How to Build a Small Hothouse - Roof

Note that wall plates are bevelled to shed condensation. and when ordering, a pattern should be sent so that two pieces can be sawn out of 3in. x 3in. stuff instead of planning all the bevel off 1 1/2in. timber and making the front edge too thin. About 1/4in. of taper is sufficient.

When the four frames are made to size, they can be bedded with mortar on to the brickwork, the halved corner joints nailed together and angle braces nailed across the top to keep them square. (Leave these angle braces on until the whole job is set.) Then proceed with the benches made from 3in, x 1 1/2in. bearers on edge and 3in. x 1in. battens about 3/4in. apart, but do not permanently nail such battens as will later be in the way when fixing the heating system.

The purpose of fixing benches at this stage is to provide comfortable scaffolding from which to erect and glaze the roof. Roof cuts can be set out by drawing a right-angled triangle 4ft. 4 1/4in. base and 3ft. 3in. high to a scale of 3in. to 1 ft. These are the measurements to the side of 1 1/2in. thick ridge, therefore no ridge allowance will need to be made later. After drawing the triangle, set out the width of a rafter below the hypotenuse as, for example, fig. 4, and mark the shape of a wallplate to get the cutting bevels. Note that this will leave a slight opening between wall plate and glass so that condensation can run down and escape over a galvanised flashing and into spouting supported on brackets.

This flashing is a strip 4in. wide. nailed to the plate before rafters are fixed, and together with the opening should prevent the rot which generally starts at this point when condensation and dirt form a paste that is continually damp.

Allowing for 1/4in. bearing on the ridge and and a 5ft. 51/4in. rafter, it will take seven 10in. sheets to glaze each roof opening with about 1/2in.lap on each sheet and 1 1/2in, overhang at the foot. Preparation of rebates is shown in figs. 1 and 9 for rafters and studs and the method of glazing in fig. 10. Before beginning to glaze, test the distance between each pair of studs or rafters with a stick to ensure they are parallel along their wholelength, and if necessary, tack on a temporary strut to keep them correct. If the setting out has been carefully done in the first place and the stuff is straight, there should be no difficulty, but if the opening is incorrect some adjustments can be made to the fillets before nailing.

Next Page >

How to Build a Hothouse