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Why the Flat Roof?

is probable, I think, that of all features characterizing modern domestic architecture it is the flat roof which has the greatest difficulty in winning acceptance from the majority of people. This is curious, because, as a rule, those who boggle at the squareness it implies are quite ready to praise good Georgian houses, the roofs of many of which might be equally flat for all that can be seen of them above the parapets. The explanation must be that they feel the former to be the result of some deliberate " cubist " perversion in the modern archi- tect rather than what it actually is—the simplest and best solution of the problems that confronted him.

There is nothing particularly and essentially natural about the pitched roof except that we hay- grown accustomed to it. It is a roundabout method of doing a simple thing, forced upon us by the faultiness of the materials at our disposal. The earliest hut builders soon found that a flat roof thatched with reeds or leaves would not keep out the rain—whereas the same thatch, if set at an angle (dependent upon the nature of its material), would throw off the rain before this had time to work its way through.

It is not generally realized how fundamentally the whole form of a building is affected by the construction of its roof. In the south-east of England we find that the most common roofing material is tiles. On account of their porosity these must usually be fixed at a steep angle, forty-five degrees or more. This steep pitch means that a great deal of roof space will be wasted unless the span from front to back is kept relatively small. Even so, in order to make use of this space, the roof is often pierced by dormer-windows to give light to what arc really attic. Further north-, slates -are more gener- ally used, and as these are less pervious to moisture they can safely be laid on pitches as flat' as thirty degrees. With these it clearly matters less how big the span may be, since little space is being wasted, and so we find that a square-shaped house is more usual. It can he seen from this that both types are the results of a compromise : neither tiles nor slates are waterproof, and so they have to be tipped up at such an angle that the rain will run off before it can soak through ; in order to satisfy this requirement, the whole form of the building must be modified. What has been wanted all the time is some material that is absolutely watertight and will remain so through all changes of weather and temperature. Once we have this, the logical shape for a roof is fiat—taking the shortest distance from wall to wall. This material we now have in concrete, either alone or topped with layers of felt and bitumas-tic preparation.

The flat roof is no new experiment ; there are flat roofs which have successfully stood the weather without attention for over a hundred years. But it is only- within the last few years that their construction has been 'made sufficiently cheap and reliable to recommend their use' for all classes of buildings. Once the architect knows that he can use a flat roof he is freed from a number of difficulties and 'restrictions that cramp hiniwhen he has a pitched roof -to consider. Be can do things on his plan that would otherwise be impracticable on account of expense or sheer structural difficulty. If one considers the complicated intersection of angles that results from even the simplest meeting Of pitched roofs, and the possibilities of bad building which it allows, one can see why he is prepared to sacrifice a considerable amount to keep the roof simple. A flat -roof calls for no such compromises : he can go out for exactly what he Pl'ants. The tendency of a pitched roof is to flatten out, pushing the walls apart ; the flat roof, being cast as part of the walls, actually holds them together. Further- more, the over-turning effect of a strong wind against a house with a pitched roof may be almost twice as great as that against the same house with a fiat roof. These two factors allow a Considerable economy of material to be effected in building the walls without in any way weakening the structure.

So much for the architect ; let us now consider the point

of view of the occupier. He has saved money on the building of his house by having a flat roof ; is it going to be as satis- factory in other ways In the first place he will find that his upper rooms keep warmer in winter and cooler in summer. The pitched roof, especially when constructed, as often, with- out an underlayer of felt or insulating board, does not show up well in this respect. Anyone who has been up in the rafters of a house on a hot summer's day will have been astonished at the almost unbearable heat that has struck through the slates or tiles. In cold weather there is a constant Circulation of air warmed from the rooms below rising to the ridge, where it is cooled against the slates, and then spreading downwards to the eaves from whence it flows again across the top of the ceilings, and so continues. The heat conductivity of bittune.n is only about half that of slates or tiles—and to this mast he added the effect of several inches of concrete (or of the joists and boards, if a timber construction has been used). Secondly, he will have what amounts to an extra floor added to his house in the pleasant form of a roof-garden. On this he can sit in peace, or his children be left to play in safety.. The real value of the roof-garden, in our towns especially, has hardly occurred to anyone yet. Even now they are by no means to be despised, and when in a few years (and may they be very few) the smoke pollution is adequately lessened, it will seem nothing short of idiocy to waste so many acres of valuable space, secluded from -the din and dangers- of traffic and raised well above the layer of petrol fumes which hangs about our streets.

In densely built areas the flat roof has another advantage that has not received the attention it deserves—the extra light which it allows the neighbouring houses. It has been calculated that in a street running at the most advantageous angle, with rows of two-storey houses standing seventy feet apart, over seven hundred more hours a year of direct sunlight are possible with flat roofs than with pitched. It is true that these are mostly at a time when the sun is laic in the sky and has little power ; but the cheering effect is there if the ultra- violet rays are diminished, and the saving in lighting bills

alone is worth counting in a; 'poor household. . . . . . •

The upkeep of a pitched roof may amount to a considerahlp figure—and there are few building firms who would be -pre- pared to guarantee one for more than twelve months. Should one slate slip or be blown off in a gale of wind, the movements of the men clambering about to repair it are extremely likely to cause damage to the rest of the roof, damage which may not show itself for weeks. It is only too true, as most householders know, that one roof repair leads to another. On the other hand, any good firm who understand the laying of a flat roof (and no other should be employed) will give a guarantee of ten to fifteen years with it—and there is no reason at all why any maintenance should be required in a lifetime. One is insured, too, against damage by flying slates—a minor point, perhaps, but one that may have a very sudden and definite application. With roofs and floors of concrete, as I pointed out last week, the risks of fire in a private house become negligible ; almost certainly the structure will not suffer, nor will the fire spread from one room to another.:

There remain only aesthetic considerations. Cart it be seriously maintained that with all these practical advantages to enforce its adoption the fiat-roofed house should be frowned

' upon because of A real or fancied ugliness Is it not,,, as so often at the inception of things, that we are too little accustomed to it to be able to judge it fairly—that we fail to see the beauty that is there because we are looking for a beauty that is not ? In any case, the whole history of architecture (and indeed of all invention) seems to show that, as the new form is persevered with, and as we grow accustomed to the new considerations which it implies, beauty will be evolved. There is an increas- ing number of those well fitted to express an opinion who

consider that this has already occurred. •

" G. M. Boumrnum