I built my two storey extension for 20% of builder's quotes

This site shows how - step by step from design to completion

Fitting Concrete Window Sills

I will ultimately be fitting UPVC windows in the extension. I know that some purists run for the hills when they here the term UPVC, but, after much research, I had UPVC windows fitted to the front of my house a few years back. I have had nothing but compliments from strangers and neighbours (even the ones that were sceptical and thought I should have had wooden windows). To get the look I wanted involved, among other things, fitting concrete window sills and omitting the UPVC sills. I intend, therefore, to do the same to my extension. A series of case study articles - Replacing Windows in a Period Property - detailing the design and fitting of the UPVC windows to the front of my house can be found here

sill_1My home has very low ceilings, so keeping an eye on heights is pretty important to me. I ensured that I could fit a standard 900mm high kitchen worksurface below window sill level then chose which brick course to install the sill. 

Finding suitable concrete window sills (they will ultimately be painted green) was not easy, builder's merchants do not stock them as standard. I eventually located some and had them delivered. I cut them over length, trying to find a convenient place to match with the brick bond.


stubb_sillMy front windows are set back about 80mm from the wall face. I wanted to get a similar look to my new windows so had to work out how far back to set the concrete window sills.

You may just make out from the top picture that there is a small UPVC stubb sill beneath the window and above the concrete sill. I contacted the window manufacturer and asked for the dimensions of the stubb sill. They sent me a dimensioned diagram which I converted into my Autocad drawing.












I drew the concrete sill too and could then work out how it would all fit together and how far in to set the concrete sills.

sill_4I wasn't sure of the correct way to fit a dpc to the sills. Most people don't fit concrete window sills, so I found it hard to get much info. Eventually, I fitted the dpc as shown in the DVD that comes with the bricky tool - he fitted sills exactly the same as mine.

The dpc runs under the sill, up the sides, under the brickwork and up the back face of the sill. I trust this will meet with BCO approval as it has made a complete sill envelope so no damp can get past. It was later trimmed neatly.



For this lift I took the advice from the insulation manufacturers and had a go at raising the outer skin first.

I fitted wall ties every second block and every block around door and window openings. Sometimes I forgot and had to remove bricks and re-lay them, but eventually my brain got into gear. As I started to define the window opening I got the sense that I may just be getting somewhere.

You can see my 'garden wall flemish bond' brickwork - 3 stretchers to 1 header.