Flat roofing specialists · Bromley, Kent & London
A properly specified warm roof keeps the insulation above the deck, the dew point out of your structure and the heat inside the building, installed as a complete build-up, not a layer of boards under a membrane. Free fixed-price quotation, 10-year workmanship guarantee.
16 years in flat roofing · full build-up specified in writing · fully insured
Overview
A warm roof places the insulation above the structural deck, with a vapour control layer beneath it and the waterproofing membrane on top. The deck and the structure below sit inside the insulated envelope, kept warm and dry. It is the standard modern build-up for flat roofs and, done properly, it solves both thermal performance and condensation in one system.
Anyone rebuilding or replacing a flat roof: extension and new build projects, homeowners converting a cold roof that suffers from condensation, and commercial owners upgrading thermal performance on units, offices and warehouses during a re-roof.
At any full re-roof or new flat roof, because that is when the build-up is open and the cost of upgrading is at its lowest. Also when a cold roof shows the classic symptoms: damp patches with no rain, mould at ceiling edges, and condensation dripping from the underside of the deck in winter.
Warm roofs fail when the layers are treated as separate items. The vapour control layer must be continuous and sealed at every penetration and perimeter, insulation has to be laid tight and correctly fixed, upstand and threshold heights must accommodate the extra build-up depth, and the whole assembly needs falls that drain. Miss one and you get interstitial condensation inside a roof that looks perfect from above.
What happens if it is left
Without a continuous, sealed vapour control layer, warm moist air from inside the building reaches a cold surface within the roof and condenses there, wetting insulation and deck from the inside where nobody can see it.
An uninsulated or under-insulated flat roof loses heat continuously. Every winter you delay the upgrade is money spent heating the sky.
Cold roof condensation shows up as mould at ceiling perimeters, staining and peeling decoration, repeatedly, and no amount of redecorating fixes it.
Deck timbers and joists that stay damp through winters lose strength quietly. By the time it is visible, the repair is structural rather than a roofing job.
Our process
We measure the roof, check the deck, review threshold and upstand heights, and establish how much build-up depth the roof can accept.
Vapour control layer, insulation type and thickness, fixing method, tapered fall design where needed and the waterproofing system, set out in a free, fixed-price quotation.
Deck prepared and made good, vapour control layer laid and sealed continuously, insulation boards laid tight and fixed, then the single-ply or reinforced liquid waterproofing installed over the top.
Upstands, kerbs, thresholds and outlets detailed at the new heights, welds probed or coverage verified, drainage checked.
Handover with a 10-year workmanship guarantee, plus manufacturer-backed guarantee options where applicable for the specified system.
What you get
Continuous insulation above the deck removes the cold bridging you get with between-joist insulation, so the roof actually performs as designed.
The deck sits on the warm side of the insulation, and a sealed vapour control layer stops moist internal air reaching a cold surface inside the build-up.
Joists and deck stay warm and dry inside the envelope, which is what gives the roof its long service life.
The build-up goes on top of the deck, so ceilings below stay where they are, important in extensions and conversions.
Tapered insulation can build correct falls into the roof during the same works, removing ponding rather than living with it.
Free fixed-price quotation, complete build-up named in writing, and a 10-year workmanship guarantee.
In detail
In a warm roof the insulation sits above the deck and below the waterproofing. In a cold roof it sits between the joists with the deck outside the insulated zone, an arrangement that depends on ventilation that is easy to block and hard to verify, which is why cold roofs are the usual source of condensation complaints. An inverted roof puts the insulation above the waterproofing under ballast or paving, useful on terraces. For most flat roofs we build, warm is the right answer.
The vapour control layer sits directly on the deck and must be continuous, sealed at laps, dressed up at perimeters and upstands, and collared around every pipe and penetration. If warm internal air can bypass it, the insulation above becomes the condensation surface. This layer takes time to do properly and is the first thing skipped on a cheap quote.
Board type and thickness are selected for the thermal performance required, the loading, the fixing method and the depth available. Boards are laid tight with staggered joints and fixed on a pattern calculated for wind uplift or bonded, depending on the system and deck. Tapered schemes are designed board by board to deliver fall to the outlets.
A warm roof conversion raises the finished roof level, so door thresholds, rooflight kerbs, wall abutments and existing upstands all need checking before work starts. Adequate upstand height above finished roof level is what keeps water out in heavy rain, a detail that gets compromised when the depth was never planned for.
The finished waterproofing is single-ply, Sika, IKO Armourplan, Danosa or Bauder, hot-air welded throughout, or a reinforced liquid system where detailing complexity favours it. The build-up and the covering are specified together, because the fixing method and the membrane choice have to suit the insulation beneath them.
On commercial units, offices and warehouses, a re-roof is the practical moment to lift thermal performance. Works are phased so the building stays weathertight, RAMS are provided, and photographic reporting can document the build-up as it goes in, useful evidence for owners, funders and managing agents.
Common questions
It is quoted per roof, because insulation thickness, tapered fall design, deck condition, access and the waterproofing system all change the figure. Quotations are free and fixed price as standard.
Usually yes, during a re-roof. The main constraints are threshold and upstand heights, since a warm build-up raises the roof level. We check that at survey and design around it.
No. The insulation goes above the deck, so the room below is untouched. The additional depth is on the outside.
A domestic extension roof is usually a matter of days; larger commercial roofs are phased over a longer programme. Timings are confirmed in the quotation.
We specify the build-up to meet the thermal performance required for the project and set out the vapour control layer, insulation and membrane in writing so it can be shown to building control or your contract administrator.
A 10-year workmanship guarantee on the installation, with manufacturer-backed guarantees available where applicable depending on the specified system.
A correctly built warm roof with a continuous, sealed vapour control layer removes the mechanism that causes interstitial condensation in flat roofs. The sealing is what makes the difference, which is why we detail it rather than rush it.
Yes: tapered insulation schemes are designed to deliver fall to the outlets, which is the most effective way to remove ponding permanently.
Bromley, Kent, London and the South East, including Orpington, Beckenham, Croydon, Dartford and Sevenoaks, plus nationwide for larger commercial projects.
Tell us about the roof and your postcode. We will inspect it, tell you what has actually failed and give you a fixed price, backed by a 10-year workmanship guarantee.
16 years in flat roofing · Sika, Danosa and Bauder trained · fully insured · 10-year workmanship guarantee