Wondering if you need planning permission for a flat roof on your garage, shed, garden room, or tiny home? If you get it wrong, you'll face a lot of trouble. This could mean delays, extra costs, or even the worst case: tearing it all down and starting over. But here's the thing: a flat roof can be a hidden blessing. It helps keep your building low-profile. This quick guide explains what you can do with outbuildings at home in England and Wales. It explains how flat roofs fit into the rules. You’ll learn how GRP and EPDM flat roof kits can create a strong, low-profile roof that lasts for years. This article is a general guide. Don’t use it as a substitute for advice from a local planning expert. Check with your local planning department first. Always double-check the details with the Planning Portal or your local council. Do this before starting any project. Permitted Development vs Planning Permission Most houses have something called permitted development rights. This means you can do some small projects without a formal planning application. But they must follow rules about size, shape, location, and use. So, where do you need planning permission, you ask? Well, it's when you start getting a bit too big for your boots, or you want to use the building as a separate home. You'll also need it if you're building in a protected area - listed building, conservation area, national park, etc. For a quick rundown on extensions and planning, we've already covered it in a previous blog: Everything You Need To Know About Extending Your Home. You can link to that for some further reading. When A Garage, Shed, or Garden Room Won't Need Planning Permission For most houses (not flats or maisonettes), you can often build a single-story outbuilding without special permission. This is true if certain conditions are met: It's got to be within the garden of your house. It can't be right in front of the main front wall of the house. It's single-story all the way. The eaves need to be no higher than 2.5m. The overall height is a bit more complicated: If it's got a slanty roof, you can go up to 4m. For a flat roof or pent roof, it's capped at 3m. If it's right up against a boundary, then the whole building has to be no taller than 2.5m. You can't cover more than half of the garden with outbuildings and any other extensions you're doing. And most importantly, it's not a separate dwelling - it's just an extra room for your home, maybe a storage shed, a workshop, a home office, or a studio. Just stick to all those rules, and you can usually get away with building a simple garage, office, or workshop in your back garden without having to do a full planning application. Why Flat Roofs Make Planning Easier The height rules above are the main reason homeowners pick a flat roof for outbuildings: Flat and mono-pitch roofs sit in the “3 m overall height” category. If the building is within 2 m of the boundary, you’re capped at 2.5 m total height, roof included. With a pitched roof, the ridge can quickly push you over 2.5 m. A flat roof has no ridge, so it's much easier to design the entire structure under the limit and still keep good headroom inside. That’s why most modern garden rooms and home offices are low, box-shaped buildings rather than tall apex sheds. For tight plots and city gardens, a flat-roof garage or shed can also help: Reduce overshadowing and improve neighbor relations. Keep the building visually lower than the main house. Create a simple footprint that suits modern flat-roof materials. Small Mobile Homes and Tiny Homes in the Garden Small mobile homes, lodges, and those "tiny homes" people are so fond of - they're a bit of a special case. A fair few of them are built to the letter of the law as a caravan or mobile home, and in some situations you might be able to put one in the garden without needing full planning permission if: It's all tucked away within the main house's grounds. You're using it as a bit of extra space to help out the main house - like a guest room or an extra family room, not as a self-contained place to live on its own. Just to be clear, every case is slightly different, so it really does pay to check in with the local planning department or apply for one of those Lawful Development Certificates before you go ahead and order a full small home. A flat roof still has its benefits here - it keeps the whole thing a bit lower and less obtrusive, so it tends to make unlikely friends with both the neighbors and the planners. Getting Official Approval You still need official confirmation from the council to demonstrate that the work is legal, even if your shed or garage meets all height and size restrictions and has a flat roof. Your Local Planning Authority (LPA) is in charge of this procedure. What You Need to Do A quick step-by-step guide to making your project official: Step 1: Choose the Right Application Type If your project meets Permitted Development rules:Apply for a Lawful Development Certificate (LDC). This provides written, legal proof that your project is compliant without needing full planning permission.Visit Gov.uk to learn more about process for obtaining a lawful development certificate for existing or proposed use If your building is larger or taller than allowed:You’ll need to apply for Full Planning Permission, where the council reviews your proposal and makes a decision. Step 2: Prepare Your Plans Provide precise drawings that show the flat-roof structure's height, dimensions, and precise location on the property. Step 3: Contact Your Local Planning Authority To find out what paperwork is needed and where each application should be filed, contact the planning office of your local council. You can find your local council (LPA) here. Step 4: Review the Rules and Regulations The council will assess your application based on planning legislation and official government guidance. Download the Technical Guidance PDF (Rule Book)This document explains measurement limits, size rules, and planning definitions in detail. Make sure you always refer to the latest, most up-to-date version directly on the official GOV.UK website, as regulations and documents can be updated. Picking the Right Roof System for a Low Flat Roof Once planning and heights are under control, the next question is how to waterproof the flat roof. For garages, sheds, garden rooms, and small homes, Apex focuses on two main systems: GRP fibreglass flat roofs A GRP roof creates a seamless, rigid shell over OSB or plywood decking. It has no joints in the main roof area. When installed correctly, it offers long-lasting, low-maintenance protection. That’s why Apex’s GRP roofing kits are ideal for single garages and full-width extensions. For roofs that wear more, like garages and garden rooms, heavier systems help. The 600grm Heavy Duty Roofing Kits offer extra impact resistance. These kits come in color options like black, white, and anthracite to fit your property’s style. If you plan to write more technical content, consider linking to Apex’s Beginner’s Guide to GRP Roofing Kits. It explains kit sizes, coverage, and basic installation steps. EPDM rubber flat roofs For simple, low-slope roofs, EPDM is a flexible single-ply option. Many smaller roofs can use one sheet, which reduces seams and leak points. Apex’s EPDM flat roof kits are great for sheds, garages, and small outbuildings. They resist UV rays and extreme temperatures for the long term. EPDM works well where the building has upstands and corners. Using GRP and EPDM roofing corners creates a neat finish at edges and parapets. This method avoids the need for complicated metalwork. For cold-weather installs, check Apex’s Best Winter GRP Roofing Kits for Cold Weather. It explains how winter catalysts help kits cure reliably in low temperatures. Quick Recap for Homeowners So if you're planning a flat roof garage, shed, garden room, or small cabin: Just get the basics right: we're talking single-story, tucked away behind the main house, and not taking up more than half the garden. Keep an eye on the height rules: anything over 3 meters overall is going to need some serious consideration, and if you're near the boundary, you'll want to stay below 2.5 meters at most. And don't forget to keep the eaves height at 2.5 meters too. Keep the use secondary: we're talking storage, a hobby room, an office, or a gym here - not a proper separate home. Then you can think about design and pick a low-profile roof with a system like GRP roofing kits or EPDM flat roof kits so the building stays dry and looks nice for years to come. Get the planning rules sorted, and everything else is just down to personal preference - what you want your roof to look like, how long you want it to last, and which kit makes it easiest to achieve.
