Close this search box.

How To Build A Flat Roof

As Leicester’s leading roofing merchant, we know a thing or two about constructing flat roofs. While it’s not a job to be taken lightly, with a little know-how and a lot of patience, you can end up with a first-rate job to be proud of.

Here’s what you need to do, and you can pick up the supplies you need and more from our Flat Roofing Materials range, many of which we keep in store.

Laying a Solid Base

It all starts with laying joists across a pair of upright supports (usually the walls of the room you are roofing). You’ll want to leave a 400mm gap between the joists, though this can vary depending on the weight of the roof.

With the joists securely in place, it’s time to cover them with some plywood decking. A key part of your flat roof construction takes place here, as you will need to incorporate a frame into the decking that will produce the slightest of inclines. Yes, we know you wanted a flat roof, but this tiny incline will allow collected rainwater to drain off without causing damage to the roof’s structure at a later date.

Putting it All Together

Slot the joists and the decking together with tongue and groove fittings. This will increase both the stability and the integral strength of the roof, improving the overall integrity of the structure and guaranteeing years of safe and effective use.

Waterproofing and Sealing

Waterproofing is, of course, essential if your flat roof is going to survive exposure to the elements. EPDM rubber is a popular choice for this and, as experienced providers of independent roofing supplies, we feel you can’t go wrong with ClassicBond – the original EPDM. Additionally, you’ll need to apply a sealant to protect the inside of the roof as much as the outside.

If you’re looking for a long lasting waterproofing solution for your flat roof, why not consider the Index and Soprema ranges of bituminous waterproof membranes? These self-adhesive systems are simple to apply and come with 10, 15, and 25-year guarantees.


It’s important to insulate the roof cavity to prevent unnecessary heat loss through your new flat roof. Whether you choose to include an air gap or not depends very much on the specifications of your roof, but you’ll find a wide range of insulation boards in stock, whichever route you choose.

If you have any queries regarding flat roof construction or need advice on the specific materials to use, call Imperial Roofing Supplies UK Ltd today on 0116 260 8494.

Leave a Comment

Your email address will not be published. Required fields are marked *