Clients of the Sydney-headquartered business "include Government, industry and corporate superannuation funds, international funds as well as individual investors via leading investment administration platforms," Ellerston said.
The Auckland-based investment specialist said: "Ellerston is looking for value, if you look at Fletcher verses its peers."
The Penrose-headquartered business was trading at a price-earnings multiple well below Australasian counterparts, he said.
That meant it was good value.
"Buying more than 5 per cent shows you're active. If you own 4.6 per cent of the company and the stories about Wesfarmers come out, you go over 5 per cent. You have nothing to lose. You've pointed out you own a big stake," he said.
He also questioned whether Wesfarmers had bought into Fletcher, following a report published in the Sydney Morning Herald last week.
It did not make sense to him that Wesfarmers would be interested in Fletcher, due to anti-competitive regulations which would restrict any takeover.
Wesfarmers via Bunnings had a share of the trade market in New Zealand but Fletcher's Placemakers had a much larger share, he said.
"There's no way the New Zealand Commerce Commission would allow a merger of those two," he said of any Wesfarmers takeover of Fletcher.
Comment has been sought from Fletcher on Ellerston's announcement.