How to Measure a Thatch Roof for a Quote

Knowing how to measure a thatch roof will not replace a professional quote, but it will let you check one. Thatch is priced per square metre of roof surface, and the single most common misunderstanding is confusing that with the floor area underneath.

How to measure a thatch roof: area is not floor area

A thatch roof at 45 degrees has considerably more surface than the footprint it covers. At 45 degrees each sloping plane is roughly 1.41 times the horizontal distance it spans. Steeper roofs are more again.

So a simple 10m by 10m building with a 45 degree gabled thatch roof has about 100 square metres of floor and roughly 141 square metres of roof. Priced at R450 to R1 000 per square metre for new thatch, that difference is not small.

When someone tells you their thatch cost per square metre and it sounds impossibly cheap, this is usually why. They divided by floor area.

The basic calculation

For a simple gabled roof, measure the length of the building and the horizontal distance from the wall to the ridge line. Multiply the horizontal run by the pitch factor to get the true slope length, then multiply by the building length, then double it for both sides.

Pitch factors: at 40 degrees use about 1.31, at 45 degrees use about 1.41, at 50 degrees use about 1.56. If you know the actual rafter length, use that instead and skip the factor entirely.

Add the gable overhangs and eaves projections. Thatch usually oversails the wall line and that material is real.

Hips, valleys and complex shapes

Most real roofs are not simple gables. For hipped roofs, break the roof into triangles and trapeziums, calculate each, and add them. For an L-shaped house, do each wing separately and subtract the overlap.

Conical lapa and boma roofs use the cone formula: the slant height multiplied by the radius multiplied by pi. For a boma with a 6m diameter and a 4m slant height, that is roughly 38 square metres.

Complexity itself costs money beyond the area. Valleys, hips, dormers and junctions all take more time per square metre than a plain slope, and a good quote reflects that.

What else drives the price

Access. A roof a truck can park beside costs less to thatch than one up a steep driveway with a hand-carry. Bundles are bulky and heavy.

Height and scaffolding. Double-storey work needs more scaffolding and more time.

Strip and disposal. On a re-thatch, removing and disposing of the old material is real cost. Check whether it is included.

Timber repairs. Unknown until the roof is stripped. A quote should say how these are handled. See the re-thatching process.

Material and grade. Covered in thatching materials explained.

Sanity-checking a quote

Work out your rough roof area, divide the quoted total by it, and see where the rate lands. Re-thatching in South Africa generally runs R200 to R400 per square metre and new thatch R450 to R1 000. A rate far below those ranges usually means thinner thatch, lower grade material, or exclusions you have not noticed.

Then check what the quote actually includes: material and grade, thickness, ridge, strip and disposal, scaffolding, fire treatment, and the position on timber repairs. Two quotes are only comparable when they cover the same scope. Our 2026 price guide and our guide to choosing a contractor cover the rest.

Do not climb up to measure

You can get everything you need from ground level with a tape measure, the building dimensions and the pitch. Walking on thatch damages it and falling off it damages you. When we quote, we measure from ladders at the eaves and from the ground, and use the plans where they exist.

A worked example

Take a simple rectangular house, 12m long and 8m wide, with a gabled thatch roof at 45 degrees and a 600mm overhang all round.

The horizontal run from wall to ridge is 4m, plus the overhang. At 45 degrees the slope length is roughly 4.6m by 1.41, which gives about 6.5m. The roof length with overhangs is about 13.2m. One slope is therefore roughly 86 square metres, and both slopes together about 172 square metres.

The floor area is 96 square metres. The roof area is nearly double it. At R450 to R1 000 per square metre for new thatch, that difference is the whole conversation, and it is why a quote based on floor area is always wrong.

When to get it measured properly

Use your own estimate to sanity-check a quote, not to place an order. Overhangs, hips, valleys and dormers all move the number, and access affects price independently of area. Our guides on thatch roof leaks and the re-thatching process cover the factors a tape measure does not capture.

Frequently asked questions

How do you measure a thatch roof for a quote?

Measure the roof surface, not the floor area. Multiply the horizontal run by a pitch factor of about 1.41 at 45 degrees to get true slope length, multiply by building length, and account for both slopes plus overhangs.

Why is thatch roof area bigger than floor area?

Because the roof slopes. At 45 degrees each plane is roughly 1.41 times the horizontal distance it covers, so a 100 square metre footprint carries about 141 square metres of roof.

How do I check if a thatching quote is fair?

Divide the quoted total by your calculated roof area. Re-thatching generally runs R200 to R400 per square metre and new thatch R450 to R1 000. Rates well below that usually mean thinner thatch or exclusions.

Should I measure my own thatch roof?

You can estimate from ground level using building dimensions and pitch, which is useful for checking quotes. Never climb onto thatch to measure. It damages the roof and it is unsafe.