Roof membrane on warehouse and commercial roofs: this is how you seal a large flat roof

A large flat roof on a warehouse, workshop or production building is rarely replaced before it is absolutely necessary. It's expensive, it takes time, and it disrupts operations. If the roof is leaking or worn, but still firm, it can be sealed with instead liquid roof membrane in one layer, on top of what is already there.

What can the roof be made of?

The membrane can be used on roofing felt, eternit, concrete, slate, zinc, roofing foil, metal and wood. In commercial construction, it is most often old roofing felt, concrete or sheet metal. The requirement is the same regardless of the material: the substrate must be clean, dry and firm.

Go through the roof before you order anything. Look for places where water remains after rain, for loose pavement and for slabs or boards that give way. The membrane must not be placed on a surface with standing water, and it does not fix a soft or weathered surface. That kind of thing needs to be fixed first. How the roof is cleaned is stated in How to prepare the roof for roof membrane.

How to calculate the consumption

A 20 kg bucket covers approx. 13.3 m² in one layer, corresponding to approx. 1.5 kg per m². On large roofs, it is easiest to think in terms of pallets:

• 120 m²: 1 pallet with 9 buckets
• 240 m²: 1 pallet with 18 buckets
• 480 m²: 1 full pallet with 36 buckets

Add a little extra for edges, skylights and penetrations, which must have more material than the surface. The entire calculation is in How much roof membrane do you need?, and pallets with a quantity discount you order on business side.

White or black on a hall?

The white membrane reflects sunlight and lowers the temperature indoors. That is why it is often chosen for warehouses, where a dark roof otherwise makes the hall warm in the summer. Black is a fine choice where the heat inside is not a problem. Both colors are resistant from minus 40 to plus 90 degrees and have enhanced UV protection. More about it in White roof membrane: therefore it is cooler inside.

Skylights, ventilation and edges first

A commercial roof often has many penetrations: skylight, ventilation system, returns and pipes. This is where leaks most often start. Brush them first and give them extra material all around, along with joins, corners and edges. When the details are closed, roll the surface.

For transitions towards walls, chimneys and skylights you can use MaxFlex covering, if the roof has a slope of at least 5 degrees.

Plan the work in fields

Divide the roof into fields with chalk string and place the number of buckets that fit each field next to it. Then you can see along the way whether the consumption lasts, and no one is left without material in the middle of the surface. Stir up the membrane and roll it on in an even and covering layer. Do not apply it too thinly, as this affects the durability.

The weather must be dry, and the temperature must be above 5 degrees, both while you work and during the drying time. There must be no rain for the first day. The surface is dry to the touch after 1 to 2 hours, and full cure typically takes 24 to 48 hours. When in the year it suits best is stated in What time of year can you apply roof membrane?

There is no welding to be done, so there is no open fire on the roof, and the work takes place from the outside. The hall can therefore usually continue to run in the meantime. If you want to know more about fire, read on Is the roof membrane fireproof?

Try it on your own roof first

If you are in doubt about how the membrane behaves on your substrate, order one test sample and place it on a corner of the roof. Then you see the result before you order pallets.

The membrane has a lifetime of up to 40 years and a 25-year product warranty. It was developed in Denmark, and we are based in Albertslund and deliver throughout the country, usually in 1 to 3 working days. See Luna Roof roof membrane and calculate the consumption, or write to us at kontakt@luna-roof.dk with the size of the roof and a few pictures, we will make an offer.