VENTILATION 61 



just pass the screws. The screws fixing the plates, where they overlap 

 at a horizontal joint, should be arranged as shown in Fig. 60, not more 

 than two corrugations apart. Halfway between those purlins which 

 are situated at each end of a sheet (i.e. below the horizontal joints), 

 another purlin — or two, in the case of longer sheets — should be provided. 

 In these intermediate purlins three screws per sheet will suffice; one 

 through each outer ridge, and one through the ridge at the middle of the 

 sheet. It may be mentioned that the purlins should never be further 

 apart than 4 feet 6 inches. 



The peak, or ridge, of the roof is protected by galvanised iron ridging 

 (Fig. 61). The two topmost purlins should be placed to receive the 

 screws that fix both the ridging 

 and the upper edge of the top- 

 most corrugated iron plates — the 

 joint between these plates and the 

 ridging being arranged similarly 

 to that shown in Fig. 60 — and the 

 edges of the ridging should be 

 hammered down so as to follow 



the corrugations of the iron below. Joints between individual lengths 

 of the ridging should have an overlap of at least 6 inches, and should 

 gape away from the direction of prevailing rain- winds. Ridging is sold 

 in 6-foot lengths and of girth varying from 15 to 22 inches. 



The peak of the roof may be provided with a 6" by 1" ridge-board 

 running longitudinally (Figs. 55 and 57). Though this feature is not 

 indispensable, it is of advantage in supporting and keeping the upper 

 line of the ridging straight. 



Ventilation. — Probably the simplest method of insuring good ventila- 

 tion in cow-byres, stables, etc., is to have the roof open along the eaves 

 and ridge, the latter opening being protected by a raised, curved capping 

 of corrugated iron (see Fig. 62). The openings along the eaves are easily 

 arranged for, either by not carrying the wall above the wall-plate or, 

 though continuing it above the wall plate, stopping it before it quite 

 reaches the corrugated iron roof-covering. 



When roofs are provided with ceilings, situated on the under-side of 

 the tie-beams, the interior of the roof between ceiling and roof-covering 

 should be ventilated. Ventilation is usually secured by the provision 

 of slatted or louvred openings in the roof-covering. These louvres are 



