DC Rowhouse Renovation - Strengthening the Original - Part 2: Floor Framing by Gregory Upwall

While the steel fabrication crew was busy installing the steel frame, our general contractor was able to work on reframing the existing floors. This is the other major type of re-strengthening work on a renovation project like ours. With the removal of the old interior walls, the original floor joists are effectively left unsupported in the middle and the distance that they “span” is now the full width of the house. Also as part of our new design, the stairway is being relocated from it’s original location to a new location along the alley side wall at the rear of the house. In order to move the stairway an entirely new opening in each floor has to be created for the stairway to fit into. All of this reframing was installed in accordance with the structural engineer’s framing plans and details.

In areas where the span distance of the original floor joists has been increased by the removal of interior walls the structural engineer has called for new wood floor joists to be “sistered” along the side of each existing joist. Sistering is a term that refers to connecting a new joist into the old joist by installing equally spaced screws through the side of the new joist into the existing joist for the entire length of the span. With the new joist “sistered” to the old the two effectively act as one stronger joist.

In certain locations (such as the perimeter of the floor openings for the new stairway) stronger wood beams are needed to carry the larger concentrated loads that occur from attaching the stairway and the adjacent floor areas. In these locations engineered lumber is typically used instead of standard framing lumber since it is stronger. The term engineered lumber is used to describe a variety of different products, but all engineered lumber products are made from wood fibers, veneers, or layers that are bonded together with adhesives in a factory. While the manufacturing of engineered lumber does come with a variety of factors that can increase it’s overall sustainability as a building product, a major advantage comes from the fact that engineered wood does not require the harvesting of large mature trees since the wood fibers used in it’s production are generally from smaller and younger trees. is For our project the engineer called for “LVL” beams (LVL stands for laminated veneer lumber) in these locations.

Removing a section of the old subfloor to create a space for installing the new beam in the floor framing

Measuring the opening for the new stairway opening

Lifting the new beam into place

Setting the new beam into place

The new beams forming the opening for the new stairway

Our framing crew had to remove sections of the old floor framing and cut “pockets” into the old masonry walls in order to insert the new beams. Once all of the new joists and beams were installed the original subfloor boards were removed and a new layer of “Advantech” floor sheathing was installed. Advantech is a great new plywood flooring and wall sheathing product that has greater moisture resistance, stiffness and fastener holding characteristics than typical plywood. The Advantech sheathing also has a “tongue & groove” profile along the edges of the panels allowing them to interlock for greater strength.

Now that all of the interior floor levels have been re-framed our contractor can turn their attention to re-building the garage at the rear of the house. Once the new garage is in place they will be able to start framing the new rear walls and then the new addition at the top of the house – very exciting!

A view of the newly re-framed upper floors (looking up from the 1st floor)

Floor framing and steel posts in place

A view below the 1st floor showing the new LVL beams, Advantech sheathing, and the new steel posts place

View from rear alley with scaffolding removed showing steel frame in place and new floor framing in progress