Sunday, February 26, 2012

Hoboken Brownstone: Steel

In the last post we talked about pouring the new basement slab... so now they were ready to start the structural work in the basement. Many brownstones in Hoboken have a beam or bearing wall that runs the length of the building to reduce the overall span for all the joists. Typically the bearing walls will create the hallways and center stair on the upper floors.  Given the 24' span on this house, the beam and column support are doing more work than on say a 14' wide brownstone.  

Basement looking towards front

We located the new steel columns under the beam in different locations from the existing columns so that new footings could be poured while the existing supports remained in place.   You can see in the photo above that we also provided a column at the end wall because we couldn't rely on the old brick and mortar to withstand the load of the three floors and roof on a 24' wide joist span. 
The undersized existing wood beam that sat below the joists was replaced with an 8" steel beam that would sit within the joist depth. This required that all the joists be cut so they could attach to the sides of the new steel beam.

Basement looking towards rear

There's a shift in the beam location that you can see here at the double column. It was required to pick up the end of each beam at the shift.  This allowed the proposed wall layout at the upper floors while maintaining the existing masonry openings at the rear facade. 

Double column at beam shift

Here's a photo of an old iron strap connection at the stair header that would be replaced...

Stair Header Connection

At what will be the future TV room in the basement, we made two smaller windows into one large opening.  We had looked at digging out the back yard to get taller windows here, but given the small yard depth we decided to maximize the yard size at one level.

Rear window at Basement

At the First Floor, we also needed steel to keep the floor plan as open as possible.  The steel columns continued up to the second floor and you can see the beam at the rear of the house where the kitchen would be.  This beam was also set within the joist depth.

First Floor Structure

At the living room the existing beam had been offset from the bearings walls at the upper floors.  It was too great a distance for the load to transfer, so we needed a beam to allow a generous opening from the entry into the living room as well as picking up the bearing walls above.   

Living Room Steel

This column at the face of the building picks up the living room beam load rather than relying on the existing old masonry and mortar. You can also see in this photo the wood that is scabbed to the sides of the steel beam to accept the hangers of the cut existing joists.

Column Support at Front Wall

At the back of the First Floor where the kitchen would be, we wanted to open up to the backyard. A steel beam and lintel picked up the masonry load for the over 9'-0" span opening.  Again, we didn't rely on existing old brick and mortar, which would have carried a significant point load at each end.  

Here it is from the outside.   We kept the existing masonry openings at the backdoor and adjacent double hung window, which will become a sunny office nook in the kitchen.

Where you see the big opening there had been two double hung windows.  It will become one large steel window wall...  but that's for another post!

Sunday, February 5, 2012

Hoboken Brownstone: Basement Slab

On the last post, I talked about digging out the basement. Test holes showed that we could gain an additional 6" in ceiling height if we aligned the top of the new slab with the top of the existing footing.  If we went deeper, we would have to underpin the foundation or create a new foundation ledge, which would have been obtrusive and taken up space.

Digging out also allowed more room for gravel and insulation under the slab.  The gravel gives us the drainage needed should there be collected moisture under the slab.  As you may have heard, a lot of Hoboken is under water during big storms so we also included a sump pump that's connected to the underslab perimeter drainpipe.  This photo shows the preparations before the slab pour.  The PVC pipe and plywood form to the right is for the sump pump and will be located in the future mechanical room.

Typically we'd call for at least 4" of rigid insulation but given the limited depth we gained, the best we could do was a blanket thickness.  We used Insul-tarp, which claims a 7.5 R-value.  We needed something since we didn't want to loose our radiant heat through the ground.   But even if you don't have radiant, all basement slabs need to be insulated... as you can lose over 20% of your room heat through the ground! 

The grid laid over the insulation is the reinforcing that will sit within the slab.  At the far end of the basement you can see the bright orange tubing for the radiant heat over the reinforcing grid.  We chose to put the tubing within the slab to limit additional thickness needed if we had put it in a subfloor above the slab.

Because we were aligning the top of the slab with the existing footing, a wood form was put at the edge.  In the photo below, you can see the exposed footing.  Later a curb would be poured over the existing footing to clean it up.  A compressible fill joint should be provided between the slab and curb to prevent uncontrolled shrinkage cracks.  We planned for cabinetry on these perimeter walls to hide the curb.  

Here are the underground utilities below the stoop.  I couldn't tell you what's what, but ultimately they will each be capped with a brass plate level with the slab. New water supply and waste lines were installed.   Sanitary and storm water waste are handled separately, each with their own valve.  This is a good thing, as you don't want storm water backing up into your basement plumbing fixtures in a big storm!    

Because we lowered the slab elevation we needed to modify the front entry stairs into the basement.  We originally hoped to just add another step at the bottom, but in the end we decided to modify all the steps to give them an easier and even rise... and just adding a step would have been tight to the basement door. 

Well, that's it for slab prep.  Next time you'll see the finished concrete and then we'll talk steel!