I want to cover and enclose the existing terrace on the front and rear of my second-floor apartment (in a house, not a block of flats) so that it is weatherproof, yet doesn’t count as a permanent structure. The building is old, and I don’t want to increase the load on the structure. Ideally, the enclosure should be easy to dismantle later. Also, we would prefer that it does not get too hot or allow surrounding sounds to enter easily.
You can simply buy and place the all-weather, lightweight, temporary structures that are popularly called portable cabins. The industry that manufactures these cabins is clearly divided into two segments: organized industrial production and unorganized fabricators. They all employ a wide variety of materials from PVC (polyvinyl chloride), GI (galvanized iron), and fibre-reinforced cement sheets to several different combinations of sandwich panels. Experience has shown poor quality of workmanship and ineffective after-sales service with both these segments, so be careful when selecting the vendor. Ask for personal recommendations. You need to personally confirm the referrals or recommendation letters provided by the fabricator. Find out if the structures fabricated by the vendor have developed problems. You also need to clearly understand what after-sales service will be provided by the vendor (if any). It is not unusual to get the structure of the proposed cabin (especially in the case of large spans) vetted by your interior design or architecture consultant.
The choice of material is very important. Sandwich panels are highly recommended over single-layer materials. Typically a sandwich panel is a combination of more than one material joined together into large, lightweight boards. These boards come in a variety of sizes and thickness (30-75mm). They can be easily sawed and joined together using metal channels, simple screws or special expansion bolts. Sandwich panels are extremely sturdy as their outer surface is made up of waterproof, scratch-resistant, dent- resistant, fire-retardant and termite-resistant material. The inner core typically consists of low-density insulation materials.
Port-a-room: Temporary structures such as these are easy to fabricate and dismantle.
Recommended outer skins or surface material for the sandwich panels (in order of preference) are:
• Pre-painted (PU, or polyurethane, paint) or powder-coated corrugated GI sheet with thickness not less than 0.58mm and corrugation not more than 20mm.
• Fibre-reinforced flat cement sheets, of thickness not less than 5mm. Do not use sheets reinforced with asbestos fibre (these are harmful to health) and avoid sheets made of wood fibre too. Polymer fibres are a good alternative.
• Pre-coloured, UV radiation-stabilized PVC (corrugated or plain) sheets. Fire is a concern.
• Waterproof and termite-proof, multi-layered, wood-based particle boards or plywood boards. Environment is the bigger concern here.
Recommended inner core material for sandwich panels (in order of preference) are:
• CFC-free PU or polyethylene (PE) foam with low thermal conductivity, which retains its form easily.
• Mineral (or rock) wool or glass wool, with low conductivity but tend to sag and collect as debris at the base of vertical panels in time.
• Foam concrete, which is stable and inert but a little less insulating than the materials above.
• Rice husk is very good insulator but difficult to work with—it goes everywhere.
Some recommended brands:
For GI and PU sheets, try products from E-pack Polymers.
For fibre boards and foam concrete, try those from Everest Industries.
For PVC and GI sheets, try the ones from Sintex Industries.
Navneet Malhotra is a Delhi-based architect.
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