the range typically required to meet Approved Document L 2021 targets (current at time of writing), subject to a project-specific U-value calculation that accounts for wall construction, ground conditions, and the overall thermal target set by the energy assessment.
What adhesive bonds Atlas Fundament 80 mm to a foundation wall?
A specialist polyurethane adhesive such as Ceresit CT84 XPS Foam is the standard route — it cures fast in cool, damp UK ground-level conditions and bonds reliably to closed-cell board surfaces. Apply in continuous beads around the perimeter plus a central bead, brush dust from the rebated edge before placement, and press firmly to spread the foam across the full bonding face.
Does 80 mm need mechanical fixings above grade?
Above ground level on plinth zones, yes — the 80 mm board's face area catches enough wind uplift that mechanical fixings are standard practice. Typical layouts run 6 plugs per m² across the field and 8 plugs per m² on exposed corners and edges. Below ground level, backfill provides permanent mechanical restraint and the polyurethane foam adhesive alone is typically sufficient.
Can I use 80 mm Atlas Fundament on a facade above DPC?
The closed-cell structure limits vapour permeability, so the main facade above DPC typically benefits from graphite EPS or mineral wool rather than foundation-grade board. The 80 mm Atlas Fundament earns its place at the plinth, foundation, and basement perimeter zones where its moisture resistance is the deciding factor — switch to graphite EPS for the elevation above DPC.
How does 80 mm compare thermally to 100 mm Atlas Fundament?
At the same declared λ of 0.038 W/mK, the 80 mm board delivers R 2.11 m²K/W and the 100 mm Atlas Fundament delivers R 2.63 — a 25% uplift in thermal resistance for an extra 20 mm of depth. The 100 mm version is the standard pick for Passive-leaning new-builds and projects pushing past typical Part L thresholds; for projects sitting on the standard threshold, 80 mm is usually the more cost-effective specification.