Removing the Bay Window

This is how I removed the ground floor bay window, blocked up the wall and kept the bedroom bay window untouched. If you attempt removing a bay window of any sort, consult a structural engineer if the bay window is supporting any structure above. You may also have top remove the ceiling plaster of the bay to expose any joists so you can see the construction better.

The cost for the amount of work I am about to do will cost for just the labour between £1000-1500 by a professional, a 2 man team.

Firstly when the original drawings were approved by the council I noticed the garage will not be able to take a long vehicle so at the foundation stage I extended the garage into the other room by a metre so the partitioning wall would sit directly below the centre of the bay window. This would also make supporting the upper bay window a lot easier as the wall would bear the load at a central point. When the roof was constructed I supported the wall plate against the bay with some acro props just in case the bay window timbers were weak under the render.


My first stage was to cut and remove the floor boards inside to expose the joists so they could be marked out, supported and cut. When the new wall will be built, these joists will be supported on top the wall so I cut them 150mm for now from the last floor board.


The joists rest on a single brick sleeper wall (an old type of floor construction). This wall will have to be completely removed as it will not support the new double brick wall. You can see over time the slate on top of the sleeper wall has cracked and moved out-of-place so the floor will have to be levelled once the wall gets to damp proof height. The good news is at some point the joists had been replaced and seem solid.


Best get removing the old copper central heating pipes and take them to the scrap yard. £3000 per Kg, that’s at least £30 here in scrap value.


I cut each joist in turn 150mm roughly away from the floor board edge. Once I have the wall built up I will cut them so they sit 100mm on the brick. I supported most joists with timber and brick underneath so the main floor will not be disturbed.

takingdown thesleeperwall

I took the sleeper wall down. It was about 1 metre in-depth until I hit the sub base. These old houses were built with no concrete foundations which made this stage very easy. I went lower than the original buildings foundations so building regs could not argue that they were not deep enough. It was about 1.5m below the floor level. I made the foundations 600mm wide x 300mm deep. I was in two minds how to build this wall. Solid double brick to match the original house or go for the 100mm cavity type. I decided to make the footings 600mm wide for now.


Sleeper wall removed with bricks nicely piled up.


I left the bricks that were keyed into the main wall. The wall above this was supporting the upstairs so I did not want to disturb this in any way. On the right of these bricks I will use a stainless-steel heavy-duty wall starter to make it solid.


I levelled the base and compacted it.


Instead of shuttering the sides to hold in the for concrete why not just mortar some old bricks. I calculated the amount of concrete required for the foundations. I will post a rough sketch later. remember I had placed 3 re-bars when the main concrete was poured to join up the foundations with the main extension.

(2.6m x 0.6m =  1.56m)  + (0.9m x 0.6m) = 0.54m
Total 2.1m x 0.3m (300mm concrete thickness) = 0.63 cubic metre.

I will need 1134kg of ballast and 202kg of cement. to make a 1:6 mix. That’s approx 8 bags of cement and 1.5 bags of jumbo ballast (850kg). To order this amount ready mixed was costing over £160 and I would then have to move it from the front drive into the bay.  The cost of mixing it myself will be under £90 so I decided to mix it myself. I placed the mixer so mixer and tipping into place was easier than having the mixer on the stand, pouring into a wheel barrel etc.


I had over 10 buckets of the same size so I threw in  6 buckets of ballast followed by 1 bucket of cement to produce a 1:6 mix. As you can see my mixer is a large type so mixing this amount was ok. I usually mix mortar by placing the sand & cement dry then adding the water after. This time I added the water first so I would not have to wait so long for each mix and avoid the risk of dry spots in the mix. It worked very well once I got the hang of adding the correct amount of water. I had some help offered however he did not turn up. It took just over 1hr to mix/pour and under 2 hours from start to finish. Job done.


A few days later I started the block work. I layed concrete blocks flat on the side as the height was different from the previous trench blocks.

baytrench blockmortar

I found by wetting the blocks with water kept the mortar more workable since these trench block suck the water out of the mortar fairly quickly. You can see you have to put plenty of mortar down so it oozes out uniformly when a block is placed in position.


I decided to construct the inner wall double brick (single block placed on the side) after taking some advice from the architect. He said it will not be supporting the upstairs just will be just acting to block up the removed bay window. I used a stainless steel heavy-duty wall starter to key in the blocks. I added some extra bolts for extra strength too.


Once I got the first level of block work in I compacted the old bricks and soil. Although it was getting compacted by me walking on it this tool made it solid. Every few blocks up I will do this the same until it’s up to hardcore level.


I got the middle support wall built up with trench block which was fairly easy and quick. It also made moving in and out of the bay easier.


I left a gap on either side of the wall so the 4 inch pipe for the air vent could pass through. I used by self leveling laser to get the same height with the pipes on the outside of the extension wall. I also left another gap so I could run any cables and the under floor heating pipes.  I cut the floor joists 100mm in-line with the center of the block work. The ends were treated with some wood preservative to prevent any rotting. I used a string line and level to check the level of the joists. Some were out so I will have to pack them with under with some treated timber as the gap was about 40mm.


I placed about half a metre of DPC cut from a wide roll under the timber. You will need to use some origami skills it to wrap it around. I secured it with a clout nail on top.


On the right hand side of the bay I used engineering brick instead of concrete block to match the rest of the garage. I built up the bricks so the last course under the joists with bear the load of the floor. Keep in mind that you have to be able to slide the DPC under and wrap.


I started to build up the corner on each end. Three bricks high before the DPC goes on. Keeping the wall plumb and level was very difficult working in such confined space.


Whilst building up the wall I left a gap for the pipes for the air vents that will run under the garage floor. If I had to drill it out after it would have been a very difficult task.

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All joists in place perfectly level and engineering bricks built right upto the DPC course. Just the middle wall to build…

Middle wall built up and DPC cut to size and put in place ready for mortar. Don’t forget the wall ties.


On the left hands side I matched the rest of the dpc that was tucked under the main dpc.


Then I decided to work from inside and work my way out so I cut notches into the thermals block that were going to be layed above the DPC as below.

Really easy to cut using the rip. Standard wood blade cuts through like butter.


I used an extra wide DPC for the internal block work. DPM tucked under with a bed of mortar underneath and over.


DPM tucked under 30mm in before applying the main DPC.


Wall ties placed approx 650mm intervals. 3 per run of wall.


Any blocks that seemed out-of-place I corrected using the long level.


Building up the corner was more tricky. I did not use any cavity closers since it’s an internal wall. Wall ties were placed every course towards the end for extra support. Best get the insulation in before I forget.


Once thermal blocks are layed the mortar goes off pretty quick so I made sure that the wall was plumb every block without disturbing any blocks under


Keying in the blocks at the middle corner involved a lot of work so I decided to key-in the blocks in 3 points. For every course in between I used 2 wall ties to tie them in. I placed the wall starter brackets on every course.


Working a couple of hours every evening the wall began shotting up. Getting in and out of the bay, stacking blocks etc.. proved very difficult.


I placed engineering bricks under the lintel. I did not go for an end bearing of 150mm as I wanted to spread the load of the main beam that would support the bay later on.


Now that the walls got to a reasonable height and that I had somewhere to stand on I marked using string line where to cut the ceiling plaster. I carried on building up the wall using this line as a guide so the wall would finish flush with the line.


I used a brand new blade in my rip saw and cut along the line. It was the old type of batten type of construction. I had to hold the saw firmly while cutting so the saw would not vibrate and loosen and plaster towards the lounge as the ceiling was sound.


An hour later, many blows with the hammer, loads of dust and mess I had the plaster ceiling out.



Almost there. Imagine working like this in the cold. It’s very time-consuming and hard work and really puts you off.


Couple of blocks over the lintel. The next step in a few days would be to bear the load of the bay on the central wall ready for placing the strong joist to support the side up.


I should of really removed the facia boards around the whole bay window at the start. I did have a rough idea how the floor joists above were when I ran the heating pipes whilst fitting a radiator in the above bedroom. I calculated the maximum size timber beam that I could slot in (9″) s0 I went and got myself a 9 x 3 beam.


The 9″ beam would not slot in so I had to chisel away the corner away on the top of the bay window. This would allow me to slot in the beam, prop it up and let the mortar dry for a couple of day before releasing the load onto the new beam. You can see I put a concrete block in place of the thermal block so it would work like a pad stone for the beam.


I had to cut and put an engineering brick in the thermal block. Then I propped up the beam on this end until it was just about to start to lift the bay. I could not actually see the lift but I knew as the main beam bent slighty under load. I placed a spacer in between the beam and brick to keep it in place.


A few days after knocking out the bay on this side it soon opened up the space. I will have to add a few more beams to brace the main beams later. Building regulations stated that the wall must be full height and fire-lined for 30 minutes to prevent a fire spreading into the rest of the house. Also a fire-door with self-closer must be fitted so the door is never left open.