referring to the drawings , a roofing sheet generally designated 1 is constructed from strips of metal upturned along the length of each side to form roofing panels 2 , 3 . to form the sheet , panels 2 , 3 are placed alongside one another on a support deck 4 beneath which there is an air gap , then insulation on top of a vapour barrier . a channel 5 is left between adjacent upturns 6 , 7 of panels 2 , 3 . jointing of adjacent panels 2 , 3 is achieved by the use of a system of cooperating clips 8 and caps 9 . m - shaped clips 8 made of 3 mm stainless steel are hooked over the edges of the adjacent upturns 6 , 7 at regular intervals and fixed into the support deck 4 in the channel 5 between panels 2 , 3 . these clips 8 act as spacers between panels 2 , 3 . the legs 10 , 11 of the clip terminate just short of the face 12 , 13 of a panel 2 , 3 . thus , no water is drawn up between a clip 8 and a panel upturn 6 , 7 by capillary action . inverted u - shaped caps 9 are then fitted over channels 5 . these caps 9 have projections 14 , 15 from the vertical legs 16 , 17 which are snap - fixed under the legs 10 , 11 of the clips 9 to achieve a ` click - fit `. the precise sizing of the clips 8 ensures a constant air gap between a cap 9 and a panel 2 , 3 . a gap 18 of 1 - 2 mm is left between a projection 14 , 15 of a cap and the face 12 , 13 of a panel 2 , 3 for ventilation these caps 9 may have perforations 19 in the projections 14 , 15 . the perforations 19 are alternative means for the circulation of air for ventilation . plentiful joints distributed throughout the roofing sheet 1 ensure even and predictable ventilation of all areas of a roof regardless of its pitch or length . since ventilation coincides with the joints which are a maximum of 600 mm apart , this ensures that no area is unventilated . the clips 8 are made from stainless steel in order that they may be used with any metal . the support deck 5 is formed from square - edged boarding 20 with gaps 21 between . the metal panels 2 , 3 are placed so that they run orthogonal to the boarding 20 of the support deck 5 in order that a cross grid of ventilation is formed between the boards . this means a gap in the roof space is not essential , allowing use of a warm roof construction . the support deck 5 may alternatively be formed from plywood or its like . in that case , prior to the cap 9 being positioned , holes are drilled in the deck 5 for circulation of air . the gap 18 between the projections 14 , 15 from the cap 9 and the faces 12 , 13 of the panels 2 , 3 , or the perforations 19 in the caps 9 further ensure that atmospheric pressure is equalised under the sheeting 1 , thus preventing each panel 2 , 3 from being subject to upward deflection regardless of wind conditions . this has the additional benefit that , since the panels 2 , 3 are not subject to cyclic stress , metal fatigue will not occur . if these gaps 18 or perforations 19 should become blocked , when a panel 2 , 3 is subject to wind suction the length of the legs 10 , 11 of the clips 8 lowers the fulcrum point of the panel 2 , 3 from the top of an upturn 6 , 7 to the bottom so that the panel 2 , 3 may deflect upwards across its width without disengaging from the clip 8 . cap joints 22 are formed by the insertion of a sleeve 23 along a channel 5 . the sleeve 23 is of external dimensions equivalent to the internal dimensions of the cap 9 , but with no projections . any space between cap 9 and sleeve 23 is filled with a silicone sealant to prevent water entering the roof by capillary action . alternatively the sleeve 23 may be soldered to one or both ends of the cap 9 making a metal - to - metal connection . the roofing panels 2 , 3 are able to expand and contract when subject to heat or cold . traditionally an edge of a panel is held by hooking it over an edge trim 25 of a roof or by welting it into a continuous tie strip fixed to the edge trim 25 , which means that panels 2 , 3 are restricted in length by the amount of expansion possible without disengaging . thus , in order that there is no restriction on panel 2 , 3 length , a bar 26 is inserted into a pre - formed panel edge 24 . this bar , which extends between the upturns 6 , 7 stiffens the edge 24 to resist wind uplift and removes the need for the panel 2 , 3 to be hooked over or welted into a roof edge trim 25 . this allows its unrestricted expansion 27 and contraction 28 . an additional feature of the cap 9 may be incorporated at the eaves of a roof . a perforated closing piece 29 may be provided to assist ventilation .