How To Lay Felt On A Flat Roof (step-by-step Guide)
Ever looked at a flat roof and thought, "That looks like a blank canvas just waiting for some serious waterproofing magic"? Well, you're in luck! Laying felt on a flat roof might not be the first thing that springs to mind when you think of DIY projects, but there’s a certain satisfaction in transforming a potentially leaky surface into a robust, weather-beaten shield. It’s a bit like giving your house a really good rain jacket, and trust us, it's surprisingly rewarding. Plus, a well-felted roof means no more dreaded water stains on your ceiling – a definite win in the home improvement game!
The primary purpose of laying felt, often referred to as bitumen roofing felt or mineral felt, is to create a waterproof barrier. Think of it as the primary defense against the elements. Rain, snow, sleet – they all have to contend with this tough, flexible layer. Beyond just keeping water out, a properly installed felt roof significantly extends the lifespan of your roof deck. Without this protection, wood can rot, and structural integrity can be compromised, leading to costly repairs down the line. It's an investment in peace of mind, ensuring your home stays dry and secure, no matter what the weather throws at it. And let’s not forget the added benefit of improved insulation; a good felt layer can contribute to keeping your home warmer in winter and cooler in summer, potentially saving you a bit on your energy bills!
Getting Ready for Felt-tastic Fun!
Before you dive headfirst into the world of bitumen and flames (don't worry, it's controlled flames!), gathering your tools and materials is key. You'll need plenty of roofing felt, ideally a good quality mineral-based felt for durability. Then comes the adhesive – this can be either a specialized cold-applied adhesive or, for the more adventurous (and experienced!), hot bitumen. We’ll focus on the more common and generally safer cold adhesive method for this guide, but it’s good to know your options. You'll also need a long-handled brush or roller for spreading the adhesive, a sharp utility knife or heavy-duty scissors for cutting the felt, and a stiff brush for cleaning the roof surface. Don't forget some tackifier or primer for ensuring excellent adhesion, especially at edges and laps. Safety first, so a pair of sturdy work gloves and perhaps some old clothes are a must – this stuff can get sticky!
Step 1: The Clean Slate - Preparing Your Roof
This is arguably the most crucial step, and while it might not sound glamorous, a clean roof is a happy roof. Start by sweeping away any loose debris, leaves, twigs, and dirt. A stiff brush is your best friend here. If there’s any moss or lichen, use a wire brush to scrub it off. Any standing water needs to be completely gone; a damp surface is the enemy of good adhesion. Take your time and be thorough. You want a smooth, dry, and clean surface for the felt to adhere to. Pay attention to any existing cracks or holes; these need to be filled and smoothed over before you proceed. Think of this as prepping a canvas – you wouldn't paint on a dusty, bumpy surface, would you? A clean start ensures a strong, long-lasting bond for your new waterproof layer.
Step 2: Laying the Foundation - The Underlay Felt
Most flat roofs benefit from a base layer of felt. This is often a lighter-weight underlay felt that acts as a sort of first line of defense and a stable platform for the main felt. If you're using a lap-based system, you'll typically start at the lowest point of the roof and work your way up. Unroll the first strip of underlay felt, ensuring it overhangs the edges slightly. Apply your chosen adhesive generously to the roof surface using your brush or roller. Don't be shy with the adhesive; a good, even coating is essential for a strong bond. Carefully press the felt strip into the adhesive, smoothing out any wrinkles or air bubbles as you go. Work from the center outwards. Overlap subsequent strips by at least 100mm (about 4 inches) and ensure these overlaps are also well-adhered. Think of this as laying the first course of shingles on a regular roof – it’s all about creating a solid, continuous base.
Step 3: The Main Event - Applying the Top Layer
Now for the star of the show! This is typically a heavier, mineral-surfaced felt that provides the primary waterproofing and UV protection. The process is very similar to laying the underlay, but with a few key differences. Again, start at the lowest point and work upwards. Apply a generous amount of adhesive to the roof surface, ensuring it's evenly spread. Carefully unroll the main felt, again allowing for a slight overhang at the edges. Press it firmly into the adhesive, using your brush or roller to smooth out any imperfections and ensure full contact. The overlaps are crucial here. You'll want to overlap the strips by at least 150mm (about 6 inches) and critically, the mineral surface of the top layer should overlap the edge of the underlay. This "cap" effect prevents water from seeping into the underlay. If you’re using a torch-on felt system (which requires specialized equipment and training), this step involves heating the bitumen to create a seamless bond. For cold adhesive, ensure the adhesive is still tacky when you lay the felt for maximum grip.
Step 4: The Finishing Touches - Edges and Details
This is where the real waterproofing magic happens, and paying attention to detail here is non-negotiable. The edges of your roof are the most vulnerable points for water ingress. Carefully trim any excess felt with your sharp utility knife, leaving just enough to turn down over the parapet wall or coping stones. Apply plenty of adhesive to the edge and the turning-down section, then press the felt down firmly. For a super professional finish, you might use a strip of flashing or a specialized edge trim. Where two strips of felt meet, or where the felt meets a vertical surface (like a wall), ensure there’s a generous overlap and ample adhesive. This creates a 'water-stop' effect, forcing water to run off rather than penetrate. It’s the little details that make a big difference in the long run, transforming your roof from merely covered to truly protected!
Step 5: The Final Seal of Approval
Once your felt is laid and all edges are sealed, give it one last once-over. Check for any loose areas, ripples, or bubbles. If you find any, carefully lift the section (if the adhesive is still workable) and re-adhere it, smoothing out the issue. Some installers like to apply a final coat of specialized roof coating or dressing over the entire surface. This can further protect the felt from UV rays, prolong its life, and give it a uniform, finished look. If you’ve used mineral felt, you’re already pretty well protected, but a coating can offer that extra layer of defense. And there you have it! You've successfully laid felt on your flat roof, creating a robust, waterproof barrier that will keep your home dry and sound for years to come. It's a satisfying job, and the knowledge that you've conquered the elements with your own two hands is a feeling that's hard to beat!