Flat Roof Extension vs Pitched Roof Extension

Flat Roof Materials: GRP, TPO & EPDM

GRP (Fibreglass)

A rigid, resin-infused coating over a multi-layered base, GRP is known for durability, smooth surface, and reltaive UV resistance. It’s often factory-finished and installed in sections to minimize seams.

• Pros: 25–30-year lifespan; seamless, watertight finish; low maintenance
• Cons: High upfront cost; repairs can be visible if not colour-matched

TPO (Thermoplastic Olefin)

A single-ply, reflective membrane welded at the seams to create a watertight barrier. TPO is increasingly popular in residential extensions.

• Pros: 25–30-year lifespan; heat-welded seams resist leaks; reflective surface reduces heat absorption
• Cons: Susceptible to punctures; requires protective layers over foot traffic areas

EPDM (Rubber Roofing)

Durable yet flexible synthetic rubber membrane, available in large seamless sheets.

• Pros: 20–30-year lifespan; excellent flexibility and tear resistance
• Cons: Black surface can attract heat; seams must be well-sealed and monitored

Pitched Roof Materials: Asphalt Shingles & Clay Tiles

Asphalt Shingles

Composed of fiberglass or organic mat with asphalt and ceramic fines, these are lightweight, cost-effective, and come in many design styles.

• Pros: 20–30-year lifespan; easy to install and replace; available in diverse textures and colours
• Cons: Less premium look; can suffer algae/mould without treatments

Clay Tiles

Natural baked clay tiles offer an elegant and traditional finish, often seen on heritage and upscale homes.

• Pros: 50–100-year lifespan; resilient to extreme weather; requires minimal ongoing maintenance
• Cons: Rigid and heavy—requires strong roof structure; higher material and labour cost

Planning Restrictions & How They Affect Choice

• Height limits: Under permitted development, flat roofs must usually remain under 3–4 m. Pitched roofs often exceed these, requiring full planning applications.
• Conservation rules: Both roof types may need style matching in conservation areas—flat roofs might be discouraged in favour of pitched ones.
• Neighbourhood impact: Pitched roofs can cast shadows or obstruct views; flat roofs are less intrusive. Neighbours must still be considered in party wall agreements.
• Construction regulations: Flat roofs require proper falls (minimum 1:40), overflow drains and insulation. Pitched roofs require structural calculations for load and wind uplift.

Common Roof Problems & Detailed Repair Process

Flat Roof

Ponding Water:

• Symptom: Water pooling in dips; visible algae or pond marks
• Repair: Add tapered insulation or re-level deck; cost ~£250–300 per beam or 1–2 m²

Membrane Tears/Punctures:

• Symptom: Water ingress, staining on ceiling, bubbling
• Repair: Clean, prepare area, apply patch and seal; cost £150–400 depending on size

Blocked Drains & Flashing Leaks:

• Symptom: Overflow during heavy rain, rust or plant growth around edges
• Repair: Clean out outlets; replace flashing and seals; £100–140/m²

Pitched Roof

1. Broken Tiles/Slates:

• Symptom: Missing tiles, visible daylight through roof, leak patches
• Repair: Replace individual pieces and reseal; cost ~£110–160/m²

Ridge/Lead Work Failure:

• Symptom: Loose ridge tiles, cracked lead, rusting
• Repair: Replace ridge tiles and re-bed with mortar or lead; cost £50–100/m run

Blocked Gutters/Valleys:

• Symptom: Overflowing gutter water, staining to timber or plasterwork
• Repair: Clean, re-level, reseal joints; add gutter guards; cost £70–100/m