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Skydome Calculator (kerb, waterproofing, fixings)

Enter the clear opening (rectangular or round), the kerb height and thickness and the number of skydomes. PRAXAO works out the overall size of the dome to order, the concrete and formwork of the kerb, the waterproofing turned up its outside face and over its top, the sealant bead and the fixings. The drawing shows the skydome in 3D, in plan and in section through the kerb. The overhang, the upstand and the fixings per metre are starting values to replace with the maker’s data.

Configuration

Dimensions

cm
cm

Measured from the structural slab. The waterproofing system and the dome maker give the minimum height above the finished roof.

cm

Kerb (costière) — The raised concrete frame cast round an opening in a roof slab; the skydome or the roof light sits on it.

cm
cm

Information only: it appears on the quote line. Insulation and light values come from the maker.

/m

Waste and cuts (pertes, chutes) — Extra material added for breakage, cuts and offcuts. It is a percentage you set: the usual figure depends on the material and the job.

%
144 cm

Drag to turn the 3D view, or use the arrow keys.

The dome profile and the slab thickness are drawing conventions; the opening, kerb height and thickness and the overhang are to scale.

Calculation results

  • Skydomes1
  • Opening area (all skydomes)1.08 m²
  • Dome overall length (hors tout)144 cm
  • Dome overall width (hors tout)114 cm
  • Kerb outside perimeter (one skydome) ?5 m
  • Kerb concrete, with waste ?0.152 m³
  • Kerb formwork (both faces) ?2.76 m²
  • Waterproofing on kerbs (outside face and top), with waste2.16 m²
  • Sealant bead under the dome frames5 m
  • Dome fixings20

Assumptions

Quantity take-off of dimensions you already have. The kerb design and its reinforcement, the dome (skins, glazing, thermal and fire performance, wind uplift), the waterproofing system and the fixings come from the maker and the engineer; it is not a design.

Preliminary estimate from the values entered: not a structural validation and not an execution plan. Check the local rules and the manufacturers’ data.

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Entered data
Opening length (clear, inside the kerb)
120 cm
Opening width (clear, inside the kerb)
90 cm
Kerb height above the slab (costière)
30 cm
Kerb wall thickness
10 cm
Dome overhang beyond the kerb (each side)
2 cm
Number of skydomes
1
Dome skins (1 single, 2 double, 3 triple)
2
Dome fixings per metre of kerb
4 /m
Waste and overlaps (membrane and concrete)
10 %

Your last inputs are kept in this browser.

Results are provided for information. Check tax rates and legal requirements that apply to you.

How to use it

  1. Choose a rectangular or a round skydome.
  2. Enter the clear opening, the kerb height and thickness, and the number of skydomes.
  3. Replace the starting values (overhang, fixings per metre, waste) with the dome maker’s data.
  4. Read the overall dome size, the kerb concrete and formwork, the waterproofing and the fixings.

Examples

Worked example — Rectangular / square skydome — Opening length (clear, inside the kerb) 120 cm, Opening width (clear, inside the kerb) 90 cm, Kerb height above the slab (costière) 30 cm

Skydomes: 2 · Opening area (all skydomes): 2.16 m² · Dome overall length (hors tout): 144.0 cm · Dome overall width (hors tout): 114.0 cm · Kerb outside perimeter (one skydome): 5.00 m · Kerb concrete, with waste: 0.304 m³ · Kerb formwork (both faces): 5.52 m² · Waterproofing on kerbs (outside face and top), with waste: 4.31 m² · Sealant bead under the dome frames: 10.00 m · Dome fixings: 40

Frequently asked questions

Does it design the kerb or choose the dome?

No. It counts what the dimensions you enter require. The kerb design and its reinforcement, the dome (skins, glazing, thermal and fire performance, wind uplift) and the waterproofing system come from the maker and the engineer.

What is the overall size of the dome?

The clear opening, plus the kerb thickness on each side, plus the overhang of the dome frame beyond the kerb on each side. It is the size to give when ordering from the maker.

How is the waterproofing counted?

The membrane is turned up the outside face of the kerb and over its top: the outside perimeter times the kerb height, plus the plan area of the kerb, with the waste you enter for laps and cuts.

Guides to go further

BUILNORA

Waterproofing Calculator

Membrane rolls and primer to waterproof a flat roof or terrace, with upstands, side laps and waste.

BUILNORA

Concrete Calculator

Volume of concrete for slabs, footings and columns, with waste margin and cement, sand and gravel quantities.