Actually Building a House Extension! - Setting out blockwork walls
Now comes the scary bit, actually building a house extension. (although I'm sure I have said every section is the scary bit)
As the bricks I would use for the extension were not exactly the same size as the old bricks of the main house, there was no point trying to key them in to one another. In my BCO drawings I specified the use of wall starters to fix the new to the old. The builder's merchants called them crocodiles, but I guess that is a trade name.
I shopped around. I often found that online stores were cheaper than the builder's merchant. I bolted a pair at each end of the extension where it joins the main building.
I laid DPC over my DPM and started building block work corners (thank you to my wife for the unflattering photo of me either getting up, getting down or getting stuck)
I found several different recommendations for wall ties spacing. Some of the insulation companies suggested the first row should be spaced at 450mm, others suggested 600mm. They all suggested 900mm centres there after. I contacted my BCO who suggested 600mm first row, but 750mm for all others, so this is what I went with.
I laid three blocks high round the entire perimeter. I guess this isn't a terribly efficient way to do it and a pro builder would have worked one section at a time, but I just felt more comfortable doing it this way. I could take measurements and check all looked on track.
You may recall that when I built below DPM I left some perps without mortar. This was so that I could fit corner profiles (see link in right hand menu). The profiles are fixed into the brickwork and adjusted for twist and plumb. The profiles are marked at 75mm increments (standard brick plus mortar) and have nylon slides that hold the string line and can slide up to each 75mm mark. In theory, this would allow me to build without first building corners. It would also keep me to gauge. I had never used any before so it was time to see if they did as they promised.
Where I had the fiddly break line and also against the existing house. I had to cobble together my own arrangements. I cut some lengths of marine ply and marked the 75mm increments from the profiles. I used my laser level and screwed a pair to the wall by the wall starters (see previous pic). Using G cramps, I levelled and positioned a pair on the inner corner. Where I had made the mark on the ply i cut a small groove with a hacksaw. This proved really useful as it is just the right size to trap the string line and keep it taught.
I used full fill cavity batts so fitted them as I went up. (I started by building the inner first but changed plank as I went - more on this later). My bricks are quite wibbly wobbly and banana shaped at times, so putting a level against them to check for plumb or maintaining a perfectly even mortar bed is not always easy or possible. However, the old house onto which I was trying to build a sympathetic extension had uneven bricks and mortar joints too. Using the profiles, It was now a case of drawing string lines and laying bricks on a DPC. Everything should stay plumb and to gauge thanks to the profiles. None the less I kept checking with my level best I could and used my level at the door openings to check for plumb.
My existing house is built with Flemish Garden Wall bond (a header every three stretchers) That said, it does vary quite a bit sometimes having two headers together, four stretchers, 3/4 size bricks. But by and large it is Flemish garden wall, so this is what I planned to do too.
I am not sure how old-style bricks are made, but it was now apparent that the rustic finish on the face of the brick rarely applies to the ends too. Most builders, even building to an old property, would only use stretcher bond so this would not pose a problem. The ends of my bricks were actually quite red and I did not want red headers among my rustic blue, black, red, yellow bricks. I decided, therefore, that despite the extra work, I would cut bricks in half so I could use the face. I would have a lot of bricks to cut so the thought of the dust created from a circular saw was not appealing.
I chose to employ white cement in my mix to help match the mortar of the existing house.