How Do You Test a Garage Roof for Asbestos? Sampling and Lab Results

Why you cannot tell by looking

Asbestos cement garage roofs are usually corrugated grey sheet, often with a weathered surface and patches of green and black moss. Plenty of modern fibre cement and plastic sheets look much the same from the ground. Age is a clue, because a garage built before 2000 is more likely to have asbestos sheets than one built later. Even so, there is no mark, texture or colour that settles the matter, and anyone who gives you a firm answer from the driveway is guessing. Our page on how to tell if your garage roof is asbestos shows the pointers worth noting.

Look for a manufacturer's stamp or label on the underside of a sheet, a date plate or old paperwork. These help, though they are not proof in themselves. The sample is what proves it.

How a sample is taken

A sample is a small piece of the material, a few square centimetres, taken from a sheet. The aim is to remove it without making dust. The person taking it wears protective equipment, wets the area lightly, cuts or snaps a small piece from an edge or damaged corner, seals it straight into a bag and labels the bag with the location. The spot is then sealed or wiped down. A new sheet is not left with an obvious hole, and the work takes minutes.

That is why it is not a job for a hammer and a carrier bag. A careless sample can release more fibre than the roof had done in years. If you do not feel able to take a sample under proper control, do not take it yourself. Hire someone who does this routinely, such as a surveyor who samples materials or a contractor who works with asbestos cement.

Where several materials make up the garage, each needs its own sample. The roof sheets, a flat section of lining board, a soffit, a flue pipe or the gutters can all be different products. A single positive from one sheet tells you nothing about a ceiling lining below it, and a single negative does not clear a rebuilt corner that used older sheets. Ask the person sampling to list each location and material on the form that goes to the laboratory.

Cost is modest compared with the price of getting it wrong. Laboratories charge per sample, and a surveyor adds time for the visit, so a few samples on a single garage is an inexpensive step before a removal quote.

Where the sample goes and what comes back

The sample goes to a laboratory that analyses building materials for asbestos, usually under a microscope, and reports whether any fibre is present and which type. Turnaround is typically a few days, depending on the lab and how quickly you ask for it. The report names the location sampled, the material and the result.

A negative result means the sheet you sampled is not asbestos, and the roof is an ordinary building material. Check that the sample came from every different type of sheet on the roof, since a patched roof can mix old and new. A positive result tells you what you are dealing with, and gives you something concrete to take to a contractor when you ask for a price. It does not mean disaster. An intact roof can be managed, and whether an asbestos garage roof is dangerous depends on its condition. The next decisions are about removal or overlay, covered in asbestos garage roof removal.

Do you need a test before roofing work?

If a roofer is going to touch the sheets, you or they need to know first. Cutting, drilling or lifting an unknown grey sheet without a result is exactly how householders and workers end up exposed. HSE guidance requires a risk assessment and trained workers for work on asbestos cement, and the starting point is knowing what the material is. The HSE page on non-licensed asbestos work sets out the categories.

When we survey a garage, we photograph the roof and its condition and tell you whether we would treat it as asbestos cement. If a lab result would change the plan, we say so. Our garage roof replacement service gives you a fixed written quote once we know what is on the roof.