How to roof a 1920s/30s factory building?

[spikey]

I need to scratch build a small factory building of the brick walls, Crittall windows and flat roof type, and I'm confident about all aspects of the build except for one - the roof. 

 

I know my Google-fu is not strong, but even so I've now tried for over an hour to find a photo of such a roof so I can work out roughly how high the parapet needs to be and how the drainage is done, but to no avail.  Can some kind soul please point me at a picture (real thing or model) which will enlighten me?

 

And am I right in assuming that pre-WW2 the roof itself would be asphalt?

[Ian Smeeton]

You could try the Britain from Above website.

 

95,000 + photos, many commissioned by manufacturers of all sorts and ages.

 

There is bound to be something there for you.

 

But *** Health Warning ***

 

Be prepared  to lose several hours if not days on this site.

 

Register (its free)  and you can zoom in

 

Regards

 

Ian

[spikey]

Thanks for that Ian.  Never thought of that one!

 

Looks like the parapet's often only 6  courses deep at the most, and at least now I'll remember to put in a trapdoor for access.

[chris p bacon]

The roof will be flat but with a slight fall to one side, at the lowest point there will be a gully approx 12 inches wide with an outlet, this will either go through the brickwork to an external downpipe (4") or just be internally. 

The parapet wall will be at least 4 courses above the highest point of the roof to allow for the flashing, this could easily be 6-8 courses at the point of the gully, the parapet will be capped with a coping stone that is 3-4" thick and has at least 2 inches overhang internally.

 

Hope that makes sense.

 

 

[spikey]

11 hours ago, chris p bacon said:

Hope that makes sense.

 

 

It does indeed.  Thank you.

 

All I need to know now is am I right in thinking that, generally speaking, pre-WW2 the roof surface would be asphalt?

[Nick Holliday]

11 hours ago, chris p bacon said:

The roof will be flat but with a slight fall to one side, at the lowest point there will be a gully approx 12 inches wide with an outlet, this will either go through the brickwork to an external downpipe (4") or just be internally. 

The parapet wall will be at least 4 courses above the highest point of the roof to allow for the flashing, this could easily be 6-8 courses at the point of the gully, the parapet will be capped with a coping stone that is 3-4" thick and has at least 2 inches overhang internally.

 

Hope that makes sense.

 

 

On a large factory building roof there would be more than one outlet gully. It is quite likely that there would be a gutter strip running along all four sides of the roof, with gentle falls from the centre, with a definite drop at the edge to form the gutter. A modern roof would have falls introduced into the gutter to each outlet, to reduce the ponding effect, but in the 1920's this may have been less of a concern, and for modelling purposes the perimeter gutter could be flat, perhaps with a few puddles left between outlets.

[34theletterbetweenB&D]

57 minutes ago, spikey said:

All I need to know now is am I right in thinking that, generally speaking, pre-WW2 the roof surface would be asphalt?

Having walked about on a few built in this style in the period proposed, built up felted was the usual covering.

12 hours ago, spikey said:

... at least now I'll remember to put in a trapdoor for access.

Not necessarily. Gated off section of an exterior fire escape stair leading to the roof is another access possibility. Then there's your sophisticated building constructed with a lift installed, and a brick built and pitched tiled roof machinery housing with a regular exit door onto the roof. Remember that the door will have a high sill to prevent any water ingress. Same applies to the trapdoor, it will have a built up coaming around it, or even a small felted over cabin above it.

[eastglosmog]

An example here https://www.warwickshirerailways.com/gwr/gwrhd716.htm

[cessfordalan]

Hi 

From what I can remember from night school about sixty years ago a flat roof would be covered in a one inch gravel grade over a felt roof.

For any other building problems try and aquire a copy of Mitchells  Building Construction, required reading in those days at night school.

 

Cessfordalan