Double lap roofing
A double lap in roofing terms refers to how much overlap there is between each layer of roof covering; tile, slate, shingle etc. A double lap is general the most common standard whereby each layer covers the layer beneath by about or less than half, so that two layers (double) overlap to create a water resistant roof cover.
Such roofs are laid from the eaves towards the ridge of the roof a row at a time, fixed into the roof battens with roofing nails. Roofing nails are short nails with a large flat round head to secure the slate or tile, and either a smooth or a corrugated shank for a more secure fixing.
Some roofing types such as scantile slate roofing found in Devon and Cornwall are laid to a triple lap, meaning each layer of slate covers a third of the slate beneath meaning three layers of slate (triple) overlap. This is considered to be more robust and weathertight for regions near the coast with high winds and salt water, with added resistance through the use of a lime mortar bedded between the slates and at the edges. A typical slate the might be used in this way is the Delabole slate which comes from Delabole quarry in Cornwall.
Because slate roofs are laid in this process with the next layer above covering the fixings of the layer below, acces to those fixings for repair or replacement can be difficult. As such many slaters or slate roofers will posses a slaters ripper or puller, which is a long thin tool (slightly longer than a slate) which can be inserted and slid from outside at the angle of the pitched of roof to rip the nail fixing the broken slate out.
[edit] Related articles on Designing Buildings
- Battens.
- Ceiling tiles.
- Ceramic tiles.
- Clovelly, a village changing hands and changing with the times.
- Conservation.
- Delabole Slate.
- Domestic roofs.
- Flashing.
- Flat roof defects.
- Heritage.
- Historic environment.
- IHBC articles.
- Institute of Historic Building Conservation.
- Nails - a brief history.
- Photocatalytic tiles.
- Pitched roof.
- Planning for sustainable historic places.
- Reconciling conservation and sustainable development.
- Roof coverings.
- Roof insulation.
- Roof slates.
- Roof tiles
- Roofing defects.
- Shingle roofing.
- Sustaining Clovelly, a history, its management and retrofit.
- Thatch roofing.
- Tiles.
- Tile roofing
- Types of nails.
- Types of roof
- Weatherboarding
Featured articles and news
Preparing safety case reports for HRBs under the BSA
A new practical guide to preparing structural inputs for safety cases and safety case reports published by IStructE.
Male construction workers and prostate cancer
CIOB and Prostate Cancer UK encourage awareness of prostate cancer risks, and what to do about it.
The changed R&D tax landscape for Architects
Specialist gives a recap on tax changes for Research and Development, via the ACA newsletter.
Structured product data as a competitive advantage
NBS explain why accessible product data that works across digital systems is key.
Welsh retrofit workforce assessment
Welsh Government report confirms Wales faces major electrical skills shortage, warns ECA.
A now architectural practice looks back at its concept project for a sustainable oceanic settlement 25 years on.
Copyright and Artificial Intelligence
Government report and back track on copyright opt out for AI training but no clear preferred alternative as yet.
Embedding AI tools into architectural education
Beyond the render: LMU share how student led research is shaping the future of visualisation workflows.
Why document control still fails UK construction projects
A Chartered Quantity Surveyor explains what needs to change and how.
Inspiration for a new 2026 wave of Irish construction professionals.
New planning reforms and Warm Homes Bill
Take centre stage at UK Construction Week London.
A brief run down of changes intentions from April in an onwards.
Reslating an ancient water mill
A rare opportunity to record, study and repair early vernacular roofs.
CIOB Apprentice of the Year 2025/26
Construction apprentice from Lincoln Mia Owen wins this years title.
Insulation solutions with less waste for a circular economy
Rob Firman, Technical and Specification Manager, Polyfoam XPS explains.
Recycled waste plastic in construction
Hierarchy, prevention to disposal, plastic types and approaches.
UK Net Zero Carbon Buildings Standard V1 published
Free-to-access technical standard to enable robust proof of a decarbonising built environment.