Screen in porch floor - to keep 2 layers orr not

[jdbs32]

Redoing a screened in portch. Existing porch floor has 2 layers - subfloor = 1"x7" boards, underlayment = 5/8" plywood, for a total of 3/4" + 5/8" = 1 3/8". Why there are 2 layers is lost in history. The plywood is covered by an outsoor carpet; as will the floors replacement.

At the porch door threshold, the porch floor is 3/4" lower than the top of the threshold. On the other side of the threshold is a small deck which is 5/8" lower than the top of the threshold.

A person at a big box store suggested I use 23/32" Advantech (he called it an OSB with a plastic coating), due to the porch being exposed to rain and snow through the screens, and Advntech's moisture resistance and stiffness quality.

I'm considering eliminating the 1"x7" subfloor boards and just going with 3/4" Advantech. This would mean the porch floor would now sit down another 5/8" below the threshold, for a total of 6/8" lower than the external deck (1/8" lower ibefore + 5/8")

btw - The external deck is 3'x20' and is there only because of a sliding door at the other end of it. I call it our running deck. And stepping out from the dining room to the screened in porch is a step down of about 7 1/2".

Two questions:

- Will the 3/4" Advantech by itself provide sufficient stability to the floor such that when you walk on it, it does not bounce or feel like it is not solid. If not, what are your suggestions?

- With only 1 layer, is the the resuting difference in floor height (3/4") between the deck and porch, a big deal?

thanks






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[jdbs32]

Any feedback?

[Garry Sorrells]

Anything a 1/2" or greater is usually considered a trip hazard. If the joist are on 16" center then the 3/4" Advantech would work out without flexing, stiff stuff.

If you look at your slider door and what you have to step over coming and going your 3/4" to door is not that bad as the duck waddles.

Now the issue is the weather getting in through the screens. It sounds like the floor is exposed to weather which is not what the Advanteck is not designed for. It will stand up to the weather which is one of the reasons to use it when building new construction. It can take the weather without blowing up till you get the roof on. It is water resistant not water proof. If the porch is to be left open permanently then you will want to rethink your materials.

It will withstand soaking and standing water. Seen it exposed for 2 months without a problem. But it is an interior product. Switch to AdvanTech

[jdbs32]

Now the issue is the weather getting in through the screens. It sounds like the floor is exposed to weather which is not what the Advanteck is not designed for. It will stand up to the weather which is one of the reasons to use it when building new construction. It can take the weather without blowing up till you get the roof on. It is water resistant not water proof. If the porch is to be left open permanently then you will want to rethink your materials.

It will withstand soaking and standing water. Seen it exposed for 2 months without a problem. But it is an interior product. Switch to AdvanTech

Thank you for the feedback. Yes, the weather does get through the screen, and yes, the porch is to be left open permanently.

I'm confused by your materials comment. AdvanTech is what I was referring to; it looks like you though I was using something else?

Can you confirm AdvanTech is what I should be using?

thanks

[Jerry Peck]

But it is an interior product. Switch to AdvanTech

Can you confirm AdvanTech is what I should be using?

Garry provided you with a link to that webpage, this is from the information on that webpage:

- http://www.huberwood.com/assets/user...de-2013-10.pdf

- Which states: (underlining is mine)

ExposureAdvanTech panels should not be used in applications that will expose the panels to weather permanently. AdvanTech panels are not approved or certified for exterior exposure. Classified as Exposure 1 under PS-2, AdvanTech panels are intended to resist the effects of moisture due to construction delays or other conditions of similar severity, but are not suitable for permanent exposure.

[Garry Sorrells]

Thank you for the feedback. Yes, the weather does get through the screen, and yes, the porch is to be left open permanently.

I'm confused by your materials comment. AdvanTech is what I was referring to; it looks like you though I was using something else?

Can you confirm AdvanTech is what I should be using?

thanks

AdvanTech is not rated for exterior, open porch, application with permant exposure to the elements. It was designed for greater stability as a sub-floor or underlayment to finished floor. Moisture resistance is the claim to fame. Often the building process leaves the sub-floor exposed to the elements prior to a house being closed in, roof walls and windows. Meaning the sub-floor will be rained or snowed on. Regular plywood or OSB will buckle, delaminate or swell just to start the list of unwanted things that can take place.

The fact that "A person at a big box store suggested I use 23/32" Advantech (he called it an OSB with a plastic coating),..." doesn't make it correct. Their knowledge is often limited as is their experience in construction.

Recommendations on what to use:
1) 3/4" pressure treated plywood that is sealed with exterior deck stain.
2) Pressure treated 2x or 5/4" pine, cedar, synthetic or Ipe decking.
3) Cement, tile, or stone.
4) T&G Douglas Fir was used for many years as decking/porch flooring when material and labor was less expensive. It was installed with a slope and sealed (painted). But it is expensive and will not last as long as other options available.

Could you use AdvanceTech? Yes. You can do anything you want. Painted (all edges and surfaces) and then maintained with the knowledge it may not last as long as you desire. When it fails you just replace it. I have never tried it as an exterior flooring but it might work, just do not know what to expect. Would be an interesting test.

[jdbs32]

Thank you for all of your responses.

But it is an interior product. Switch to AdvanTech

Okay, now I see my confusion. I had taken the 'switch to' as saying what I should use, not as a pointer to read supporting information; thus my follow-up for clarification. And yes, I agree that big box stores have very limited knowledge, thus the reason why I ask in forums like this.

Given the recommendations of what to use, my best choice is

3/4" pressure treated plywood that is sealed with exterior deck stain.

For the subfloor, I'll use either 1"x7" boards like I have now, or regular 3/4" plywood. Either will give me the height to match the small 3'x20' deck next to the screened in porch.

Will the chemicals in the pressure treated plywood leach out and discolor the gray outdoor carpet that will cover it?

[Garry Sorrells]

As I suggested, seal the PT Plywood with deck stain. A solid color stain will seal the plywood and prevent water logging and causing a shortened life. You will not be happy if you do not seal the plywood. You will want to allow the plywood to completely dry out before you seal it. Pressure Treating the plywood is not turning it into marine grade plywood and even then it is more about the glue than the wood. So, best seal the PT plywood.

Oh, use stainless steel screws for the plywood. Costs more but worth it in the long term.

[Jerry Peck]

As I suggested, seal the PT Plywood with deck stain. A solid color stain will seal the plywood and prevent water logging and causing a shortened life. You will not be happy if you do not seal the plywood. You will want to allow the plywood to completely dry out before you seal it. Pressure Treating the plywood is not turning it into marine grade plywood and even then it is more about the glue than the wood. So, best seal the PT plywood.

Oh, use stainless steel screws for the plywood. Costs more but worth it in the long term.

I'm not sure I would recommend even PT plywood for floors exposed to the weather.

Think of it as using 2x4 PT posts into the ground for a small fence around garbage cans ... whoa! ... the 2x4 PT wood is unlikely to be treated enough to "Ground Contact", most likely the 2x4s will be "Not for Ground Contact" (which means you would need to go with 4x4 PT, which is typically treated to "Ground Contact" levels).

PT plywood is likely treated sufficiently for exposure to the weather in vertical applications, but may not be suitable for horizontal exposure to the weather applications. I would say to contact the manufacturer of the PT plywood and get their opinion - they may say 'sure, as long as there is a slope to drain dry', or 'sure, no problem', or even 'only if you thoroughly protect it with an elastomeric roof paint' ... I would get the manufacturer's okay first.

[jdbs32]

Will the chemicals in the pressure treated plywood leach out [through the solid color stain] and discolor the gray outdoor carpet that will cover it?

Thanks

[Garry Sorrells]

If the PT plywood is dry and then sealed with deck solid color stain the chemicals will not bleed through. the ketch is """DRY""" then sealed. I have some that is 10 years old and counting. Sort of a guinea pig test that I did. T&G fir painted did not hold up, CDX painted did not hold up, PT plywood with solid color deck stain has 8 years and solid with no issues.

The issue is that the most common PT material is copper and it will eat up zink and steal if wet. Stainless steel will hold up and not react.

Why not just put down a plastic or composite deck material and not have any worries? For a few dollars more and no worries for 30+ years. I understand want to go cheap, but there is usually a price you pay for the attempt. The adage, "Pay me now or pay me later" , may be at work here.

[jdbs32]

Again, thanks to all.

Big box stores sell radius edge pressure treated southern pine deck boards. Might this be a better choice than the PT plywood underlayment?

If desired, I could still palce an outsoor carpet over it.

Regardless of whether I use pressure treated southern pine or PT plywood for the underlayment, what should I use for the subfloor under it? Stay with the 1"x7" boards as is now, or another 5/8" or 3/4" layer of non-PT plywood, PT plywood, or?

Note: the screen inserts sit on top of whatever material is on the subfloor.

Thanks

[Jerry Peck]

If desired, I could still palce an outsoor carpet over it.

That just delays the ability of the flooring to dry out.

Regardless of whether I use pressure treated southern pine or PT plywood for the underlayment, what should I use for the subfloor under it? Stay with the 1"x7" boards as is now, or another 5/8" or 3/4" layer of non-PT plywood, PT plywood, or?

The subfloor, if exposed to the weather as you describe, should also be PT wood (otherwise it will rot out below the flooring ... you just won't see it until you fall through).

[jdbs32]

The subfloor, if exposed to the weather as you describe, should also be PT wood .

Okay, subfloor will be PT plywood.

Back to the underlayment question ...

Big box stores sell radius edge pressure treated southern pine deck boards. Might this be a better choice, or an acceptable alternative to using PT plywood for the underlayment?

thanks

[Jerry Peck]

First - All wood used to frame and floor a deck or porch needs to be PT.

Second - Why do you need a subfloor?

Third - Have you considered using composite for the flooring? Make sure that the floor joists are spaced as needed for the composite flooring as recommended by the manufacturer.

[jdbs32]

All wood used to frame and floor a deck or porch needs to be PT.

Agree - my wife nixed using the radius edge deck boards. So 5/8" PT plywood subfloor, and 3/4" underlayment it is.

Why do you need a subfloor?

2 reasons - more stiffness given my 16" oc joists, and without it, the porch floor is 5/8" lower than the adjacent deck separated by a threshold.

Your thoughts?

Have you considered using composite for the flooring?

No, I can't justify ithe added cost.

[Jerry Peck]

2 reasons - more stiffness given my 16" oc joists, ...

16" o.c. joists should provide for a fairly stiff floor anyway with a 3/4" thick T&G flooring.

... and without it, the porch floor is 5/8" lower than the adjacent deck separated by a threshold.

Add a 5/8" thick 'shim' along the top of all the floor joists - you have now achieved the height needed without the subfloor.

No, I can't justify ithe added cost.

Now you can justify the added cost - no subfloor cost.

[jdbs32]

16" o.c. joists should provide for a fairly stiff floor anyway with a 3/4" thick T&G flooring.

Add a 5/8" thick 'shim' along the top of all the floor joists - you have now achieved the height needed without the subfloor.

I like the idea of the 5/8" shim to eliminate the subfloor - great idea!

I'll double check my numbers for using composites.

As a follow-up question:

If I use the same 5/8" shims for all floor joists, with the 16" oc joists, will 3/4" PT plywood provide sufficient stiffness for a single layer floor as you suggest compositte would? That is, not have a springy-feeling deck?

Thanks

[Garry Sorrells]

Warning this will give some a head ache to read.

I started to attempt to connect the posts and reply's. To big a head ache. So have written an epistle.

Jdbs;
As you have been told all material exposed to weather must be PT, composite, Ipe, cedar, teak or a wood that will width stand the exposure.

PT plywood is rated for ground contact as are PT 2x4, PT 5/4, and PT 1x6. Note: you will have a hard time finding 5/8" pt plywood. Normal stock is 1/2" (15/32) and 3/4" (23/32).

You want to have a floor that is 1 1/2" thick and spend as little as possible in the process.

If your joist spacing is 16 OC then there will be little flex in the floor using 3/4 plywood or 5/4 deck boards. If you do not like the radius edge on the boards then cut them off.

For what you have indicated as specification on floor thickness at 1 1/2" options are:
1) PT 2x6, PT 2x8
2) 5/4 PT as a sub floor with 1/2" PT plywood on it. Be smart and seal all materials.
3) 1x6 PT as a sub floor and 3/4" PT plywood on it. Be smart and seal all materials.
4) 3/4" PT plywood as sub floor and 3/4" PT plywood on it. Be smart and seal all materials.
5) Use stainless steel screws because the copper in hte PT treatment will react with every thing else that you could use except for copper nails/screws and you will not spring for them.

Shimming the joist is another option of the options above, using PT materials.

The sealing is to prevent rot and YES PT MATERIALS WILL ROT. Also, sealing will prevent reactions from the PT treatment from reacting with anything coming into contact with it. Another Also, PT plywood is made from veneers of thin wood. This wood will expand and contract causing general buckling, surface veneer to buckle and surface fuzzing. So if you do not want it to look like crap SEAL IT (after it has completely dried out) !!

I hope you have have/will design in method for the water that enters porch to drain off.

Good Luck....

[Jerry Peck]

If I use the same 5/8" shims for all floor joists, with the 16" oc joists, will 3/4" PT plywood provide sufficient stiffness for a single layer floor as you suggest compositte would? That is, not have a springy-feeling deck?

Most conventional floor framing is 16" o.c., with an OSB subfloor, with carpet or other floor covering over it, so ... I would think ... (dangerous last words, kinda like 'Hey, Bubba, watch this ... ' ) ... I would think that 3/4" T&G plywood would have the same strength (load and span) rating.

Composites ... you would need to check what they recommend for joist spacing, which may vary based on thickness of the composite material used, but 16" o.c. is a very common floor joist spacing. I don't recall seeing any which have been over 12" o.c. floor joist spacing.

Select the floor material/thickness; accurately measure the total floor thickness needed to match the other floor; deduct your floor material thickness from that total; the remainder is shim thickness. If you come up with 3/16" difference, take 2x4 PT and rip off 2x3/16" strips, attach those to the tops of the joists and - if your measurements and ripping were correct - the floor should be at the correct height ... and if the floor on the joist at the meeting point is slightly off (before nailing the flooring in place) then adjust that one strip shim thickness as needed to be thicker or not as thick to get 'as close as you want' the too floors to be in height.

[Garry Sorrells]

Jerry; odd that we posted 1 min apart.

Most conventional floor framing is 16" o.c., with an OSB subfloor, with carpet or other floor covering over it, so .................

Composites ... you would need to check what they recommend for joist spacing, which may vary based on thickness of the composite material used, but 16" o.c. is a very common floor joist spacing. I don't recall seeing any which have been over 12" o.c. floor joist spacing.

.................

All of the composite decking materials that I have seen at 5/4" are acceptable for a span of 16" OC application with the exception of areas that will have unusual loads sitting on them where 12" OC is required.

24" OC requires the composites to be 1 1/2" thick (such as 2x6)

Standard interior sub-floor is 3/4" T&G plywood or OSB.
The spring in a floor is usually from the joist flexing and not the sub-floor.
So yep, exterior floor with 3/4 PT T&G plywood should be the same.
Else double up the plywood and make sure you off set the joints/seams.

[Jerry Peck]

Jerry; odd that we posted 1 min apart.

Guess I am just a slower typist?

I was probably typing the last sentence when you clicked on the submit button.