Installing Curved Windows in CMU Openings is a difficult
procedure because the concrete block, or even poured 
concrete lintel is difficult to make perfectly smooth and
round, and join the rough opening jambs seamlessly.
The applied buck is made from a flat stock - either 3/4”
thick or 1-1/2” thick and this stock is not easily bent 
to a shape.  If it can’t be bent well, the circular window
cannot easily mount weather tight and water and moisture
penetration resistance like the rectangular units can be.
Fabricating the opening to accept a curved window
requires on of two approaches:
1. Kerfing the stock (as shown) by slicing a 
multitude of grooves in the surface
2. Utilizing a free foam, cellular pvc stock 
which can be bent to a radius in a smooth fashion.
Accommodating the
Curved Window
The Opening must be level, plumb and square, and the
mortar properly applied to allow no voids, cracks or
clumps that might allow water infiltration.
A proper sill must be accommodated either with a pre-cast
sill, or an applied buck with a sill pan installed as shown.
Note: Florida Building Code Requires that 
products tested for wind and debris - especially for hurricane 
and high wind zones - be installed as they were tested. 
This can mean anything other than a wood buck sill may 
void hurricane and wind approvals. 
Window Fitters Guide to Window Installation 
132                ©2022 AWDI, LLC Do not reproduce without permission
CMU Curved-Top Installation with Buck
Precast
Lintel
Poured
Sill
SAMPLE MANUAL

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