In 1916, Bishop Roper appointed Robert Jefferson to take over from Mark Malbert. Mr. Jefferson came to Holy Trinity from Franktown and Montague and was inducted on December 24th of that year. The bishop described him as a "young, energetic Irishman" and Wilfred Bradley (in his book The Life and Times of John Charles Roper) called him, "a canny, warmhearted Ulsterman," with, "the mind of a Scot and the heart of an Irishman". His coming, after the dithering of an aging, querulous Frederick Squires, was welcomed with enthusiasm. He conducted three Sunday services: 8:00 a.m. communion, 11:00 a.m. morning prayer and 7:00 p.m. evening prayer with church school, young men's and young women's Bible classes in the afternoon. He led a weekly Bible Study on Wednesday evenings. Baptisms were held on the first Sunday of the month and by appointment.

Robert Jefferson had a lot of innovative ideas, and he brought about what one admirer called "remarkable growth" in the parish. Clubs and organizations proliferated under his guidance. While he continually despaired of the choir (in the 1920s he was still complaining about the fact that Ascension was the "only church in the city" without a choirmaster), Sunday school flourished, the Babies Branch of the Women's Auxiliary regularly had between twenty and thirty members (at a yearly fee of seventy-five cents). There was again a branch of The Brotherhood of St. Andrew and the members of the Men's Club played billiards and carpet ball in tournaments with men's clubs from other churches. Mr. Jefferson, because he wanted his parishioners to feel like a family, promoted frequent picnics and, because he was a great proponent of outdoor sports, saw to it that there was a church tennis club. After the move to the new church, he oversaw the building of a tennis court next to the church.

Patriotism was running high in these war years. After Canadian soldiers in France had captured Vimy Ridge and Courcellette from the Germans in 1917, Robert Borden's Conservatives won the federal election on a vote for conscription. Patriotic songs were sung everywhere. War-bond drives increased in number and fervour. In churches there were more and longer prayer vigils. Bishop Roper declared diocesan-wide days of prayer. When the department of health closed all public buildings during the 1918-19 influenza epidemic that killed so many people, the bishop was reluctant to decree that the churches were to comply, but, finally, he had to.

Despite the continuing worry about the war and the flu epidemic, there was a feeling of buoyancy at Holy Trinity. The congregation had been steadily growing, the financial situation had improved and the parish decided it needed a bigger church. A building committee was struck, plans were underway and Captain Andrew Acres, the parish treasurer, began organizing campaigns to raise money. Campaigners canvassed the parishioners and all their friends and relations. The Men's Club had dinners, the choir and the Dramatic Society put on plays, the Ladies' Guild had suppers, bazaars and rummage sales. For several years, that guild operated a booth at the Exhibition where they sold cakes, bread, jams, pickles and crafts.

The war was over in November of 1918. The church was open for prayers of thanksgiving on that day. The armistice was signed on November 11th at 11:00 o'clock - and that day, Armistice Day, (now called Remembrance Day) was declared a national holiday for all the years to come. The Winter family gave the church the pulpit in thanks for the safe return of their son and daughter. The Guy family contributed to the purchase of the prayer desks in thanks for their son's safe return; the Boscall family contributed to the prayer desks in memory of a husband and father who were killed.

By the following summer, the Holy Trinity congregation had amassed enough money to buy "three lots south of the Ottawa East bridge" (at a cost of $4,000). Amid the relief and the prayers of thankfulness, Archdeacon Arthur Mackay turned the first sod for the new church in June of 1919. (Mr. Mackay had been Holy Trinity's priest back when it had been under the care of St. John's.)

Then, on Saturday, the 27th of September, the bishop, the rector, the wardens, visiting clergy and the congregation formed behind a "colourful" banner anchored between two "ornate staves" and solemnly processed to the new site. Bishop Roper gave a speech in what Ted Gunderson described as his "pure, deep baritone voice" and laid the cornerstone for the new church. Mr. Gunderson never forgot it (one reason being that it was his 21st birthday).

According to Charles Winter (by then Colonel Winter) who wrote the church's 1944 commemorative pamphlet, the old church was "advantageously disposed of by sale". (There are records and letters to say that attempts were made to sell it in 1925, but there doesn't seem to be a record of an actual sale until 1977 when it was sold to the Portugese Community Association which still owns it.)

The new church, to be called The Church of the Ascension, was dedicated on the feast of the Annunciation, Maundy Thursday, March 25, 1920. The name change was at Bishop Roper's recommendation. The diocese of Ottawa already had Trinity Church on Bank Street in Ottawa South, which was older than Holy Trinity (by a year), and he wanted to avoid confusion. The total cost of the new church, according to Colonel Winter, was $23,000. Insurance for it was so hard to get that quite a few members of the Advisory Board (later the parish council) took out one- thousand-dollar life-insurance policies, naming the church as beneficiary.

The church bell (the old train-engine bell) was moved from the old to the new building, as were the organ, the lectern, the pews, other minor furnishings and the memorial windows. While much of the church's interior was still rough, Mr. Jefferson and his congregation began at once to worship in it.

In 1923, the parish council decided to buy the two lots next to the church for a rectory and a new parish hall and, for the time being, took out a three-year lease on 223 Echo Drive (at the corner of Hawthorne and Echo), the rector's then residence. In the meanwhile, work on the existing parish hall and the church interior was being completed. The Men's Club, under the direction of their president G. C. Armstrong, did the actual work themselves and paid for the materials with the proceeds from a play they were putting on. The hall and the sanctuary floor were both finished by Christmas.

In Ascension's first year, the parish started a monthly magazine called The Church of the Ascension Parish Magazine, founded by the Young People's Association and published by the Men's Club. It was an ambitious project, professionally printed and paid for with ads and subscriptions at one dollar a year. It contained a regular rector's letter, plus reports of organization meetings and synopses of vestry meetings.

Not long afterwards, Henry Humphries, active Men's Club member, started a scout troop (the 29th Troop), which was active all through the 1920s. It lapsed in the early '30s, was re-activated later in the decade, but it didn't really flourish again until the 1970s and '80s.
In May of 1927, when Robert Jefferson left to become the priest at St. Matthew's in the Glebe, there were 235 families in the parish (about 900 people) with 250 children in the Sunday school. The parish had its 50th anniversary that year.