Building a porch

[4x4ford]

Building a new deck at my sister in laws will be 12x24 one side supported by the house bolted to the concrete wall of the basement the other on 6x6 posts. Starts at about 8 ft elevation on one end and ends at about 3 ft on the other. Was planning on using 2x12 for outside framing with 2x8 joists and 5/4 decking. Longest span will be about 20ft as the stairs are set in. Was planning to use one post in the center with two 2x12 spanning the length do I need to use more posts and set them about every 5 ft or will the one at 10ft be enough. Current porch is supported by 4x4 and only uses 2x8 for joists and framing

 

[skyking1]

sketch please

 

[4x4ford]

Hopefully this helps posts will be set in concrete for time being as eventual plans are to dig out and build a patio underneath in about 5 yrs when money allows

 

[Tinkerer]

My reply isn't about the build method.
But, if you are going to spend a huge amount of money for treated lumber now why not spend that money on the patio now ?
The maintenance (repeated staining) is time consuming and expensive . I had re-stain mine every 3 or 4 years to keep it looking nice.
I removed my wood deck and replaced it with a red brick paver patio. I wish I had never wasted my money on that dam wood deck.
You would be surprised at the cost difference in the two.
I can post some photos if you would care to see them.

 

[skyking1]

thanks for sketch. Are you planning to sandwich the 6x6 between the 2x12's?

 

[Old Doug]

This farm house of moms is about 20years old it has 3 decks /porches and 2 were recycled they all need to be replaced.

 

[673moto]

I’d run an actual beam and cantilever the joists past a couple feet...would allow for larger post spacing. ..but that might interfere with the plan for below as the posts would be around 9-10’ out from house.
from this chart I’d say post every 6’ to be safe

 

[4x4ford]

The deck will be staying when the patio is done as there is French doors off the dining room that open to the deck on the 8ft tall end. The current deck is 10 feet. If I sandwich the 6x6 posts with 2x12s at ten feet then run the joists out to 12 would that be enough to support the 20ft with only one post in the center

 

[673moto]

No, according to chart, double 2x12’s at 10’ out need a post every 7’6”... and I believe that doubled 2x12 (correctly nailed/joined) will span more than 2x12s on either side of a 6by post.

edit: according to chart you could triple 2x12s to get that 10’ span. Please use appropriate hardware to connect to top of 6x6 posts tho

2nd edit: please verify with local building codes... as this is just a random chart I pulled off a quick google search

 

[skyking1]

yeah I would look at that, and do 3 spaces. Two intermediate posts.
I would also put flashing or tar paper over every lower wood member, and be sure to have decent spaces between deck boards too. That way the moisture does not stay there and also the accumulated dirt can be cleaned out. It will last a long time with those precautions.

 

[4x4ford]

This is what I am replacing. 2x12s will be bolted to 6x6s with 1/2 inch galvanized bolts will do 4 posts just to be safe so will have one every 5ft on backside will only have to dig one extra hole no biggie will do a bolted splice where 2x12s will meet in the middle

 

[fastline]

As some of this is down my lane, I will add a few general comments.

1. I like to hover around L/240 deflections (stiffness). In most lumber construction cases, deflection drives the design. It might be 'safe' but a bouncy floor is not pleasant.
2. I have no idea as to your area soil or wind design parameters, but it is total ignorance to build anything without uplift performance in the design. A deck can get some nasty uplift in high wind. Uplift provisions can be done easily with a galvanized bolt or two about 6-8" up from the bottom of columns if you are going to concrete them in. Then dig slight outshoots in the bore hole so concrete cannot come straight out. Takes 5min. For a mental picture just imagine pulling up a perfect cylinder out of the dirt, vs a cone shape. You don't need to go nuts.
3. Off the cuff, 3ft column depth is likely in the ballpark to achieve moment resistance in the ground.
4. Again, I don't know your soil, but usually about 1500psf for bearing (down force) is reasonable for columns. Absolutely never just put support columns in the ground without a footing! You need to add up all loads and consider practicality. Lets say your deck is 10x12, and we want 40psf live (people on it) and 10psf dead (weight of the deck). That is 120sf*50psf. That is 6000lbs. half of that is supported by the home, so now 3000lbs to the front columns. If you have two, that is 1500lbs on each one. If soil capacity is 1500psf, you need 1sf of footing to support that properly.

As for the footing, it can be as simple as putting a little quickcrete in the bottom, but I like to use precast cookies. Can get them anywhere. 3" thick will probably do here.

Lost count how many decks I have seen where those columns are literally sitting on concrete piers just sitting on the dirt! Yep, $10,000 deck with no footings or uplift protection. Also a guarantee to see settling or frost heave in other parts of the globe.

5. Oh, I forgot. Use hangers! AND, NEVER use deck screws to attach them! Use proper hanger screws or nails. Does not cost much.

 

[4x4ford]

Yes will be using hangers and appropriate nails planning to put posts 3 ft in the ground with concrete and will put a footer down also was thinking of using a piece of rebar through the post to make sure it does just pull up out the concrete

 

[suladas]

You could get away with a 20' span on the beam but it really comes down to how big of a deal the posts are underneath, 10' is likely more cost effective.

As others have said wood decks suck. Staining constantly to look nice. It's not cheap but duradeck or something like it is so much nicer. Also if you plan to dig out below one day and have a deck there you want the above deck to be waterproof.

With some of these things there is a difference between what makes sense and what the city wants. It wasn't long ago a 8"x10' concrete pile was sufficient, then 12'x12" now the minimum to be considered a pile here is 12"x16', it's just insane.

 

[Tinkerer]

A picture is worth a thousand words !
I can see what what you meant about adding a patio underneath it.

 

[Welder Dave]

Yes will be using hangers and appropriate nails planning to put posts 3 ft in the ground with concrete and will put a footer down also was thinking of using a piece of rebar through the post to make sure it does just pull up out the concrete

Don't put concrete around the posts. It will rot them. Concrete cookies or Quickrete in the bottom is good. Best to put washed rock around the posts so water doesn't soak into posts and drains. Need to know how far down the frost goes in your area to determine depth of posts. Have to be below frost line. Many fence's and older pole sheds have failed because the posts were cemented in. Use pressure treated posts designed for in ground use not standard pressure treated for above ground use. I had a pole shed built a few years ago. It used 4 laminated 2x6's nailed and glued for the posts. The bottom 8ft. of the posts were pressure treated for in ground use. The upper portion is standard lumber but is inside protected from the weather. Use pressure treated for exposed posts. The holes for the posts were 24in. dia. so lots of room for drainage with the washed rock. I think if you're going to do something like this you should do it right the 1st time. Several people told me I shouldn't put up a pole shed because the posts will rot. I built the area up for drainage and the posts weren't cemented in. After about 7 years of harsh Alberta weather, the posts are like brand new. I'm confident the posts will last 100 years plus.

 

[digger doug]

www.eng-tips.com is the place to get your answer.

 

[cuttin edge]

seems everyone around here now is going with screw piles instead of concrete. Works out to be around the same cost, but you don't have to do any digging. Plus as soon as they are installed, you can start building.

 

[Tinkerer]

In my area footers are required under posts and poles.
I suppose there are calculators for determineing the size.

 

[4x4ford]

The plans are within the next five years to dig out from under the porch and a concrete slab will be poured with the posts anchored to the slab