Modern Tomato Glasshouses

New Zealand Journal of Agriculture, Volume 80, Issue 1, 16 January 1950, Page 35

Modern Tomato Glasshouses

By

I. L NOTTAGE,

Orchard Instructor,

Department of Agriculture, Auckland.

THE recent very rapid expansion of glasshouse A tomato production in the Auckland district has been paralleled by a marked improvement in glasshouse designs particularly suited to this area. Most of the houses constructed within the past few years have been based upon designs similar to the two described in this article and, despite certain inherent disadvantages, wooden frameworks, with inside supporting posts, have been retained. WHILE modern steel and wood frames have indisputable advantages, all-wood frames are a little cheaper and timber is easier to obtain and to handle where growers want to do as much as possible of their own building. Moreover, the older steel designs had serious faults, and, remembering that, growers are inclined to let “the other fellow” experiment with the new steel designs, which are obviously much better. For these reasons a proportion of the growers probably will continue to prefer woodenframed glasshouses. The salient features of the newer houses proving most satisfactory at the present are: 1. Greatly-improved, simple, easily-operated, and very efficient ventilation systems most important features in glasshouses designed for the warm, frequently very humid conditions of the Auckland district. 2. Much wider spacing of rafters and the use of the lightest and least possible number of wooden members in the supporting frameworks. 3. High side walls to give ample air space for the plants and, incidentally, more comfortable conditions in which to work. 4. Sloping side walls to allow better air circulation round the sides of the houses and to assist stability. 5. Reinforced concrete posts, giving firm foundations and a rugged basis upon which to build the wooden frames. The design of all the newer glasshouses is based upon reinforced concrete side-wall posts. They are the foundations as well as the principal wall members and it is upon them that houses depend largely for their stability and strength. The posts are 9ft. , Bin. long where houses have sides 6ft. high— most-favoured height. The

posts, which slope inward at the rate of 1 in 6, are sunk 3ft. 6in. in the ground and are further supported by concrete collars (Fig. 1) or by filling the holes excavated to take the posts with concrete instead of the soil which was removed. Perfect alignment of the posts is essential and is perhaps the most difficult part of the job. Bolts to hold wooden members of the framework must be set accurately when the concrete posts are being made. Growers usually mould their own posts. Concrete building blocks or - short concrete posts sin. x sin. x 3ft. 6in. are used as foundations for the inside supporting posts, to support end bottom plates, and as intermediate supports for bottom plates between the main side posts. These blocks project about 12in. above ground level. Bottom plates are about Ift. above ground level, but on the side walls the exact height of the plates is influenced by the size of panes of glass used. Asbestos board is used to fill the space between the ground and the bottom plate. Two styles of wooden framework are used. That illustrated in Fig. 2 is suitable for glasshouses about 30ft. wide, while Fig. 3 shows the framework used for houses about 40ft. wide. Ridge ventilators of the type shown in Fig. 4 are almost always fitted, while side ventilators running the full length of the house are, fitted at the tops of both side walls. It is usual to build a sash ventilator above the door at each end of the house. In the Auckland district satisfactory temperature and humidity control are impossible without side-wall ventilators, but the entry of air through ventilators situated low down in the walls creates draughts, which have detrimental effects on plant growth and on disease control Two types of ventilators, illustrated in Figs. 5 and 6, provide thoroughly-efficient air circulation without harmful draughts. Chiefly for reasons of economy glasshouses are being built with rather low-pitched roofs. While it may be claimed that a higher pitch would absorb more warmth from the sun, it has been found that the low-pitched style

is satisfactory for Auckland conditions and it has the additional advantage of offering less wind resistance. In the houses described here rafters are inclined at from 23 to 25 degrees to the horizontal. Side walls have been built with vertical studs or with horizontal bearers for glass, the latter method being an innovation, at least as far as Auckland is concerned. HOUSE 30ft. (APPROX.) WIDE Most of the details ' given in this article relate to a house 34ft. wide at the base and 32ft. wide at the eaves, the maximum width for the type.. The rafters, which are 18ft. long, are supported at only three points, 9ft. apart —longer spans would be undesirable. The walls are 6ft. high and the ridge 13ft. 6in. For convenience the house shown in Figs. 1,2, 4, and 6 is described. It has sin. x sin. x 9ft. 6in. main concrete posts, ridge ventilator, upright side-wall studs, and outside, hinged-flap ventilators at the tops of the side wallsfeatures which are interchangeable with those for the wider house. The spacing measurements quoted apply if the glass used . is 20in. x 14in. and rafters, • etc., are spaced to take the . glass the . wide way. The • timber measurements quoted are for undressed material.

It will be noticed that the sin. x sin. concrete posts are set between the side studs and therefore the end posts are not at the corners of the house. That is necessary because the rebated, lower outside edge of the 4in. x 3in.. top wall plate (Fig. 7) runs flush with the outer sides of the concrete posts and also flush with the outer sides of the tops of the wooden side studs. The bottom wall plate is attached to the outer sides of the main posts. When the concrete posts are moulded provision must be made for insetting

9in. x jin. bolts, projecting 3Jin. to take the top plates, and 6Jin. x jin. bolts also projecting 3 Jin. for attach- • „ in £ bottom plates - The concrete posts are set at a slope of 1 in 6 and are Bft. lOin. apart, measured from the centres of posts, The spacing provides for 5 20in. glass panes, each with Jin. clearance, and for the widths of studs less the rebates for glass - The post s Sr must be calculated accurately, accordjng f o the spacings required for the size. o glass to be used, because with this • method of construction posts mus t fall between the wooden side studs. . A . n . T 5 m side support posts—4m. x 3m. x 9ft., set on concrete building blocks are surmounted by 4in. x 3in. plates, which support the rafters midway between wall plate and ridge. One

edge of the plates should be bevelled slightly to fit the angle of the rafters. Collar ties 6in. x l|in. join the tops of alternate pairs of inside posts. The posts are suitably rebated and bolted to the ties. Angle braces of 3in. x 2in. timber are placed as shown ,in Fig. 2. There are braces between the centres of collar ties and the ridge and between collar ties and inside posts. Where there are no collar ties the inside posts are braced to the plates which support the rafters. At the ends of the houses 2in. x Tin. roof braces, which are attached to the under sides of the rafters, run at angles from the corners of the house to the ridge (Fig. 2). Similar braces are used at the centres of very long houses. Angle bracing has not been found necessary for the side walls. Spacers 2in. x lin. are attached to the under sides of the rafters midway between ridge and centre plate (Fig. 4) and between centre plate and eaves. The ridge plate is 6in. x IJin., while rafters and studs are 3in. x 2in. With the exception of those joining the door posts, which are 4in. x 3in., studs are 3in. x 2in. An outside sliding door is shown (Fig. 1) but if desired, the door can be hung inside. Some growers prefer hinged doors of the divided or “stable door” type, as the top half may be opened to admit air while the closed lower half prevents damaging draughts. Others use sliding doors with sacking half doors, or screens, to stop draughts, x A hinged or swinging sash above the door is desirable, though it may not be used very frequently. For a north-south house, the south end is usually of wood, but otherwise similar to the north end; houses sited differently should be glassed at both ends. Ridge Ventilators The ridge ventilator shown in Fig. 4 has been used on most of the larger modern Auckland glasshouses. It is a movable ridge of 24-gauge iron which can be raised and lowered on a series of iron . connecting bars operated by a lever. A 2in. x lin. board is rebated into the rafters to leave a space Bin.. wide each side of the ridge plate.

The roof is glazed up to the lower edge of the board. The 24-gauge iron is attached to a wooden centre plate 3in. x ljin., to which it is braced, at about 3ft. intervals, by lin. x jin. iron straps. The outer edges of the iron are turned downward to give extra strength and to fit over the 2in. x lin. board on the rafters when the ventilator is closed. Pairs of Din. x fin. iron bars, which are bolted to the ridge plates of the ventilator and of the glasshouse (Fig. 4) give an Sin. lift before the bars are vertical, so that the ventilator will return to the closed position when the lifting lever is released. The length of movable ridge sections varies according to the over-all length of the glasshouse, but 70 to 90ft. sections operate quite successfully. The centre pair of iron bars in each section is extended downward as' far as possible, leaving 6ft. clearance from ground level when the ventilator is lifted.

The lower end of the lever is connected to one of the cross-members of the glasshouse framework with sash cord running through small pulleys. Sections of the ridge ventilator are operated separately and may be set at any level up to the maximum lift of Bin. The ridge is heavy and provided that the lift bars are not raised to the vertical position, it is unlikely to blow over. and close the wrong way. In any case, this may be stopped by placing the bars illustrated so that the rafters will check them if they' travel too far. A chain (not shown in the diagrams) from the lower end of the long lift bar to a point 8 to 10ft. back along the house ridge plate could be employed as an additional safeguard. At each end of the house and at points where two sections of ridging meet, a short piece (18in. to 24in.) of permanent iron ridging covers the opening to prevent rain entering in windy weather. If birds are troublesome, Jin. bird netting is needed to cover the ridge ventilator openings; it is rarely if ever necessary on the side ventilators. Side-wall Ventilators Details of the outside flap ventilators are shown in Fig. 6. which also shows how the side studs are fitted. The bottom plate is bolted to the outer sides of the concrete posts. The top plate is fitted so that the • lower, rebated edge is flush with ’ the outer sides of the tops of the posts. The outer sides of the studs are flush with the lower, rebated edge of the top plate and the outer side of the bottom plate. Thus the sluds slope away a little from the concrete posts and the wall glass is kepi clear of the concrete. The end stud continues to ground level. The space below the bottom plate is filled with a sheet of asbestos board and the plate is supported mid-way by a short concrete building block.

The ventilator opening is 12in. deep, with a 2in. x lin. board running along its lower edge. The wall <is glazed from the bottom plate to the lower edge of the 2in. x lin. board, which is rebated into the studs. The ventilator flaps are wooden, 13|in. wide, and hinged at the upper edges to fit

into the lin. x lin. rebate on the lower outside edge of the wall top plate. When closed they overlap the 2in. x lin. board at the lower edge of the opening. The flaps may be in 10 to 12ft. sections, operated individually and controlled by suitable window brackets, or they may be operated simultaneously along the full length of the house by a multiple bracket. In either case ventilator flaps should be designed so that they may be set at any of several points, according to requirements at different times or seasons.

The spouting illustrated in Fig. 6 is of special design. It has a lin. wide inner flap which slips into slots cut into the ends of the rafters just below the glass. The spouting also covers the gap which would otherwise be left between the top wall plate and the glass of the roof. It will be noted that the lower ends of the rafters are flush with the outer top edge of the wall plate. HOUSE 40ft. (APPROX.) WIDE The details set out here are for a glasshouse 40ft. wide at ground level, with walls 6ft. high, and ridge 14ft. high. This gives a slightly lower pitch than in the 30ft. house. (Features shown in Figs. 3, 4, and 5, including 6in. x 3in. main concrete posts, horizontal bearers for side-wall glass, and louvre ventilators at the sides, can be used for the 30ft. house also.) Reinforced concrete posts 6in x 3in. x 9ft. 6in. are more suitable for the

40ft. house than the sin. x sin. x 9ft. 6in. posts previously described and the tops should be shaped (Fig. 5) to allow for the inside ventilator flaps. The inside bevels at the tops of the posts commence 3in. from the outer edges (half the width of the posts) and the bevels are 6in. long. This leaves a 3in. bearing surface for the top plate and a 6in. opening for the ventilator. The top plate (Fig. 7) is

fitted so that the rebated lower outside edge is flush with the outer top edges of the concrete posts. The plate is bolted to the tops of the posts as described for the 30ft. house. When the posts are moulded provision must be made for insetting 9in. x jin. bolts at the top and also 7in. x jin. bolts projecting Jin. to take the specially-cut wooden members shown in Figs. 5 and 7, which are cut

from Sin. x 2in. timber. Holes must be left to take bolts for the lower ends of braces (Fig. 3). Louvred Side-wall Ventilators The top board is attached to the inner sides of the concrete posts (Fig. 5) with its upper edge flush with the lower edges of the bevelled tops of the posts. The remaining three horizontal pieces are placed in the order and positions illustrated and are spaced according to glass measurements, leaving the bottom plate about 12in. above ground level. The wooden ventilator flap, which is 6ft. wide, is hinged at its lower edge to the inside, board at the bottom of the bevel. It opens inward, being controlled by suitable brackets. From the rebated, lower edge of the inside horizontal board glass panes slope downward and. outward to the rebated, upper . outside . edge of the top horizontal member on the outer sides of posts. The glass, which should be 20in. to 24in. long, if possible, is carried by the' rebates in the timber, but sloping wooden supports are provided beside the concrete posts, chiefly to enable the joins to be sealed. This method provides stormproof and efficient side ventilators which do not cause draughts.

The remaining two lower members are spaced to take the size of glass to be used. The glass is laid in two long horizontal strips instead of between vertical studsthe more usual manner. . The ridge ventilator is the same as that previously described (Fig. 4), while the ends of the house are similar to that shown in Fig. 1, but modifled to suit the extra width of the house. . . . - Main rrame The main framework of the 40ft. house is shown in Fig. 3, but because the glass is laid horizontally on the

side walls, spacing of reinforced conCrete posts is entirely independent of glass measurements. As there are no vertical side studs to assist in supporting the top-wall plates and as the extra width of the house calls for additional strength in the principal supports and . foundations, concrete posts are placed 4ft. 6in. apart. Pairs of inside posts are 9ft. apart, corresponding with alternate pairs of side posts. The rafters, which are 20ft. 6in. long, are supported at two intermediate points, giving three equal spans. This is accomplished by placing the 4in. x Sin. inside posts on concrete foundations so that they carry

a 4in. x 2in. plate to support the rafters at a point one third of their length from the 6in. x 2in. ridge. The tops of the posts are cut to take the 4in. x 2in. rafter supports at the correct angle for the rafters to bear upon their upper, 2in. sides. A 6in. x 2in. collar tie, projecting at each end to carry the second 4in. x 2in. intermediate rafter support, is bolted to each pair of inside posts. The rafter support is further strengthened by a 4in. x 2in. angle brace, which is bolted to a concrete side post and to the end of the collar tie. Additional 3in. x 2in. angle braces run from the ridge plate to points below the collar ties on the inside 4in. x 3in. posts. The outer sides of the latter posts are braced to the collar ties by short 3in. x 2in. braces. Roof braces of 2in. x lin. timber . (Fig. 2) are used. There are also four pairs of lengthwise braces not shown in the diagrams. From points on the collar tie 3ft. on either side of each end inside post pairs of 4in. x 2in. braces run inward and upward, converging to meet near the top of the second inside post, where they are attached. (These braces could not be shown clearly in the diagrams without making them too complicated.) Angle braces may be used in the side walls, but it is doubtful if they are necessary with so many sturdy reinforced concrete posts to take the strain, and they interfere to some extent with the sloping glass louvres of the ventilation system. In some housesincluding the 30ft. typehaving fewer concrete posts no wall braces are used nor do they appear necessary. GENERAL CONSIDERATIONS In constructing a glasshouse all level wooden surfaces should be bevelled slightly to allow condensed moisture to run off readily. However, in the houses described all members are inclined because side wall posts, slope

inward, and it is not necessary to do the bevelling. Oregon pine is the most suitable timber for glasshouse construction and should be used if possible, especially for rafters and studs which are to be rebated to carry the glass panes. All timber should receive a coat of priming paint before being erected or at least before the glass is laid. The under coat and subsequent coats should be applied after laying the glass, and will help the putty to seal the joints between glass and timber. The finishing coat should be white. Because of trouble arising from corrosion due to the moist conditions

inside tomato houses, galvanised nails and bolts should be used. Copper nails are even better, but are verydifficult to obtain. Brass brads with small heads are used to hold the glass in position. Large glass panes to 24in. long are recommended, with rafters, etc., spaced to take them the wide way, as it is surprising how much difference this arrangement makes to admission of light and warmth. Glass panes should not be overlapped more than jin. The spraying of glasshouse roofs with a protective wash in very hot weather is more likely to be necessary with a new house than with an old one, as new glass is very clean and clear. \ Moisture courses should be used in all wood-to-concrete joins. Water pipes and spray pipes (if a stationary spray plant is used) may be suspended from the cross-members of houses, above the centre pathway. With suitably-spaced taps for hoses overhead piping systems are handy and are out of the way when not in use. Glasshouses should be built in positions where the soil is well drained or can be drained. Spouting should be used or concrete gutters should be provided along the outsides of side walls to carry away surplus water. Houses should be built where they can be reasonably well protected from winds, especially cold windsa wellfavoured section without glass is almost as good as a badly-sited one under glass and is a great deal less expensive. Acknowledgments The glasshouses described and illustrated are not exact descriptions of particular buildings—the designs given combine the best features of a, number of houses. The author wishes to acknowledge the assistance given by Auckland glasshouse tomato growers, especially Messrs. A. C. Mann, E. E. B. Wood, F. W. J. Jennings, and H. R. Lupton.