Carpenter turned founder raises $70m for construction AI firm

Sarah Buchner's father was a carpenter in Austria. When the family needed money he took his children to job sites, and she started working as a carpenter as a teenager.

She spent more than a decade in the industry, working her way up to general contractor running large projects in Europe.

Then a worker died on one of her sites. She told Crunchbase News that the death changed how she saw the job: "Once you realize that people die under your management, you just look at life differently."

Her response was to build a health and safety app for construction workers. That was a separate company, and it pulled her into software.

She followed it with a PhD on data science in construction and early artificial intelligence. The research turned up the problem that became her business: construction firms generate enormous quantities of information, scattered across systems and buried in documents.

The data was there, she said, but it was "so messy and so unstructured" that conventional analytics could not do much with it.

She moved to California in 2019 for Stanford's business school and founded Trunk Tools in 2021, before graduating in 2022. On her account the company did not find a product that worked in a market until 2023, by which point large language models had made unstructured documents tractable.

Buchner estimates an average construction site involves three to four million pages of documentation. Trunk Tools connects to the systems holding it and runs agents on top that review contracts and drawings, flag inconsistencies and handle specifications, submittals and bidding.

She gave Crunchbase News two examples. In one, an owner requested a change on a roughly $100m project; the software calculated it would add nearly $4m, and once the contractor showed the owner the number, the change was dropped. In another, a worker got chemicals in an eye and a colleague asked an agent what to do, receiving step-by-step instructions.

The company is based in New York and has more than 100 staff. Buchner is a solo founder and says her PhD gave her enough technical grounding that she did not look for a technical co-founder, though she hired experienced AI engineers early.

Trunk Tools had two live agents a year ago and now has more than 10, she says. It has raised about $70m from investors including Insight Partners, Redpoint and Innovation Endeavors, most recently a $40m Series B in 2025 at a $325m valuation. She says revenue grew fourfold last year and is on track for roughly 3.5x this year.

Early fundraising was harder, she said, because she did not look like the founder investors picture. Once the company had traction, the same background became the pitch: she had done the work her customers do, and could answer detail in the room.

Construction has been slower than finance or law to buy software, she argues, because the person signing the cheque sits in an office and the person expected to use the product is on site. Margins are thin, so a bad purchase costs more.

That is the lesson for founders selling into industries they know from the inside. Trunk Tools now sells training and change management alongside the software, because shipping the product was not enough on its own.

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