Extending the floor

After almost a month in New York, I'm back in London again. Now that the shower is finished (!), I'm going to shift my efforts towards finishing the remaining "heavy construction" so that we can try to wrap up the major work by the of the summer.

What that means is that I'll now be focusing on the preparations for the new staircase that will eventually go upto our new loft & dormer. This will include:

• Extending the floor so it meets the correct location of the new stair. Besides adding around 15 sq ft to the overall area of our flat, this extension will also provide the necessary floor area to locate the new door into the bedroom (currently, "The box"). So this extension is critical to the new layout & design of the flat.
• Re-framing the structural wall (adjacent to the staircase) so that the new door into the bedroom can be opened.
• Once the structural wall is re-framed, it needs to be sheathed in structural plywood and then covered in "fire-proof" plasterboard (1hr rated to be precise), as per the instructions from our council's Building Control officer.
• Build and install the landing for the new staircase - it needs to be built first because it will help hold up the stairs...also, it will give the stairs something to frame into
• If the above items go well...start building the staircase...!

The existing staircase (down to the flat's entry door), with the structural wood wall next to it

Before extending the floor, I needed to open up the existing floor and determine the exact location and level of the new beam that will carry the new floor area as well as the new staircase. Because this is the only remaining area of the floor that was not leveled, the contrast (between the old sloping floor by the stair and the new leveled sub-floor) became quite obvious...with a difference of over an inch!

Morning of March 26th - the existing conditions and original end of the floor.

Sub-floor removed, exposing the joists underneath

The level shows the extreme difference between the old sloping floor/joists and where it should be so it's level.

Because of the extreme slope of the old floor, I realized that it will be necessary to reconfigure the top of the stair to get everything level. This required pulling off the top step so as to fully expose the beam below. Once the joist was fully exposed, I was able to set-up a string line and determine the future leveled location of the new beam.

Removing the original top step to expose the beam below

The string line and level - note the difference between the string (which is level) and the slope of the old floor/beam!

The location on the structural wood wall were the new joist will go. Removing the plaster to expose the wall plate below where the beam will sit. (A wall plate is a horizontal stud within a wall - usually in between floors)

With the location of the beam determined, it was time to create the openings for it to go into and determine the structural support that will hold it. On the side of the exterior wall, I cut into the wood trim and exposed a wooden wall plate that holds the joists (the wall plate sits on top of the brick wall below). On the other side (at the structural wood wall) I also found a wooden wall plate that was conveniently at almost the exact location I needed to sit the new beam on. Once everything was opened, I cut the new wood beam and inserted it in place. It took some time to set it at the exact level, but I was eventually able to get there.

Afternoon of March 28th - locating the wall plate that will hold the new beam (at the exterior wall) and establishing the correct level there. This required a thin steel plate to get it to the exact height needed.

The new beam at the correct level (notice the difference between it and the old beam)

Once the beam was set to the correct level, a second beam was cut and they were fastened together (this is known as sistering) to create an extra strong beam. This double beam was then fastened to the old, sloping beam to help stabilize it and prevent any further settlement or sloping.

The double beam fastened in place

Now the fun part started...I was able to remove the old railing and start setting up for the actual floor extension. This again required using string lines to determine the correct location of the new joists (that will frame into the double beam). Once everything was worked out, I was able to to cut the wood and install special steel clips (called joist hangers) that help make the structural connection between the joists.

Morning of March 29th - The new double beam in place...then removing the original railing.

String lines locate the positions of the new joists.

With everything cut and the joist hangers in place, I was then able to insert the new joists and fasten everything together. Within a few hours they were structurally sound, and i was able to add a layer of plywood so we could walk on our new extended floor!

The joist hangers in place, holding the new joists

The completed framing

Adding a piece of plywood so we can walk on it...