dcf.cymru stimulus sheet · Design Technology · Year 9
Six possible materials for one product. The school and its eco-committee are invented, and the prices are illustrative figures for this lesson, not a supplier's price list. The properties described are real.
The eco-committee at Ysgol Llanbedr-ar-Fryn wants 20 nest boxes for blue tits to put up around the school grounds before the spring nesting season. Year 9 will make them in DT. The committee has £100 for materials. The boxes will be outside all year, through a wet Welsh winter, and the committee would like them to last several seasons.
Bird charities such as the RSPB advise solid timber at least 15 mm thick, so the box does not get too hot or too cold; an entrance hole of 25 mm for blue tits; and, if a preservative is used at all, a water-based one on the outside only.
| Material | Cost of material for one box | What it is really like for this job |
|---|---|---|
| A. Pine, 18 mm, FSC-certified, untreated | £3.20 | A softwood. Easy to saw, drill and nail with school tools. Good insulation, and it breathes, so the inside stays dry. It will weather and eventually rot outdoors; a water-based preservative on the outside slows that down. Grown in managed forests and replanted. |
| B. Oak, 18 mm | £9.60 | A hardwood. Very durable outdoors with no treatment at all, and excellent for the birds. Heavy, and hard to saw and nail by hand — screw holes need drilling first. Oak grows slowly, so it is a less renewable choice than pine. |
| C. Exterior plywood, 18 mm | £4.10 | Thin layers of wood glued together with a waterproof glue. Resists warping and is fairly durable outside, but water gets in at the cut edges unless they are sealed. Easy to cut on a band saw. The glue makes it harder to recycle or compost at the end of its life. |
| D. MDF, 18 mm | £2.40 | Wood fibres pressed together with resin. The cheapest and the easiest to cut cleanly. It is not made for outdoor use: once it gets wet it swells and crumbles. Cutting it makes fine dust, so it needs dust extraction. |
| E. Recycled HDPE plastic board, 12 mm | £7.50 | Made from recycled plastic such as milk bottles. Will not rot, so it lasts for many years outside. It does not breathe, so condensation can build up inside, and a dark board in full sun gets hot. Cannot be glued well; it needs screws. |
| F. Acrylic sheet, 5 mm | £8.80 | Weatherproof, and it can be laser cut. Clear or thin sheet gives the nest no shelter from heat, cold or light, and it does not breathe. Brittle: it cracks if drilled carelessly. Made from oil. |
Each material has been scored from 1 to 5 on four criteria. 5 = excellent for this job, 3 = acceptable, 1 = unsuitable. These are the department's judgements, made from the descriptions above. The fifth criterion, cost, you score yourself.
| Material | Durability outdoors | Bird welfare | Ease of making in school | Sustainability |
|---|---|---|---|---|
| A. Pine | 3 | 5 | 5 | 4 |
| B. Oak | 5 | 5 | 2 | 3 |
| C. Exterior plywood | 4 | 4 | 4 | 3 |
| D. MDF | 1 | 3 | 5 | 2 |
| E. Recycled HDPE | 5 | 2 | 3 | 4 |
| F. Acrylic | 4 | 1 | 2 | 1 |
| Cost of material for one box | Cost score |
|---|---|
| Under £3.00 | 5 |
| £3.00 to £4.99 | 4 |
| £5.00 to £6.99 | 3 |
| £7.00 to £8.99 | 2 |
| £9.00 or more | 1 |
A weight says how much a criterion matters. Each score is multiplied by its weight, then the five results are added.
| Criterion | Weight |
|---|---|
| Durability outdoors | × 3 |
| Bird welfare | × 3 |
| Cost | × 2 |
| Ease of making in school | × 2 |
| Sustainability | × 2 |
The weights add up to 12, so the highest possible total is 12 × 5 = 60.