How to specify fascias and soffits
What a fascia and soffit clause has to settle, from board type and fixing to eaves ventilation, fire and colour, and how to write it in CAWS and in Uniclass.
Photo: U.S. Navy, Christian Kinney, Public domain, via Wikimedia Commons.
.jpg){kind=link}
How do you specify fascias and soffits?
To specify fascias and soffits, state whether boards are full replacement or capping over existing timber, the material (PVC-U, timber or metal), the board profile, depth and thickness, and the colour or finish. Then specify the fixings and support centres with allowance for thermal movement, the eaves ventilation the condensation design needs, firestopping of eaves boxes at compartment walls, and the reaction to fire class where the building or fire strategy calls for one.
Fascias and soffits are usually drawn as a line at the eaves and specified as "uPVC fascia and soffit, white". That leaves out most of what matters: whether new boards replace the old timber or cap it, what they are fixed to and how often, how the roof void is ventilated through the soffit, and what happens to the eaves box where it crosses a compartment wall.
This guide takes the common UK case, cellular PVC-U roofline boards, as its worked example. Uniclass codes them as Pr_35_90_28_62 Plastics and composite material trim boards. Timber fascias are Pr_35_90_28_97 Wood trim boards, and metal fascias have their own codes such as Pr_35_90_28_02 Aluminium fascias. Fascia, soffit and gutter units made as one piece are coded separately again, in the gutters group.
What does a fascia board clause need to cover?
Some properties are specific to fascias and soffits. Others belong in every product clause. A clause that leaves either out gives the contractor room to substitute.
Properties of fascias and soffits
- Nominal sizeBoard depth to suit rafter feet and gutter.
- Edge treatmentLipped or returned edges and how soffit meets fascia.
- AccessoriesJoint and corner trims, box ends, soffit vents.
- Material gradeCellular PVC-UE core with impact-modified skin.
- Corrosion protectionStainless steel nails and screws.
- Reaction to fire classificationNever guessCheck against the fire strategy, especially on relevant buildings.
- Movement jointsExpansion gaps at board ends and joint trims.
- ThicknessFull replacement boards are thicker than capping boards.
- Product typeFascia, soffit, bargeboard, capping or box end.
- FixingsType, length and centres into sound timber.
- FinishWhite, coloured or foiled; no site painting.
What every product clause needs
- Manufacturer and product referenceNamed roofline system and board references.
- Product standardBS EN 13245-2 for PVC-U profiles, or a third-party certificate.
- Installation methodManufacturer's instructions and the certificate's installation section.
- Technical submittalsCertificate, vent areas and reaction to fire evidence.
- Operation and maintenance informationCleaning agents to avoid and clearing of soffit vents.
- MaterialCellular PVC-U, timber or aluminium.
- ProfileSquare, bullnose or ogee edge; flat or tongue and groove soffit.
Uniclass Pr_35_90_28_62 Fascias and soffits. Not every property applies to every project; where one does not, say so rather than leaving it blank.
Fields marked Never guess (reaction to fire classification) depend on the project and should never be filled from a default or a previous job. If the information is not available yet, the clause should say so with a TBC and a reason.
Which decisions does the clause depend on?
Most properties follow from the product you choose. These depend on the project, so they need a decision from the designer before the clause is written.
- 01
Full replacement or capping
Board typeRoofline systems come in two kinds. Full replacement boards are thick enough to fix straight to rafter feet and carry the gutter. Capping boards are thin skins designed to cover existing timber, and are only as good as the timber behind them. Capping over rotten fascias hides the problem and leaves the gutter fixed to failing wood. The BBA certificate for one PVC-U system recommends replacement rather than over-fixing, and requires capping boards to be fixed to sound timber or a plywood backing board. The clause should say which is intended and what is done with the old timber.
How to decide
- New build: full replacement boards fixed directly to rafter feet or a soffit bearer.
- Refurbishment: survey the existing timber; replace rather than cap if it is decayed or out of line.
- If capping is allowed, require sound timber or a backing board behind every length.
Write it asFascia: Full replacement cellular PVC-U board, existing timber fascias removed. Capping over existing timber not permitted. - 02
Eaves ventilation through the soffit
VentilationOn a cold pitched roof the soffit is usually where air enters the roof void. Vented soffit boards, soffit ventilator strips and over-fascia vents each have a declared free area per metre, and that area has to match what the condensation design needs. The vent is useless if loft insulation is pushed against the underside of the roof at the eaves, so an eaves tray or rafter roll is part of the same detail. Some roofs with vapour-permeable underlays or warm roof construction need little or no eaves ventilation, so take the requirement from the design rather than fitting vents by habit.
How to decide
- Take the eaves ventilation area from the condensation risk assessment to BS 5250 and the underlay's certificate.
- Choose vented soffit or ventilator strips with a declared free area at least equal to that need.
- Keep a clear air path past the insulation at the wall plate with an eaves tray or rafter roll.
Write it asSoffit ventilation: Continuous, free area not less than that required by the condensation risk assessment to BS 5250, with insect protection. Submit declared vent area. - 03
Reaction to fire, eaves boxes and taller buildings
Never guessPVC-U roofline boards are often described by an old national surface spread of flame class on their certificates, while Approved Document B now works in Euroclasses to BS EN 13501-1. Ask for the Euroclass of the board actually supplied. On a relevant building under regulation 7(2), ask the fire engineer whether the fascia and soffit form part of the external wall: the BBA certificate for one PVC-U system notes that regulation 7(2) may restrict its use. Separately, where a boxed eaves runs continuously between dwellings, it has to be firestopped at the compartment wall.
How to decide
- Ask for the reaction to fire Euroclass of the specified board and finish.
- On buildings with a storey at 18 m or more, confirm with the fire strategy whether a non-combustible fascia and soffit is needed.
- Show firestopping in eaves boxes at every compartment wall.
Write it asReaction to fire: Euroclass as declared to BS EN 13501-1, to suit the fire strategy. Eaves box firestopped at each compartment wall as drawing. - 04
Support, fixings and thermal movement
FixingPVC-U expands and contracts much more than timber, so boards are fixed to allow movement: gaps at board ends hidden by joint trims, and no continuous lengths glued at both ends. Fixings go into sound, preservative-treated timber at close centres. The BBA certificate for one roofline system calls for centres not exceeding 600 mm, at least two fixings per rafter, stainless steel nails or screws, and a gap at board joints for expansion. Fascia boards are not loadbearing beyond the gutter, so satellite dishes and cable brackets must fix through to structure.
How to decide
- Follow the manufacturer's certificate for fixing type, length and centres.
- Provide noggings or soffit bearers so every board edge is supported.
- Check gutter bracket centres against the fascia and gutter manufacturers' limits.
Write it asFixing: Stainless steel nails or screws as manufacturer, at not more than 600 mm centres and not less than two per rafter. Expansion gaps at joints, covered by joint trims. - 05
Colour, foils and heat
AppearanceWhite PVC-U is the default, but most systems are also made in coloured or woodgrain foils. Dark colours absorb more heat, and a dark board on a south-facing elevation moves and may distort more than a white one. Painting PVC-U on site is generally not recommended by manufacturers because paint can affect the board and dark paint adds to heat gain. If the design needs a dark or bespoke colour, choose a factory-finished board in that colour and check the manufacturer's movement guidance for it.
How to decide
- Choose colour from the manufacturer's factory range, not site painting.
- For dark colours, check fixing and movement guidance for that finish.
- Match fascia, soffit, bargeboard and gutter colours on one sample board.
Write it asFinish: Factory foiled, colour as manufacturer's range. Site painting not permitted.
The values under "Write it as" are examples. The right value depends on the location, the use and the fire strategy.
Which standards should the clause cite?
Cite the product standard the declaration of performance refers to, the code of practice for installation, and the test method behind each value you set. A value without its test method cannot be checked against a submittal.
- BS EN 13245-2
- Plastics. Unplasticized poly(vinyl chloride) (PVC-U) profiles for building applications. PVC-U profiles and PVC-UE profiles for internal and external wall and ceiling finishes
The product standard for PVC-U and cellular PVC-UE finishing profiles, covering properties such as impact resistance, durability and reaction to fire.
In the clause "Boards: Cellular PVC-UE profiles to BS EN 13245-2".
- BS 5250
- Management of moisture in buildings. Code of practice
Condensation risk and roof void ventilation, which sets the eaves ventilation the soffit has to provide.
In the clause "Eaves ventilation: as condensation risk assessment to BS 5250".
- BS EN 13501-1
- Fire classification of construction products and building elements. Classification using data from reaction to fire tests
The Euroclass system that Approved Document B now uses for reaction to fire.
In the clause "Reaction to fire: Euroclass as declared, to BS EN 13501-1".
- BS 476-7
- Fire tests on building materials and structures. Method of test to determine the classification of the surface spread of flame of products
The older national test whose classes (such as Class 1) are still quoted on some roofline certificates. Approved Document B guidance now uses Euroclasses instead.
In the clause Do not use it as the requirement; ask for the BS EN 13501-1 class.
- BS EN 607
- Eaves gutters and fittings made of PVC-U. Definitions, requirements and testing
The product standard for PVC-U gutters that are usually fixed to the fascia board.
In the clause Cite it in the rainwater clause; the fascia clause refers to "gutter brackets fixed as section R10".
- BS EN 1462
- Brackets for eaves gutters. Requirements and testing
Gutter bracket strength, which together with the fascia fixing sets bracket centres.
In the clause "Gutter brackets: to BS EN 1462, centres as gutter and fascia manufacturers".
- BS 8417
- Preservation of wood. Code of practice
Use classes and treatment for timber, relevant to timber fascias and to the timber bearers and noggings behind PVC-U boards.
In the clause "Timber supports: treated to BS 8417, use class 3".
Confirm the current edition of each standard at every issue. Avoice's State of UK Specifications 2026 found a withdrawn standard cited in 40% of specifications at contract issue.
For the regulations behind these choices, see Approved Document B explained, Higher-risk buildings explained, or search the Avoice Regulations library.
How do you write it in CAWS?
CAWS has no roofline section of its own. NBS puts fascias, bargeboards and soffits in G20 Carpentry/ timber framing/ first fixing, as clause 950 Fascias/ barges/ soffits, whatever they are made of, and eaves soffit ventilation as a separate G20 clause. NBS Source lists PVC-U fascia boards against G20 clause 950.
The 950 clause is a product-and-fixing clause rather than a big type clause: it names the board, its material, finish, depth, edge profile, support and fixings, and the installer. It relies on the general G20 clauses for protecting timber and components on site, jointing and fixing, and on section Z12 for preservative treatment of the timber it is fixed to. Gutters fixed to the fascia are in R10.
- Description
- Full replacement fascia, bargeboard and soffit, existing timber removed
- Manufacturer
- Submit proposals
- Product reference
- Submit proposals
- Material
- Cellular PVC-UE core with impact-modified PVC-U skin, to BS EN 13245-2
- Fascia and bargeboard
- 18 mm thick, nominal depth to suit rafter feet as drawing
- Soffit
- Vented soffit board, as clause 910
- Edge profile
- Square
- Finish
- Factory foiled
- Colour
- TBC Colour to match new windows, which are still at tender. Resolve before ordering.
- Support
- Treated softwood bearers and noggings so every board edge is supported
- Fixings
- Stainless steel, as manufacturer, at not more than 600 mm centres and not less than two per rafter
- Joints
- Expansion gaps at board ends covered by joint and corner trims
- Eaves box
- Firestopped at each compartment wall as drawing
- Reaction to fire
- Euroclass as declared to BS EN 13501-1, to suit fire strategy
- Installer
- A contractor approved by the system manufacturer
Illustrative, not from a real project. One property is left as a TBC with a reason so it can be tracked and closed before issue.
Clauses the type clause relies on
- G20/451
- Moisture content testing Checking the timber the boards are fixed to before cladding over it.
- G20/510
- Protection Storing timber and components dry, supported and undamaged.
- G20/570
- Jointing/ fixing generally Fastener selection where not specified, with section Z20.
- G20/910
- Eaves soffit ventilation Vent type, free area and insect mesh at the soffit.
Clause numbers vary between NBS versions and practice masters; 950 and 910 follow NBS-format specifications issued on Public Contracts Scotland and Sell2Wales, and NBS Source lists PVC-U fascia boards against 950.
How do you write it in Uniclass?
Uniclass has no dedicated fascia system, so the eaves is usually written under Ss_30_25_10_28 External soffit systems, with the fascia called up as part of the same build-up. The system clause describes the support framing, the boards, the ventilation and the firestopping at compartment walls.
The boards are a product clause under Pr_35_90_28_62 Plastics and composite material trim boards. Fascia, soffit and bargeboard in the same range can share one product clause with separate type marks, so colour and finish change in one place.
- Description
- PVC-U fascia, bargeboard and vented soffit at eaves and verges
- Support
- Treated softwood bearers and noggings, every board edge supported
- Boards
- Pr_35_90_28_62 Plastics and composite material trim boards (FB01)
- Ventilation
- Free area as condensation risk assessment to BS 5250
- Fixing
- Stainless steel, not more than 600 mm centres, two per rafter
- Firestopping
- Eaves box firestopped at each compartment wall
- Reaction to fire
- To suit fire strategy, Euroclass to BS EN 13501-1
- Manufacturer
- Submit proposals
- Product reference
- Submit proposals
- Standard
- BS EN 13245-2, or current third-party certificate
- Material
- Cellular PVC-UE core, impact-modified PVC-U skin
- Fascia thickness
- 18 mm, full replacement board
- Edge profile
- Square
- Finish
- Factory foiled; no site painting
- Colour
- TBC Colour to match new windows, which are still at tender. Resolve before ordering.
- Accessories
- Joint trims, corner trims and box ends from the same system
- Reaction to fire
- As declared, to BS EN 13501-1
Illustrative. Performance of the finished system sits in the system clause; properties of the product sit in the product clause.
In NBS Chorus the Uniclass product clause also carries the NBS reference 45-75-30/330 for plastics and composite trim boards; use one referencing system throughout the specification.
What goes in the spec, and what goes in the schedule?
The specification defines each type once. The schedule and drawings say where each type goes.
In the specification
What the product is and how it performs and is installed. Written once per type.
In the schedule or drawings
Where each type goes and how much of it. Changes with every plan revision.
Write the roofline type once and show depths, soffit widths and compartment walls on the sections and roof plan. Depths often change between the main roof and dormers, so dimension them on the drawings rather than in the clause.
What are the common mistakes?
Most problems are a missing property, a property filled with the wrong kind of value, or a decision left silently open.
- Capping over rotten timber. Capping boards hide decay and leave the gutter fixed to failing wood. Survey, and say whether replacement is required.
- "Ventilated soffit" with no free area. The vent must provide the area the condensation design needs. State it and ask for the declared value.
- No firestopping in the eaves box. A continuous eaves box between dwellings needs firestopping at each compartment wall. Draw it and write it in.
- A surface spread of flame class as the requirement. Class 1 to BS 476-7 is an old national class. Ask for the Euroclass to BS EN 13501-1.
- Boards glued at both ends. PVC-U needs room to move. Leave expansion gaps and cover them with joint trims.
- Site-painted PVC-U. Manufacturers generally advise against it. Choose a factory colour if white is not wanted.
How Avoice helps
Avoice drafts roofline clauses from your sections and elevations, and holds the open decisions in one TBC register.
- Drafts from your drawings and schedules
It reads eaves and verge details from sections and elevations, picks G20 clause 950 or the Uniclass soffit system, and fills in board depths and soffit widths where they are drawn.
- Leaves a TBC where the information is not there
If the board colour waits on the window package or the fire strategy has not said whether the eaves needs to be non-combustible, the clause says TBC with that reason, and it joins the project TBC register.
- Writes in your format and your style
Choose CAWS or Uniclass. Avoice adapts your practice's G20 master, so your standard roofline clause keeps its wording.
- Checks the clause against everything else
QA/QC flags a ventilated soffit in the clause with no vent shown on the eaves detail, a compartment wall with no eaves firestopping, or a fire requirement written as a BS 476 class.
- Keeps product data in one place
The roofline system's certificate, vent areas and reaction to fire evidence live in the Product Room, linked to the clause, so an alternative system is checked against the same values.
Related guides: How to specify rainwater goods, How to specify dry ridge and verge systems, How to specify breather membranes.
Software can draft and check. The designer still chooses the product and is responsible for the specification.
Draft your fascia board clause in Avoice
Upload your drawings and schedules. Avoice drafts the clause in CAWS or Uniclass, cites the standards and flags anything your information does not settle.
This guide is for general education and is not professional advice. Check current editions of standards and Approved Documents, the manufacturer's data, and the requirements of your project before relying on any clause.