Roof membrane or new roof? How to calculate the price

A leaky roof almost always ends with the same question: should we put in a new roof, or can we just seal the one we have? The price difference is big, and most people are surprised by how big. Here's the math, so you can make the decision based on numbers instead of gut feeling.

How much does a new corrugated iron roof cost?

A new roofing felt roof on a flat roof typically lies between 700 and 1,200 DKK per m² incl. labor costs when the old one has to be removed first. The price varies with access conditions, insulation, flashing and how much has to be driven to the landfill. On top of that comes scaffolding, container and the days the building is open.

It's a real investment, and on a roof that's worn down all the way through, it's also the right solution. But many roofs aren't worn down. They're leaking at the joints.

How much does a liquid roof membrane cost?

A 20 kg bucket of Luna Roof roofing membrane covers up to 13.3 m² in one layer. With a liter price of DKK 2,880, the material price comes to approx. 215 DKK per m²If you apply it yourself, that's the entire cost. If you hire a craftsman to apply it, you typically have to add a few hundred kroner per m², and the work takes hours instead of days.

There is no demolition, no container, and the roof is dry again the same day.

The calculation for a 150 m² roof

• New roofing felt: 150 m² x approx. 900 DKK = approximately 135,000 DKK.
• Roof membrane, do it yourself: 150 m² x approx. 215 DKK = approximately 32,000 DKK. (12 buckets)

The difference is over DKK 100,000 on a regular flat roof. Even if you pay a craftsman for the application, you are still far below the price of a new roof.

The figures here are indicative. Always ask for a specific quote for your own roof, and remember to add 10% to the material because the substrate absorbs differently.

When can you not settle for a membrane?

The membrane seals the surface. It cannot save a roof where the problem is below the surface. Choose a new roof if:

• The insulation is wet and has been for a long time.
• There is rot in the sub-roof, rafters or pressure-distributing layers
• The roof is dented because the structure has settled.
• The fall is so bad that there are large lakes of water after rain.

If, on the other hand, the roof is dry inside and just worn, cracked or leaking at the joints, then a membrane is the cheapest way to a tight roof.

How to calculate your own roof

Measure the length times the width of each surface and add them together. Divide by 13.3 to get the number of buckets, and round up. If you have a lot of flashing, skylights or ventilation hoods, add an extra bucket, as more is used along the edges.

You can also just enter the square meters into the calculator on product page, then it automatically puts the right number of buckets in the basket.

What about the warranty?

Luna Roof roofing membrane has a 25-year product warranty and an expected lifespan of up to 40 years. It is UV-resistant, elastic and can withstand temperatures from minus 40 to plus 90 degrees, so it can keep up with the roof's work in summer and winter.

In short

If the construction is sound, it typically costs a quarter to seal the roof rather than replace it, and you're done in a day instead of a week. If you're unsure whether your roof can handle a membrane, send us a few pictures and we'll take a look.