WashDad Builds His Dream Deck

Parent Cafe
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<p>The old 16x12 second-story cedar deck outside my kitchen was so rotten (more than 25 years old), that TallSon and I demolished it and took it off to the dump two weeks ago. A great use for teenage muscle. Now, I need to get a permit from the county to build a new deck. I’m going to expand it to 20x15, but it’s in the same spot and will pretty much be the old deck, only slightly bigger. </p>

<p>In researching what it takes to get a building permit I finally gave up on the King County Website and called the Dept of Development and Environmental Services (DDES). The nice woman there directed me to <a href=“http://apps01.metrokc.gov/www6/ddes/scripts/formsDetail.cfm?ListForm=1#Residential%20-%20Addition/Remodels,%20Decks,%20Garages,%20or%20Sheds[/url]”>http://apps01.metrokc.gov/www6/ddes/scripts/formsDetail.cfm?ListForm=1#Residential%20-%20Addition/Remodels,%20Decks,%20Garages,%20or%20Sheds&lt;/a&gt; and helpfully pointed out that I don’t need to pay attention to Bulletins 9a or 12. This leaves only 14 other forms and bulletins that I have to abide by and/or fill out to build a wooden deck structure. In part, I have to have a septic plan, certify that it is not an environmentally sensitive part of my backyard, and there is plenty of water available. My deck, of course, has no water supply, toilets, sinks, and – since it is replacing one that has been there nearly 30 years – will have minimal environmental impact. I figure that filling out these forms will take longer than actually building the deck itself.</p>

<p>I asked if there was a publication that outlined to technical requirements for a code-conforming deck, since I’ve seen a bunch of other counties on the Internet that provide this helpful information, and was told that the International Residential Building Code provides all the information I need. I went to the library to read this document and discovered that it is hundreds of pages long and contains all the information I would need to build a 3-story house nearly anywhere in the country. All I really wanted to know is if 2x8 joists are big enough for a 7-foot span with joists on 16-inch centers. Even after reading several sections of the IRBC I’m not sure. I did find the deck building guide for Johnson County, Kansas, online though, so I think I’m good. This is a terrific document, and you can find it at <a href=“Building Codes | Johnson County Kansas”>Building Codes | Johnson County Kansas. It’s at least 100 times more helpful than anything from my own county.</p>

<p>The nearby city of Redmond, by comparison, has a 2-page “Guide to Building Decks in Redmond.” I don’t love King County so much.</p>

<p>Oh, and she couldn’t tell me how much it costs to get a deck permit. A builder friend told me to count on $400-600. Not for the deck – just for the permit.</p>

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<p>oh dear… this is why you replace the supports first, then the decking, so you can call it repairs instead of a new deck…</p>

<p>Our deck, just a few miles away from yours, used 2x8 joists on 8 foot centers, so you should be fine.</p>

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<p>dmd77 said:</p>

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<p>No, this is why you hire someone to build your deck and sweat out all the other stuff for you.</p>

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<p>2 x 8s are not even listed as floor joists in my AIA Grpahic Standards. Normally, 2 x 10 would be the minimum for floor joists carrying large live loads (ie lots of people on a deck). </p>

<p>2 x 10 at 16" centers can span a max distance of 10-4 for an 80# live load. </p>

<p>3 x 8 at 16" centers can span 10-4 for an 80# live load.</p>

<p>Don’t you have a friend who is a structural engineer?</p>

<p>PM Mathmom to see if she has the American Structural guides handy. She might be able to give a better opinion on the 7’ span.</p>

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<p>Using milk jugs or dead cellulose? </p>

<p>Our beach deck is 33? and parts need to be replaced-I am dreading this and I imagine its going to be cedar again. but first got to figure out dry rot around Mom’s house windows.</p>

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<p>We just finished up a similar project, so I am sending positive thoughts your way!</p>

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<p>Cheers, joists on a deck don’t span much of a distance compared to a house deck. With a 6-foot span between supporting beams you might use joists as small as a 2x6. The live load standard for decks is usually 40-50 psf, and the dead load is 10 psf. Table 2308.8(2) from the IBC shows #2 2x6 Hem-Fir as spanning up to 10 feet with a 40 psf live load. My new deck as currently designed is going to have 6-foot spans and use 2x8 joists for a 51 psf rating. I have no idea if this going to make the King County building people happy until I pay to have them review the plans. Unlike other jurisdictions, they don’t publish deck standards. (I took my scantlings – that’s what it would be called in boats, don’t know the house term – from the Johnson County deck guide and then fed them through an online deck design tool which calculated the 51 psf figure. I assume that if they pass code review I got them right.)</p>

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<p>Didn’t know what size deck it was --or what the purpose was.</p>

<p>Building depts don’t normally check structural calculations–but they often require a registered architect or structural engineer to sign off on the calcs.</p>

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<p>Cheers, I even get that. It’s just that decks are such cookie-cutter construction that a simple rectangular design can be done off a recipe. Getting a PE signature would be a significant part of the construction.</p>

<p>Since the old deck lasted nearly 30 years with a ledger board held to the house with 18 16d nails driven through the cedar siding, anything new is going to be a big upgrade. When I found out that it was held up on one side by a handful of nails I wasn’t amused. Modern codes would call for removing the siding and then bolting the ledger board to the second floor rim joist with two 1/2-inch stainless or HD galvanized bolts or lag screws every 16 inches. Decks nailed into houses fall down and hurt people.</p>

<p>It’s not that I’m opposed to getting plans reviewed and pulling a permit. I’m in favor of things that don’t fall down. I guess I was just sharing a “what are they thinking” moment about the County building department. I can tell from other websites that not all building departments are this opaque. We have nice trees, though.</p>

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<p>Ahhhhh…It’s all in the liability.</p>

<p>Trust me, when government takes rensponsibility for construction, things get even murkier.</p>

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<p>Mathmom checking in. The easiest way to figure out the spacing for a deck is to go to the library and check out a “How to” book about decks. Deck spans vary a bit by wood species, but 2x8’s should be able to span at least 10 feet even if you use the least strong ones (western pine, cedar, redwood, spruce). The books generally have a pretty big safety factor built in since they don’t know load requirements of your area. Here we have a snow load of 45 psf, I add 10 psf dead load. Don’t know what your requirements are. On the occasions I take a deck to my engineer (for extra long spans) he also has to look at uplift at the house edge and snow drifts.</p>

<p>There are also some good online sources. My biggest concern is that your new footings are big enough. This article explains how to calculate the right size: <a href=“http://www.nwbuildnet.com/articles/deck_loads.html[/url]”>http://www.nwbuildnet.com/articles/deck_loads.html&lt;/a&gt; Fairfax county, VA has a very nice pdf of “Typical Deck Details” and The Colorado Chapter of the International Code Council also has a good pdf called “Single Family Residential Uncovered Decks and Porches”. In our state all decks need architectural drawings. Some towns require much more. I just lost a job because that town requires a complete survey of the property with elevations. That would have set them back $1500, not counting my fees. So they are going to continue using their illegal deck which has no foundations at all. Ugh.</p>

<p>WashDad, I’m in the process of legalizing a deck addition where the contractors extended a deck by 12 feet by screwing the new joists to the old joists with two screws, using a strap designed to hold posts vertical. Actually they had three screws, but since the third one went between the old and new joists it hardly counts. And that’s only one of the many many screw-ups with this particular deck addition.</p>