Case study · Ruthin, Denbighshire
Stripped, insulated and finished as a warm roof.
In one day.
A brick semi in Ruthin with a flat roof over the garage and porch, the original felt covering at the end of its life and very little under it keeping the heat in. Energy Giants stripped it to the deck, rebuilt it as a warm roof with a thick layer of PIR insulation above the joists, and finished it in black EPDM with new white fascias, between a Monday lunchtime and teatime.
The job in numbers
1day
On site
Stripped after one o’clock, membrane down and fascias on by seven. Every photograph on this page was taken on the same Monday.1
5
Layers
Deck, vapour control layer, PIR insulation, new OSB deck, EPDM membrane. A full warm roof build up, not a recover over the old felt.
100mm+
Foil faced PIR
Measured against the tape on the day. The insulation now sits above the structure, so the timber stays on the warm, dry side of it.2
0
Nights open
The roof was stripped and made weathertight inside the same working day. Nobody moved out and nothing was left under a tarpaulin.
Download the one page summary (PDF) · the job, the build up, certification and guarantee on a single A4 sheet. Download the slide version (PDF) · the same job as ten swipeable pages, for sharing.
Before and after
The same roof at lunchtime and at teatime.
Two photographs from the pavement, six hours apart. On the left the original felt roof over the garage and porch, with its tired timber fascia. On the right the finished warm roof: black EPDM turned down over a new drip edge, and new white fascia boards along the front.
13:04, before
18:59, afterThe work
A garage roof at the end of its life, rebuilt properly.
Thousands of houses built in the 1960s, 70s and 80s have a flat roof like this one: a felt covering over a timber deck above the garage, the porch or a side extension, usually with little or no insulation underneath. When the felt wears out, the cheap answer is to lay another covering on top. That keeps the rain out for a while and does nothing for the room under it.
We took the roof back to the deck instead. A blue vapour control layer went down first, to stop warm, moist air from the house getting into the insulation. On top of that, foil faced PIR insulation boards, over 100 mm thick, laid tight and taped. Then a new OSB deck over the insulation to give the membrane a flat, firm base, and finally a single sheet of black EPDM rubber, dressed over new drip trims and finished with new white fascias.2
That is a warm roof: the insulation sits above the joists rather than between them, so the whole structure stays on the warm side and the risk of condensation in the timber goes away. It is the build up we use on individual homes and on housing programmes alike, and this one went from stripped to finished in a single working day.
Certified and guaranteed
PAS 2030:2023 certified. Energy Giants holds PAS 2030:2023 certification for flat roof insulation (measure B5) and is TrustMark registered. It is the installation standard government backed retrofit requires for each measure, and the warm roof build up on this page is the one we deliver on housing programmes.
Insurance Backed Guarantee, issued by Energy Giants. Every flat roof we install is handed over with an Insurance Backed Guarantee issued by Energy Giants and insured through the Bluedrop facility, so our workmanship guarantee is protected by an insurer as well as by us.
Certificate SICI23052 P2030 1, measure B5 flat roof insulation, held by Efficient Energy Systems Ltd. See our accreditations or view the certificate.
Layer by layer
What went into it, in the order it went on.
We photograph every layer on every roof we do. Partly so the customer can see what they paid for, partly because on housing programmes the photo record is part of the handover. Here is Monday, layer by layer.
StripBack to the deckOld felt off, deck checked and swept. Anything soft would have been replaced here; this one was sound.
Vapour controlThe blue layerA vapour control layer over the deck, lapped and sealed, so moisture from the house cannot reach the insulation from below.
InsulationOver 100 mm of PIRFoil faced PIR boards, measured against the tape on the roof. This is the layer that changes how the room below feels.2
InsulationLaid edge to edgeBoards cut tight to the edges and upstands, joints staggered and taped, so there are no gaps for heat to find.
DeckA new deck on topOSB fixed through the insulation into the joists. It gives the membrane a flat, firm base and ties the whole build up together.
- MembraneOne sheet of EPDM
A single sheet of EPDM bonded to the deck, with no seams across the roof and the edges dressed down over new trims.
FinishNew fascias and trimsNew white fascia boards and a black drip edge along the front, so the roof looks finished from the street as well as from above.
What this means for you
One garage roof, two reasons to read about it.
If you own a house like this
Your flat roof can be warm, dry and done in a day.
If the flat roof over your garage, porch or extension is older than you can remember, it is almost certainly uninsulated, and the room under it will tell you so every winter. The signs it is time to act:
- Blistered, cracked or pooling felt, or moss holding water on the surface
- Damp patches or staining on the ceiling below
- A room under the roof that is cold in winter and hot in summer
- A recover already done once, with the same problems back
If you manage housing stock or run a programme
The same build up, roof after roof, with the evidence to match.
This is a single roof, but the method is the one we deliver across streets and schemes for housing providers and their main contractors. What you get on every roof:
- Each roof surveyed and priced individually, not by the metre
- A warm roof build up with the insulation above the deck, so the structure is protected as well as the home
- A photographic record of every layer, ready for your handover and funding evidence packs
- Flat roof insulation delivered under our PAS 2030:2023 certification as a TrustMark registered installer, where the programme requires it
Flat roof insulation near you: East Lancashire · Greater Manchester · South Ribble and Leyland. Anywhere else in the North West or North Wales, start here.
What was delivered
The specification.
| Property | Semi detached brick house, Ruthin, Denbighshire. Flat roof over the attached garage and porch |
|---|---|
| Roof before | Original felt covering on a timber deck, at the end of its life, with the timber fascia worn |
| Roof type | Warm roof: insulation above the structural deck |
| Build up | Existing covering stripped to the deck; vapour control layer; foil faced PIR insulation boards, over 100 mm; new OSB deck; EPDM single ply membrane; new drip trims and white fascias2 |
| Time on site | One working day, Monday 14 September 20261 |
| Access | Edge protection scaffold to the front elevation |
| Delivered by | Energy Giants (Efficient Energy Systems Ltd), Clitheroe, Lancashire |
| Guarantee | Insurance Backed Guarantee issued by Energy Giants on completion, insured through the Bluedrop facility |
| Certification | Energy Giants holds PAS 2030:2023 certification for flat roof insulation (certificate SICI23052 P2030 1, measure B5) and is TrustMark registered. See our accreditations |
- Step oneSurvey
The roof measured, the deck and the fall checked, the fascia and outlets looked at, before a figure is given.
- Step twoStrip and prepare
Old covering off first thing, deck inspected and any soft timber replaced.
- Step threeInsulate and deck
Vapour control layer, PIR boards laid tight and taped, new OSB deck fixed through to the joists.
- Step fourMembrane and finish
EPDM bonded and dressed, new trims and fascias, site cleared and the roof handed back the same day.
Questions people ask
Flat roof insulation, answered.
How long does it take to replace and insulate a flat roof?
A garage or porch roof like this one is usually stripped, insulated and finished in a single working day, weather permitting. Larger extension roofs can take two. We do not strip more than we can make weathertight the same day.
What is a warm roof, and why does it matter?
A warm roof puts the insulation above the structural deck, with a vapour control layer beneath it and the waterproof membrane on top. The joists stay on the warm side, so there is no cold surface inside the roof for condensation to form on. A cold roof, with insulation pushed between the joists, needs ventilation to stay dry and is much harder to get right on an existing building.
Can you just put a new covering over the old felt?
Sometimes, but it does nothing for the insulation and it hides whatever the old covering is sitting on. If the roof is at the end of its life we would rather take it back to the deck, check the timber and rebuild it as a warm roof, which is what happened here.
Do you cover North Wales as well as Lancashire?
Yes. We are based in Clitheroe and work across Lancashire, Greater Manchester, Merseyside, Cheshire and North Wales. This roof is in Ruthin, Denbighshire; we have delivered flat roof insulation as far as the Conwy valley and Merseyside.
Got a flat roof like this?
Tell us where it is and what is under it, send a photo if you have one, and we will come and measure it. Homeowners get a fixed price for a warm roof, done in a day where the roof allows. Housing providers and contractors get a roof by roof survey and a build up that stands up to audit. Start on our flat roof insulation page or get straight in touch.
Notes on the figures
- Timings are from the timestamps on our own site photographs, taken on Monday 14 September 2026 between 13:04 and 19:01. The before photograph was taken at 13:04 and the finished roof at 18:59.
- Insulation thickness is read from a tape measure held against the board in our site photograph, which shows over 100 mm of foil faced PIR. The exact board and thickness for any roof is set at survey and stated on the quotation. Certification: PAS 2030:2023, measure B5 flat roof insulation, certificate SICI23052 P2030 1, held by Efficient Energy Systems Ltd trading as Energy Giants; TrustMark registered. The customer’s address and details are withheld at their privacy.