The Unitarian Chapel, situated off Field Row in Belper, was constructed with the help of Jedediah Strutt and his family. They have become synonymous with the chapel, and it was their last resting place.
Although I am not fully acquainted with the construction of the chapel, I will try to give a personal overview here, and make some common-sense suggestions based on the available material.
The starting date for construction is normally given these days as 1788. In the absence of any definite data to the contrary, I can only agree with that date, although pointing out that Glover's "History of Derbyshire" written in 1829 has the date as 1782. Another work, a booklet on Derbyshire Nonconformity written by Stephen Orchard (produced for the Derbyshire Family History Society in 2001) gives the date as 1786.
The Deeds relating to the chapel land purchases have been compiled and deposited in the Matlock Record Office. The earliest date mentioned is December 1789 and refers to the land as having already "a building thereon used as a Unitarian Chapel" thus we can safely assume the chapel was built by the end of 1789.
HOWEVER, the land purchases referred to in the deeds that I have transcribed and put on this site, it seems to me, refer to parcels of land bought AFTER the main chapel was erected, in order to provide for a burying ground, back yard, and two extensions to the main building.
In order to discover the exact start-date for the building, we need to discover when Jedediah bought, or was given, the land owned by the Statham family ("Shortlands") on which he built the first part of the chapel.
Amongst the deeds of the Statham family, we see one relating to the very piece of land, and it seems to have changed hands in April 1788. The money owed to Henry Statham was paid off in full by April 1789. Whether or not the chapel was planned and its building begun before that time, we cannot know.
By the way, the Stathams at that time were also staunch members of the Unitarian chapel, and their baptisms were recorded by the Unitarian Minister of that time. They would presumably not have had any objection to a small portion of their land being sold for the purpose of building a chapel, although it is still a moot point whether or not they approved of ALL the land and property being bought up by the Strutts and used for gardens and shops. (By the year 1788 the house on Shortlands was being rapidly surrounded by three-storey mill workers' houses, so perhaps they felt they had nothing to lose.)
Looking at the picture above (which is a much-enlarged portion of a very distant ariel photograph taken in the 1960's) it is tempting to think that the chapel has always been this shape. Not so!
Whatever the start date, it is certain that the chapel has been altered over the years. From looking at the exterior and interior evidence, it is safe to say that the central portion is the oldest.
On James Hicking's map of Belper (1805) the chapel is shown with East section only, this presumably having been built at some time between 1789 and 1805. The West section shows up in maps from 1825 onwards, and may have been in existence earlier, for it contained the crypt, and George Henry Strutt, who died in 1821, was buried there.
The deeds record the dates of land purchase for the East section as 1792 and the West section as 1808, so this fits with the known evidence. All the land had been bought by 1847.
The original entrance door and porch seem to have been located in the North end (the part nearest to you on the photo above). Today this part is a kitchen and porch, but the path that led up to the chapel from Green Lane still enters the yard door on this side.
Also on this side of the building is the special "Strutt Entrance" so-called. This is a "hidden" door leading to a short flight of steps that wind up to the row of pews on the West side.
If the story is true that the Strutts entered by this door, it would allow them to come and go at will, without disturbing the meeting. It was, I suppose, their VIP entrance!!
But my point is that this door was set in the NORTH end, and not the South, which is the location of today's main entrance.
At the main entrance today, we find an impressive cantilevered staircase leading up to the gallery. Inside, this gallery, standing on typical Strutt iron pillars (compare the ones in his mills!) runs the full width of the entrance hall. Was this for the choir? Or, just for extra seating? But whatever the use, those who sat in the gallery had their own entrance and exit, so it would have been a perfect way to replace the "Strutt Entrance" at that time when the chapel door changed ends.
I'd like to hazard a guess that this gallery was added as "stage two" of the building, along with the cottage standing alongside it, and the East side of the chapel. Before that time, with the entrance at the North End, and with no access to the land (Hutfall Field) where we now find the graveyard and front path, this Field Row side of the chapel would have been the BACK.
As you'll be able to see from the slide-show of photographs of the chapel, the walls of the original chapel have been opened up, braced on iron pillars and extensions have been added to allow for more pews. The joins where extensions have been added to the original are visible on the exterior and interior walls.