Container homes are everywhere now, garden offices, holiday lets, tiny homes, off-grid studios. Every week we get calls from customers turning a 20ft or 40ft shipping container into a proper living space, and one question keeps coming up: Do I actually need a fibreglass roof on it? The short answer: not always, but in the vast majority of UK builds, yes. If you want a roof that lasts 25 to 30 years, doesn't leak, and gives you a clean walkable finish, fibreglass (GRP) is hard to beat. Have a look at our full range of GRP roofing kits here, but read the rest of this first, we'll explain when it's the right call and when something else might suit you better. Why Container Roofs Cause Problems . Before we discuss fibreglass, it helps to know what you're dealing with. A typical container roof is constructed from thin (16 to 18 gauge) corrugated Cor-Ten steel. It was never intended to be the roof of a building that a person lives in, it was only meant to protect the cargo from salt water for a few transatlantic crossings. The issues we see again and again: Water pooling: Container roofs are technically flat. The corrugations don't drain properly, so puddles sit and slowly eat the steel. Dents: Containers get knocked about during shipping. Every dent becomes a little bowl that holds water. Rust: Once the factory paint wears off, and it does, rust sets in fast, especially in the UK. Seam leaks on multi-container builds: Joining two containers creates a gap that's genuinely awkward to seal. Condensation: Steel sweats. Without proper insulation, you get moisture dripping down the inside walls. If you're using the container for dry storage, you can live with most of this. If you're sleeping in it or letting it out, you can't. What a Fibreglass (GRP) Roof Actually Is GRP stands for Glass Reinforced Plastic - the same material used in boat hulls, motorway signs, and aircraft parts. In roofing, it's applied wet, chopped strand matting saturated with polyester resin, then finished with a coloured topcoat. When it’s cured the entire roof becomes one solid waterproof coating with no weak areas, overlaps or joints. A GRP roof, when installed correctly, can last 25 to 30 years and will resist direct sunlight, snow, people walking on it and any water pooling on top. So, Do You Need One? Honest take after years of supplying this market: Go with fibreglass if: You're using the container as habitable space (living, working, renting) You're joining two or more containers together You want to walk on the roof for cleaning or solar panels You want a long-term solution, not a five-year patch You probably don't need it if: The container is purely for dry storage in a sheltered spot It's a short-term build you'll replace in a few years You've already fitted a pitched timber roof with tiles or sheets For most container home builds, garden offices, holiday lets, tiny homes, GRP solves the flat roof problem, the seam problem, and the rust problem in one go. If you'd rather a softer single-sheet system, our EPDM rubber roof kits are a solid alternative, slightly faster to install, equally watertight, just less impact-resistant. How It Goes On You can't bond GRP directly to corrugated steel, it needs a flat, rigid surface. Most installers fit firring strips across the container roof to create a slight fall, lay OSB3 board on top, fit edge trims, then bed the matting in resin and roll out the air bubbles. Once cured, you apply the coloured topcoat with a roller. Done. It's well within reach of a confident DIYer. Watch our step-by-step fibreglass installation tutorials before you order, they walk through every stage. Which Kit Should You Choose? For a typical container home roof, we'd point you to: 450gsm GRP kit - our most popular option for standard domestic flat roofs. Perfect for a single 20ft or 40ft container. 600gsm Heavy Duty GRP kit - if you want foot traffic, a roof terrace, or extra impact resistance. Cure It ONE single-coat kit - a faster install with a 20-year guarantee. Fire-rated GRP kits (Silverseel, Pro 25, Res-Tec 1010) - if your build needs to meet BS476 fire regs. All our kits include the resin, hardener, matting, topcoat and mixing chart. You'll just need to add trims and tools. A Few Tips From People Who Sell This Daily Don't skip the timber deck. GRP needs OSB3, not bare steel. Build in a fall. Even a 1:80 slope helps water move. Order 10% extra matting. Running out mid-job is no fun. Check the catalyst grade. We do summer and winter, make sure you've got the right one for the season. Insulate underneath. Cold steel under a warm container means condensation. Use a vapour barrier and proper PIR. FAQs How long does a fibreglass roof last on a container home? If installed properly, a GRP roof will last for 25-30 years and more. The laminate is a single sheet, no seams or overlaps, and can last for 20 years with the material warranties of our kits, which will not peel, lift, or fail as older felt systems do. Can I install a fibreglass roof on my container myself? Yes, many of our customers do. You'll need basic DIY confidence, a dry weekend with mild temperatures, and the right kit. We'd strongly recommend watching our video tutorials all the way through before you start, ordering about 10% more matting than you think you need, and having a second pair of hands on the day. It speeds the job up massively. Can I walk on a GRP container roof? Yes, provided you've used 600gsm matting and built the laminate up properly. Our heavy-duty kits are designed for foot traffic, which makes them ideal if you want to clean the roof, maintain solar panels, or even use the space as a roof terrace. The lighter 450gsm kits work fine for most installs but aren't rated for regular walking. Will a fibreglass roof stop my container rusting? On the top, completely. Once cured, the GRP forms a complete waterproof barrier over the steel, leaving the roof below dry. Sides and base of the container must still be protected, typically with rust-resistant paint, cladding or an appropriate damp-proof base. Fibreglass only protects what it covers. Will GRP crack in cold UK winters? No. Once cured, GRP is resistant to cold, freezing and hot weather. It was originally designed for boats and so cold and wet conditions suit it well. The key is installing it in the right conditions, above 5°C, dry, and with the correct seasonal grade of catalyst. We supply both summer and winter grades. The Bottom Line Container homes are brilliant, but they're only as good as their weakest point, and on a flat steel roof, that's almost always water. Fibreglass solves it for two or three decades at a stretch. Not sure which kit suits your build? Give us a call on 0800 612 7903, we'd rather you got the right thing the first time. Or browse all our GRP roofing kits here, 10% off until the end of May.
