Flat Roof Calculator
Build the right roof system and quantities before you order.
Choose your roof project
Select the route that matches the job. Roof Mate will guide the calculation and build the materials list.
Choose your roof shape
Select the closest roof layout. Detailed measurements, trims and roof system choices follow in the next steps.
Select your existing roof surface
Choose the surface that best matches the roof. Roof Mate will apply the correct coverage rate before calculating tins and optional extras.
Choose the roof surface you are repairing
Select the closest match around the wheel. The recommended coverage and preparation guidance update instantly.
Selected roof surface
Felt / Bitumen
2kg per m²
Felt / Bitumen / Asphalt
Built-up felt, mineral felt, asphalt and bituminous roof coatings.
Enter the repair details
Roof Mate now uses the selected surface to calculate the coating quantity.
Optional repair extras
Build your roof edge plan
Enter the roof dimensions, then click any edge on the bird’s-eye roof plan to choose its GRP trim detail. The drawing updates immediately so the customer can see where drip, raised, wall and other trims will sit.
Section A
Section B
L-shape edge trim selector
Match each letter on the L-shape visual to the real roof edge. GRP Roof Mate auto-calculates the edge lengths from your L-shape sizes, so you only choose the trim type for each edge.
Add skylight opening(s)
Enter skylight length and width above. GRP Roof Mate calculates the D260 quantity from the opening perimeter. D260 is used where the roof meets a vertical upstand, wall, skylight kerb or abutment.
Roof fall direction
Required for roofs over 50m². GRP Roof Mate will automatically add E280 expansion trim in the direction of the roof fall to split the roof for expansion.
Choose your GRP kit
Choose how the roof will be used, then select the system type and weight. GRP Roof Mate will select the closest matching kit size for your roof area without assuming that a walkable roof needs extra laminate layers.
How will this roof be used?
This changes the specification guidance, not the measured roof area.
CRS does not automatically recommend a 2 × 450g laminate simply because a roof will be walked on. Adding a second laminate layer increases stiffness and can reduce flexibility and movement accommodation.
More laminate is not automatically better. Choose the build-up around the deck or substrate, expected movement, drainage and detailing, finish and level of foot traffic. Two layers should only be used where the chosen system or project specification specifically calls for them.
Standard GRP kits
Premium quality GRP kits for normal flat roof work. Select a weight below.
Fire-rated GRP kits
Premium quality fire-rated kit options where a fire-rated specification may be required.
Trade Choice GRP kits
Premium quality all-rounder kit choice, advertised as our trade-style choice without bundled tools.
Select another kit option
No mapped GRP kit was found for this roof size, kit weight or selected system. Please choose another kit option before continuing.
Add tools and extras
Tools ?Tool packs are optional and added separately from the GRP kit. Choose the pack that best matches the roof size and level of kit you already have.
Tools are optional. If you already have rollers, buckets, brushes and trims tools, choose no tools needed.
Allowance and adhesive
Adhesive updates automatically when extra trims are added.
Your GRP Roof Mate plan
Add more items to cart
Optional extras can be added in the checkout before you complete your order. Trim adhesive updates automatically from the final trim count.
Overlay existing roofs
without stripping.
The TekGuard FLEXI-GRP system is a cold-applied, fully reinforced liquid roofing system for felt, GRP, concrete and metal roofs.
What are you overlaying?
Choose the existing substrate for preparation guidance, then set the surface texture and guarantee tier — these two drive the exact coverage rates from the TekGuard installers guide and are independent of which substrate you picked.
What condition is the roof in?
Select every scenario that applies. These are the exact preparation checks from the TekGuard installers guide, and can be combined.
What size is the roof?
Enter the overall roof area, or the length and width if that's easier — no shape or trim detailing is needed for this material estimate.
Area used for calculation: 0 m²
Site temperature and extras
Select the deck / material temperature at the time of application. The correct catalyst type and addition rate is applied automatically from the TekGuard catalyst addition chart.
Your TekGuard overlay system
Quantities use the exact TekGuard coverage and catalyst addition rates for your selected surface and temperature, plus the 10% material allowance recommended in the installers guide. Every line is rounded up to whole tins, rolls or bags — you can't buy part of one — so the pack count can cover more area than the roof actually needs.
Installation sequence
A clear order of work for the selected overlay system.