Can You Felt Over Old Felt on a Shed Roof? The Truth Behind the Shortcut

The temptation is there when it comes to adding new felt to your shed roof, just layer it over the old stuff. But is it wise, can you felt over old felt on a shed roof?

Well, in the same way that putting a clean shirt over a sweaty one doesn’t actually make you clean, felting over the old stuff isn’t a smart idea. While you technically can do it, there’s a very fine line between a clever time-saver and accidentally turning your shed roof into a soggy, heavy sandwich of root. 

At Atlas Sheds, we’ve seen enough ‘double-felted’ disasters to know that what starts as a 20-minute shortcut often ends in a weekend of regret. Before you start nailing, let’s look at why your shed might be begging you to strip it off and start fresh. 

The pros and cons of over-felting 

Here’s the honest tradeoff: over-felting can look like a quick win, but the downsides usually show up later, and they’re rarely cheap to fix. 

Why professionals (and Atlas Sheds) advise against it 

Over-felting is one of those jobs that seems sensible until you understand what’s happening between the layers. Most shed roof failures after a quick refelt come down to three issues: 

Trapped moisture 

Even if your shed roof looks dry, old felt often holds damp in tiny cracks, nail holes, and along the edges. When you cover it with a new layer, you can trap that moisture in place. 

That damp has nowhere to evaporate, especially if the shed roof gets warm in the sun and cool at night (hello, condensation). The result is a perfect environment for: 

• Rapid rot in the roof boards

• Soft spots and sagging 

• Mould growth and a musty shed interior 

In other words, over-felting can turn a minor leak into a much bigger timber repair job. 

Uneven surface 

Old shed felt is rarely a nice, flat surface. It tends to be: 

• Brittle and cracked 

• Bubbled or wrinkles 

• Lifted at edges where the wind has got underneath 

When you lay fresh felt over that, it won’t sit tight to the deck. Any bumps or voids become weak points where water can track underneath, and once water gets between layers, it can spread further than you’d expect. 

You might get it looking neat on day one, but it’s far harder to get a proper seal at joins, edges and corners when the base layer isn’t sound. 

Weight issues

Felt itself isn’t massively heavy, but two layers plus absorbed water adds up. If moisture gets trapped, the roof can become a water-holding sandwich. That extra load can: 

• Encourage roof sagging

• Stress the shed’s frame, especially on lighter sheds 

• Make the felt more likely to shift, ripple and lift in the wind 

So, even if over-felting works briefly, it can quietly shorten the life of the roof, and sometimes the shed structure with it. 

The do it right process 

If you want a shed roof that stays watertight through proper UK weather, a clean replacement beats a quick cover-up every time. Here’s the simple, professional-grade checklist we recommend at Atlas Sheds: 

The 4-step checklist 

1. Strip 

Remove the old felt completely, including every loose strip, tack and clout nail. Don’t be tempted to leave the bits that seem stuck. Those are often the bits hiding cracks, damp or rotten timber. 

2. Inspect 

Check the roof boards carefully for any weak areas. Press along the surface with your hand: 

• Soft spots 

• Spongy sections 

• Dark staining or crumbling edges 

If it feels springy, it’s usually damp damage and needs attention before new felt goes down. 

3. Prep 

A solid finish depends on a solid base. Before you re-felt: 

• Make sure the surface is fully dry 

• Brush off dust, grit, and moss 

• Replace any damaged boards 

• Smooth down raised edges (even small bumps can telegraph through felt and create a weak point)

4. Apply 

Use a high-quality mineral felt, laid flat with the correct overlap at joins so water sheds properly. Fix it with clout nails at sensible spacing, keeping everything neat at edges and corners. 

The goal is a roof that’s tight, smooth and sealed, not one that looks okay until the first hard rain. 

When is it actually okay to over-felt? 

It’s almost never okay to felt over old felt on a roof shed, but there are a couple of very specific situations where over-felting can be acceptable as a temporary emergency patch, not a proper job. 

Rare scenarios where it can make sense 

• Storm damage in the middle of winter: you’ve got water getting in, the weather is brutal, and you can’t safely strip and re-felt properly until conditions improve. 

• Short-term protection: While you’re waiting for materials, trades or a dry spell, especially if you’re aiming to do the full replacement in spring. 

If you must over-felt, keep it strictly temporary 

If you’re using it as a stopgap: 

• Only do it when the existing felt is mostly flat and firmly attached, no big bubbles, no loose edges.

• Make sure the surface is as dry as possible before covering 

• Treat it like a bandage, not a finish; plan to strip and replace properly as soon as you can 

The key takeaway: over-felting is only OK when the alternative is active water ingress, and you need a short-term fix to protect what’s underneath. For anything intended to last, stripping back and doing it properly wins every time. 

How to tell if your shed roof is beyond repair

Sometimes the felt isn’t the real problem; it’s just the first thing you can see. If the structure underneath has started to fail, simply re-felting (or worse, over-felting) is like putting a plaster on a broken bone. Look out for: 

• Soft, spongy roof boards: Especially around the edges, as this can be a sign of damp or rot

• Sagging or a dip in the roofline: This can be a sign of weakened boards or supports 

• Damp that won’t shift: Damp inside the shed, plus mould/black staining or a musty smell 

• Rot at edges, joins or under the drip line: This is likely timber damage and not just a felt issue 

• Fixings won’t bite: Nails pull out or the timber breaks away when refixing 

• The whole shed feels tired: Wobbling/racking, swollen doors, widespread decay

Can you felt over old felt on a shed roof? The final answer 

Yes, you can felt over old felt on a shed roof, but it’s usually going to create bigger problems later. Trapped moisture, uneven layers and extra weight can shorten the roof’s lifespan and turn a simple fix into rotten boards, sagging panels and repeat leaks. 

A proper strip and replace might take a little more time and effort, but it’s a job that’s going to add years to the life of your shed. 

If your roof boards have seen better days, it might be time for an upgrade. Browse our range of durable, hand-crafted timber sheds built to withstand the British weather.