What Should a Flat Roof Refurbishment Specification Include?

The short answer: It should describe the roof as a survey found it, the refurbishment route and why, the system and build-up in general terms, every detail, falls and drainage, access and protection, fire risk where a torch is used, the handover, and the maintenance the product guarantee asks for. Then every contractor prices the same job.

Written for the people who draft and check specifications: building surveyors, consultants, managing agents and owners. It sets out what a refurbishment specification usually covers and leaves the design itself to whoever signs the document.

Why does a refurbishment specification matter?

Because it makes every price describe the same roof. Without one, each contractor fills the gaps with assumptions of their own about the deck, the details and the access, and the lowest figure is often the one that assumed the least. A clear specification writes those assumptions down once, so the prices can be compared line against line.

It also moves surprises off the roof and onto the page. A question settled before work starts costs a conversation. The same question found halfway through costs a variation, a delay and sometimes an open roof waiting on a decision.

What should it say about the existing roof?

What is there now and what state it is in, taken from evidence gathered on the roof rather than from memory or an old drawing. A roof patched for years rarely matches its original record.

• The build-up, from the covering down: the covering, any insulation, the vapour control layer and the deck itself.
• Its condition: where the covering has failed, whether moisture has reached the insulation and whether the deck has kept its strength, from cores and readings rather than a look from the ladder.
• The drainage as found: outlets, gutters and any area where water stands after rain.
• What limits the work: plant, cables, rooflights, neighbouring roofs and the routes on and off.

A specification written without that evidence is a guess about the roof underneath, and every contractor will read the guess differently. A written condition survey supplies it, with the readings and photographs to back each finding.

How should it state the route and the system?

Route first, with the reason. There are four: retain the roof with maintenance, repair the parts that have failed, re-cover it with a new layer, provided the existing layers are dry, firmly stuck down and sound, or replace it by stripping to the deck and rebuilding. The reason, drawn from the evidence, tells a contractor what the existing roof can be trusted to do.

Then the system and its build-up, in general terms: the type of waterproofing, the layers it goes down in, how each is fixed or bonded, and what sits beneath. Reinforced bituminous membrane (RBM), laid as torch-on felt, and cold-applied liquid waterproofing suit different roofs and different details, and the document should say which is wanted where. Whether it names a product or describes a performance with equivalents allowed is the specifier's call; saying how an alternative will be approved heads off an argument later.

Insulation needs a sentence of its own. When the work renews a substantial share of the roof, the Building Regulations generally make its thermal performance part of the job, so the specification should state whether insulation is included, where it goes in the build-up and who confirms the requirement with building control. Leaving it out does not remove the question. It only moves it to site.

Which details does a specification need to spell out?

All of them, because the details are where flat roofs leak first and where prices drift furthest apart. Each one should be described or drawn rather than left to the person laying it.

• Upstands: how far the waterproofing turns up a wall, parapet or kerb, and how its top edge is protected, whether by a flashing, a chase or a trim.
• Outlets: the roof's rainwater drains, renewed or kept, how the new covering joins them, and whether there are enough for the area they serve.
• Rooflights: kept, replaced or raised, and how the waterproofing meets each kerb.
• Thresholds: where a doorway meets the roof, how the covering finishes beneath it and how water is kept back from the sill.
• Edges: drip trims, verges and gutters, and how the covering ends at each.

Falls and drainage belong beside them. If water stands on the existing roof, the specification should say whether the falls are to be corrected, with tapered insulation or with firrings under a new deck, and whether extra outlets are wanted. A new covering laid to the old falls inherits the old ponding.

What about access, protection and fire risk?

They move the price as surely as the roof does, so they belong in writing too.

• Access: how the roof is reached, scaffold or edge protection, where materials are lifted and stored, and any limits on when and where work can happen.
• Protection: leaving the building weathertight whenever work stops for the day, protecting finishes and plant below, and keeping occupants, tenants or pupils clear of the work and its routes.
• Fire risk: where a torch is used, a fire risk assessment before any flame is lit, a watch kept after the last torch goes out, and the places where flame is ruled out altogether.

Those no-flame places, beside exposed timber, under overhangs and around plastic rooflights, are where cold-applied liquid waterproofing earns its keep. Marking them on the drawings means every contractor prices them the same way.

What should it ask for at handover and afterwards?

A file that explains the finished roof to someone who was not there: the build-up as laid, photographs of every stage with their dates, any detail that changed on site, and the guarantees, with who stands behind each one.

It should also name the maintenance those guarantees depend on. A product guarantee usually comes with conditions, such as inspections at set intervals, outlets kept clear and repairs recorded. Written into the specification, they can be budgeted from the start, and a planned maintenance programme keeps the dated records they call for.

Which gaps turn into variations?

Three in particular, and each can be closed before the documents go out.

• No survey behind it: the build-up is assumed, and the first core taken on site disagrees with the drawing.
• Deck replacement left unstated: nobody sees the deck until the covering is off, so the document should carry a provisional sum or a measured rate for renewing it, rather than leave each contractor to guess.
• Details left "to suit": a phrase that hands the design of a junction to whoever prices it, so every price assumes something different and the disagreement starts on the roof.

Every one of these is cheap to settle on paper and expensive to settle on a roof that is already open to the weather.

Where can a contractor help before it goes out?

With a practical read of the draft, while changing it is still free. A contractor can say which details will be hard to build as written, where the build-up raises a question, and what tenderers are likely to ask. Our support for consultants and specifiers covers exactly that, and reading a draft costs nothing.

Where the route itself is undecided on a large roof, a commercial roof assessment gathers the evidence and argues which of the four routes the roof should take, ready for the specification to be written around. Its written survey is chargeable: the fee is settled with you before anyone books the visit, and it counts against the works that follow.

The specification stays yours throughout. Our part is practical: what will build, what will leak and what each junction demands on site. We never design the roof or calculate its structure, and anything that calls for a designer or an engineer goes back to you as such.