Fascia & Soffit Replacement
Step-by-step guide to replacing old timber fascia and soffit boards with low-maintenance PVC-U, including ventilation and gutter re-fixing.
Safety Warning — Working at Height
Plan and risk-assess all work at height. Roofline replacement normally requires a suitable working platform with collective fall protection. A ladder should only be used where the assessment shows low risk and short duration and that equipment offering greater protection is not justified. Check for overhead services, secure the work area below, and use access equipment assembled or inspected by a competent person.
Check for Asbestos Before Removal
Fascias, soffits, gutters, downpipes and adjacent eaves products on buildings constructed or refurbished before 2000 may contain asbestos. Check the building information and have suspect materials assessed before drilling, cutting or removal. Stop work if the material is uncertain or damaged and follow the current HSE asbestos guidance, including any licensing, notification and waste controls that apply.
What You'll Need
Tools
- Scaffold tower or mobile platform
- Crowbar and wrecking bar
- Circular saw or handsaw
- Drill/driver with bits suitable for the specified fixings
- Spirit level
- Tape measure
- Snips or multi-tool for trimming
- Caulking gun
Materials
- 16mm Kalsi PVC-U replacement fascia boards
- Kalsi flat or hollow soffit boards selected for the roof design
- Starter trims / F-section or J-section
- Corner joints and inline joints
- Kalsi-specified stainless steel or PVC-U-headed nails/screws
- Ventilation components with confirmed declared free area
- Compatible Kalsi joint covers, corners and finishing accessories
- Suitable treated structural timber where repair or support is required
Technical Specifications
Technical basis: Kalsi document TDS-RF-FA-001, issue February 2026, and the published soffit product dimensions. Check the current fascia data sheet before installation. Obtain the current profile-specific soffit fixing diagram and declared vent free area from Kalsi Technical before setting out the supports; roof ventilation must follow the condensation-control design for the particular roof.
Step-by-Step Installation
1 Remove Existing Guttering
Carefully remove the existing guttering system — brackets, downpipes, and all fixings. If the guttering is being reused, label each section for re-fitting. If replacing, remove completely. Plug or cap any open downpipe connections to prevent debris falling into the drainage system during the works.
2 Strip Old Fascia and Soffit
Remove the old timber fascia board first, then the soffit. Use a crowbar and work carefully to avoid damaging the rafter ends. Old timber can be heavy and may break unpredictably — keep the area below clear. Remove all old nails, screws, and fixings from the rafter ends and wall plate. Bag and dispose of old timber responsibly.
3 Inspect and Treat Rafter Ends
With the old boards removed, inspect every rafter end, bearer and fixing point. Do not fix new roofline products over damp, soft, decayed or inadequately supported timber. Have structural deterioration assessed and repaired by a competent person, using suitably graded and treated replacement timber designed to restore the required support. Establish a straight, secure fixing line before proceeding.
4 Fit the Soffit Bearer and Wall Trim
Install the appropriate Kalsi edge trim at the wall and provide sound treated-timber bearers in the positions required by the current profile-specific soffit diagram. Arrange the supports for the chosen board direction and width so every edge and joint is held. Fix trims and bearers securely to the appropriate substrate; the fixing type and embedment must suit the masonry or timber being used.
5 Install Soffit Boards
Cut the selected soffit boards square and fit their edges into the specified trims, allowing 3mm at board ends for movement. Fix each board at every designed bearer/support using the fixing type, number and pattern in the current Kalsi profile-specific schedule. Where roof ventilation is required, use a vented soffit, continuous strip or over-fascia vent with a declared free area sufficient for the roof-specific design. Do not assume that a nominal slot size or the word “vented” establishes compliance.
6 Fit the Fascia Board
Use 16mm replacement fascia and fix it directly to sound rafter feet or designed battens. Install at least two Kalsi-specified stainless steel or PVC-U-headed nails/screws through the board width at every rafter, with support centres no greater than 600mm; provide additional support where the board or loading requires it. Leave 3mm at board ends and cover joints with the matching accessories without fixing the run rigidly at both ends.
7 Ensure Ventilation Compliance
Before closing the eaves, verify the complete ventilation path against the current condensation-control design and, for work in England, Approved Document C guidance; elsewhere in the UK, use the applicable national building regulations. The required low- and high-level equivalent areas depend on the roof build-up, pitch, underlay, insulation and vapour-control provision, so this guide does not set one universal gap. Confirm the declared free area of every Kalsi vent product with Kalsi Technical, keep the air path clear of insulation and fit eaves trays where specified.
8 Re-install Guttering and Finish
Re-fix gutter brackets through the fascia into the support required by the selected gutter system, using compatible corrosion-resistant fixings with adequate embedment. Fit Kalsi joint covers, corners and closures as detailed for the selected profiles. Use sealant or adhesive only where the current accessory instructions call for it; do not block ventilation openings or bridge movement gaps. Clean with mild detergent and water, then inspect alignment, support and drainage.
Common Mistakes to Avoid
- Fixing over unsound timber — Roofline boards need continuous support from sound rafter feet, battens and bearers. Have decayed structural timber repaired before covering it.
- Assuming one ventilation gap suits every roof — Preserve the designed air path and verify the required equivalent area and vent-product free area for the particular roof.
- Using unsuitable fixings — Use only the Kalsi-specified stainless steel or PVC-U-headed nails/screws, in sufficient length for the support and exposure.
- No movement allowance — Leave the specified 3mm at board ends and do not lock long runs rigidly at both ends.
- Insufficient structural fixing — Fascia needs at least two fixings through its width at each rafter, with support at no more than 600mm centres.
- Installing outside the stated range — Install between 5°C and 30°C and avoid frost or direct strong sunlight.
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