Replacement
Flat Roof Replacement: Strip, Deck and Rebuild
When a flat roof is truly finished, the honest job is to take it back to the structure and build again properly. Across South London, Pluvian Roofing strips, re-boards where needed, insulates to what the specification for your roof requires and lays a new covering, felt or cold-applied liquid as that specification decides.
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The short answer: Full replacement becomes the honest answer when the deck itself has gone: boarding soft underfoot, insulation holding water, or a roof already renewed more than once. Nobody can confirm that from above, which is why a quotation separates the known work from the provisional.
Straight talk
When is replacement the honest answer?
Three findings close the argument: saturated insulation, a failed deck, and a roof whose one sensible overlay has already been used. Water that has spread through the boards cannot be dried out by anything laid on top of it, and rot or sagging in the structure is not a covering problem. How that verdict gets reached belongs to the refurbishment options guide, and what a dry deck actually proves is the repair or replace test; this page is what happens once both have spoken. Before a big commercial roof is stripped on the strength of a hunch, an assessment of the roof tests whether replacement is the route at all.
The deck decides
Here is the truth that shapes every replacement quotation we write: nobody can price what is under a saturated roof until it is open. Pretending otherwise produces either padded quotations or mid-job renegotiation. So ours separate the known from the provisional: the strip, build-up and covering are priced firm, and boarding or joist work carries stated rates that only apply if the opened roof shows the need. The surprise, if there is one, is procedural, not financial. What replacing boarding and joists actually involves sits with the structure and decking work rather than here.
The decision
What a proper strip and renew involves
- Strip. Every layer of old covering comes off and into the skip, down to the deck. Overlays hide history; the strip ends the guessing. On an older building the layers are checked before any of that starts, because old bituminous products can carry asbestos, and where there is any doubt a sample settles it in a laboratory rather than on the roof. Where plant, aerials or service runs stand on the covering, isolating, lifting and reinstating them belongs to whoever owns and maintains them, and that is programmed before the strip rather than discovered on the morning of it.
- Deck inspection: the moment of truth. With the structure exposed, its condition is photographed and assessed against the quotation's provisional items, with you informed before any extra work proceeds.
- Re-board where needed. Failed sections are cut out and renewed; where decay is general, a full redeck gives the new roof a sound start.
- Insulation. New boards to the specification, which is also where regulatory upgrade requirements are met. With the old covering already off, this is the cheapest point at which to turn a cold roof warm, and the job of a warm roof conversion is explained on its own page.
- The new build-up. A fresh felt system, laid as specified, with liquid waterproofing at any detail the fire risk assessment keeps flame away from; or, as the alternative, HYDRONYLON liquid-applied waterproofing across the whole roof.
- Details and handover. Upstands, edges, outlets and penetrations finished properly, then a photographed record of the completed roof for your file and the guarantee's.
Alternatives
Nothing to strip? That is a different job
Where there is no old covering, none of the above applies: no verdict to wait for and no provisional rates, because everything is visible from the drawings. That work has its own page, new roofs on extensions and outbuildings. Either way, once a roof is finished a planned maintenance programme produces the dated records a product guarantee asks for, where the finished roof carries one. Which guarantee applies to yours is set down beside the price rather than assumed here.
There is one building type where the sequence above holds but nearly every assumption behind it changes. A roof over an unheated garage has no insulation to condemn, no ceiling below to warn anybody, and a perimeter doing more work than the field, which is why garage roofs are worked through separately.
What moves the scope
Honestly, and without a price list: the area and its access, how many layers the strip removes, what the deck inspection finds, the insulation the regulations require, and the count of details to rebuild. Access can rival the roofing itself on a small or awkward building, and it is arranged by us and shown in the quotation rather than left for you to buy separately, which is the whole argument about scaffold in one sentence. An inspection turns those unknowns into a scoped, written quotation before anyone lifts a torch; a condition survey is a separate, paid document for a building that needs its findings on file.
The things worth doing while the roof is open
A strip buys you an open roof and paid-for access, and both are expensive to arrange twice. That is the moment to form a new opening or rebuild a tired rooflight kerb, because a new kerb entering the waterproofing sequence costs a fraction of one retrofitted into a cured membrane afterwards. It is also when the fascias, soffits and gutters at the edge should be dealt with, since the scaffold is already there and a tired gutter will attack a brand new edge detail within a season. And where the completed roof is intended to carry people rather than merely shed water, a terrace is designed at this stage or not at all: the falls, the outlet positions and the balustrade fixings all have to be settled before the membrane goes down.
A roof taken back to the deck and rebuilt is the easiest kind to keep in condition, and we offer a recurring maintenance visit on it afterwards, priced by its size and access rather than at a standard rate. The aftercare section says which parts of that visit the fee covers and which are quoted separately.
Questions
Frequently asked questions
Can you replace just the felt without the boards?
Where the deck proves sound, yes, and that is the cheaper job. The catch is that nobody knows for certain until the old covering comes off, so our quotation states the price for the expected case and a pre-agreed rate for boarding work, and the strip itself delivers the verdict.
Do you replace roof decks?
Yes. Re-boarding, whether patching bad sections or a complete redeck, is part of the replacement trade, not an extra we shy away from. Rotten or delaminated boards are cut out and renewed before any new build-up goes down, because membranes are only as good as what carries them.
Can you install a brand new flat roof on an extension?
Yes, and it is a wholly different job to a replacement, with its own page on this site. Nothing has to be uncovered first, so the build-up, the falls and the covering are settled from the drawings and priced without provisional rates.
How long does a flat roof replacement take?
We will not invent a number here, because size, access, weather windows and what the strip reveals all move it. What you get instead is a written programme before work starts, updated the moment anything found on the roof changes it, so the schedule you hold is always the real one.
What happens if you find rot?
It is shown to you and priced at the provisional rates already agreed in your quotation, then fixed once you have said yes. Finding rot under an old flat roof is common; being surprised by the bill for it should not be.
Review
What a client said
Kamil inspected the roof, explained the issues clearly and gave me a few options. He later came back and completed a full re-deck with a new torch-on felt system. Really happy with the workmanship and attention to detail.
Is the roof past saving?
Whether it is or not, the next step is the same: tell us about the building and we will look before we quote.
We need a little more before we can send that: a name, the postcode of the roof, what is happening with it, and either a phone number or an email address.
Please check the postcode of the roof: it should have letters and numbers in it.
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Coming out and pricing the work is free, and every quotation for an existing roof comes with photographs of it. A written condition survey carries a fee, agreed before the visit and taken off the price of the work if you go ahead.