A bathroom has a large radiator but almost no shelf space for toiletries. The area above the radiator is warm and unused. The occupant wants a shelf that si...

(a) Four functional points [4 marks]

1. Allow hot air to circulate — A radiator heats a room by convection: cool air is drawn in at the base, heated, and rises from the top. A solid shelf covering the radiator would trap rising air and reduce heating efficiency. The shelf surface must include gaps, slots, or mesh panels to let warm air pass through freely. [1]
2. Resist moisture and humidity — Bathroom air contains high levels of water vapour from baths and showers. Materials that absorb moisture (such as untreated MDF or softwood) would swell, warp, and eventually develop mould. The shelf must be made from naturally moisture-resistant material or be sealed with a waterproof finish. [1]
3. Protect surfaces from scratching — The shelf rests on or hooks over a painted radiator and may touch the wall behind it. Hard contact points would scratch the radiator paint or mark the wall surface. Protective pads (felt, rubber, or silicone) at every contact point prevent damage and also stop the shelf from sliding. [1]
4. Stability against tipping — Toiletry bottles are often placed near the front edge of a shelf. If the centre of gravity shifts forward, an unsupported shelf could tip off the radiator. The design must ensure the shelf is balanced or anchored so it remains stable even when items are placed at the front. [1]

(b) Two resting methods [4 marks]

Method 1 — Hook-over brackets: Two inverted U-shaped metal brackets (made from 3 mm mild steel rod) hook over the top of the radiator. The inside of the U matches the radiator's top profile (approximately 50-60 mm wide). Felt pads are glued to the inner faces of each bracket to prevent scratching the radiator. The horizontal top of each bracket extends outward to form a flat base plate (50 mm x 100 mm) that is screwed to the underside of the shelf. The shelf can be lifted off the radiator for cleaning. [2]

Method 2 — Freestanding leg frame: Four tall legs (two at the front, two at the back) straddle the radiator and rest on the floor on either side. The shelf spans across the top of the frame, positioned above the radiator with a clearance gap of at least 20 mm to allow air circulation. The floor-standing design avoids any contact with the radiator itself, but the legs take up floor space beside the radiator. Rubber feet prevent the legs from sliding on a bathroom floor. [2]

(c) Three design ideas [12 marks]

Idea 1 — Slatted timber shelf on hook-over brackets: Five hardwood slats (each 30 mm wide, 15 mm thick) are spaced 10 mm apart and housed into two cross-rails at each end. The gaps between slats allow warm air to rise through the shelf surface. Two steel hook-over brackets support the assembly. A 20 mm back lip runs the full width to prevent items from falling behind the radiator. The warm colour and texture of timber suits a bathroom environment, and the slatted construction is straightforward to make in a school workshop. [4]

Idea 2 — Metal mesh shelf on freestanding frame: Two tiers of galvanised steel mesh panels sit on a freestanding tubular frame that straddles the radiator. The open mesh allows complete airflow. The upper tier holds display items and the lower tier holds heavier bottles. This design requires metalworking skills (welding or brazing) that may not be available in all school workshops, and the metal surface can feel cold to touch in a bathroom. [4]

Idea 3 — Perforated acrylic shelf on adjustable clamp arms: A single wide shelf is laser-cut from acrylic sheet with a pattern of ventilation holes. Side arms with thumbscrew clamps grip the radiator to hold the shelf at an adjustable height. The acrylic is waterproof and easy to clean, but acrylic can become brittle when exposed to heat cycling near a radiator, and the clamp mechanism must not damage the radiator fins. [4]

(d) Evaluation and justification [8 marks]

Idea 1 (Slatted timber) — Strengths: timber is warm to touch (pleasant in a bathroom); slatted design provides excellent airflow through gaps; simple flat-panel construction within school workshop capability; hook-over brackets allow removal for cleaning. Weaknesses: timber requires a moisture-resistant species or waterproof finish; the unit protrudes slightly in front of the radiator.

Idea 2 (Metal mesh frame) — Strengths: maximum airflow; two tiers double the storage capacity. Weaknesses: requires welding equipment; metal feels cold; industrial appearance may not suit a domestic bathroom.

Idea 3 (Perforated acrylic) — Strengths: waterproof; modern aesthetic. Weaknesses: acrylic can become brittle and crack under prolonged heat exposure; thumbscrew clamps may mark the radiator; drilled perforations weaken the sheet structurally.

Chosen idea: Idea 1. The slatted timber shelf combines effective airflow, warm aesthetics, and school-workshop-appropriate construction. Teak (or another naturally water-resistant hardwood) eliminates the need for a plastic film finish. The hook-over brackets are simple to bend from steel rod and give a secure, removable mounting. [8]

(e) Full solution — construction details [12 marks]

The solution is drawn as an exploded isometric view.

• Shelf surface: Five slats, each 600 mm long x 30 mm wide x 15 mm thick, with 10 mm gaps between them. Overall shelf width: 600 mm. Overall shelf depth: 190 mm (5 slats x 30 mm + 4 gaps x 10 mm).
• Cross-rails: Two hardwood strips (190 mm x 30 mm x 15 mm) at each end, with five housing joints (5 mm deep, 30 mm wide) cut to receive the slat ends.
• Back lip: A strip 600 mm x 20 mm x 15 mm, housed into the rear cross-rail ends. Prevents bottles falling behind the radiator.
• Hook-over brackets: Two brackets bent from 3 mm mild steel rod into an inverted U-shape, 160 mm tall (to clear the radiator top). Each U is approximately 60 mm wide at the inside to straddle the radiator. A flat base plate (50 mm x 100 mm, 2 mm mild steel) is welded to the top of each U. Two 4 mm clearance holes are drilled in each base plate for screws that fix the bracket to the underside of the shelf cross-rail.
• Protective pads: Self-adhesive felt strips on the inner faces of each bracket where they contact the radiator.

(f) Materials [4 marks]

1. Teak hardwood (15 mm) for the shelf slats, cross-rails, and back lip. Teak contains natural oils (tectoquinones) that make it resistant to water absorption and fungal growth, which is essential in a humid bathroom. It does not warp or swell when exposed to steam, and has an attractive warm brown colour. Teak can be finished with yacht varnish or left unfinished to develop a silver-grey patina. [2]
2. Mild steel rod (3 mm diameter) for the hook-over brackets. Mild steel is easy to bend into shape in a school workshop using a metalworking vice and a bending jig. It is strong enough to support the shelf and its contents (toiletry bottles typically weigh 2-5 kg in total). The brackets can be powder-coated or spray-painted to resist rust in the damp bathroom atmosphere. [2]

(g) Manufacturing one slat [6 marks]

1. Select and mark out: Select a piece of teak approximately 650 mm x 35 mm x 18 mm (oversized to allow for planing). Mark the finished length (600 mm) and width (30 mm) using a pencil, steel rule, and try square. [1]
2. Plane to size: Plane to finished dimensions of 600 mm x 30 mm x 15 mm using a jack plane. Check width and thickness with a steel rule and squareness of edges with a try square. [1]
3. Cut notches: Mark a 5 mm x 5 mm notch at each end (where the slat will sit in the cross-rail housing) using a marking gauge. Cut the notches with a tenon saw and pare to the marked line using a bevel-edged chisel. [1]
4. Sand: Sand all faces and edges progressively from 120-grit through 240-grit to 320-grit abrasive paper, working along the grain direction. Round all edges slightly with the sanding block to prevent splinters. [1]
5. Apply finish: Apply two coats of exterior-grade yacht varnish using a clean brush. The first coat seals the open pores of the teak; sand lightly with 320-grit between coats to provide a key for the second coat. The varnish creates a waterproof, glossy barrier that protects against bathroom moisture and is easy to wipe clean. [2]