Porch/Deck Help

[HunterdonPaul]

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]

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]

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]

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]

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]

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]

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]

<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]

The 1/2 inch probably would not meet code.

Egon

 

[JohnMiller3]

<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