Porch/Deck Help

HunterdonPaul · Aug 2, 2003

Hi everyone -

We are in the middle of putting a 42' x 10' covered porch on the back side of our home. The contracter that is doing it seems to know what he is doing (I ask a ton of questions). The one potential problem I see is that the floor joists are 16" on center. We are putting mahoganey flooring on it - I think it is around 3/8" or 1/2" thick (have to check). It seems however that although this wood is very strong, that it may not be thick enough for the distance of the joists. I don't want the floor to bow when given a point load. Its true that the load won't be that much, just people, chairs and a table or so.

Can anyone give their opinion as to if I am making a mistake? If I am, can you use subflooring (e.g. 3/8" exterior plywood) to strengthen the floor? Would adding the plywood create any problems?

Thanks for your help.

Paul

CountryBoy · Aug 3, 2003

16" span is good,but I would want at least a 1/2 " thickness if not more.Also tongue and groove is a plus,makes it a lot stronger TREX My uncle and I built a massive wrap around porch on my has last winter and for a decking board he suggested TREX it is wonderful.No splinters will not rot.After seeing a sample of the TREX it did not take long for me to make up my mind what I wanted.

Why would you need an exterior sheeting for the subfloor? If the porch has a roof over it,it should not get wet. The subfloor is where I would recommend the tongue and groove.

Slamfire · Aug 3, 2003

I've walked on many a subfloor made of 1X's, 3/4 inch over 16" centers and couldn't feel any give. It would be a little springy on 2' centers though. But then so would 1/2 inch plywood.

CountryBoy · Aug 3, 2003

Slam,
I would consider using a ring nail
and maybe even putting a glue on the centers in addition.I hate to put a floor down and have nails come loose and have a squeak in the floor.

ejb · Aug 3, 2003

On my porch I am just finishing up, I built it with 12" on center joists, instead of 16oc, and used full 1" thick mahogany boards. I should think on yours you should either go 12" on center, or use a thicker floor board if you are concerned about it...much cheaper to built it stronger to begin with than to fix it (or be unhappy with it) down the road.

On your 42' porch, going 12" on center instead of 16 only means using about 10 extra 2x joists, so maybe another $100 dollars or so in materials, plus labor.

RichC · Aug 3, 2003

I'm no general contractor, but I've repaired a lot of stuff and built stuff. I would strongly suggest the use of plywood underlayment for strength. Today's "mahogany" probably isn't old growth honduran that will be used.
Furthermore, it only takes a one time accident to damage the floor - usually its an event that no really anticipated. Then, when you go to repair it, you'll find the color dosen't match (unless you paint it) due to aging. Put in the underlayment.

Mark_in_NH · Aug 3, 2003

Heres my 2 cents worth.
In 25 years of being in and around the building trades, I can't honestly recall having ever seen a 3/8 flooring installed without a SUBFLOOR. Does this 3/8 Mahogany flooring come like the typical hardwood flooring. ie. "Random Length, Tounge & Groove" ?
If it does, Unless your planning to cut and break all your flooring joints on the joists, your going to need Something underneath to support and secure the butt joints.
I would most definatly install a subfloor.
The Mahogany decking that is quite commonly used here in NH is considered 1x4 and goes down just like standard 2x6 or the more comon 5/4 x 6. It does not require a Subfloor, but then again it is a lot thicker and stronger then 3/8 or even 1/2".

JohnMiller3 · Aug 3, 2003

<font color="blue">( mahoganey flooring on it - I think it is around 3/8" or 1/2" thick )</font>

I'd have a minimum 1 1/4" total floor on 16" o/c joists even on a porch area...

Using your min. 1/2" mahogany and 3/4" t/g plywood as a sub-floor will give you that "solid feel" that you're looking for... /forums/images/graemlins/smile.gif

Egon · Aug 3, 2003

The 1/2 inch probably would not meet code.

Egon

JohnMiller3 · Aug 3, 2003

<font color="blue">( I don't want the floor to bow when given a point load. )</font>

For the "most" desirable stiffness of a floor, you would increase the depth of your joists, more so than just spacing the joists closer together...

Rule of thumb for joist depth would be span / 16... so in your case I would use 2 x 8 joists (not 2 x 6- though it would meet code for up to 10' span) (or overkill 2 x 10 for extreme stiffness)... and by using a 3/4" ply sub-floor, you can eliminate any cross bridging underneath the deck... and being an "outside" porch, I'll assume 3/4" finish floor minimum (not 1/2" as previously listed) ... /forums/images/graemlins/wink.gif

HunterdonPaul · Aug 3, 2003

I just received some new information.

The flooring will actually be 1 1/4" Mahogoney, not 1/2" as I originally had thought. I was confused a bit based on previous conversations that I had with the contractor. Also the joists are just under 10' long and are made from 2 x 10" s. Given this, should I have any problems?

Also should there be any sort of wood that prevents the joists from twisting such that you might see in a basement (lookin up)? In my basement there are two 1 x 4" which are sort of criss crossed perhaps to keep the joists from twisting.

Just wondering...

And BTW thanks for the great advice as always. I am always at wits end when it comes to handing $$$ to contractors. I have some really good experiences and some not that good.

Thanks,
Paul

Egon · Aug 3, 2003

x bracing never hurts. It's what your local codes demand that must be met.

The new dimensions sound a whole lot better.

Egon

Slamfire · Aug 3, 2003

CB, The floor on my porch is 2x6 treated southern pine. We used 2x6s for joists on 2' centers. The floor feels real stiff when people walk on it. When my chiuahua trots across the floor though, the whole porch vibrates like an earthquake was happening. /forums/images/graemlins/crazy.gif

Yes the x braces, will stiffen up the spacing between the joists, nail the tops before putting down the flooring, and the bottoms afterwards. /forums/images/graemlins/wink.gif

ejb · Aug 3, 2003

>>The flooring will actually be 1 1/4" Mahogoney, not 1/2" as I originally had thought. I was confused a bit based on previous conversations that I had with the contractor. Also the joists are just under 10' long and are made from 2 x 10" s. Given this, should I have any problems?

No you won't. Sounds like a well built porch. Only improvement you *could* make would be 12oc instead of 16oc..maybe overkill, but not a lot of extra cost. With an 10' span my guess is you could have got by with something smaller, like a 2x8, but I definetely would have picked a 2x10 too. I also braced/blocked each joist twice roughly at the 1/3 and 2/3's point, whereas 1 blocking would be sufficient. (again, about $20 extra materials)

DieselD · Aug 6, 2003

I have the same size porch made on 16oc with 1 1/4 X 3 T&G mahogany floor down for 3 years now. Its built like a tractor.
You don't need subflooring, this will make it warp. (wont dry evenly when it gets wet). Just make sure you seal the bottom of the boards before you put the down & use stainless nails.
even though you don't see them, they'll still be there in 50 years and so will your floor.
Danny

HunterdonPaul · Sep 19, 2003

Thanks for everyone's help. You guys are the greatest. The porch is just about done (5/6 weeks late and $4000 over budget) and it looks great.

Paul

tonyw · Sep 19, 2003

Countryboy, We built a house in 2000 and installed Trex on both porches. We are glad we did; it doesn't bow, swell, split, etc. I was satisfied with the color it weathered to... a light gray, but we decided to paint it to better match our house. It takes paint very well and has been really easy to clean. I sure am glad we didn't listen to the contractor and use concrete, Trex is a lot more forgiving when you have small kids.

ejb · Sep 19, 2003

>>The porch is just about done (5/6 weeks late and $4000 over budget) and it looks great.

Yikes!...isn't that the way it always is, especially when you hire out...thats why I do all the work myself. (I still end up over budget, but at least I work for free /forums/images/graemlins/smile.gif )

Junkman · Sep 21, 2003

My contractor started the porch 20 years ago and is just getting around to finishing it now...... started work again in the spring and took the summer off.... more fun to play on the tractor than pound nails...... The wife has been nagging the contractor for about 30 years now and the more she nags him the slower he works....... You might have guess by now that I am the contractor. Don't ever believe in rushing the job...... Only bad thing is that now I have to replace the decking on the original part because it doesn't match the new material that is now available. Do it right the first time and it will last a lifetime......