Fixing down UPVC door sills

4 Jan 2009
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True North
United Kingdom
Hi, I'm looking at window sills for a self build with a cavity wall and want to know how entrance door and sliding patio door sills are secured to the brickwork.

I will have 1 x patio door 1800mm wide with short sill, a 1000mm wide side door short sill, and a 1000mm wide front door with low level threshold.

I know that window and door frames are fixed through the sides into the brickwork or via window straps to the inner cavity wall, but are the plastic sills mechanically fixed down into the brick work penetrating through the DPC, or are the sills only screwed into the door frame and then the only fixings are then through the frame sides or via the straps?
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Ideally and best practice the cill should be screwed up from underneath into the frame before it's fitted, don't forget to seal the frame and cill together AND fill in the gaps at the end
Thanks, i fit some double glazed upvc windows to a garden room but its was years ago. I set the sill onto packers until level, then removed it, added a U shape bead of silicone to the sides and back then screwed it to the frame.

I cant remember if i also added some sealant around and between the packers before fitting the sill and frame together.

I won't be fitting the house windows but would like to know if its a similar process to how I've described or if they screw down through the sill into the brickwork? It doesnt seem right that they would puncture the dpc.

Im wanting to set the frames back 25mm over the cavity so if they do screw down, it might miss or be close to the brick edge.

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