Читать книгу Garden Carpentry - Span, Roof, Greenhouse, Toolshed, Wheelbarrow, Gates, Garden Lights, Summer House, Shelter Etc. - Various - Страница 7

THE construction of a span-roof greenhouse of the type usually favoured by amateur gardeners is not a difficult undertaking. The house described is built in sections, which makes for greater strength and has the advantage that the structure can be easily assembled and taken apart.

Throughout the construction an endeavour has been made to specify material of standard size which is normally easily procurable. The precise dimensions of the house are largely determined by these sizes. For instance, it is intended that 21 oz. horticultural glass 24 ins. by 12 ins. should be used, and the exact length of the roof frames is found by allowing 1 ft. 0 1/8 in. between the bars plus the widths of the roof timbers. The width of each roof frame ends, allowance should be made in their lengths for the thickness of these ends, also the inch hang-over of the roof frames. The bars should be positioned similarly to those of the top frames, the side ventilator openings being arranged accordingly. The members of each frame are tenoned together, open mortise and tenon joints being used at the corners.

Referring to Fig. 2, it will be seen that the centre rails are bevelled slightly, and it is necessary to cut the shoulders of the lower tenons to suit this bevel. Some of the members are ploughed to take the glass. Care should be taken to position the grooves so that they agree with the rebates on the bars. Before assembling each frame 1/2 in. holes for the securing bolts should be bored in the positions is ascertained in a similar way, but in this case 1/2 in. should be allowed for the overlap of the glass panes and 1 in. where the lower panes overlap each bottom rail.

SPAN-ROOF GREENHOUSE BUILT IN SECTIONS. SIZE (AS SHOWN) 10 FT. BY 6 FT.

Dimensions may be modified as required. Height to eaves is 5 ft. Ridge height 7 ft. 6 ins.

The nominal sizes of the timbers are given, but if prepared stuff is obtained (which is to be preferred) it will, of course, be slightly less in size. The roof frames when in position should overhang the gable ends by 1 in. Before commencing construction it is advisable to determine the precise size of the roof frames as the other sections are dependent on these dimensions.

Side Frames (Fig. 1).—As these butt against the gable indicated on the drawings. The joints are put together with thick white lead paint and secured with dowels where indicated. Finally each frame should be given a coat of red lead priming.

Gable Ends (Fig. 3).—The pitch of the end frames may be found by setting out on two rods a length corresponding to the width of a roof frame, plus half the thickness of the ridge plate. The two rods are then nailed together with a cross member equal in length to the estimated width of the gable end. The rods when put together will have the form of a triangle. The position of the eaves should correspond with the height of the side frames. Similar joints are employed to those described in connection with the side frames.

KEEP YOUR GREENHOUSE WELL PAINTED

Certain of the members comprising each frame require to be ploughed for the glass. The position of the plough grooves are indicated by dotted lines in the drawings. Figs. 4 and 5 show the joints at eaves and ridge respectively. Before finally securing the joints it is advisable to lay one frame on the other to see that they agree. Each frame is put together in a similar manner to that already described. As before, each completed frame should be given a coat of red lead priming.

Roof Frames (Fig. 6).—The top rails are secured to the stiles by mortise and tenon joints, the tenons being wedged. When cutting the shoulders of the tenons allowance should be made for the rebates on the stiles. It is usual to chamfer the top rails and stiles to agree with the chamfer on the bars, but this complicates the joints and is not necessary. The top rails are ploughed for the glass and the stiles rebated.

The bottom rail of each frame is secured to its respective stiles by bare-faced mortise and tenon joints. The mortises are slightly below the rebates; thus, when the glass is in place it will be slightly above the surface of each bottom rail. This provides a space whereby the moisture collecting on the interior of the glass can find exit. The underside of each bottom rail is ploughed close to its outside edge to provide a drip. It is also advisable to provide similar grooves on the underside of each stile where it projects from the gable end.

The edge of the top rail is bevelled to fit closely to the ridge plate. The bottom ends of the bars are housed into bottom rail. The form of joint shown prevents any moisture getting into the joint and causing rot. Care should be taken to see that the rebates are level with those on the Stiles. The transoms for the top ventilators are scribed to the bars and secured in position by oval nails.

Side and Top Ventilators.—The construction of the ventilators is not illustrated as the joints employed are similar to those used for securing the top rails to the stiles in the roof frames. Moulded stuff of suitable section for the side ventilators can be obtained, but as the top ventilators require to be 1 1/4 ins. thick only, the material will have to be specially prepared. The top ventilators are duplicates in miniature of the roof frames, but in this case there is no need to provide condensation spaces. The hanging joint is shown, in Fig. 7. This arrangement is effective in preventing water reaching the interior of the house via the joint.

Door (Fig. 10).—The design of the door shown is probably the best for a greenhouse, but if the worker finds that it is beyond his capabilities, a plain ledged and braced door formed from matching will do quite well.

Erection.—It is advisable to rest the house on a 4 ins. by 2 ins. plate so that the lower members of the house are clear of the ground. The plate is halved together and treated with creosote. In order to prevent any possible subsidence, each corner should rest on bricks, or a concrete slab, let into the ground. Care should be taken to see that the bricks or concrete are level. When the plate is laid down, a gable end can be placed in position and secured to the plate by coach bolts. A side frame is then rested on the plate in its correct position and the holes for the fixing bolts continued through the end already in position. The two frames can then be bolted together. The side frame is also secured to the plate by coach bolts.

A similar procedure is followed in connection with the erection of the other sides. When the sides are assembled the corner battens can be nailed in place, their position being shown in Fig. 8. The sills are bevelled at a similar angle to that of the middle rail of each side frame and rebated to take the ship-lap boarding. Reference to Fig. 2 will make this clear. The sills are mitred at corners and particular care should be taken to see that the joints are well painted. It is advisable to screw the sills in place. In nailing the weather boarding it is necessary that the nails should be driven into the framing so that it is possible at any future time to take the house apart.

It is necessary to remove the apex of each gable end so that a flat surface is provided on which the ridge plate can rest. As shown in Fig. 9 the ends of this member are flush with the gable ends. When one roof section is in position the ridge plate is nailed to this section and the other roof section is brought into position so that it abuts against the ridge. Both roof sections are secured to the gable ends by screws so as to be removable. At this stage the finials can be fixed, each finial being accommodated in a slot cut in the roof frames. The capping is cut so as to fit tightly between the finials and is nailed to the ridge plate. White lead paint should be freely applied to all joining surfaces.

FIG. 10. DETAIL SNOWING DOOR CONSTRUCTION.

Glazing.—In order to secure the glass it is only necessary to embed the panes in putty. Top putty does not serve any useful purpose but has a disadvantage inasmuch that it tends to crack, and the rain settling in the cracks will in time cause the timbers to rot. Each pane is made secure by panel pins.

Gutter.—It is advisable to provide the house with a gutter; otherwise the surrounding earth will become saturated with water to the detriment of the house. The gutter shown comprises two 4 ins. by 3/4 in. battens nailed together to form a V. Each length of gutter is supported by brackets, each bracket having a V-shaped notch in which the gutter rests. The gutters should be arranged so as to have a slight fall. As the gutter at the end opposite the door has to drain into the side gutter, the end gutter will have to be positioned above the side gutter and be provided with a hole so that the water will flow into the side gutter and then by way of an extension to a water butt.

Painting.—The outside and inside of the house should be given two coats of white lead paint, and further coats at yearly intervals. A pleasing appearance can be obtained by giving the ship-lap boarding a coat of green paint.