ᐅ Flat roof garage on new garage construction

Created on: 19 Jun 2025 16:03
M
Marcel1981
M
Marcel1981
19 Jun 2025 16:03
Hello,

I had a garage built.
The dimensions are 4.60 m x 10.50 m (15 ft 1 in x 34 ft 5 in). The masonry (24 cm (9.5 inches) thick block) rests on a fully poured concrete slab.
The top finish is a continuous ring beam.

I want to build the flat roof myself using timber construction.
The layers will be (from bottom to top):
- Gypsum board
- Vapor barrier
- Rafters with insulation between
- Fire protection boarding or rough boards
- Roofing with bitumen sheets or EPDM membrane

Now my question is, how far should or must the cross rafters rest on the ring beam? If I lay them across the entire ring beam length (25 cm (10 inches)), I can no longer add insulation on the outside.
Also, the exterior plaster would not really adhere to the wood of the cross rafters. Can anyone help me here or am I making a mistake in my thinking?

Thanks in advance.