Description
The XPS foundation board 80mm from the Renders World XPS foundation board range is a blue, water-repellent XPS board, 1000 × 500 mm, sold singly. Its job is the plinth under an 80 mm insulated wall, and the foundation below it.
Where the XPS Foundation Board 80mm Belongs
Facade boards are made for render, not for standing in splash water and wet soil. So the wall is insulated in two zones: a facade board above the damp-proof course, an XPS foundation board below it. When the facade is 80 mm, this board keeps the bottom of the wall at the same depth:
- Plinths from the DPC down to ground level, finished flush with the 80 mm facade.
- Foundation walls below ground, continuing the same insulation plane into the excavation.
- The foundation perimeter, where the wrap turns the corners of the building at the same depth.
Why Choose the 80 mm XPS Foundation Board
- About 2.10 m²K/W of thermal resistance: 0.080 ÷ 0.038 = 2.11, rounded down to 2.10.
- The same depth as an 80 mm facade board, so the mesh and render run over the DPC line without a step.
- 100 kPa compressive strength, enough for backfill and paving loads against the plinth.
- Water absorption of 5 % under long-term immersion and 150 kPa bending strength, from the board's CE marking.
Specification — XPS Foundation Board 80mm
| Property | Value |
|---|---|
| Board | XPS foundation board, blue, water-repellent |
| Thickness | 80 mm |
| Board size | 1000 × 500 mm (0.5 m²) |
| Sold as | 1 board |
| Thermal conductivity λD | 0.038 W/mK |
| Thermal resistance | 2.10 m²K/W (0.080 ÷ 0.038 = 2.11, rounded down) |
| Compressive strength | 100 kPa |
| Bending strength | 150 kPa |
| Water absorption, long-term immersion | 5 % |
| Reaction to fire (the board alone) | Class E |
The Wall Above and the Parts Around It
Above the DPC, the 80 mm graphite EPS facade board takes over at the same depth. The rest of the plinth comes from three shelves: adhesives and basecoats for insulation boards to bond the boards, insulation fixing accessories for the starter track and anchors, and mosaic plinth renders for a finish that copes with splash water. The plinth thermal bridge guide shows how the two zones meet at the DPC.
80 mm in the Range
| Board | Thermal resistance (thickness ÷ 0.038) | Typical place |
|---|---|---|
| 30 mm | 0.75 m²K/W | Thin plinths where little depth is free |
| 50 mm | 1.30 m²K/W | Shallow plinths and foundation wraps |
| 80 mm (this board) | 2.10 m²K/W | Plinths under an 80 mm facade |
| 90 mm | 2.35 m²K/W | Plinths under a 90 mm facade |
| 100 mm | 2.60 m²K/W | Deepest wrap, 100 mm facades |
Every depth has λD 0.038 W/mK. To see what 80 mm does for the whole wall, use the U-value and insulation thickness guide.
How Many Boards
Each XPS foundation board 80mm covers 0.5 m², so two make a square metre. Take the plinth length times its height, double the result, round up, and allow a few boards for cuts around corners and openings.
FAQ — 80 mm XPS Foundation Board
What size is one board, and how many make a square metre?
1000 × 500 mm and 80 mm thick, so one board covers 0.5 m² and two cover a square metre. It is sold one board at a time.
Can I carry it up the wall above the DPC?
Above the DPC the wall takes a facade board made for render. Keep this board to the plinth and the foundation, and continue at 80 mm with the graphite EPS facade board so the render runs over the joint without a step.
80 mm or 100 mm?
80 mm gives about 2.10 m²K/W, 100 mm about 2.60. Match the facade above; where it is 100 mm, take the 100 mm foundation board.
Which adhesive do I use for the 80 mm board?
An adhesive for insulation boards, from the adhesives and basecoats range. Check that the adhesive's own data sheet covers XPS boards and, below ground, damp conditions.
What does fire class E mean for a rendered plinth?
Class E is the board's own reaction-to-fire class. A rendered plinth is assessed as a whole system, so the finished wall takes its class from that system, not from the board.