44 roofing terms explained in plain English — everything you need to understand a survey, quote or repair on a Winchester property.
📞 01962 809171 — Free SurveyThis glossary explains the roofing terms you will come across when getting a survey, reading a quote, or having work carried out on a Winchester property. Definitions are grouped into five categories — materials, defects, components, standards and processes — covering 44 terms in total. Each definition includes how the term applies specifically to Winchester and Hampshire housing stock.
A flat, low-profile roofing tile made from fired natural clay, typically 265×165mm, nibbed to hook over battens as well as being nailed. The original roofing material on the majority of Winchester's Victorian, Edwardian and 1930s properties. Correctly maintained clay plain tiles have a design life of 80–150+ years — the tiles themselves rarely fail; the lead flashings, ridge mortar and felt underlay beneath them fail first. Required material for like-for-like replacement in Winchester conservation areas.
Related: Concrete Interlocking Tile · Conservation Area · Ridge Tile
A large-format roofing tile (typically 380×230mm or 420×330mm) with interlocking side edges that reduce the number of tiles needed per square metre and speed installation. Introduced to UK housebuilding in the 1950s as a cheaper, faster alternative to clay plain tiles. The dominant material on Winchester's post-war estates (Stanmore, Harestock, Badger Farm, Boyatt Wood). Design life 30–50 years — the tile surface usually outlasts the iron fixing nails, which corrode and cause nail sickness.
Related: Clay Plain Tile · Nail Sickness
A thin, cleaved sheet of natural metamorphic rock used as a premium roofing material, typically Welsh (Penrhyn or Ffestiniog) or Cumbrian (Burlington) in origin. Found on higher-specification Victorian and Edwardian Winchester properties — the larger villas of St Giles Hill and some Hyde properties. Welsh slate lasts 80–150+ years. Spanish slate, introduced in the 1980s, absorbs more water and lasts only 30–50 years, and is not compliant for Winchester conservation area work.
Related: Clay Plain Tile · Conservation Area · Disc Rivet
A manufactured slate substitute made from cement reinforced with cellulose fibres, designed to replicate the appearance of natural slate at a lower cost. Available from manufacturers such as Marley and Cedral, with a design life of 40–60 years. Used on some Winchester re-roofs where budget or structural load prevents natural slate specification. Not appropriate for conservation area or listed building work requiring natural slate.
Related: Natural Slate · Conservation Area
Glass Reinforced Polyester (fibreglass) flat roofing, applied in situ as a liquid laminate of catalysed resin and glass matting over a clean deck substrate, curing to a seamless waterproof surface. The current standard for replacing failed felt flat roofs on Winchester extensions. 25-year manufacturer warranty when installed by a certified applicator. Requires a fully stripped, dry deck — GRP applied over existing felt does not bond correctly and voids the warranty.
Related: EPDM · Bitumen Felt · Deck · Warm Roof
Ethylene Propylene Diene Monomer — a synthetic rubber membrane used for flat roofing, supplied in large single sheets that minimise joints. Highly durable and flexible, with a design life of 30–50 years. Suited to larger or more complex flat roof shapes on Winchester properties where a single-sheet installation is advantageous over GRP. Requires a clean, prepared deck substrate.
Related: GRP Flat Roofing · Bitumen Felt · Deck
Traditional flat roofing material made from bitumen-saturated fibre matting, applied in layers (built-up felt) or as a single torch-on membrane. Design life 10–20 years. The original flat roof covering on most Winchester 1960s–80s rear extensions — now typically at or past end of life. Superseded by GRP and EPDM for most modern replacements due to its shorter lifespan and jointed construction.
Related: GRP Flat Roofing · EPDM · Deck
A polypropylene membrane installed beneath roof tiles that allows water vapour to escape from the roof space while preventing liquid water ingress. Eliminates the condensation risk in cold roof construction and removes the need for a separate ventilation path required by traditional bitumen felt. Design life 40–60+ years. Standard specification on all Winchester re-roofs. Compliance is governed by BS 5250 for moisture management.
Related: Bitumen Felt · Cold Roof · Ventilation
Rolled lead used for weatherproofing roof junctions — chimney flashings, valleys, back gutters and abutments. Specified by code number under BS EN 12588, where a higher code means thicker, heavier lead. Winchester period properties have original lead now 80–130 years old and typically at end of life. Correctly installed lead is one of the longest-lived roofing materials, lasting 50–80 years.
Related: Lead Code · Soakers · Step Flashing
The corrosion of the iron nails used to fix concrete interlocking roof tiles, causing tiles to lose their mechanical fixing and rely only on gravity and adjacent-tile overlap. Widespread on Winchester post-war estates built 1950–1980, now 50–75 years old — beyond the 40–50 year design life of iron nail fixings. Diagnosed by a percentage survey pressing each tile; addressed by stainless steel clip repair (below 25% affected) or full re-roofing (above 25%).
Related: Concrete Interlocking Tile · Clip Repair · Stainless Fixings
The flaking and breaking away of a brick or masonry surface, caused when trapped moisture freezes and expands, or when hard cement mortar transfers thermal stress to softer period brick. A common — and irreversible — result of repointing a Victorian Winchester chimney with Portland cement instead of lime mortar. Once spalling occurs, affected bricks must be cut out and replaced.
Related: NHL Lime Mortar · Repointing · Chimney Stack
Standing water that fails to drain from a flat roof surface, typically caused by inadequate fall, a blocked outlet, or deck deflection. Ponding accelerates membrane failure by 2–5 times compared to a free-draining surface, as prolonged water contact degrades the covering and adds structural load. Found on approximately 60% of Winchester flat roof surveys, usually linked to blocked outlets.
Related: Deck · Fall · GRP Flat Roofing · Outlet
The chemical process by which lime or cement mortar reacts with atmospheric carbon dioxide over decades, gradually losing its adhesive strength and becoming friable. The primary cause of ridge and hip mortar failure on Winchester period properties — original mortar that has fully carbonated must be raked out and rebedded rather than simply repointed over.
Related: Ridge Tile · Repointing · NHL Lime Mortar
The separation of the layers of a built-up flat roof membrane, or the lifting of a GRP top coat from its substrate, allowing water to enter the cavity between layers. On Winchester extension flat roofs, delamination of aged bitumen felt at the UV-exposed leading edge is one of the most common failure modes.
Related: Bitumen Felt · GRP Flat Roofing · Ponding
The tile capping the apex where two roof slopes meet, most commonly half-round in profile, bedded in mortar on Winchester period and post-war properties. Ridge mortar carbonates over 20–35 years and requires rebedding in flexible modified mortar — not sand and cement, which cracks under thermal movement. Chalk ridge Winchester properties (Kings Worthy, Teg Down, Harestock) experience accelerated ridge failure from wind exposure.
Related: Hip Tile · Carbonation · Flexible Mortar · Dry Ridge
The tile covering the external sloping junction (the hip) of a hipped roof, bedded in mortar in the same way as ridge tiles and failing on the same schedule. On Winchester's 1930s hipped detached properties in Weeke and Chandler's Ford, hip rebedding is almost always required at the same time as ridge rebedding, as both elements are the same age.
Related: Ridge Tile · Flexible Mortar · Carbonation
The internal V-shaped channel where two roof slopes meet, concentrating rainwater from both slopes into a single drainage path. Winchester period properties use lead-lined valleys (code 5 lead); post-war estates often use mortar valleys. Valley failures cause interior damp that appears 1–3 metres from the actual failure point, as water travels horizontally along ceiling joists before dripping — a frequent source of misdiagnosis.
Individual lead pieces set between each tile course and a chimney or wall side face, forming the primary waterproof seal at side junctions. Hidden beneath the visible step flashings. A chimney fitted with step flashings but no soakers behind them has only one waterproofing layer at the sides and fails significantly sooner — a common defect found on Winchester properties where previous work cut corners.
Related: Step Flashing · Lead Sheet · Lead Code · Chimney Stack
The visible stepped lead pieces dressed into the mortar joints of a chimney or wall, overlapping the soakers beneath to weatherproof the side junction with the roof slope. Set into raked-out masonry chases to a minimum depth and secured with lead clips. Works in combination with soakers — one without the other is an incomplete detail.
Related: Soakers · Lead Sheet · Chimney Stack
The lead-lined channel behind a chimney stack (on the upslope side) that collects water running down the roof above and directs it around the stack. One of the most failure-prone lead elements on Winchester period chimneys — a failed back gutter causes damp on the ceiling below the chimney breast, often mistaken for a pointing or apron problem.
Related: Soakers · Step Flashing · Front Apron · Lead Code
The lead flashing on the downslope face of a chimney stack, dressed over the tiles below to shed water clear of the junction. One of the four lead elements of a complete chimney weatherproofing set, alongside soakers, step flashings and the back gutter.
Related: Back Gutter · Soakers · Step Flashing
The board running horizontally along the lower edge of the roof, closing the gap at the rafter feet and carrying the guttering brackets. Winchester post-war timber fascias from the 1960s–80s are now 40–65 years old and frequently at end of life. Replacement requires checking the rafter feet behind — new fixings into rotten timber pull out within months.
Related: Soffit · Rafter Feet · Guttering
The board fitted horizontally beneath the fascia, closing the underside of the roof overhang. Often ventilated to allow air into cold roof spaces. Blocking soffit ventilation when replacing boards — fitting solid soffits where vented sections are required — creates a condensation problem in the roof space within a few years.
Related: Fascia · Ventilation · Cold Roof
The lowest ends of the roof rafters, where they meet the wall plate at the eaves. Fascia boards fix to the rafter feet. Where long-term gutter overflow has caused the rafter feet to rot, they must be repaired or replaced before new fascias can be fitted — new fixings will not hold in rotten timber.
The structural boarded base of a flat roof — typically plywood or OSB — onto which the waterproof membrane is applied. Deck condition is critical: soft or rotten boards must be replaced before any new membrane is laid, or the covering fails within 2–5 years. Sounded (tapped and pressed) at every Winchester flat roof survey.
Related: GRP Flat Roofing · Bitumen Felt · Ponding
The masonry structure projecting through the roof to carry a flue. Winchester period chimney stacks require lime mortar repointing and lead flashing renewal as their primary maintenance items. Redundant stacks generating ongoing maintenance cost can be removed to below roofline with full roof reinstatement.
Related: Soakers · Step Flashing · Back Gutter · NHL Lime Mortar · Repointing
The point where a flat roof or gutter discharges water into a downpipe or drainage system. Blocked outlets are the single most common finding at Winchester flat roof surveys, causing ponding and accelerated membrane failure. Cleared as standard on every survey and maintenance visit.
The channel fixed at the eaves to collect and discharge rainwater from the roof. Winchester properties use uPVC (post-war), cast iron or cast aluminium (period properties). Correct fall is 1:350 gradient toward the outlet. New guttering brackets fix into the fascia — rotten fascias must be addressed first.
The specification system for lead sheet thickness and weight in roofing, defined in BS EN 12588. Code 4 (1.80mm, 20kg/m²) is the minimum for chimney flashings and soakers. Code 5 (2.24mm, 25kg/m²) is required for back gutters and valley linings. Using an underweight lead code — Code 3 in a valley, for example — cuts the service life from 60–80 years down to 20–30.
Related: Lead Sheet · Valley · Soakers
Natural Hydraulic Lime mortar, classified by compressive strength — NHL 3.5 being the standard grade for repointing Victorian and Edwardian Winchester chimney stacks. Softer and more flexible than Portland cement, it accommodates the movement of period brickwork without transferring stress to the brick face. Requires above 3°C for application and 48–72 hours frost protection. The correct specification for all pre-1940 Winchester masonry.
Related: Repointing · Spalling · Carbonation · Chimney Stack
The expansion gap and clip spacing built into lead sheet installations to let the metal expand and contract with temperature without stress-cracking. Lead expands roughly 0.03mm per metre per °C. BS 6915 sets maximum bay lengths and specifies stainless clips at 450mm maximum centres. Insufficient allowance — or lead nailed rigidly through its face — causes cracking within 5–10 years regardless of lead code.
Related: Lead Code · Lead Sheet · Step Flashing
A roof construction where the thermal insulation is placed at ceiling-joist level, leaving the roof space above cold and requiring ventilation to prevent condensation. The common construction on Winchester post-war properties. When breathable underlay is installed, the separate ventilation path requirement can be eliminated.
Related: Warm Roof · Breathable Underlay · Ventilation · Soffit
A roof construction where insulation is placed at or above rafter level, keeping the roof structure within the heated envelope and eliminating the condensation risk of cold roof construction. Best practice for Winchester habitable loft conversions, typically using PIR insulation board.
Related: Cold Roof · Ventilation · GRP Flat Roofing
A designated area of special architectural or historic interest where development is controlled to preserve character, under the Planning (Listed Buildings and Conservation Areas) Act 1990. In Winchester this includes Cathedral Close, Hyde, Kingsgate and St Cross among others. Within the boundary, roof material changes require like-for-like replacement — clay for clay, natural slate for natural slate — with concrete alternatives not permitted.
Related: Clay Plain Tile · Natural Slate · Listed Building
A building of special architectural or historic interest included on the statutory list, where any alteration affecting its character — including most roofing work — requires Listed Building Consent from the local authority. Winchester has numerous listed buildings, particularly in St Cross and the city centre. Consent typically takes 8–12 weeks and must be obtained before work begins.
Related: Conservation Area · Natural Slate
The complete replacement of a roof covering — stripping the existing tiles, felt and battens, inspecting and treating the timbers, then laying new breathable underlay, treated battens and tiles with stainless fixings. The appropriate solution for a Winchester roof with widespread nail sickness (above 25%), failed felt, or age beyond 55–60 years. A 3-bed Winchester semi re-roof costs £6,500–£14,000 depending on material.
Related: Nail Sickness · Breathable Underlay · Stainless Fixings
Raking out failed mortar from masonry joints to a depth of 15–20mm and refilling with fresh mortar, restoring weather resistance and structural integrity. On Winchester chimneys, the mortar specification is critical — NHL 3.5 lime for pre-1940 properties, flexible modified mortar for post-war. Portland cement on period brickwork causes irreversible spalling.
Related: NHL Lime Mortar · Spalling · Chimney Stack · Carbonation
The repair of nail-sick concrete tiles by fixing stainless steel clips to secure tiles that have lost their nail fixing, without a full re-roof. Cost-effective where nail sickness is below 25% and localised. Above that threshold, full re-roofing is usually better value over any horizon beyond ten years.
Related: Nail Sickness · Stainless Fixings
A stainless steel fixing used to secure replacement natural slates that have slipped due to nail failure, without re-roofing the whole slope. The correct modern fixing for slate repair — along with code 3 lead hooks — as iron nails corrode and release slates over time.
Related: Natural Slate · Stainless Fixings
A mechanically fixed ridge system that secures ridge tiles with screws and clamps rather than mortar bedding. Standard on new-build properties from the 2000s and available for re-roofing. Eliminates the mortar carbonation that causes traditional ridge failure, though it requires a compatible tile profile and periodic inspection of the mechanical fixings.
Related: Ridge Tile · Flexible Mortar
A modified mortar that remains slightly flexible when set, accommodating the daily thermal movement of a roof without cracking. The correct specification for ridge and hip rebedding on Winchester properties — it lasts 25–35 years, compared to 15–25 years for rigid sand-and-cement mortar, which cracks and fails prematurely.
Related: Ridge Tile · Hip Tile · Carbonation · Dry Ridge
Corrosion-resistant stainless steel nails, clips and screws used in place of iron fixings, which corrode and cause nail sickness. Every fixing used in Winchester Roofing Experts repair and re-roofing work is stainless steel throughout — using iron fixings in work meant to last 30+ years is not correct practice.
Related: Nail Sickness · Clip Repair · Disc Rivet
The deliberate gradient built into a flat roof or gutter to ensure water drains to the outlet rather than standing. The correct fall for guttering is 1:350 (about 3mm per metre); for flat roofs, a minimum of 1:80 is typical. Loss of fall — through bracket failure, fascia movement or deck deflection — causes ponding and overflow.
The controlled airflow through a cold roof space that prevents condensation forming on the underside of the roof covering. Provided at the eaves (through vented soffits) and sometimes at the ridge. Blocking ventilation paths with insulation or solid soffits — or failing to provide them — causes damp and timber decay in the roof space.
Related: Cold Roof · Soffit · Breathable Underlay
If a term you are unsure about is not listed here, ask us directly. Call 01962 809171 or email info@winchesterroofers.co.uk for a free survey and a plain-English explanation of anything found on your Winchester roof.
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