BEFORE THE ARCHITECT – THE BIG PICTURES
A MUST READ. New, 823-page House Designing & House Construction Best-Seller -"Home Design Standards-Home Building Standards" 4Q08
RESIDENTIAL DRAWINGS – WOOD DECK DESIGNS,
BUILDING DECK PLANS
"In the animal kingdom it'd be mighty unusual for me to come across critters with two heads. That's so. Well, that's so until I get up to the top of the food chain, and consider folks I meet with remarkable regularity. Even our language makes plenty of 'em with words like duplicitous, ambiguous, double-talker, two-faced, forked tongue, of two minds. I call 'em unclients." AG
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These wood deck designs in deck plan form are an interesting an example of what you sometimes have to do to get wood deck designs done right as it is about what clients have to do to get it all wrong. Wood deck design have a well-earned reputation for being underbuilt [that's a euphemism for inadequately attached to structure and inadequately supported, done cheap and easy]. Think about it: add a large gazebolike structure on top of a deck and invite a deckful of folk or add a 50#/square foot snow load and Humpty-Dumpty could have a great fall.
These two folks wanted building deck plans for a wooden deck design of their general outline. The wooden deck design was to be applied behind their house - building deck plans for a deck big enough to cook out on, eat out on, and eat in on inside a 16' on-a-side architecturally sympathetic Craftsman Style screened porch. This isn't about the concept and design phases of our work. That went swell. We collaborated and succeeded in a design that worked for them and worked for to us.
Then we got to drawing up the building deck plans. Dupayosh and dupayosha soon learned that this wasn't going to be among the wood deck designs for do-it-yourselfers. This deck was bigtime. They got scared, blamed anything they could think of on someone other than themselves, knew they were skills-wise over their heads, kept our intellectual property (see below, and, like common thieves, left. Since it is a management policy not to brake for low-life types, we moved on, recognizing in their weasel worded shove-it note that two of our 19 Deadly Sins were broken - just realized that they had a budget and we were busting it; couldn't be so complicated.
This case study is to point up that sometimes, things get complicated. And there's no helping it.
What made this deck so tough on the two misguided souls of our clients? When Before The Architect starts drawing construction plans, we look up the design standards applicable to the geography with which we're working. These design standards include seismic zone, rainfall rates, wind loads, and, among others, snow loads. The latter stat, along with some others, is organized by county for every county in the U.S. The design standard for snow load in Dakota County, Minnesota is 50#/SF.
What does that mean? Well, when you design houses and such, you design them to meet or exceed certain physical forces - in this case, a heap of snow all over the place. Compression forces can be measured in pounds per square foot (#/SF) and related to specially prepared tables of how much different-dimensioned lumber materials over different spans can take - joists, beams, and posts - in this case. These tables for joists and beams are called "span tables", and they define qualified spans for joists and beams of different sizes and under different loads. These tables conventionally stop at 60#/SF load.
We have 50#/SF baked in our snowcake -
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Before we add folks on the deck, say, shoveling. |
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And before we add the deck itself. |
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And Before The Architect cuts off the last 15% of any span table entry and moves up a notch as is our common practice. |
So we had to extrapolate the heck out of the tables with which we chose to work (in this case, Texas Department of Insurance span tables - toughest span tables we've come across).
Essentially, we cut spans and deepened lumber. And this meant that we increased the number of posts here and there, especially for beaming to overcompensate for the largest "tributary load" we could reckon on the deck.
We drafted the .pdf to follow, and sent it in its still incomplete form, to make sure our clients knew what they were getting up against, concerned that this construction was no place for beginners.
Note some of the text detail to get a flavor for that which is standard practice out of this shop.
Note the Detail drawings, especially the two to compensate for a cheap, corner-cutting application of "Rim Boards" in lieu of end and head joists for attaching the deck ledger.
Note particularly the drawings that look like peacock tails - those are our confection borne of near-disastrous frustration siting a lot of footings and posts especially on uneven ground.
Note, too, the extensive Key To Abbreviations. Imagine the clutter of those words and terms spelled out all over the sheet.
We note separately that it was not just snow load that concerned us with this deck's structural design. Close up second was the wind resistance generated by that big, screened porch set away from the house with a 4/12 roof of characteristically large overhangs and soffits and, in lieu of breezy rails, solid walls to 3' over floor level. That's where the frequent triangulation and frequent, full-depth solid blocking came into play.
So here it is, the incomplete draft of worthy deck plans for unworthy clients. There's a lot to learn from these drawings and the text. Take your time. And please, there's no call to get scared.
Wood Deck Designs, Building Deck Plans
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