In order to conform to the Act of Parliament already cited (8 & 9 Vict. c. 126), it became necessary, in 1847, to provide an additional pauper lunatic asylum for the county of Middlesex. Architects were invited to compete for the design of the building. Thirty-nine competitors sent in plans accordingly, and from these the county magistrates selected three as deserving of reward. The architects thus signalized, were, for the first prize, of 300l., Mr. Daukes for the second prize, of 200l., Messrs. Harris and Godwin; and for the third, of 100l., Messrs. Allom and Crosse. The design submitted by Mr. Daukes has been accordingly adopted, and the building, of which the erection was commenced in the spring of 1849, is now completed. Before describing it. however, it will be interesting to notice the instructions issued by the magistrates upon the occasion of inviting the preparation of designs.
    The land for the building is situate at Bet's Stile, near Colney Hatch, between Finchley Common and Southgate, and consists of 119 acres, lying on both sides of the Great Northern Railway, and having a gradual and general slope towards the south-east. The accommodation to be provided is for 1000 patients, of both sexes, in separate departments for the several classes of patients, and in separate buildings for the two sexes, either wholly unattached, or connected only by the chapel and offices common to both. The accommodation for the female patients to be one-third greater than for males. Besides the asylum, airing-grounds, &c., the following buildings and offices to be provided. A chapel for 400 persons; apartments for two resident medical officers, one for each sex; apartments for a resident superintendent, and for a resident matron; a committee-room, and rooms for the reception and examination of patients of each sex on admission, and for visitors to patients of each sex; a surgery and infirmaries, baths, and all domestic offices, as storehouses, brewhouse, bakehouse, laundries, workshops, and farm buildings; also, at the entrance, a porter's lodge, with accommodation for a man and his wife, on one side, and clerks' offices on the other side of the gateway. Provision to be also made for manufacturing gas within the premises, and for employing it in the general lighting of the establishment. Suggestions were also officially made upon the following several points:-
    Form and Site for the Building.-The form to be such as to afford an uninterrupted view of the country, and the free access of air and sun. The several galleries and wards to be so arranged that the medical officers and others may pass through all of them without retracing their steps. The site of the building to be selected with the indications of surface such that the day rooms, corridors, and airing courts have a southern or south-eastern aspect. Those portions of the asylum to be occupied by patients, to have not more than two storeys - that is, ground and first floors.
    Arrangements for Classes, Attendants, separate Rooms, &c.---For each class, besides the exercise galleries, a room should be provided with an open fire-place, easily acessible from the kitchen, and equal in dimensions to about ten superficial feet for each patient to be received therein. The attendants upon earls class are also to have separate rooms placed so that they shall be in close proximity with the dormitories and the closets containing stores, &c. The separate sleeping-rooms to be 9 feet by 6 feet 6 inches and from 11 feet to 12 feet 6 inches in height; and the dormitories should contain 48 feet superficial, and about 576 cubical feet for each patient. The several galleries, day rooms, dormitories, and cells should be distinguished by numbers, and the portions of the building assigned to the several classes of patients, by letters. The staircases should be without winders, or long straight flights, and the wells built up. Three distinct classes are to be provided for amongst the patients of each sex. Of the sleeping accommodation one third should be provided in separate rooms, and the remainder in dormitories, each containing from three to twelve beds. The aged, dirty, infirm, and epileptic patients to be accommodated on the ground-floor, and the violent and noisy patients removed as far as possible from the other patients. The staircases to be of stone, and the building, as far as possible, of fire-proof construction.
    Warming, Ventilating, and Supply of Water -  Complete arrangements should be made for warming and ventilating the whole of the building, and for supplying hot water. Descending or horizontal smoke flues, if used, to be constructed entirely of brickwrok, rendered or pargeted inside and out; and if flues from any of the furnaces are carried up through any of the main walls, they should be constructed with a hollow space round them, to prevent the transmission of undue heat inwarm seasons, and allow a moderation of the temperature of the building whenever desired. The supply of  water to be equal in quantity to 40 gallons per day far each patient and should, if possible, be obtained at such a level that it may reach the highest parts of the building, without forcing.
    The asylum recently erected at Colney Hatch, from Mr. Daukes' design, is in the Italian style of architecture, with stone groins and dressings, and has an extreme length of 1881 feet 8 inches, and depth of 670 feet 6 inches. The total number of rooms, including the common offices, chapel, infirmaries, &c. is 987. The corridors, centre colonnade, &c., are paved with the patent metallic lava of Messrs. Orsi and Armani; and the terraces, flats, &c., are roofed with the same material, which is said to be perfectly impervious to moisture. An Artesian well, 350 feet in depth has been sunk for the supply of water. Among the principal apartments is one 112 feet long, and 58 feet 6 inches wide, fitted with an orchestra, for balls, concerts, &c., for the amusement of the unfortunate occupants of the asylum. The board room is 30 feet by 20 feet, and has the walls covered with modern Venetian stucco, coloured and polished to represent borders of Carrara marble, and panels of Scienna.

The Pictorial Handbook of London, 1854