Flat-Roof Extensions & Homes
Typical flat-roof extensions & homes system
| Typical system size | 3-10 kW |
| Typical panels | 7-22 |
| Usable roof area | 24-80 m² |
| Indicative project value | £5,000-£13,000 |
| Annual generation | 2,600-8,800 kWh |
| Indicative payback | ~9 years |
Indicative ranges. Every figure is confirmed against your roof survey and half-hourly consumption data, not a rule of thumb.
Solar on a flat-roofed home
A great many homes have no usable pitched roof for solar but do have a flat one — a flat-roofed rear extension, a garage, a dormer, or a modern flat-roofed house. “Solar panels for flat roofs” is as much a domestic question as a commercial one, and the good news is that a flat roof works well for solar at home too. Instead of lying flat, the panels sit on a small tilted frame at about 10 to 15 degrees, facing south for peak yield or east-west to spread generation across the day, and the system is sized to your household’s use — typically 3 to 10 kW on 24 to 80 square metres of roof.
The job is genuinely different from a pitched-roof install, which is why it pays to use someone who understands flat roofs: the mounting, the membrane and the deck all need handling correctly, and a pitched-roof installer working on a flat roof for the first time is where problems start.
Pair it with a battery
The one real difference from a commercial roof is when you use power. A business uses most of its electricity in the daytime, when solar generates, so it self-consumes a lot. A home is often empty during the day, so without storage a lot of the generation would be exported cheaply rather than used. That is why a domestic flat-roof system is usually best paired with a battery: the battery stores the daytime generation and releases it in the evening when the household actually uses power, lifting the share you use yourself from perhaps a third to two-thirds. On a home, the battery often makes a bigger difference to the return than on a commercial site, and we size it against your actual usage rather than selling it as a default.
Mounting without harming the roof
A domestic flat roof is usually felt, EPDM rubber, GRP fibreglass or single-ply, and the array must not compromise it. On a strong enough deck a small ballasted frame sits on the membrane on protective slip-sheets and never pierces it. Where the deck is lighter — many extension roofs are — a lightweight or sealed-fixed system is used, with any fixing sealed to the membrane manufacturer’s specification. Either way the aim is the same: the panels go on and the roof stays watertight, with the waterproofing guarantee intact. A wind-uplift check still applies, scaled to the small roof.
Do the roof first if it needs it
A solar array is a 25-year fixture, and a flat felt roof may not have 25 years left. So we check the membrane’s condition and remaining life as part of the survey, and if the felt is near the end of its life or the roof ponds, we will say so and recommend renewing it before the panels go on — it is far cheaper than lifting a new array to re-roof underneath it a few years later. On a sound roof we fit straight onto it; on a tired one we sequence the roof and the solar properly.
0% VAT, MCS and the grid
Domestic solar currently qualifies for the 0% VAT rate on residential energy-saving materials under VAT Notice 708/6, a relief that is time-limited and currently set to revert to 5% on 1 April 2027 — so a home installed before then benefits from the zero rate while it lasts. The install is MCS-certified by a RECC or HIES-registered installer, which is what lets you access the Smart Export Guarantee for the surplus you export and evidences the quality of the work. Most domestic rooftop solar is permitted development, though a listed home or a conservation area can change that, and the system is notified to your network operator under G98 (or G99 for a larger installation). We handle the MCS certification, the DNO notification and the paperwork.
Planning and appearance
Because a flat-roof array sits on a tilt frame that raises the panels above the roof line, the projection above the roof is checked against the permitted-development limit — on most homes it is within it, but it is confirmed rather than assumed, and a listed building, a conservation area or an Article 4 direction is checked specifically. On a flat roof the panels are often less visible from the street than on a pitched roof, sitting low behind a parapet, which many homeowners prefer.
What we do
We assess your roof, your usage and your budget, model the system and a battery where it earns its place, confirm the membrane and the deck, and fit the array so your roof stays watertight. You get an honest view of what a flat-roof system will generate and save for your home, the 0% VAT applied while it is available, and MCS certification and SEG registration handled for you.
An asset, not an expense
A flat-roof array is a 25-year-plus asset that turns an empty roof into generation you own. Rather than renting your power from the grid every year, you own the means of producing it. Commercial solar is eligible for capital allowances via the Annual Investment Allowance (AIA) — it is special-rate plant, so the route is the AIA, not full expensing — and it can be funded from capital, through asset finance or leasing, or under a power purchase agreement (PPA) with no upfront cost. Your accountant confirms the tax treatment for your business.
Self-consumption first, export second
On a commercial flat roof the money is in self-consumption — the units you generate and use on site instead of buying from the grid. The surplus you do not use is exported and paid for under the Smart Export Guarantee (SEG), with rates that vary by supplier and are quoted as at the current date, never as a fixed promise. We model the split from your actual half-hourly data and, where it earns its place, size a battery to lift the share of generation you use on site.
Common concerns on a flat roof
Will fixings void my roof warranty?
Not with a ballasted, penetration-free system — it is weighted with concrete blocks on protective slip-sheets and never pierces the membrane, so the waterproofing guarantee stays intact. Where a mechanical fixing is unavoidable, every penetration is sealed to the membrane manufacturer's own specification.
Can the deck carry the weight?
A ballasted array adds roughly 15 to 25 kg per square metre plus wind uplift. We confirm the deck's residual capacity with a structural engineer before design, and use a lighter system or recommend strengthening if it cannot.
What if the roof is near the end of its life?
We survey the membrane's remaining service life first. If it is life-expired, we say so and recommend renewing the roof before the array goes on — no one lifts a 25-year array to fix a leak underneath it.
No pushy sales, no obligation
Every proposal is itemised in writing, with the wind-uplift and structural design, the DNO position and the self-consumption model set out in full. The installation is covered by a workmanship warranty and an insurance-backed guarantee, panels carry a 25-year performance warranty, and we will tell you honestly if your roof does not suit solar. Your survey is carried out by a named surveyor who visits the site, not a call-centre.
Get a free flat-roof extensions & homes quote
Responds within one working day
- 1. Free desk feasibility from your meter data and roof, no obligation.
- 2. Site survey and a fixed-price proposal, itemised in writing.
- 3. Install and aftercare by MCS-certified engineers.
- MCS Certified
- NICEIC
- RECC
- TrustMark
What happens next
- Step 1 — free desk feasibility from your roof and half-hourly data, within one working day, no obligation.
- Step 2 — site survey by a named surveyor: deck, membrane, wind zone and shading, then a fixed-price itemised proposal.
- Step 3 — install and aftercare, DNO connection handled, monitoring active, workmanship and insurance-backed guarantees in place.