Capping Board vs Full Replacement: Which Approach?
You can cap over old fascia boards with thin (9 mm) PVC cover boards, but only if the existing timber underneath is structurally sound — no rot, no warping, and no deterioration of the rafter ends behind. If the timber is compromised in any way, capping hides the problem and leads to more expensive repairs later. Full replacement with 16 mm PVC-U boards, where the old timber is removed entirely and the new board is fixed directly to the rafter ends, is always the better long-term solution. Capping costs 20–30% less upfront but carries risk; full replacement costs more initially but delivers a genuinely maintenance-free roofline for 30+ years.
This is one of the most common decisions in roofline work, and one where the cheaper option is not always the sensible one. Capping has a legitimate role in certain situations, but it is often used as a shortcut by companies who want to quote low and install fast. Understanding the difference helps you make the right decision — and ask the right questions when getting quotes.
What Is Capping?
Capping means fitting a thin PVC-U board (typically 9 mm) over the face of the existing timber fascia board without removing it. The PVC acts as a weatherproof cover — the timber underneath does the structural work.
How it works:
- The old paint is scraped or sanded where necessary
- The 9 mm PVC capping board is cut to length
- It is pinned or screwed through into the existing timber
- Trims and joints are fitted as normal
- Guttering brackets screw through the PVC cap and into the timber behind
What Is Full Replacement?
Full replacement means:
- Removing the existing timber fascia board entirely
- Inspecting and repairing the rafter ends behind
- Fitting a new 16 mm PVC-U fascia board directly to the rafter ends
- The PVC board is the structural board — there is no timber behind it
Head-to-Head Comparison
| Factor | Capping (9 mm) | Full Replacement (16 mm) |
|---|---|---|
| Old timber removed? | No — stays in place | Yes — removed entirely |
| Rafter ends inspected? | No (hidden behind timber) | Yes — fully visible |
| Rot risk | Hidden rot may continue | Rot is found and fixed |
| Board thickness | 9 mm | 16 mm |
| Structural strength | Relies on timber behind | Self-supporting |
| Gutter bracket support | Screws into timber through PVC | Screws into rafter ends through PVC |
| Installation time | Faster (no removal/repair) | Slower (removal, inspection, repair, fitting) |
| Cost (typical semi) | £1,500–2,500 | £2,000–3,500 |
| Lifespan | Depends on hidden timber | 30–40 years (independent of timber) |
| Guarantee | Often 10 years | Typically 15–20 years |
| Peace of mind | Low — what is underneath? | High — everything has been checked |
When Capping Is Acceptable
Capping is a valid approach in specific circumstances:
1. Timber Is Genuinely Sound
The existing fascia boards are firm, dry, straight, and show no signs of rot. The screwdriver test confirms solid timber throughout. The paint is sound with only superficial wear.
2. Rafter Ends Are Known to Be Good
If the property has been recently inspected (e.g., during a roof repair) and the rafter feet are confirmed sound, capping the fascia as a cosmetic upgrade is reasonable.
3. Budget Is a Hard Constraint
When the homeowner genuinely cannot afford full replacement but needs to address a deteriorating appearance, capping provides a weatherproof covering at a lower cost. This is a pragmatic compromise, not an ideal solution.
4. Temporary Measure
On a property being prepared for sale, or where a full roofline replacement is planned in the next 5–10 years as part of a larger project, capping provides a clean appearance in the interim.
When Capping Is a Bad Idea
1. Any Sign of Rot
If the screwdriver test reveals soft areas, if there is visible fungal growth, or if the paint is blistering in patches, the timber is compromised. Capping over rotten timber:
- Traps moisture between the PVC and the timber, accelerating rot
- Hides progressive damage to rafter ends
- Creates a future problem that is more expensive to fix than doing it properly now
2. Warped or Bowed Timber
The 9 mm PVC capping board is thin and flexible — it conforms to the shape of the timber behind it. If the timber is bowed, the PVC will follow the bow, creating a visibly uneven fascia line.
3. Gutter Problems
If the gutter is sagging, overflowing, or the brackets are pulling out, the fascia behind is likely soft. Capping will not fix the underlying bracket support issue.
4. North-Facing Elevations
North-facing fascia boards are the most likely to be moisture-damaged because they dry slowest after rain. Capping north-facing timber is particularly risky — the trapped moisture has no escape route.
5. The Salesman Says “It’ll Be Fine”
Some roofline companies push capping because it is quicker and cheaper to install (higher profit margin). If you are told capping is “just as good as replacement” without anyone inspecting the timber first, be sceptical. Ask them to do the screwdriver test on the existing board before you commit.
The Hidden Cost of Getting It Wrong
| Scenario | Outcome |
|---|---|
| Cap over sound timber | Good result. PVC protects the timber. 15–20 year life. |
| Cap over timber with early rot | Rot accelerates behind PVC. Within 5–10 years, gutter brackets fail, water damage to rafter ends. Remedial cost: £1,500–3,000. |
| Cap over badly rotten timber | Gutter may fall within 2–5 years. Rafter ends rot extensively. Full structural repair needed: £3,000–8,000+. |
| Full replacement (finding and fixing rot) | Sound result. 30–40 year life. No hidden surprises. |
The worst case — capping over badly rotten timber — costs more in the long run than full replacement would have cost in the first place. And the damage to rafter ends and roof structure may require scaffolding, a roofer, and a carpenter, not just a roofline installer.
How to Check Before You Decide
Before committing to capping or replacement, carry out these checks (or insist the installer does):
- Screwdriver test — press firmly into the timber at the bottom edge, near joints, and behind gutter brackets. Does it resist or sink in?
- Visual check — are there soft patches, discolouration, fungal growth, or blistered paint?
- Tap test — tap the fascia with a knuckle. Solid timber sounds firm; rotten timber sounds hollow or dull.
- Check behind the gutter — remove a section of gutter and inspect the fascia behind. This is the area most likely to be damaged.
- Look from inside the loft — can you see daylight at the eaves? Is there evidence of water ingress on the rafter feet?
If any check raises concerns, full replacement is the right decision.
Our Recommendation
Kalsi Plastics manufactures both 9 mm capping boards and 16 mm full-replacement boards in the complete roofline range. Our recommendation is:
Choose full replacement (16 mm) unless you are certain the existing timber is in excellent condition. The modest extra cost buys you a genuinely independent, maintenance-free roofline that does not depend on hidden timber you cannot inspect once the PVC is fitted.
If you do opt for capping, choose a supplier and installer who will inspect the timber first and give you an honest assessment of its condition. Do not let cost alone drive the decision.
Frequently Asked Questions
Can I cap over old fascia boards?
Yes, if the existing timber is structurally sound — firm, dry, straight, with no rot. Use 9 mm PVC-U capping board pinned over the timber surface. If the timber shows any sign of rot, warping, or softness, full replacement with 16 mm board is the correct approach.
Is capping as good as full replacement?
No. Capping is a cosmetic improvement that relies on the structural integrity of the timber underneath. Full replacement removes the old timber, reveals and repairs any rot, and installs a self-supporting PVC board with a 30+ year independent lifespan. Full replacement is always the superior long-term solution.
How much cheaper is capping vs full replacement?
Capping typically costs 20–30% less than full replacement — roughly £400–800 less on a standard semi-detached house. The saving comes from faster installation (no timber removal, no rafter inspection) and thinner material. However, if hidden rot later requires remedial work, the total cost exceeds what full replacement would have been.
Will capping over rotten wood cause problems?
Yes. Capping traps moisture between the PVC and the rotten timber, accelerating decay. The rafter ends behind the fascia are also at risk. Within 5–10 years, gutter brackets may pull out, the board may sag, and structural damage can become extensive and expensive.
How can I tell if the fascia is sound enough for capping?
Use the screwdriver test: press firmly into the timber at multiple points, especially the bottom edge, near joints, and behind gutter brackets. If it resists penetration, the timber is likely sound. If the screwdriver sinks easily, the timber is rotten and capping is not appropriate. A reputable installer will carry out this test before quoting.
