6"X6" Max span and sources for the Simpson galv post offsets


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Old 02-16-10, 08:19 AM
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6"X6" Max span and sources for the Simpson galv post offsets

Hi all,
In beginning stages of replacing concrete slab for front home entrance with a free-standing wooden deck - approx. dimensions 26'W X 10'D X 8' High. And the first thing I noticed is the very limited selection of 6"X6" posts available at one of the big box stores - only had the 8' length. Everything seems geared towards the use of 4"X4" posts including the galvanized Simpson post offset bases that are inserted in the concrete pedestals when the concrete is poured.

My thought is that the 6"X6" posts would provide sufficient wood for notching ledgers on the deck corner supports for the front and side - 2"X8" boards which would be carriage bolted through the top of the remaining wood on the 6X6.

Anyway, I also thought that the 6"X6" would provide a slightly wider span and hence I'd wind up having to use less of them than an equal number of 4"X4" posts; not to mention they would probably last longer.

The one thing that will be different that we'd like to do, is that on the left side of the deck we would like to incorporate the last 5 ft. of the deck as a cantilevered design, that is with no corner post, the last set of posts would be installed 5 ft from the end of the deck - is that reasonable with the material dimensions for the posts and framing I've indicated?

My questions are:
1. What are general span distances for using 6"X6" posts with 2"X8" framing boards compared to 4"X4" posts;
2. Does anyone know retail/internet stores that handle the 6"X6" Simpson galvanized post bases and associated hardware? I live in the SW Pa area, right in the corner of the state.
3. And if you could provide some general comments on construction such as the number of piers/posts needed with the larger post dimensions that would be appreciated.
4. We want to maximize the user space underneath the deck, what if any, underneath support is required by building code for a 10' deep span?
Thanks,
Greynold99
 
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Old 02-19-10, 01:57 PM
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1) Use of 6x6 versus 4x4 doesn't determine span. The horizontal lumber size determines span. The larger the vertical piece, the more weight it can handle. HOWEVER, using the 6x6 allows you to inlet your rim joists for a neater application. 2x8 southern pine pressure treated can span just under 12'.
2) Most better lumber yards will have a good supply of them. Big box stores have limited supply as I have found out myself.
3) As stated, the span of the posts would be approx every 8 feet for uniformity, and it would be the same for 4x4 or 6x6, but due to your height, 6x6. Your better lumber yard will carry longer sticks of 6x6 pt.
4) If you span the 10' direction, you will only need the exterior support, unless you chose the left coast option of post and beam. You will need to excavate to below your frost line and pour footings in 12" sonotubes over a layer of gravel in the bottom so it can drain, and install Simpson post bases, either set in concrete or drilled after drying for the support required.
Be sure to check with your local authorities as the advice we give here is really generic. Get a permit as you will be changing the footprint of the house and heed their advice.
 
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Old 02-23-10, 07:04 PM
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Exactly what Larry said, so my only thought to add would be to get out of a big box store and go to a LUMBER YARD!! They'll have 6X6 posts in much longer lengths than 8'!
 
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Old 02-24-10, 06:58 AM
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Reply to Chandler and Lefty

Thanks for each of your replies... I've read other postings from each of you and value your opinion as guys actually doing this type of work for a living. Knowing the limitations of even asking, would either of you be able to give me a rough idea of the cost of decks you've built with the earlier dimensions outlined 26' W X 10' D X 8' H pressure treated wooden deck on 6"X6" p.t. posts on concrete sonoform piers with 2"X8" p.t. framing with a simple 40" W stairway coming up from the ground, parallel to the long side with entry to the deck approx. 4'-6' from the right-end .
Again, not looking for anything exact just a rough cost estimate for your area.

Even though I asked for a very rough costing for a wooden deck, I actually like the aluminum deck planks by LockDry or VersaDeck with the rain-guard interlock so you can use the underneath of the deck during rainy weather. I also know that since the deck will not have a roof and with its southern exposure a completely wooden deck will have a shorter life span and will require staining or painting to delay deterioration.

One last question... my main focus right now is that the current concrete slab has only a partial block foundation on the left-side and a 16' by 21' mound of dirt on which right-part of the slab rests on (hence the need to replace as the slab has cracked end where it sits on the dirt mound or unsupported block foundation and has sank about 6" over the years). In order to use the underneath of a new deck we need to remove the dirt mound but will require installation of a 6'-corner retaining wall on the right.
The other complication is our driveway comes up (curves) around the outside of this dirt-mound to the East entrance of the house - so you see the design problems needing addressed?
Any ideas for who best to contact for this preliminary site prep work? I've seen ads of outfits specializing in this type of work, just don't have any names right now.
Thanks,
Greynold99
 
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Old 02-25-10, 01:48 AM
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Well, you are asking two diverse sections of the US to attempt a cost estimate, which is almost impossible, since your profile doesn't say where you are located. Mike is in Washington State and I am in Georgia. We build decks differently in each location. Differences in terrain, substrate, deck materials all play a part of the cost. I have never installed metal decking, so I'll leave that to someone who has. Remember with any product other than wood for decking, the decking will last only as long as your sub structure (which is wood), so invest wisely.
You will need to cut out the existing slab and dig a solid footing below your frost line and pour it, usually in a sonotube to give good vertical support for your posts. You can't install the deck on a slab.
IMO, your grading requirements are more than DIY at this point, but you would have to check locally for someone to help with getting it in shape for your deck.
 
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Old 02-25-10, 08:20 AM
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Reply to Chandler

Chandler,
Yes, I agree with you on the landscaping/retaining wall project - this is just bit beyond my experience and I've started to look for contractors specializing in retaining wall systems after trying to describe situation here. Unfortunately I suspect both projects - deck & retaining wall will probably have to span a couple of years financially to get it all done properly.

My location is SW Pa in the left lower corner of the state. I read Lefty's reply to a later question posted here about cost estimate for a deck roughly similar in dimensions to what I want to do and saw that the aluminum decking will add approximately $2K-$3K to price he estimated. The companies I'm looking at are LockDry (Al) and VersaDeck (Mn). The former even sent samples of their decking-plank product lines and LockDry has installation video if you're able to take a look and let me know what you think. It's an interesting concept but simple - only thing is, looks like you might go through several cases of silicone adhesive, sealing up everything.
Thanks again though,
Greynold99
 
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Old 02-25-10, 12:42 PM
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The aluminum decking may prove to be warmer to the bare foot than wood or composite materials, and if you miss one of those seals and don't find out about it until the deck is installed, you will have a leaky ceiling below. I don't know that I would opt for the decking just for the ability of shedding water. You may want to look into an under deck drainage system. That coupled with either wood or composite may be cheaper than the aluminum decking. Just food for thought.
 
 

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