Saturday, June 5, 2010
Entry Porch Rescue, Part II: Shoring Things Up
In the previous posting, What Damage Hath Water Wrought, I described how water infiltration gradually rotted the bases of the two columns supporting my front porch roof, effectively detaching the bases from the infrastructure, and how heavy snow-loading this past winter apparently forced both columns to spread slightly. This posting provides an account of the steps I took to temporarily stabilize the undermined columns. I went to work on this immediately after discovering that the column bases had shifted, and most of what's described here was accomplished in the better part of an afternoon.
Right now, I am planning a complete overhaul and rebuilding of much of my front porch infrastructure, which has certainly seen better days. About thirty five years worth of wear, insects, sun, snow, and rain have all taken their toll, and it's time to get this porch back into sound shape. However, I couldn't drop everything and immediately get started on this larger effort. So instead, I did the best I could to immediately ensure the near-term safety of the porch.
There were two objectives that needed to be accomplished right away:
1) Get the columns back to their original positions, and prevent any further movement.
2) Ensure the columns themselves could still safely support the roof.
But a constraint I wanted to adhere to was to achieve all this in situ; that is, I had no desire, say, to jack the roof up and begin splicing new column bottoms. That sort of effort could wait until the larger repair effort. I just wanted to shore everything up for the time being without removing or replacing any of the existing structure.
With all that in mind, I set about doing the following....
The first order of business was to prop the decking up in the vicinity of each column and construct something of a stopping block to ensure that each column base couldn't possibly get knocked forward or laterally to the side. So I wedged two PT 2x6s between the edge/ends of the decking and the slab:
You can see from the photo below that this had the effect of making the decking reasonably level again, and well supported in the vicinity of the column. I secured the 2x6s by sinking long exterior grade screws through each 2x6, right through the fascia, and into the PT 6x6 corner post beneath the porch, which appeared to be in sound condition despite all the damage above it. I joined the two edges together with screws, as well:
Next, I built up a second "half box" on top of the first, likewise securing both its joint and connection to the lower half-box with screws. Then, I nailed several angles over the joint, just for added strength:
Of course, I built an identical stopping block wrapping the column base on the other (south) side of the porch, as well:
I temporarily wedged some 1x scraps between the stopping blocks and the front and outer side of each column. Now, there was no chance of either column base getting accidentally knocked outward and off the decking. So once this was all in place, I gently pushed (actually, tapped) the column bases back to their original positions. This went reasonably well, considering the uneven decking around the columns and the deteriorating column siding and post bottoms:
Once each column was more or less where it was supposed to be, I fashioned a shear plate by cutting a notch in a length of PT 2x12 to fit around the column on three sides. The purpose of this plate was threefold: To prevent movement of the column in three directions (the front was handled by the scrap block inserted between the column and the upper stopping block), to effectively tie the separating decking boards back together via insertion of screws, and to provide a stable base for a vertical "T" to ensure support of the column:
Once the plate was in place, I sunk several courses of screws into it, making sure that the plate was joined to both the rim joist and the nearest decking joist, just to make sure the plate wouldn't move. Other screws simply served to hold the decking boards in place.
Next, I set about constructing a T as a sister to the column. For this, I joined together a 2x10 and a 2x6 to form the T, cutting notches in the tops of both to accommodate the knee braces of the columns. The top of the T would butt against the overhead bearing beam, with the bottom resting on the plate. One of the notched 2x10s is shown below:
The bottom of the T would be toe-nailed to the plate with screws. Two sides of the T would also be fastened to the column via screws sunk into the inside post. While cutting the lumber for the T, I had been debating whether the T ought to be independent of the column, or joined directly to it. Keeping it independent would've required a positive connection between the top of the T and the bearing beam above, and I didn't want to start sinking fasteners into that beam.
So I decided instead to attach the T to the column along its length. Doing so hopefully would make both T and column a cohesive, unified whole, stronger than the column had been by itself. This was based on my assumption, of course, that the inner post above the column base was sound. Drilling a number of probe holes confirmed that it most likely was. I was also making an implicit assumption that the connection between column and overhead beam was also sound, but I could find no evidence to the contrary. The photo below shows the T as viewed from above, looking down toward the supporting plate:
And below is another view of the dreaded "Flying Dutchman" after the assembly and joining of the T. Note the scrap block wedged between the stopping block and forward face of the column:
Although I didn't believe it totally necessary, I attached another T to the column at the south end of the porch. This column appeared to have far less damage than the north one, but it also had moved farther away from its original position. I felt it prudent, in any event, to likewise sister this column with a T:
A nice view of how the T on the south column butts up against the bearing beam while not interfering with the knee braces:
....And a view of the base of the T on the south side, where I joined it to the supporting plate (I took this photo before I re-attached the railing):
In the interest of having a strong, cohesive column structure, I also added some angles to make sure the outer trim and inner post were all one, but in retrospect this was really unnecessary. All in all, the solution appears to be sound. It's not nice to look at, for certain. But it's not too obtrusive either. And it's only temporary until I rebuild the infrastructure properly:
Epilogue: The 100 Year Porch Project
As mentioned previously in this posting, I am planning a comprehensive overhaul of my front porch this summer. Naturally, I would like to retain as much of the original structure as possible. However, as a relatively recent addition, the front porch is not that historically significant, compared to other parts of the house. Furthermore, it's an exterior structure exposed to the elements, necessitating periodic repair and replacement of componets. So as a preservationist, I have no difficulty in replacing as much of the porch as necessary to ensure both its safety and utility to me as a home owner.
I have absolutely no intention, however, of eliminating the front porch altogether and replacing it with a more historically accurate pediment, as some had suggested I ought to do. The front porch adds tremendous comfort to anyone using the front entry way in bad weather. And despite its small size, it provides a rather nice place to hang out on sunny afternoons.
What I do have every intention of doing, however, is engineering the new porch infrastructure to last as long as possible with regular annual maintenance. This will include the use of highly rot resistant natural materials and incorporation of modern design techniques for water-resistant structures. My preferences tend toward things that not only are well made, but also possess maximum utility and last a very long time. My front porch is no exception to this ethic. So I refer to this rebuild effort of mine as the "100 Year Porch Project," and will present the overall design and construction strategy for the replacement infrastructure in several upcoming postings.