What is the Best Type of Flat Roof?

As you might expect, there’s an abundance of confusing terms and jargon out there about flat roofing construction and the different types. In reality they are very straight forward, so we have compiled this little guide to make sure there’s no confusion. Flat roofs might be slightly more troublesome to insure, but at JCM Roofers we offer quotes for any type of job on any type of flat roof, whether it be a repair to the structural deck or a full new EDPM roof.

Structural Deck

This is the base construction of the roof. The stronger the material the better in order to avoid sagging. For commercial premises we mostly recommend concrete but this would be rare to find on domestic homes. We would suggest you go for timber or plywood, and avoid chipboard and particle board. These alternatives cost less, but can cause issues down the line as they like to absorb moisture. This layer sits just on top of the normal ceiling joists – these are the long and strong planks which hold everything up.


This is one of the oldest types of flat roof and is made by felt being bonded with asphalt in a factory. It is then rolled out and can be secured ith nails or a specific cement. It’s standard for there to be multiple layers, the outer of which gravel coated. It is cheap but needs regular maintenance/replacement.

Reinforced Bitumen Membranes (RBMs)

RBMs are made of multiple layers of waterproof materials – felt for example – rolled out then bonded together with hot bitumen. This creates a waterproof membrane.

RBM roofs usually require a layer of protection on top of the membrane, so gravel or shingle is usually applied. These help to hold the membrane down in strong winds, as well as provide protection from the sun as well as from feet walking around on it.


Occasionally flat roofs are designed to be regularly walked on, a balcony for example, so a more robust material is needed. Tiles come in a variety of materials and designs, and therefore prices, so are a popular choice for the right occasion. They could be rubber, porous concrete, plastic, bitumen, and fibre cement. As with any surface it’s important that the materials used are strong enough to hold the increased weight of whatever’s on top of them.


Lead is a flexible material which is common on many historical buildings. It is tough and has a very distinguishable look. Lead is affordable, but is strong so there’s no need to continue investing into it once it’s installed. Copper and Zinc are two other metals that are gaining popularity, often on more design-focused new builds.

Single Ply

Single ply membranes are very strong and flexible, a polymer material made from PVC. It usually comes in rolls of 20m and has 1-2mm thickness. The membrane is held in place by long plastic tubes with short screws which penetrate through to the structural deck, called mechanical fasteners.

There are many other kinds of flat roofs, but we hope this covered some of the types which you might be considering! If you have any further questions on this topic don’t hesitate to get in contact with us.

JCM Roofers Oxford
65 Oliver Road

Phone: 01865920244

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