Jump to content

P.T. Wood: Not all P.T. Wood is For Ground Contact


Recommended Posts

In another thread, I saw where one of the brethren told an inspector that all pressure-treated wood is designed for ground contact. That's a fallacy and is simply not true.

Some pressure-treated wood that's designed for use in fences, balustrades and deck surfaces is not adequately treated for ground contact and should not be used in applications where it might come into contact with soil.

Other pressure-treated wood is designed for ground contact and the choice of fastener is going to depend on whether it's going to constantly stay very wet or whether it's not expected to stay continuously wet and will dry out somewhat between wetting.

Keep in mind that treatments don't always protect all of the wood anyway. When you cross-cut a piece of P.T. wood, you'll find that only about the outer 30 to 35% of the board is actually treated and that the rest at the core is untreated; so it will still absorb moisture and that moisture still cause it to eventually rot and become insect infested. Treating the end grain and waterproofing P.T. lumber will help to slow down degradation but it's still going to eventually rot, even if it never comes near soil.

Sometimes it's possible during an inspection to know what concentration of preservative has been used. Just look for the tag left nailed to the end of the lumber. I find them all the time.

Here's some helpful information I scarfed up from the Simpson site:

For Above Ground use/exposures the following retentions are typical: (i.e. wood not in contact with soil)

0.25 pcf for ACQ, CCA-C, MCQ

0.20 pcf for CBA-A

0.10 pcf for CA-B

For Ground Contact use / exposures the following retentions are typical: (i.e. wood in contact with soil)

0.40 pcf for ACQ, CCA-C, MCQ

0.41 pcf for CBA-A

0.21 pcf for CA-B

For wood with actual retention levels greater than 0.40 pcf for ACQ MCQ, 0.41 pcf for CBA-A, or 0.21 pcf for CA-B (Ground Contact), Stainless Steel connectors and fasteners are recommended. Verify actual retention level with the wood treater.

To read an excellent FAQ section about P.T. wood on the Simpson site, click here.

ONE TEAM - ONE FIGHT!!!

Mike

Link to comment
Share on other sites

In our area (meaning lumber coming from suppliers in this region) my work has shown that the treated lumber with the incisement marks is ok for ground and concrete contact.

The dark colored stuff without incisement marks is only for above-ground work.

Every time I've been able to read product info. or markings on the lumber still attached, this is the case.

Link to comment
Share on other sites

Mike,

Go ahead and single me out, I can take a spanking when I deserve it. While I am well aware that there are several grades of treated lumber I was refering specifically to PT stair stringers being written up for ground contact. There is nothing wrong with that application, if PT stringers can't touch the ground what exactly are they supposed to rest on? I placed the stringers in contact with the ground when I built my parents deck over 20 years ago and they are still in good condition.

I admit that I was generalizing a bit, I'll try to be more specific.

Tom

Ready for my lumps.

Link to comment
Share on other sites

. . .I was refering specifically to PT stair stringers being written up for ground contact. There is nothing wrong with that application. . .

If the lumber wasn't specifically treated for contact with the ground then it is a problem

I think that was Mike's point. Most of the time we can't tell what's approved for ground contact unless we can i.d. the treatment on the wood which is impossible without seeing the printed data.

In my area, though, I'm pretty familiar with the lumber suppliers. If I see incisement marks, I know it's ok for ground contact. If I see darkened "pressure treated" wood without incisement marks and the wood is touching the ground, I call it wrong.

This strategy won't work everywhere else. From what I read and understand there is ground-contact-wood out there without the incisement marks. I suspect in that case, it'd be almost impossible to i.d. if the wood is ok to touch the ground.

Link to comment
Share on other sites

Hi Tom,

Well, I wasn't actually trying to do that. If I'd wanted to do that, I could have done it in that thread. It is a generalization that I hear, or read, way too often. In fact, 14 years ago I would have agreed 100% with that statement. However, since moving out here, I've learned that quite a bit of what I thought I knew about how wood and houses behave in response to weather and moisture has been less-than-accurate.

I'd probably meant to throw up something about P.T. lumber at least a hundred times but kept putting it off, and off, and off.....

ONE TEAM - ONE FIGHT!!!

Mike

Link to comment
Share on other sites

There is nothing wrong with that application, if PT stringers can't touch the ground what exactly are they supposed to rest on? I placed the stringers in contact with the ground when I built my parents deck over 20 years ago and they are still in good condition.

I have seen this set-up only a few times, here's the right way yo install exterior steps:

The bottom of the stringers shall rest on a landing. It is recommended that this landing be concrete. The bottom of the stringers shall then be notched over a treated 2x4 sleeper which shall be attached to the landing or the stringers could be notched so they would lock in behind the concrete landing itself. Either way effectively locks the stringers in place so they cannot move.

Link to comment
Share on other sites

  • 2 weeks later...

There is nothing wrong with that application, if PT stringers can't touch the ground what exactly are they supposed to rest on? I placed the stringers in contact with the ground when I built my parents deck over 20 years ago and they are still in good condition.

I have seen this set-up only a few times, here's the right way yo install exterior steps:

The bottom of the stringers shall rest on a landing. It is recommended that this landing be concrete. The bottom of the stringers shall then be notched over a treated 2x4 sleeper which shall be attached to the landing or the stringers could be notched so they would lock in behind the concrete landing itself. Either way effectively locks the stringers in place so they cannot move.

I could add one thing - treat the cut end.

There has to be an angled cut at the bottom end and that is where the moisture can wick up into the core. If the stringers touch dirt, in my climate, they will be wet more than half the year. I call that out as a future repair, if they're not already showing soft spots.

I call them "machine marks", made that up muself. Happy Holidays to all. [:-party][:)][:-party]

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...