For most straightforward domestic flat roofs, a smooth 1.2 mm EPDM system is the sensible starting point. A lighter membrane can be enough for a shed or simple garden building, while a 1.5 mm or specialist system earns its place where the roof is larger, more exposed, regularly accessed or difficult to detail.
The membrane is only part of the decision. Deck type, roof shape, penetrations, sheet size, adhesives and the installer's familiarity with the complete system all affect the result.
Start with the roof, not the brand
Before comparing systems, record the finished deck dimensions, every upstand and outlet, the substrate, and how much foot traffic the roof will see. A simple 3 m × 4 m garden-room roof and a refurbishment with rooflights, pipes and awkward abutments are not the same job.
Stonegate's RoofBuildr EPDM calculator helps turn the roof measurements into a materials plan. For sheds and small rectangular roofs, the roof kit calculator is the quicker route.
The main EPDM choices at Stonegate
SkyGuard 1.0 mm: simple, cost-conscious roofs
SkyGuard is the lighter smooth EPDM option in the current Stonegate range. It makes practical sense for sheds, workshops, summer houses and uncomplicated garden buildings where the roof is unlikely to be used as a working platform.
That isn't a second-rate choice. It is a proportionate specification for a simple roof. Paying for a heavier or specialist membrane on a small shed may add cost without solving a real site problem.
ClassicBond 1.2 mm: the general-purpose choice
ClassicBond 1.2 mm suits the bulk of normal domestic flat-roof work: garages, extensions, larger garden rooms and similar projects on a sound timber deck. It is a smooth, non-reinforced EPDM membrane supplied as part of a system with compatible adhesives, tapes, primers and details.
For an installer who wants one familiar system for everyday work, 1.2 mm is usually the most balanced specification. It gives more material than the 1.0 mm option without the extra weight and cost of 1.5 mm.
ClassicBond 1.5 mm: extra material where it matters
The 1.5 mm sheet is 0.3 mm thicker than the 1.2 mm sheet — a 25% increase in nominal thickness. That extra rubber can provide a larger margin against incidental damage, but it also makes the sheet heavier to handle and normally more expensive.
Consider it for higher-value domestic work, roofs that need occasional maintenance access, exposed sites or contracts where a heavier membrane has been specified. It is not automatically necessary for every extension or garage. See the detailed 1.2 mm versus 1.5 mm comparison before stepping up the specification.
ClassicBond PRO: a fleece-backed alternative
ClassicBond PRO is a different construction rather than simply another thickness. Its fleece backing changes the bonding method and can be useful where the substrate or refurbishment build-up calls for a fleece-backed system. Follow its specific adhesive and installation instructions; do not assume the smooth-membrane method transfers unchanged.
RESITRIX: specialist detailing and welded seams
RESITRIX is reinforced EPDM with a polymer-modified bitumen backing and hot-air-welded seams. It is aimed at demanding waterproofing and complex detailing rather than the typical one-piece shed roof. It can be a strong choice for trained installers dealing with multiple penetrations, intricate junctions or specification-led commercial work, but it brings a different installation method and cost level.
Four checks that decide the system
1. Can the roof be covered in one sheet?
A single sheet removes field seams, but it still has to be moved, positioned and relaxed safely. Check the available sheet dimensions against the roof, including the manufacturer's required allowance at edges and upstands. On a larger roof, a manageable multi-sheet layout installed to the system instructions may be better than wrestling with one oversized sheet.
2. What is the roof deck?
ClassicBond water-based deck adhesive is intended for suitable absorbent timber surfaces. The manufacturer's installation guidance directs installers to bonding/contact adhesive for other surfaces and for perimeter details. Metal, existing GRP, sealed boards and some insulation facings are not interchangeable with clean OSB3.
The deck must be sound, clean, dry and free from dust, grease and protrusions. If the substrate falls outside the system guidance, confirm the build-up with the manufacturer before ordering adhesive.
3. How complicated are the details?
Internal corners, wall abutments, outlets, rooflights and pipes consume time and accessories. Count them before pricing. A cheap membrane can become an expensive job if the basket is missing primer, flashing tape, termination details or the correct outlet.
4. Who is installing it?
System familiarity matters. A trained installer with hot-air welding equipment can make use of a specialist system that would be inappropriate for a general builder fitting an occasional garden-room roof. Keep the method within the installer's competence and the manufacturer's published instructions.
Do not choose adhesive by habit
Water-based deck adhesive, contact adhesive, spray adhesive and polyurethane adhesive do different jobs. For a conventional smooth EPDM installation on suitable timber, water-based adhesive is normally used across the main field and contact adhesive at perimeters, upstands and other non-horizontal details. Fleece-backed systems have their own requirements.
Our EPDM adhesives guide explains the roles and the ordering checks. You can also browse the current roof adhesives range.
A practical specification guide
| Roof or project | Starting point | Why |
|---|---|---|
| Small shed or simple garden building | SkyGuard 1.0 mm or a complete small-roof kit | Proportionate specification and straightforward ordering |
| Normal garage, extension or garden room | ClassicBond 1.2 mm | Balanced general-purpose system with compatible details |
| Higher-value roof, exposed location or occasional access | ClassicBond 1.5 mm | Extra membrane thickness where the project justifies it |
| Compatible refurbishment or specialist substrate | ClassicBond PRO | Fleece-backed construction and system-specific bonding |
| Complex detailing or welded-seam specification | RESITRIX | Reinforced specialist system for trained installers |
This is a selection guide, not a substitute for the relevant technical manual. Roof loading, fire performance, substrate compatibility and any warranty requirements must be checked against the exact system and build-up.
What should be included in the quote?
- Membrane with the correct edge and upstand allowances
- The adhesive type and quantity for the actual substrate
- Primer and compatible tapes for seams and details
- Edge trims or termination bars
- Internal and external corner details
- Pipe boots, outlets and rooflight details where required
- Rollers, scissors and other system tools
- A realistic wastage allowance for the roof shape
Compare the complete installed basket, not the membrane rate in isolation. Use RoofBuildr to plan the roof, then check the selected system's current product information and installation manual before fixing.
Frequently asked questions
Is thicker EPDM always better?
No. A thicker membrane gives more material, but specification should follow the roof's risk, access and detailing. A well-installed 1.2 mm system on the right deck is normally more useful than a 1.5 mm sheet paired with the wrong adhesive or poor detailing.
Can EPDM be installed directly onto OSB3?
Many smooth EPDM systems are designed to bond to suitable clean, dry OSB3 using their approved water-based deck adhesive. Check the board face, moisture condition and exact system instructions; sealed or contaminated boards can prevent a reliable bond.
Should every roof be a single sheet?
No. One sheet is attractive because it reduces seams, but handling and safe positioning still matter. Use a sheet size the team can manage and form any required seams strictly to the system method.
