Capping Board Installation
How to fit 9mm PVC-U capping boards over existing timber fascia for a quick, cost-effective roofline refresh without full replacement.
Safety Warning — Working at Height
Working at eaves level requires appropriate access equipment. Use a scaffold tower for extended sections or a properly secured ladder for short runs. Follow the Work at Height Regulations 2005. Check for overhead cables before erecting scaffold.
When to Use Capping Board
Capping boards are only suitable when the existing timber fascia is structurally sound. If the timber is rotten, soft, or delaminating, you must strip and replace with full replacement fascia board instead. Capping over rotten timber will fail — the fixings won't hold and the rot will continue behind the PVC. Press a screwdriver into the timber at several points — if it penetrates easily, the board needs replacing, not capping.
What You'll Need
Tools
- Scaffold tower or secured ladder
- Tape measure
- Fine-tooth handsaw or circular saw
- Pin nailer (18 gauge) or hammer
- Caulking gun
- Screwdriver (for testing timber)
- Sandpaper or scraper
Materials
- 9mm PVC-U capping board (5m lengths)
- PVC adhesive (grab adhesive / panel bond)
- Stainless steel pins (25mm)
- Inline joint strips
- Corner joints (internal/external)
- Colour-matched silicone sealant
- Timber treatment (for any surface prep)
Technical Specifications
Step-by-Step Installation
1 Assess Existing Timber
Before ordering materials, thoroughly check the existing timber fascia. Press a screwdriver into the timber at multiple points — if it sinks in, the wood is rotten and must be replaced. Capping board is only appropriate where the underlying timber is structurally sound. Check behind the fascia where possible — hidden rot at rafter junctions is common. If more than 20% of the timber is compromised, full replacement is the better option.
2 Remove Guttering
Carefully remove the existing guttering to provide clear access to the fascia. Note the bracket positions — you'll need to re-fix them onto the capping board (which will now sit 9mm proud of the original surface). If existing screws are rusted into the timber, they may need drilling out. Store gutter sections carefully to avoid damage.
3 Prepare the Timber Surface
Scrape off flaking paint and loose material from the existing fascia. Sand any high spots or rough areas — the capping board needs a reasonably flat surface to bond to. Remove protruding nails or screws. Apply a coat of timber preservative to any bare wood. The surface doesn't need to be perfect, but major bumps will telegraph through the 9mm capping board and show from ground level.
4 Measure and Cut Capping Board
Measure each section of fascia and cut the capping board to length. Use a fine-tooth saw — a coarse blade will chip the PVC surface, especially on woodgrain finishes. Allow for 3–5mm expansion gaps at each joint. In cold weather, boards contract, so work to the lower end of the gap. In warm weather, work to the upper end. Measure the board width too — the capping must cover the full face of the existing timber.
5 Apply Adhesive
Apply a grab adhesive (such as a PVC panel bond or construction adhesive) in a zigzag pattern across the back of the capping board. Apply a continuous bead along the top and bottom edges and a zigzag along the centre. The adhesive provides the primary bond — the pins provide temporary hold while the adhesive cures and act as a secondary fixing. Do not rely on pins alone; adhesive is essential.
6 Fix the Capping Board
Press the capping board firmly against the existing timber, ensuring full contact. Immediately pin through the capping board into the timber at 300mm centres using 25mm stainless steel pins. Use an 18-gauge pin nailer for speed and a clean finish, or hand-drive pins. The pins hold the board in place while the adhesive sets (typically 24 hours for full cure). Work from one end to the other, pressing out any air pockets as you go.
7 Fit Joint Strips and Corners
Where capping boards meet, use inline joint strips to create a neat, weather-sealed junction. The joint strip slides over both board ends, concealing the expansion gap. At corners, use dedicated corner pieces for a professional finish. Apply a thin bead of colour-matched silicone inside corners and at any point where water could track behind the board. All joints and corners should look seamless from ground level.
8 Re-fix Guttering and Final Check
Re-fix gutter brackets through the capping board into the timber beneath. You may need slightly longer screws (add 9mm to the original screw length) to account for the capping board thickness. Check the gutter fall is still correct — the additional 9mm of board thickness shouldn't affect the fall, but verify. Clean the finished capping boards with warm soapy water. Inspect from ground level for alignment and finish quality.
Common Mistakes to Avoid
- Capping over rotten timber — The single biggest mistake. Capping board is a cosmetic covering, not a structural fix. The rot continues and the board falls off within months.
- Pins only, no adhesive — 25mm pins into a 9mm capping board have minimal grip in the timber behind. Without adhesive, boards will work loose, especially in wind.
- Wrong width capping board — The capping must cover the entire face of the existing fascia. If the existing board is 200mm, use 200mm capping. Undersized board leaves exposed timber at the edges.
- No expansion gaps — Butting boards tightly together in warm weather leaves no room for further expansion, causing buckling. Always leave 3–5mm.
- Forgetting to extend gutter screws — Standard gutter bracket screws may not reach through 9mm of capping + existing timber into the rafter end. Use 9mm longer fixings.
Related Products
Need Technical Help?
Our technical support team can talk you through any installation query. Available Monday to Friday, 8am–5pm.
0121 693 0373 Contact Technical Support