How to Build a Deck or Porch with a Roof…Part 1

My wife wanted the front door to be located on the side of the house shown in the first pictures, so, we removed a window and framed in a new front door expecting to build a front porch to go with it.  With a mobile home, my goal was to keep the weight of the porch roof primarily supported by the porch structure as opposed to the mobile home itself.  So, without further explaining, let’s get started!

We knew we wanted the porch to be roughly 10′ by 24′ with, after much deliberating, a roof that would reach almost to the peak of the house and with roughly a 2′ overhang.  After drawing up the basic plans, building a material list, building a budget, and making sure there was nothing buried where we would be building, the work began.  We first used the box blade to slope the area slightly away from our home for water runoff.

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We wanted the posts to have a small gap between them and the fascia for painting and any future changes.  So, we measured from the exterior wall to the edge of the fascia, and then added 5″ to the mark on the ground to show where the inner edge of the posts would need to be set.  Once we knew the distance from the home the posts would set, we adjusted the deck length of 24′ to where we wanted it to set along the face of the home.

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Since the deck length is roughly 24′ we wanted a post set at 12′ to support the roof and floor (again, wanting the mobile home to bare minimal load).  Also, wanting to have some margin for error, although we were using 24′ boards, we set the posts to have about 2.5″ overhang on each side when attaching the 2″ x 12″ x 24′ board.  We marked the first three post holes and then used our PTO driven auger with a 9″ blade to dig the holes.  We used 6″ x 6″ x 20′ pressure treated posts set in the ground roughly 4′ – as a rule of thumb, 25% of total length should be in the ground.  We figured once we set the first three posts, we would lay out the remaining posts based off of their positions.

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After placing the posts in the holes, we used about three 80lb. bags of concrete per hole to keep them from moving.  We like to pour the concrete in the hole a foot at a time, add water, and then use a long piece of 1′ angle iron to repeatedly “poke holes” in the mixture to stir it up, and then repeat the procedure to the top of the hole while re-leveling each time.  The benefit to doing it this way, as opposed to bracing the post using 2bys, is that you don’t need to wait overnight for the concrete to set up because the post is “packed” in concrete and doesn’t move; thus, allowing you to begin framing to the post the same day.

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The first three posts are set in concrete.  At this point, we decided to frame these posts together.

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Before nailing the first floor joist (2″ x 12″ x 24′ board) across the bottom using exterior 3″ framing nails, we needed to know the height it would need to be in order for the deck boards to be level with the exterior door threshold.  So we screwed a mock header just below the threshold and leveled off a deck board to find the exact height the floor joist would set.  Since there was only two of us, we used cinder blocks with a 1′ wood shim on the other end to get the floor joist level before nailing it to the posts.

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It is very important that this floor joist is the correct height and level, as this board will effect the entire floor of the deck.

We set the upper roof support next (2″ x 12 ” x 24′ board) using a make shift harness and a couple of screws:  it was a little more work than shown in the picture.  Our roof joists, which are 2″ x 12″ x 24′, will rest on, be attached to, and run perpendicular to the roof supports attached to the posts.  Because of this we had to find the best angle for attaching to the mobile home roof, which has a low slope, and maintaining the desired height for the porch along with having an adequate slope for water runoff.  The slope we landed upon was 1.5″ drop over 12″.  This is a little less than I wanted but it was the best we could do with the variables we were working with.  To find this angle:

  1. We measured 24′ (the length of the roof joists) from where we wanted the new roof to intersect the current roof; about 1.5′ below the peak.
  2. Shooting for 2″ slope over 12″ (since we were mating up against a low slope on the current roof), we adjusted the 2″ x 12″ x 24′ roof support board to get as close to that as we could without sacrificing the height of the roof for when we’re standing on the deck.  As said earlier, we ended up at 1.5″ drop over 12″.

Once it was in place, remembering to leave at least 1.5″ overhang on both ends past the posts for the outer roof joists to rest upon, we nailed it into place using exterior 3″ framing nails.  It will make more sense as we move further along in the process.

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Now it was time to mark and drill the remaining post holes.

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Before laying out where the posts furthest from the home would set, we took a few things into consideration:

  1. Deck boards we were using were 10′ long and we wanted to have a minimal 1.5″ gap between the edge of the home and the edge of the deck boards.
  2. The 2″ x 12″ floor joist that would be attached to the post, and would extend out 1.5″ from the edge of the post.
  3. The 1″ overhang we wanted the deck boards to have past the 2″ x 12″ floor joist.

We had to take all these things into consideration before making the decision as to where to set the outermost posts.  You can always trim off a little at the outer edge of the deck boards, but you can’t easily add to the length:  so give yourself a little margin by erring on the side of bringing the outermost posts slightly closer to the home as opposed to further away.

Once we finalized these details, we measured in an X pattern to make sure the posts would be square (both diagonal measurements should be the same).  Then, we marked where the remaining six posts should go using string and black spray paint.  In order to keep the auger straight, sometimes it requires a little extra “elbow grease” to get the job done:  thank you Christian.  All posts were pressure treated 6″ x 6″ – 7 were 20′ and 2 were 8′.

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After setting all the posts in the holes, we filled the holes that run lengthwise with concrete following the same procedure described earlier on this page, and then used string to guide us in setting the three remaining posts in concrete that are sandwiched in between to make sure everything stayed square; or, as close as we could.  Now on to framing…