Preparing Your Shed Roof for New Felt
Before you can begin laying new roofing felt on your shed, meticulous preparation is key to a lasting, waterproof finish. The existing roof covering, whether it's old felt, shingles, or even bare timber, must be removed entirely. Any remaining nails, staples, or debris will prevent the new felt from adhering properly and can create weak points susceptible to water ingress.
Inspect the shed's roof deck – the timber boards beneath the old felt. If the timber is rotten, damaged, or warped, it must be repaired or replaced. Laying new felt over compromised wood is a false economy; it will not protect your stored items and will likely lead to premature failure of the new covering. Ensure the roof deck is clean, dry, and smooth. Any unevenness can telegraph through the new felt, creating potential areas for water to collect.
When preparing the roof edges, consider adding a drip edge. This is a metal or plastic flashing that extends slightly beyond the fascia board, directing water away from the timber and into a gutter or off the side of the shed. While not strictly essential for felt-only roofs, it significantly enhances protection against water running down the side of the shed and into the structure. For a professional finish and added durability, particularly on the eaves and ridge, consider using capping felt or mineral-finished felt designed for these areas. These often have a more robust granule surface and can be more resistant to UV and physical damage.
Gather all your tools and materials before starting. This includes the roofing felt itself (ensure you have enough, accounting for overlaps), appropriate felt adhesive (often a cold-applied adhesive or bitumen-based solution), felt nails (galvanised, with wide heads), a sharp utility knife or felt knife, a tape measure, a chalk line, a hammer, a pry bar for removing old felt, a stiff brush for cleaning, and safety gloves and eyewear. Having everything to hand prevents interruptions and ensures a smoother workflow.
The structural integrity of your shed's roof frame is paramount. Ensure all rafters and supports are sound. If you are building a new shed or significantly refurbishing an old one, consider the pitch of the roof. A minimum pitch of 10-15 degrees is generally recommended for effective water run-off when using roofing felt. Too shallow a pitch can lead to standing water, which will inevitably find its way through even the best-installed felt over time.
Essential Preparation Checklist
- Remove all old roofing material.
- Inspect and repair/replace any damaged roof deck timber.
- Clean the roof deck thoroughly.
- Consider installing metal drip edges.
- Plan for capping felt on edges and ridge.
- Gather all necessary tools and materials.
- Ensure adequate roof pitch for water run-off.
Thorough preparation is the bedrock of a waterproof and long-lasting shed roof.
Applying the First Layer of Roofing Felt
With the shed roof deck meticulously prepared, you're ready to lay the initial layer of roofing felt. This underlayment layer provides a critical secondary barrier against moisture and ensures that even if the top layer sustains minor damage, your shed remains protected. It's common practice to apply this layer horizontally, running parallel to the eaves.
Begin by unrolling the felt across the shed roof, allowing it to overhang the eaves and sides by at least 100mm (approximately 4 inches). This overhang is crucial for directing water away from the main roof structure. Once positioned, secure the felt temporarily. Some adhesives are designed to be applied before unrolling, while others work best once the felt is in place. If using an adhesive, apply it evenly to the roof deck according to the manufacturer's instructions. If using nails, tack the felt down sparingly along the top edge to hold it while you work.
The first sheet should be laid flush with the top edge of the roof, just below where the ridge cap will eventually sit, or at the highest point of the roof if it's a single-slope design. This ensures the subsequent layers overlap correctly to shed water downwards. When you start the second strip, it must overlap the first by a minimum of 100mm (4 inches). This overlap is critical for preventing water from seeping between the sheets. For the best results and enhanced weather resistance, apply a bead of cold adhesive along the top edge of the previous felt strip before laying the next one.
If you're using a roll of felt that is wider than your shed, you'll typically cut it to size. Always make cuts with a sharp utility knife on a flat surface for a clean edge. The felt should be taut but not stretched, as stretching can cause it to split or pull away later. Roll the felt out carefully, smoothing out any wrinkles or air bubbles as you go. Ensure it lies flat against the timber deck.
Nailing is often used in conjunction with adhesive. Use galvanised felt nails with wide heads, spaced approximately 50-75mm (2-3 inches) apart along the edges and where sheets overlap. For the first layer, securing the top edge firmly is important. As you proceed, continue to adhere and nail each strip, ensuring a consistent overlap and smooth finish.
A common mistake is not allowing sufficient overhang. This means water can run down the fascia or directly onto the side walls. Always ensure that excess felt is folded over the eaves and secured, typically with nails and a dab of adhesive on the underside. This creates a drip edge naturally from the felt itself, or it can be secured to a pre-fitted metal drip edge.
Fix the top edge of the first felt strip securely, as it will bear the weight of subsequent layers and help prevent lifting.
Laying the Top Layer of Roofing Felt
The top layer of roofing felt is the primary defence against the elements, so its installation requires precision. This layer is usually laid horizontally, starting from the lowest point of the roof (the eaves) and working upwards towards the ridge. This ensures that water flows unimpeded over the seams and off the roof.
Begin by cutting your felt to the required length, allowing for an overhang of at least 100mm at both the eaves and the sides. Apply a generous amount of cold adhesive along the top edge of the first horizontal strip of the underlayment felt, extending it up to where the top edge of the new felt will sit. This bond is vital for preventing the top layer from lifting.
Carefully unroll the top felt strip over the adhesive, ensuring it overlaps the first strip by at least 100mm (4 inches). For a truly watertight seal, you should also apply adhesive along the edge of the underlayment felt that this new strip will cover. Press the felt down firmly, working from the centre outwards to expel any air bubbles and ensure a complete bond with the adhesive. Use a stiff brush or a roller designed for felt application.
Continue this process, laying subsequent strips. Each new strip must overlap the previous one by at least 100mm. The key is to maintain consistent, generous overlaps. Where the felt meets the side walls, the overhang should be folded over the edge and secured, often with a dab of adhesive on the underside. If you have installed metal drip edges, the felt should be laid over these.
The final strip of felt at the ridge needs special attention. It should overlap the uppermost horizontal strip by at least 150mm (6 inches) and extend down the other side of the roof by at least 100mm. To finish the ridge, you can use a dedicated ridge capping felt, which is often mineral-finished for extra durability, or a carefully cut section of standard felt. Apply adhesive generously to the top edge of the uppermost horizontal strip and the underside of the ridge felt. Fold the ridge felt over the apex of the roof and press down firmly to create a watertight seal.
When using nails, ensure they are driven in straight and flush with the felt surface. They should be galvanised to prevent rust. Space them about 50-75mm from the edges and along the overlap lines, but be mindful that excessive nailing can create potential entry points for water. Often, the top edge of the felt, where it is most vulnerable to lifting, is secured with nails and then covered by the next layer or the ridge cap, hiding the fixings.
The overlap is your primary defence against water ingress; never compromise on its width.
Finishing Touches and Maintenance
Once the main body of the roofing felt is installed and secured, attention must turn to the finishing touches that ensure its longevity and your shed's protection. The edges and ridge are the most vulnerable points, requiring careful sealing. Any felt overlapping the eaves should be neatly trimmed or folded over and secured with adhesive. For a cleaner, more professional look, metal or plastic finishing trims can be fixed along the eaves and sides, butting up against the felt to provide a neat edge and an extra layer of protection.
The ridge detail is critical. If using standard felt for the ridge, ensure it overlaps sufficiently on both sides and is well-adhered. Dedicated ridge capping felt, often available in mineral-finished varieties, offers superior durability and weather resistance due to its thicker construction and protective surfacing. Apply a generous amount of adhesive to both the top layer of felt and the underside of the ridge capping before positioning and pressing it firmly into place. Ensure there are no gaps where water could penetrate.
Regular inspection and maintenance are vital for extending the life of your shed's felt roof. Schedule checks at least twice a year, ideally in spring and autumn. Look for signs of wear and tear, such as cracking, blistering, or splitting, particularly around edges and seams. Check for any areas where the felt may have pulled away from the roof deck or where nails have worked loose. Accumulated debris, such as leaves and moss, should be cleared away promptly, as it can trap moisture and promote rot.
Minor damage, like a small split or a loose edge, can often be repaired using felt adhesive and a patch of new felt. Clean the affected area thoroughly, apply adhesive to both the roof and the patch, and press the patch firmly into place, ensuring good contact. For larger areas of damage or widespread deterioration, it may be more cost-effective and reliable to replace the entire felt covering. When repairing, always ensure the new felt patch overlaps the damaged area sufficiently and is well-sealed.
Consider the environment around your shed. Overhanging tree branches can cause physical damage and shed leaves that lead to moisture build-up. Pruning branches back can help. Also, ensure good ventilation around the shed; damp air trapped underneath the roof can contribute to rot and decay of the timber structure, even with a waterproof felt covering. While shed paint colours can enhance aesthetics, they do not protect the felt itself. The felt's protection comes from its material composition and correct installation.
Periodically clear debris from your shed roof to prevent moisture build-up and premature degradation of the felt.
Careful finishing and regular maintenance are non-negotiable for a long-lasting shed roof.
Choosing the Right Roofing Felt and Adhesive
Selecting the appropriate roofing felt and adhesive is fundamental to achieving a durable and effective shed roof. Standard shed roofing felt, often referred to as 'bitumen felt', is the most common choice for garden sheds. It's typically a heavy-duty, bitumen-saturated felt material, often surfaced with mineral granules for added protection against UV radiation and physical wear.
Felt is usually sold in rolls, with common widths of around 1 metre. The thickness, or weight, of the felt can vary, with heavier grades offering greater durability. For most standard sheds, a good quality 20kg or 24kg felt is generally sufficient. However, for sheds in exposed locations or those intended for heavy use, a more robust felt might be advisable. You'll need to calculate the total area of your shed roof, adding at least 10% for overlaps and waste.
Beyond standard grey or green mineral-surfaced felt, you might encounter other options. 'Underlay' felts are lighter and designed to be used as a base layer beneath a more substantial top coat. 'Cap sheet' felts are designed for the top layer and often have a more resilient finish. For very low-pitched roofs or for enhanced aesthetics, some may opt for EPDM rubber roofing or specialised shingles, but for traditional shed roofing, bitumen felt remains the go-to material.
The adhesive is as critical as the felt itself. Cold-applied adhesives, specifically designed for roofing felt, are the most common. These are typically bitumen-based mastics or glues that provide a strong, flexible bond. Ensure the adhesive is suitable for the type of felt you are using and for exterior application in varying weather conditions. Some adhesives are designed for specific temperatures, so check the product's suitability for your climate.
Application methods for adhesive can vary. Some come in tubs requiring a trowel or spatula, while others are in cartridges for use with a sealant gun. Always follow the manufacturer's instructions for application thickness and drying times. A common mistake is using insufficient adhesive, which leads to the felt lifting, especially at the edges and seams. Conversely, excessive adhesive can ooze out and create an untidy finish.
When purchasing, consider the lifespan you expect. Cheaper felts might last five to ten years, whereas higher quality, heavier grade felts can potentially last 15-20 years if installed correctly and maintained. Always buy from a reputable supplier to ensure you are getting a product that meets the advertised specifications. The weight and quality of the felt, along with the correct adhesive and a well-executed installation, are the key factors determining how long your shed roof will remain watertight.
Choosing a heavy-grade, bitumen-saturated felt with a mineral finish offers the best balance of protection and longevity for most garden sheds.
Alternative Shed Roofing Materials
While roofing felt is the traditional and most common choice for shed roofs, a variety of alternative materials are available, each offering different benefits in terms of durability, aesthetics, and cost. Understanding these alternatives can help you make an informed decision based on your shed's intended use, your budget, and your desired lifespan for the roofing.
One popular alternative is EPDM (ethylene propylene diene terpolymer) rubber roofing. EPDM is a highly durable synthetic rubber membrane that is extremely resistant to UV radiation, extreme temperatures, and punctures. It's often installed as a single sheet, which significantly reduces the risk of leaks associated with seams. EPDM is typically adhered using a specialised adhesive and is known for its exceptionally long lifespan, often exceeding 20-30 years. It offers a sleek, modern appearance and is a robust choice for shed roofs.
Another option is cedar or treated timber shingles. These provide a natural, attractive look that can blend well with garden environments. Cedar shingles are lightweight, durable, and naturally resistant to rot and insects. However, they require more maintenance than felt or EPDM, and their installation is more complex, often requiring specific underlayment and nailing techniques. The lifespan can vary significantly based on climate and maintenance, typically ranging from 15 to 25 years.
For a more industrial or robust look, corrugated metal sheeting, such as galvanised steel or aluminium, can be used. These are lightweight, fire-resistant, and highly durable, with lifespans potentially reaching 50 years or more if properly coated. Installation involves overlapping panels and securing them with special roofing screws equipped with rubber washers to prevent leaks. While cost-effective for larger areas, metal sheeting can be noisy during rain or hail and may be prone to denting.
Composite or recycled plastic roofing tiles offer an environmentally friendly and low-maintenance option. Made from recycled materials, these tiles are designed to mimic the look of traditional slate or wood shingles but are significantly lighter, more durable, and resistant to rot, mould, and insects. They are generally easy to install and come with long guarantees, often 25-50 years.
When considering alternatives, weigh the initial cost against the expected lifespan and maintenance requirements. Roofing felt is often the most budget-friendly option for a basic shed, but it typically has the shortest lifespan. EPDM and metal offer greater longevity and performance but at a higher upfront cost. For many, the decision comes down to a balance between cost, durability, and the desired aesthetic for their garden structure. Regardless of the material chosen, proper installation and adequate roof pitch are critical for performance.
When exploring alternatives, consider the long-term cost of ownership, not just the initial purchase price.