Flat Roof Construction
The general process for flat roof construction involves several key steps to ensure durability, proper drainage, and weather resistance. Here’s a breakdown of the typical process:
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What are the first steps for flat roof construction?
1. Planning and Design
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Assessment of building requirements, local climate, and load-bearing capacity.
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Selection of materials: insulation type, membrane system (e.g., EPDM, TPO, PVC, bitumen), vapor barrier, etc.
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Slope design (typically 1/4″ per foot) to allow proper water drainage.
2. Structural Deck Installation
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Install the roof deck, which may be made of:
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Concrete
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Plywood or OSB (oriented strand board)
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Metal decking
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Ensure the deck is level and properly supported.
3. Vapor Barrier (if needed)
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Applied over the deck to prevent condensation within the insulation.
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Especially important in colder climates or buildings with high humidity.
4. Insulation Installation
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Rigid foam boards (like polyiso, EPS, or XPS) or spray foam are common.
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May be adhered, mechanically fastened, or loose-laid depending on the system.
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Installed in one or more layers to achieve desired R-value.
5. Roofing Membrane Installation
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Main waterproofing layer.
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Types include:
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Single-ply membranes: EPDM (rubber), TPO, PVC
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Built-up roofing (BUR): multiple layers of bitumen and felt
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Modified bitumen: asphalt-based with modifiers for flexibility
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Installation methods:
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Adhered (glued)
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Mechanically fastened (screws and plates)
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Ballasted (weighed down with gravel)
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6. Flashing and Edging
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Install flashing around roof penetrations (vents, HVAC, skylights) and along edges to prevent leaks.
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Use compatible materials to avoid chemical reactions or deterioration.
7. Drainage System
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Install drains, scuppers, or gutters to ensure water flows off the roof.
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Verify slope and drainage efficiency.
8. Final Inspection and Testing
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Check for membrane integrity, proper adhesion, and flashing quality.
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Perform water tests if needed to ensure there are no leaks.
9. Optional: Protective or Reflective Coating
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Some systems may include a reflective cool roof coating or protective gravel ballast to extend membrane life.
What Else Should I Consider When Looking for a New Flat Roof?
Beyond the basic construction steps, there are several important additional considerations when getting a flat roof. These can affect performance, longevity, cost, and maintenance. Here’s what else you should keep in mind:
1. Roof Purpose and Accessibility
Will the roof be accessed frequently? Consider reinforced systems or walk pads.
Will it be used as a living space? (e.g., rooftop deck or green roof) – this requires special structural and waterproofing design.
2. Drainage Planning
Flat roofs aren’t truly flat – they require a slight slope (minimum 1/4” per foot).
Consider:
Internal drains vs. scuppers vs. gutters
Backup overflow drains in case of blockages
Preventative maintenance for keeping drains clear
3. Roof Penetrations and Details
Skylights, vents, HVAC units, solar panels – all these increase the risk of leaks.
Each penetration needs proper flashing and integration into the membrane system.
4. Thermal Performance
Ensure adequate insulation (R-value) for energy efficiency.
In hot climates, consider reflective “cool roof” membranes (like white TPO or reflective coatings) to reduce heat absorption.
5. Fire Rating
Check for fire resistance of the membrane and insulation.
Some jurisdictions require minimum Class A fire ratings for roofing systems.
6. Environmental Considerations
Interested in sustainability? Look into:
Green roofs (vegetative systems)
Solar PV integration
Recyclable membranes (TPO, PVC)
Low-VOC adhesives and coatings
7. Cost vs. Longevity
Not all flat roofs are created equal:
Built-up roof (BUR): lower initial cost, shorter life
EPDM: budget-friendly, good lifespan (~20-25 years)
TPO/PVC: more durable, UV reflective, slightly higher cost
Modified Bitumen: good for durability and foot traffic
8. Warranty and Contractor Quality
Get a warranty (manufacturer + contractor).
Use licensed, experienced installers familiar with the membrane system.
Poor installation is the #1 reason for early failure.
9. Maintenance Requirements
No roof is truly “set and forget.”
Schedule biannual inspections (spring and fall)
Look for ponding water, membrane tears, flashing separation, and debris
Clean drains and remove vegetation
10. Local Building Codes and Permits
Codes may specify:
Minimum slope
Fire and wind resistance
Drainage requirements
Always confirm with your local authority before work begins.
Contact Us
Address
Dobson Roofing Services Ltd,
109-111 Chesterfield Road, Dronfield, Derbyshire, S18 2XE
Phone
M: 07711770081