We are considering putting a deck on our 20 foot wide town home. The
back of the home has a 2 car garage and a driveway and the deck will
be directly above the driveway.
Are there any special considerations while putting a deck of this
nature? Do you recommend more than 2 wood beams to hold the deck?
Recommendations? Hire a structural engineer, this puppy is huge. Setting
posts & beam in the middle of the driveway to cut the span down to
manageable size would still require some serious wood beams and joists.
And that would not be eye appealing or safe. Come home drunk and end up
with who knows how many tons of lumber on your head - ouch!
I built decks a long time ago (80's) and just to give you some
perspective: At the time 2x6 treated pine joists 16" O.C. were rated at
8' max. span. So you are looking at 16" O.C. 2x8 joists with solid
blocking over 3 beams to create two 10' spans. For a car to pass under
requires a height that throws you into 6x6 post range. Beam size depends
on post spacing, beams of doubled 2x10's for 6' to 8' post spacing is
When I was doing this sort of thing for a living there is no way I would
take on this job without an engineer, its just too large. This is not a
do-it-yourself thing, consult a pro at least in the design stage.
If it is attached townhouses, you likely have an HOA and/or CCRs on the
deed and/or local code that dictate what you can build, especially if
the front yard isn't very deep. Check those out before you spend any money.
Aside from the fact that I believe it's a backyard deck, it's good advice.
Add-on decks are frequent subjects of news articles like "Deck collapses
injuring 20" because they are often built ad-hoc by people who are not quite
up to the engineering part of the task.
Yeah, but . . . homemade decks are often built by people who didn't just
guess wrong about loading factors or stress vectors. They just didn't even
know about that stuff and threw some lumber against the wall. Hell, some of
them don't even know about triangular bracing and their decks collapse like
a scissor jack with stripped lift screw.
Back in the days when I was a police reporter three things happened like
clockwork in the hot summer months. Toddlers drowned in swimming pools,
babies and dogs died in locked up in cars and homebrew decks collapsed. I
guarantee they'll be one coming up this Fourth of July. Drunk people
overload the deck and can't hear the squeaking as nails pull out just before
The collapsed decks I've seen were pretty much "gee, I wonder why it took so
long for this inadequately braced and nailed together POS to fall?"
Everybody knows someone with a deck like that. It's the American way. (-:
DIY, even if you don't know exactly what you are doing.
And yes, PE's make bad mistakes too. My dad was one of many that helped
investigate the infamous Hyatt Regency walkway collapse. The structure,
though a series of communication mistakes, was barely sufficient to support
its own weight, let alone that of spectators. Over 100 people died.
Is there a Homeowner's Association (HoA) for your townhouse ?
If yes, then they would have to approve of any modifications to
the external appearance of your town home... The HoA board
or management company will have more information for you
about how that process works and what size and design the deck
can be along with the requirements for the insurance your contractor
must have and the correct legal names for the "additional insureds"
your contractor will have to produce certificates of insurance to
If not, then hire a contractor who is familiar with the requirements
of your local AHJ as far as the construction of proper code-compliant
decks... Just be aware that your design might be driven by whether
or not your deck or anything adjacent to/underneath is considered
an egress pathway from your house... That generally means some
sort of fireproofing as a design factor in your deck...
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