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T&G porch flooring

pizza's picture

Hi. I'm rebuilding an old porch that has tongue and groove decking that has started to rot due to plastic sheets that were placed over top of them. I will be replacing the tongue and groove with new T & G yellow pine decking. The porch is bounded on three sides by brick walls and it is not a covered porch. My question is, "How much of a gap should I leave between the new decking and the brick walls to allow for expansion?" Also, I must make this new porch so that no rain leaks below it since we use the space underneath to store things. I will be soaking the ends in sealer/waterproofing prior to priming and painting with a good porch floor paint. I appreicate any tips or techniques in doing this job. Oh yeah, I do not want to use pressure treated wood. The old decking (most likely more than 60 years old) would have lasted if not for that plastic that was laid down on top of it. Also, I don't want too much buckling to occur, any suggestions on that issue too would be appreciated.


(post #92979, reply #1 of 19)

I don't think expansion should be your main concern here. Your main concern should be to keep water away from the new decking. The best way to do this is to run continuous flashing around the perimeter of the 3 walls, and then space your ledger off the flashing about a half of an inch by placing 4 stainless steel washers between the ledger and the side of the house on every lag. You can then close the gap down a little by running your decking slightly over the ledger leaving a 3/8 of an inch gap or so between the house and the decking.

I recently did my front porch over with T&G Douglas fir, yellow pine has a greater tendency to warp so just take your time and get the boards in tight before you nail them. Here are a few things I did, that you may want to try.

  1. backprime all the flooring before installing

  2. If you use PT lumber for the framing like I did, order it a few weeks ahead of time and let it air dry for a few weeks. You don't want to put your decking down and then watch it all separate as the framing lumber dries out! With decks this isn't as much of an issue but with T&G you want it to stay as tight as possible, although a few boards will eventually separate no matter how careful you are.

  3. I found it beneficial, (although it took a little longer) to hang my joists by cutting each one a hair too long. Then I clamped a joist hanger onto the end with a small one handed clamp. This allowed me to place the joist in between the two beams. Because the joists were a hair to long friction held them in place. I could then carefully tap each one into position with a hammer and screw it in place exactly level with the beams. Then I would remove the clamp, move to the other end of the joist and clamp another joist hanger on and repeat the process. This will make it easier to keep the joist exactly level with the top of the beams, which is important for t&g flooring. The reason I use screws is because I think it makes a stronger connection. Also I don't have to worry about an errant hammer strike knocking the joist hanger out of alignment. And if you do screw one up it's a lot easier to remove and adjust.

  4. I also primed the tongues of each board as I went along nailing them in place. (This might be overkill, but it was for my own house and I had nothing else to do!)

I hope this helps! I tried to find a few pics of the process I took while doing my porch but my picture collection is a mess! If I can find them later I will post them for you. Good luck!

I don't understand! I cut it twice and it's still too short!

I don't understand! I cut it twice and it's still too short!

(post #92979, reply #2 of 19)

If you will use the more traditional Fir for this, you will find it much more stable, strong, and rot-resistant. Then expansion will be relatively small. I would feel comfortable with a half inch. SYP might want an inch.

Seal ALL surfaces before using either wood. ALL six sides and down the grooves.

After it dries, then install it.

You cannot make it 100% dry underneath without expensice roof detailing

But what I have been doing in circumstances like this, is to use Gorilla Glue in the grooves when installing. It expands to fill and glue the pieces together and is water-resistant. It seems to reduce the amt of water that can run between the grooves considerably.

Traditionally T&G was used where there was a porch roof covering and square edge used for open decks. When rain is allowed to fall and remain directly on the deck, it gets trapped in the grooves and stays there longer to cause the rot. Square edge lets it drain and dry.

You are trying to make a roof out of a deck, which is a compromise in function and longevity, You can see the results of one atempt with plastic in the rot.


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #92979, reply #3 of 19)

Thanks for the advice, I appreciate you guys taking the time to reply. Looks like I'll go with the Doug fir then , it sounds like I'm better off with that. This brings up a question about the priming of the deck pieces. If I prime all six sides first including the grooves, won't the Gorilla glue have trouble adhering? I plan on using a Behr Primer and sealer product prior to painting with a porch paint. Thanks.

I've attached pictures of the porch that I'm about to re-do. For a clearer understanding of the job for you. The joists underneath lay into notches in the stone wall below, only one may need replacing. For that I'll use PT most likely.

Edited 7/21/2003 7:46:20 PM ET by pizza

(post #92979, reply #4 of 19)

Thanks for the pictures, but they're a littel larger than I care to try downloading on my dialup. If you can resize to about a quater the size file it is now, that would be better for many of us.

The Gorilla glue won't have any problem sticking to anything. It is more likely that the primer would have trouble sticking to the wood.

You'll want an oil based primer that is specific for the cedars and firs. Fir is one of those woods with lots of resin - that's partly what makes it more rot resistant - but the resin makes it hard for some paints to stick.

Oils are more compatable, and slower curing lets them seep into the wood to bond better. Read the label of the paint rpoduct to get one right for the job


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #92979, reply #5 of 19)

Thanks piffin, great help. I'll do what you've suggested. Would you recommend 5/4 thickness on the planks? Does Doug fir T&G come in that thickness as a standard size? If not would 3/4" be OK? #/4" seems a little thin to me for a porch that will be walked on.


(post #92979, reply #6 of 19)

The fir is stronger than pine or cedar so 3/4" is OK over framing 16"OC. 5/4" is available in some places.

one other thing, since the glue will foam/ooze out a little, don't overdo it and plan to sand the ooze out off after it sets up and then a second surface coat of primer where you scuff it sanding.


Excellence is its own reward!

Edited 7/21/2003 8:21:54 PM ET by piffin



Oh Well,

We did the best we could...

(post #92979, reply #17 of 19)


I just did some measuring today and found out that my joist spacing is 19 1/4" between  5 joists and a 25" spacing on the last pair of joists. I'm hesistant, now, to use the T & G 3/4" thick planks offered at my lumber yard. But I have a new strategy on this and I'd like to know what everyone thinks.

I saw that the lumber yard sells yellow pine stair treading that measures an inch thick and about 9" wide. I was thinking about buying that stuff and cutting the bull nose off and then cutting a rabbet in the edges to create a square ship lap joint between the planks. I figure the ship lap joint would be a lot easier to do ( with my router) rather than trying to set up and do T & G's on a long board on my table saw (that can get awkward and maybe even dangerous) within the cramped area of my "shop".  Plus this joint would afford me some water leakage protection thru to the underside of this porch. Whad'ya think? Thanks for the help. Remember I want to create a leak free (hopefully) porch floor that won't soak the stuff I have stored under it. The old rotting T&G boards measured near 1". Also, when I install the boards do I need to tightly fit them together at the joint or should I leave some room for expansion and contraction , say 1/8" at each joint?

(post #92979, reply #18 of 19)

Setting another joist or two will be way much easier thandoing all that work to rabbit out for the wider, thicker decking.

And mainly, the reason I would advise against this, is that the wider boards will expand and shrink more than the narrower ones. Let's assume that it all moves a quarter inch per foot. That 9" board will expand or shrink 3/16". That is nearly the size of the t&G.

but put down 1x4 which measure 3" surface approx. and it will move 1/16" at each T&G gap which is tollerable.

If I remember right, you have your joists set into notches in the masonry wall so adding more jhoist might be difficult. You could sister to each side of what you have with PT lumber to add to strength and decrease the open span the 1x4 has to cross.


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #92979, reply #19 of 19)


(post #92979, reply #12 of 19)

I finally downloaded irfanview

Heres the resized pics, they even took a moment to load on my cable line.


P.S. You should really look into DSL or Cable, it's not much more then dial-up, if you can get it on the island??  Once you go there, you will hate using a dial-up connection

Never be afraid to try something new. Remember, amateurs built the ark, Professionals built the Titanic.

06042003pics_0013.jpg36.49 KB
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(post #92979, reply #14 of 19)

Thanks CAG. I haven't figured out how to reduce the photo file sizes yet for posting on this forum.

(post #92979, reply #15 of 19)


I'm won't be able to explain it as well as others here but if you go here:

and download the program, it is very easy.


Never be afraid to try something new. Remember, amateurs built the ark, Professionals built the Titanic.

(post #92979, reply #7 of 19)

pizza-- another alternative you might want to check out is Tendura flooring. Its a T & G composite decking that installs just like regular flooring. I used on my own front porch and have been very happy with it. It was a little more expensive than the yellow pine, but I prefer doing jobs only once. The quality of the  decking I've seen available  now just doesn't  seem to match what was there.

(post #92979, reply #10 of 19)

What technique did you use to prevent water drainage thru the Tendura planks?

(post #92979, reply #16 of 19)

pizza-- sorry I didn't get back to you sooner- got involved in a couple of projects and was away from the computer for awile. I'm not sure I quite understand your question about water draining thru - I installed the decking with a slight pitch on the porch so that any water will drain off, approx. 1/4" per foot is about right. This should be done on any porch with T & G decking. Hope this helps you.

(post #92979, reply #8 of 19)

 Piffin is right about the gorilla glue, I used it on my end boards were I couldn't nail a full piece. It's totally water proof and expands to fill anything, but make sure your pieces are nailed down good. The glue exerts decent pressure as it expands and can actually push the pieces apart if they aren't secured good.

 I didn't mention it before but he is also right about primers. An oil based primer will 'soak' in a lot better. The fir in my area comes 3/4" standard. I nailed mine 12"o.c. and have had no problems, but 16" should be ok. Just make sure your joists and beams are nice and flush, because if they are not they will "telegraph" through your floor boards before long. That's why I stressed taking your time with the joists in my earlier post, because I have seen it happen.

 I used a Zinsser Alkyd primer on all 6 sides and an epoxy based porch paint over it. It still looks excellent. If you space your ledger off the house you won't have to worry about water being trapped against the end grain

I don't understand! I cut it twice and it's still too short!

Edited 7/21/2003 8:56:17 PM ET by Manroot

Edited 7/22/2003 11:00:35 AM ET by Manroot

I don't understand! I cut it twice and it's still too short!

(post #92979, reply #9 of 19)

What was the brand on that epoxy based porch paint? Thanks for all the help everyone!

(post #92979, reply #11 of 19)

Ben moore has an epoxy in their industrial line works great use quality paints and you won't be sorry. Remember "Oats that have already been through the horse are always cheaper than oats that haven't"

(post #92979, reply #13 of 19)

The paint I used was Benjamin Moore's epoxy resin porch and patio paint. It's only been on a year or so, but it has held up very well to foot traffic and weather so far. I did 3 coats.

I don't understand! I cut it twice and it's still too short!

I don't understand! I cut it twice and it's still too short!