Laying the fist row of blocks for the walls was the most difficult part of the whole wall-building operation, partly because of several problems I encountered, but mainly because I was conscious that I had to get everything just right, or I would be messing things up for later stages.

Firstly, I had to set everything out accurately and mark the positions of the walls properly. I drew the verticals on the existing wall accurately, and fixed the wall starters for the inner leaf of the cavity. The outer leaf of the cavity was going to be keyed in to the existing house, so I didn't need wall starters for those. Once I had the verticals marked properly, I then screwed blocks of wood to the walls at ground level, and attached string markers to those to stretch out across the foundations to mark the leaves of the walls. The whole marking out process took ages because I constantly checked and rechecked everything I did.

The next big problem, once I knew were the walls were going, was to bridge the drain pipe that ran across the foundations. The drain pipe was run inside a corrugated casing, but it still needed lintels put into the wall at each end of the porch to support the walls above the drain properly. This wasn't particular difficult, but it was very tedious cutting and fitting the lintels into position. The photo on the right shows the lintels in place.

The third problem I encountered was that the groundworks contractor's had built the step in the foundation in such a way that the higher part of the step was too high to allow a full-height block to be laid directly onto the foundation and match against the house courses. I had to trim all of the blocks on the higher part of the foundations down by about 5cm to fit properly. Again, easy but tedious.

I concentrate on getting the inner leaf of the cavity wall up first to brush up on my block-laying skills. By the time I'd build up the first row and a half, I then began on the outer leaf, with the nice facing blocks from Wheelers.

In my original plans, I had thought that I needed to use the final matched mortar for building the outer leaf. Fortunately, someone on uk.diy pointed out that I could point up the blockwork when I'd finished with the correct mortar, and for the main construction I could use the same mortar as for the inner leaf. This was both cheaper, and easier to do, because I didn't need to keep swapping between different types of mortar for the two leaves.

Once I started to build the outer leaf properly, I put the positions of the foundations steps and the positions for the window frame and the air vents into a Sketchup drawing. I could then `virtually' plan how the higher courses of blockwork would be laid out, which meant that I could optimise my use of the blocks, and get the perps to line up nicely. You can see my diagram of the blockwork taped to the window in the photos.

Once the blockwork had been laid up to the DPC, and the cavity filled with a weak concrete mix, I had to fill in the floor. First I put down some more MOT down to level things out, and then put in 50mm of sand blinding. I called the BCO at this point to inspect. He was happy with the walls, and the blinding. The approved plans had called for a DPM to be laid over the sand and up the walls to tie in with the DPC, but the BCO said not to bother; the foundations were very thing, the porch was on a terraced slope with good drainage, and its not a radon area, so a further 50mm of concrete on top of the sand was sufficient. I did this a few days later, and it took about a morning to mix and lay.

The final job before moving onto the construction of the higher parts of the walls was to put in a vertical DPC. This was necessary to stop dampness from tracking across the face of the existing house wall and into the new interior of the porch. I had to cut a vertical slot all the way through the house wall - 100mm - and insert a DPC into the slot. I was initially going to put in a Type B Vertical Tray, but was horrified at how much that would cost to have delivered (£25 for delivery, £6 for the trays themselves). No-one locally stocked these, so I used old-fashioned DPC instead, which worked just as well!

Cutting the slot looked like to would be tricky. My biggest angle-grinder - a 9" beast - wouldn't have made a deep enough slot. The guys on the uk.diy newsgroup suggested several novel ideas (diamond tipped chainsaw!) and the most promising looked like hiring an Arbotech Wallsaw. Unfortunately they weren't terribly cheap to hire locally, and the blades would have to be rescharpened or replaced depending upon how much wear I put on them, which could have made it even more expensive. I then discovered that special blades existing for cutting masonry with a reciprocating saw. I didn't have a reciprocating saw at the time, but I'd been thinking about getting one, and this was an ideal excuse! I always prefer to put money towards buying tools where I can, rather than hiring them. For other intended uses for the saw (e.g., cutting up a huge pile of logs at the far end of my garden), it made most sense to get a cordless saw, so I got a Makita 18V Lithium Ion saw, and a Bosch Masonry Blade.

To start off the vertical cut, I ran my small angle grinder up the wall to form a clean slot, and then started to make the cut with the reciprocating saw. The saw made an excellent job of cutting the slot. Each block (215mm) took about 90 seconds to cut through, and the saw managed about 8 blocks on each battery. I can see that this would be an easy, and relatively dust-free (compared to an angle-grinder) way of cutting out door openings as well.