Building a Hidden Roof or Flat Roof the Right Way

A hidden roof or flat roof can give your building a clean and modern look, 

but many people get it wrong. When the structure is not designed properly, 

the walls soak up water during heavy rains, the roof leaks, and the building becomes 

weak over time. A flat roof is not truly flat. It still needs a controlled slope, 

proper woodwork or skeletal framing, reliable roofing sheets, and strong waterproofing 

on all exterior and interior walls.

Many builders don’t know these details. They assume that hiding the roof is simple, but the real strength of a hidden roof depends on the work you do under the surface. If you follow these steps, you will avoid future structural damage, paint peeling, dampness, mold, and expensive repair work.

Key Things You Must Do

1. Build a Proper Sloped Skeleton/Woodwork

A hidden roof still needs a gentle slope so that water can flow out easily.

The slope prevents water from sitting on top of the roof, which is one of the biggest causes of leakage and rot.

A well-designed skeletal frame should:

• Create a uniform slope toward the drainage points

• Support the roofing sheets without bending

• Allow proper water flow to the gutter channels

• Prevent water from sitting on the roofing surface

If the slope is wrong, the entire flat roof will fail, no matter what materials you use.

2. Use Short-Gutter Long-Span Roofing Sheets (0.45 Complete Gauge)

For hidden roofs, long-span roofing sheets with short gutter designs perform better because they:

• Fit perfectly into the slope

• Reduce water backflow

• Provide a tighter seal

• Are more durable under constant rain and sunlight

The thickness matters. A real 0.45 gauge sheet has enough strength and lifespan for this type of roof. Anything less will rust faster, vibrate, leak, or collapse after a few rainy seasons.

3. Apply Chemical Waterproof Plastering (Inside and Outside Walls)

This is where many people get it wrong.

Since the roof is hidden, rainwater hits the walls directly.

Without waterproof plastering, the walls absorb water over time.

This leads to:

• Weakening of the blocks

• Cracks

• Dampness

• Paint bubbling

• Mold and algae

• Structural weakness after several seasons

Chemical waterproof plastering creates a protective layer that stops the walls from drinking water like a sponge.

This waterproofing must be done:

• Before painting

• On all exposed areas

• On inner parapet walls

• On external walls around the hidden roof

When done correctly, the building remains strong and dry for many years.

Step-by-Step Guide to Building a Durable Hidden Roof

Step 1: Plan the Slope

• Decide your drainage direction

• Create a 2%–5% slope depending on the building size

• Make sure water can move freely to downpipes or gutters

Step 2: Build the Skeletal/Wood Structure

• Use seasoned wood or metal trusses

• Install them at the correct angle

• Add bracing to prevent sagging

• Confirm alignment with a leveling tool

Step 3: Install Short-Gutter Long-Span Roofing Sheets

• Use original 0.45 gauge sheets

• Start from the lowest part of the slope

• Overlap the sheets properly

• Screw them tightly to prevent wind uplift

• Seal all joints to avoid leakage

Step 4: Create Proper Water Channels

• Install gutter lines

• Install downpipes

• Ensure water flows out of the roof fast

• Add splash blocks or drainage outlets

Step 5: Apply Chemical Waterproof Plastering

• Mix the waterproof chemical with cement and sand

• Apply two coats on the exterior wall

• Apply on interior parapet walls

• Smoothen the surface and allow curing

• Test with water spray before painting

Step 6: Paint and Finish

• Use weatherproof exterior paint

• Seal edges and corners

• Inspect yearly for cracks or blocked drainage

My final thoughts: A hidden roof is beautiful only when the unseen details are done right. The slope, the roofing sheets, and the waterproofing all work together. If one part fails, the entire system fails.