What Preparation Does a Flat Roof Deck Need Before EPDM in Aberdare?

EPDM Rubber Roofing › Aberdare › Guide

People often ask about the membrane, but the deck is where an EPDM roof succeeds or fails. In Aberdare, where heavy rain and old timber go together, a flat roof deck can be damp, soft or poorly drained long before the covering shows it. This is what we look at and put right first.

Is the deck sound and dry?

We look at the boards for softness, staining, rot and movement. Water that has sat under old felt for a long time soaks into the timber. We press and probe the boards from inside where we can, and lift sections of covering to see them.

A deck that is only damp on the surface can be dried. One that has gone soft needs cutting out and replacing. We show you what we find, with photographs from the roof, so you can see exactly why any board is being replaced.

Falls and drainage

A flat roof is never truly flat. It needs a fall towards the gutter or outlet so water does not pond. Ponding water adds weight, and puts stress on every joint and edge. Many older roofs in Aberdare have sagged and hold puddles.

If the fall is poor, we can correct it with firring strips or by relaying the deck. We would rather fix it now than lay a new membrane over a pond. Cutting the problem out now costs less effort than chasing a leak across a new membrane later, and it gives you a roof that drains properly from the first rain.

• Check for puddles or staining after rain.
• Look for sagging between the joists.
• Confirm the gutter or outlet is clear and low enough.
• Add firring if the fall needs improving.

Insulation and ventilation

The deck build matters for condensation. A warm roof, with insulation above the deck, keeps the timber dry. A cold roof needs ventilation through the void beneath. If neither is right, damp air condenses inside and rots the boards from underneath.

On extensions and dormers in Aberdare houses, we check what insulation is there and how it was built, then explain what can be improved. Where the build is wrong, a vapour barrier or extra insulation can be added at the time, and we explain the choices without pushing anything you do not need.

Edges, walls and penetrations

Before the membrane goes on, the edges and wall junctions are looked at. The upstand at the wall needs a sound surface to bond to, and any old flashing or loose pointing has to be dealt with. Chimneys, vents and rooflights need their own detail.

On a terrace extension, the wall where the roof meets the main house is often the weak point. We deal with that before the sheet is laid. A new upstand bonded to crumbling mortar will not hold, so repointing or a fresh surface is done first, and we tell you what that involves.

Final cleaning and priming

The last step is cleaning the deck. Dust, grit, old adhesive and sharp fixings are removed, because they will show through or damage the rubber. The surface is dry and swept when the adhesive goes on. Nothing is skipped. Nothing is rushed.

Only then is the membrane laid. If there is any doubt about the deck, we tell you before that point. Our Flat Roofing South Wales section covers other options when a deck is beyond saving. That keeps the decision with you.

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