About this calculator
This calculator helps estimate the quantities for a vented facade — framing, insulation, wind/vapour membrane, and fixings — enter the wall dimensions, the framing spacing and dimensions, the insulation thickness, and the board size. Works for planning a facade with a vented air gap behind the cladding (timber battens, composite panels, or another hung cladding) system. The cladding itself (panels, battens, and so on) is not included in the calculation.
Formula
Framing (vertical members at a fixed spacing, "fencepost" style):
full-bay count = floor(wall length / framing spacing)
remainder = wall length − full-bay count × framing spacing
vertical member count = full-bay count + 2 (if remainder > 0, otherwise +1)
bay count = member count − 1
cross-batten count = floor(wall height / cross-batten spacing) + 1
(0 if cross-batten spacing = 0 — a single-layer framing with no cross-battens)
timber volume = vertical members (count × height × depth × width)
+ cross-battens (count × length × air gap depth × width)
Insulation: unlike the bonded (ETICS) wall-insulation calculator, insulation here isn't laid across a continuous surface — it fills the bays BETWEEN vertical members:
insulation area = wall area − (member count × member width × wall height)
boards across the bay (by width) = ceil(clear bay width / board width)
boards along the height = ceil(wall height / board length)
boards required (excl. waste) = bay count × boards across × boards along
where "clear bay width" = framing spacing − member width. All bays, including the last (closing) bay at the wall's far edge, are treated as the standard-spacing width — a simplification that only becomes inexact when the wall length isn't an exact multiple of the framing spacing.
Membrane (wind/vapour barrier film): courses are laid bottom to top, each later course adding only its effective (post-overlap) coverage:
membrane course count = 1, if wall height ≤ roll width;
otherwise 1 + ceil((wall height − roll width) / effective coverage)
effective coverage = roll width − overlap allowance
membrane area = course count × wall length × roll width
rolls required = ceil(course count × wall length / roll length)
Fixings: for each member, fixing count = ceil(wall height × fixings/m / 1000),
multiplied by the member count. Fixing length = framing depth + embedment depth (chosen by
substrate type — masonry or timber).
Build-up depth: framing depth + air gap depth + a fixed illustrative cladding-zone constant (30 mm, not a value you entered).
R value (insulation layer only): R = insulation thickness / λ (ISO 6946), the same as
the wall-insulation calculator.
Worked example
Defaults: wall length 4 m, height 2.5 m, no openings, framing spacing 600 mm, framing depth and width 45 mm each, no cross-battens, insulation thickness 100 mm, board 1200×600 mm, air gap 25 mm, membrane roll 1500×50,000 mm, overlap 100 mm, 3 fixings/m, masonry substrate (embedment 40 mm), λ = 0.035 W/(m·K), waste 10%.
full-bay count = floor(4000 / 600) = 6
remainder = 4000 − 6×600 = 400 mm (> 0)
member count = 6 + 2 = 8
bay count = 8 − 1 = 7
timber volume = 8 × 2500 × 45 × 45 = 40,500,000 mm³ (no cross-battens)
insulation area = 4 m × 2.5 m − (8 × 45 mm × 2.5 m) = 10,000,000 − 900,000 = 9,100,000 mm² ≈ 9.1 m²
clear bay width = 600 − 45 = 555 mm
boards across = ceil(555 / 600) = 1
boards along = ceil(2500 / 1200) = 3
boards excl. waste = 7 × 1 × 3 = 21
waste boards = ceil(21 × 10 / 100) = 3
total boards = 24
membrane courses = 1 + ceil((2500−1500)/(1500−100)) = 1 + 1 = 2
membrane area = 2 × 4000 × 1500 = 12,000,000 mm² = 12 m²
rolls required = ceil(2 × 4000 / 50,000) = 1
fixings per member = ceil(2500 × 3 / 1000) = 8
fixing count = 8 × 8 = 64
fixing length = 45 + 40 (masonry embedment) = 85 mm
build-up depth = 45 + 25 + 30 (schematic cladding zone) = 100 mm
R = 0.1 / 0.035 ≈ 2.86 m²·K/W
For these inputs the calculator returns exactly this: 8 vertical members, timber volume 40.5 million mm³, insulation area 9.1 m², 24 boards total (21 + 3 for waste), membrane area 12 m² (1 roll), 64 fixings of 85 mm each, and R = 2.86 m²·K/W.
FAQ
Are openings (doors, windows) deducted from the framing, insulation, or membrane quantity? No. Unlike the bonded (ETICS) wall-insulation calculator, openings aren't deducted from any quantity here — the calculator doesn't collect an opening's horizontal position on the wall, so it can't know which particular bay between members an opening replaces. Opening area is shown only in the informational "net area" field, with no effect on the framing, board, membrane, or fixing count.
Why is the insulation area computed differently than in the bonded (ETICS) wall-insulation calculator? Because here insulation isn't laid across a continuous surface — it fills the bays BETWEEN vertical members. So the insulation area is the wall area minus the members' own footprint, and the board count depends on the clear (member-width-reduced) bay, not on a flat plane.
Are all bays between members the same width? In the calculator — yes, a deliberate simplification: every bay (including the last one, at the wall's far edge) is treated as the standard-spacing width. This is exact only when the wall length is an exact multiple of the framing spacing — otherwise the real last bay may be narrower.
Does the R value cover the whole wall assembly, including the framing? No. The R value is computed only for the insulation layer, using the ISO 6946 formula (the calculator's own R-value result says so explicitly). The timber members themselves are a thermal bridge (timber conducts heat more readily than insulation), which this R value doesn't account for.
Does the calculator include the cladding itself (panels, battens)? No, the cladding is outside this calculator's scope. In the build-up depth drawing, the cladding zone is shown only as a fixed schematic 30 mm constant, not a real cladding thickness dimension.
Assumptions and limits
meta.standards cites ISO 6946 — the source of the R = thickness / λ formula, applied only
to the insulation layer. No standard was found for the framing/board/membrane/fixing
quantity calculation — these depend on the specific product and site practice, not one
universal standard.
Openings are not deducted from any quantity (framing, boards, membrane, fixings) — the same conservative logic as the wallpaper calculator: the calculator doesn't collect an opening's horizontal position, so it can't know which particular framing bay an opening replaces. Opening area is shown only in the informational field.
Board count is computed using the nominal (standard-spacing) bay width, not each bay's exact width — the last bay at the wall's edge may in reality be narrower, if the wall length isn't an exact multiple of the framing spacing.
λ, fixing density, and embedment depths (masonry and timber) are user inputs with sensible defaults, not constants derived from a standard — they depend on the specific product's own technical approval.
The R value covers only the insulation layer — the timber framing members are a thermal bridge that this value doesn't account for. The cladding itself (panels, battens, and its own fixing system) is outside this calculator's scope — in the layer cross-section drawing, the cladding zone is a fixed schematic constant, not a real dimension.
The layer cross-section drawing itself is schematic: only the framing/insulation cavity depth and the air gap depth are drawn to their real thickness. The substrate, membrane, and cladding zone layers are illustrative only.