12x16 screen porch addition

[secordpd]

Hi everyone, been reading here for a few months - this site definitely satisfies my 'info junkie' needs.... If I could design my dream 'building info' site this would be it   ! Even though I haven't posted I feel like I know you all, and am happy to join this great community and hope to contribute also.

Well, on with my project.  I'm taking down a 12x16 deck I built hastily 11 years ago. The only pt wood was the posts. There is some rot, but not as much as you would think   ...  The reason it's coming down is because I want a screened porch and it is not beefy enough.  Also, it was built on 12x12 cement pads, and in all this time it never shifted from frost heaves.  The soil is pretty much all sand.  But decided to put cement sonar tubes in since this will be quite a bit more load bearing.

My question is how many piers do I need for 16 ft. I see some here use 4 piers for 16ft, but would like to use 3.  It is going to be free standing, I believe the snow load here is 60. Will call building code office tomorrow for exact #, but pretty sure that is it).  I was planning on doing a post and beam type structure (screened in) then rafters with collar-ties for the roof (metal).

Also, do you think I could I get away with 2 2x8x16 for beams or do I need 3.  Or would it make more sense to go with 2 2x10x16.  Also can I use 2x6x12 for joists or do I need to step up to 2x8x12.  I'm using rough sawn 1x5 (which is actually 1x5) planks for floor. This is because I have them already.  

Any help would be greatly appreciated. I know this isn't a actual house or building, but maybe it will help someone down the road who would like to add a screen porch to their home.   This is also my practice run, hope to build a guest cottage next year.  Already live here, w/ water/sewer etc. Have building permit, to 'screen in my deck', just didn't realize I was going to have to rebuild until I started reading all the good info here.  We have International building code here.  Code officer is good guy, just want things done safe. Thanx in advance.

Helen~`~`~`   I live in the Seacoast area of NH.

[alcowboy]

I am building something similar myself. I am currently working on a free-standing 10x15 screen room. For mine, I used 4x4 posts cemented into the ground with 3 posts along each 15 foot side. There is also 2x6 boards bolted to the outside of each post to create the "rim joist" for the flooring. I also put a double 2x6 beam down the center running the length of the 15 foot of the building. For support I would suggest at least two support posts under this. I have and I my floor is pretty sturdy.  I then staggered 2x6 floor joists running the 10 foot length (appx 5 foot each) 16" on center. The roof has been done on a 3/12 done on appx 24" on center using 2x4.

Guys, I think by doing this I have gotten some good working knowledge on how to build me a decent 20x30 home. Any comments welcome. Send privately as not to hijack this thread.

[secordpd]

Here is some pics, of the way it was built, post is from ground up.  Used the posts to hang plants.  After listening to the wise people here I want to build pier and beam foundation.  I was talking to a contractor that builds sunroom additions and he said the snow load here is 60.  He said I need to use 2x8 for rafters.  Does this sound right?

[secordpd]

OK  can I start over.  I read my first post and It sounded like I was babbling


Question #1- How many piers do I need for 16 ft.beam?

I see some here use 4 piers for 16ft, but would like to use 3.  It is going to be free standing, I believe the snow load here is 60.  I was planning on doing a post and beam type structure (screened in) then rafters with collar-ties for the roof (metal)

Question #2 - Do you think I could I get away with 2 2x8x16 for beams or do I need 3.  

Or would it make more sense to go with 2 2x10x16.  

Question #3  -  Can I use 2x6x12 for joists or do I need to step up to 2x8x12.  

Any suggestions would be greatly appreciated. Thanx Helen~`~`~`

[glenn kangiser]

Hi Helen --I think it is great the way you have jumped right in here and got on with posting.  to the forum.

Sorry I'm not more help lately but I have a big contract going right now that takes most of my time.  Just time for a comment or two  and to kill the spammers.

There are lots of great helpful people here though.

You can edit your previous posts also if you want to .  Glad you are here.

[MountainDon]

#1    The number of piers depends partly on the ability of the soil to bear the loads. To use one of John's plans as an example it calls for 4x4 piers on 4 foot centers. They support a 4x8 beam (built up from 2-2x8's is okay).  Note 4 foot spacing on a 16' length means 5 piers per 16 feet. That may seem obvious to you but someone here once made incorrect mental calculations on that. 4 piers per 16 ft would mean 5'4" approx spacing.

It is my feeling, I'm not an engineer, that to use three piers with a 4x8 beam spanning 16 feet, would not be advised, even if the ground could safely support the load. It's always better to err on the side of caution.

#2   You can use two beams (no central beam) if you size the floor joists correctly. There is a joist and rafter calculator available online at  http://www.awc.org/calculators/span/calc/timbercalcstyle.asp.

#3   Using the above calculator you will see that 2x6 floor joists will not span the 12 foot width, but could be used with a central beam. 2x8 floor joists (#2 hem-fir, 16" OC) would just barely make the cut. That's using a floor load of 40 psf. Maybe you could get away with calculating for a lower load since it's a porch, but I'm conservative so I wouldn't.

You can play around with different size joists and three beams vs two. You may find a trade off where the two beams with 2x10 floor joists would be better as there are fewer holes to dig. Or maybe the cost would be less with smaller joists and more piers.     I ran lots of numbers in the planning stages of our cabin.

[John Raabe]

Do you have any structural plans to work with or modify? You design a structure from the roof down to trace the loads to ground and see what is carrying what. That can sometimes be interesting with an addition.

This forum can help a lot with specific questions but you should start with a safe design that ties in well with the existing structure and meets local snow and wind loads. Then we can be more help.

[secordpd]

Thanx for the welcome Glenn, I know there are helpful people here and everyone seems wonderful.

John and Don, I was planning on building similar to 'Modern Manshed'.  I absolutely have no problem using more piers and beefier lumber.  I guess I'll play around with the numbers. 

What do you think of the 'Modern Manshed'.  It looks like 4 piers per 16 ft, beams built up 2x10x16.  Then 2x8x12 for joists. 

[glenn kangiser]

Helen, you might check out this plan John has - really inexpensive and may save a lot of trial and error.

http://www.jshow.com/y2k/listings/29.html

That would get you the basic support info then you could modify or attach it from there as needed.  It has a shed roof design also.

Just an idea.

[secordpd]

Thanx Glenn, I'll think about the plans.

[secordpd]

Any one ever see anything like this before? Its called Pin Foundation.  They have videos, it's pretty cool, a little expensive, they are located in Gig Harbor, WA so shipping would not be a problem for people out there, but anywhere else would be crazy I imagine.





I'd like to try out on my screen porch, but to much money

[soomb]

Like you I have the site bookmarked, and I think there was a discussion in the General Forum, but I know of no one who has used them.
Update:
http://countryplans.com/smf/index.php?topic=4313.0

http://countryplans.com/smf/index.php?topic=6512.20

Mountain Don has links on the first page of this post (topic=6512.20) to other mentions.

[secordpd]

Does anyone know where to buy the type of piers that Don P suggested and that mountain Don used

posts they should be treated to .60 pcf or better, foundation grade is the best if available. They specify no heartwood in that grade, heartwood is impervious to treatment, so foundation grade is treated to the core.

Been looking on internet for a while and can't find a place.  HD has some 40% but not 60.

Do local lumber yards carry them, or maybe someplace that sell docks?

[poppy]

FWIW, I have all of my pins driven for "Poppy's Pin Pier Plan".  For those new here, I looked into the Pin Foundation concept and liked the idea but did not like the cost.

I designed my own system and used 1.5" sch. 40 galv. pipe.  The original plan was to cap it off with 12" dia. concrete piers (Sonotubes), but that didn't give me enough clearance around the top of the pipes, so I'm using 12" square forms for the concrete.

I have the forms complete, and am now bending rebar to tie the whole system together. Should be pouring (actually placing) concrete (not cement) in the next couple of weeks.

Since I drove all the pins with a sledge hammer, the work was just as hard as digging holes, but I had a lot of fun and there will be no other cabin in these parts with such a unique foundation.

I have been photo documenting the progress and still plan to start a build thread, as soon as I conquer Photobucket.

[secordpd]

Cool Poppy, can;t wait to see your 'inventiveness'  I guess that's why I love this site, everyone seems so creative....  Let's see some pics soon Poppy and 

Photo bucket is very simple if you just follow Mountain Dons instructions, he really is a great instructor!!

[secordpd]

Well, I've been wanting to teach myself sketch-up (lots of good tutorials on youtube-aidranchopa was the best I thought) and I'm glad I did.  It really helped visualize.  So here goes



I'll try this, if it goes ok I'll post the others. 

This is an addition to a older mobil home.  I'm going to be building this free standing, because the mobil home is not on frost depth piers.  I'm hoping to get experience with this before I build my house next year, and then rent this out.

[secordpd]

Well, that one came out pretty good so here are the other views. Any and all comments welcome.....

[John Raabe]

It looks like the gable end addition will be self-supporting without much if any load transfer from the mobile. That makes that part simple. If the mud room extension porch is also a new addition then it will be adding 1/2 its load to the roof and floor system of the mobile. You will want to spread this load out as much as possible so as to not overload the headers and foundation beams. What does the mobile have for a foundation?

[secordpd]

The MH foundation is just sitting on 16x16 cement pads.  The mudroom/side porch will also be free standing..  This is sandy soil, MH has never moved from frost heaves.  The deck I'm replacing never moved and that was on pads, but side porch which is also being replaced did heave a little, esp. when there wasn't a lot of snow to cover and insulate the ground.  (will do screen porch first, then side porch/mud room after).

I'm planing on 4 piers per beam for screen porch.  It is 18 feet long.  I was going to use a 12" auger, down 4', then dig a wider footing similar to what mountain Don did. Do you think I can get away with 8" sonar tubes, or should I go with larger ones.  I am going to rent a cement mixer, but handling 30 -60lb bags for 8 tubes, plus what I need for the footings makes me ache already...

Any advise would be greatly appreciated.. thanx  H

[John Raabe]

Well, that will be a big step up from the MH foundation. 8" diameter tubes should provide plenty of bearing. Is frost depth at 4'?

You may have seen my article on the post and pier foundation here: http://countryplans.com/foundation/index.html

[secordpd]

I thought the frost depth was 42" but the code officer said 4'... I asked if he wanted me to call when they were dug to inspect and he said no, but I'm renting an auger like manshed so whats a couple extra inches...Will allow footing to be bigger...deeper..

                    IF IT EVER STOPS FRIGGING RAINING

It looks like you guys in the Pacific Northwest is getting our weather, and we are getting yours  



Yes John I've seen your post and pier foundation article.  Very informative.

[secordpd]

I'm a little confused and wonder if anyone can help clear up this question

John states in his "building the low cost get away cabin'

With both beams in place the 2x6 floor joist are laid out every 16 inches. Notice that the joists cantilever over either end of the beam. This actually makes the floor stronger.

I can understand how that would make the joists more rigid,  but I some what agree with Beavers

I've read on this website a few times that it is better to have your walls sitting directly over the piers.

.

The walls sitting over the piers just seems to me, to make more sense (but what do I know )

Am I on the wrong track.... could anyone elaborate?

[John Raabe]

Cantilevered joists with walls out 2' will shorten the span of the joists and turn it from a simple span to a compound beam calculation with a stiffening effect on the longer span. I do this only in the Little House plans to get the posts and beams back under the house to simplify skirting. This is more complex loading and should not be done on anything but small buildings without a second floor load. In all my other plans the walls are over the beams and carry the loads straight down.

Note: On a floor system you can normally cantilever the depth of the joist without changing the load path to the foundation.

If you think you may add onto a Little House building later put the beams under the walls.

[secordpd]

Thanx John, that cleared that question up quite nicely

[secordpd]

Well, I dug my holes, and just like I thought I hit water 3'6"...

The building inspector suggested dumping dry bags of quikrete for footings. 

I'm just curious about what others think about that?   I was wondering if it would be better to do separate pours for footing and pier or do as Glenn suggested on another thread where you lift the tube up 6 or 8 inchs then let the cement flow out from the bottom like a bigfoot form.  Also what about the rebar, could I just stick a few crisscrossed into the footing, sticking up thru the tube?

Or dump the dry mix in, lay down an x of rebar into the footing, then:
1) let it dry, then pour the pier or;
2) pour the pier as soon as i get the dry mix worked into the water for the footing?

I did dig the bottom out around the edges should be 14 or 15 inches wide

Any advice would be greatly appreciated



pics of fish nests in my pond, the fish just stays there keeping the nest free of debris..