Pressure treated or regular wood on slab
I have a single-story slab home that was built as part of subdivision in 1979 or 1980 in San Diego, CA.
I currently have several walls open, and today I noticed that the some of the bottom plates in the home are pressure treated, and some are regular wood (all 2x4s). All of the bottom plates (that I can see) on exterior walls are pressure treated. But only some of the bottom plates inside the home are pressure treated. Others are regular wood.
I guess I could see requiring all of the bottom plates to be pressure treated lumber, or requiring just that all exterior walls have pressure treated bottom plates. But the mix confuses me. Is this likely just some sort of screw-up, or due to having more pressure treated lumber than they needed?
If you were building a house today, would pressure treated wood usually be required for bottom plates?
Thanks!
Replies
"If you were building a house today, would pressure treated wood usually be required for bottom plates?"
Yes indeed.
And there's a new type of PT being used today that requires Hot-Dipped Galvanized, or stainless steel fasteners as it is more corrosive than the old.
Thanks for all the replies. Everything that's being posted here, and everything that I've read elsewhere, seems to agree that sill/bottom plates that touch concrete should be pressure treated lumber, or some other form of water resistant material, etc.
Like anything else in construction, it seems the requirements vary depending on where you are. From what Dirtyturk says, the requirements are pretty stringent in Charlotte.
If someone reads this who knows about the particulars of southern California, San Diego in particular, I'd really like to have their input, too.
From what i understand the warmer the climate the more termites are a problem. They do like moisture but warmth is the biggest factor. The house where we had a persistant infestation in an inside wall was in So Cal. It was a dry well drained site. There was a layer of organic material on average about two feet thick over the sub-soil.
I'm no expert but from what I understand the termite nest can be very old and deep in the ground. They tunnel to find food. So when you have a nest nearby you have to be dilegent about not feeding them. My experience with our inside wall was that after it was treated with chemicals preasure injected through the slab they still were active in the wall. Not to active mind you. But still there.
So if you don't have a nest nearby the threat isn't nearly as big. The decomposed granite might have something to do with that. Over the years there probably hasn't been very much for them to eat. So there isn't an established nest nearby.
We lived in Wisconsin and there were very few bugs period. I don't remember termites being a big problem up there. To cold.
There are 2 types of termites. Look at this web page.
Subterranean are the type that is most prevalent where I live and through out the USA. Look at this map. True enough though - in the OP's area dry wood termites are probably more prevalent.
Subterranean termites need moisture. For example, where I live it's common to have a termite warranty, and when the guy from the pest control company comes out, the 2 things he does is a visual inspection, and then check the moisture content of the wood (floor joists) in the ceiling of the crawl space.
As an aside - from what little I've read, Formosa termites, I guess a subset of subterranean termites, are supposed to be a real nightmare. I know our pest control contract excludes warranty from Formosa termites...
BTW - where do you live? and, how about filling out some info in your profile - you've been around long enough...
I've fiiled it out several times. I'm not sure why it isn't there. I really dislike the way computers do that. I'll fill it out again. Maybe this time it will stick.
Yea - my profile has got blanked out once or twice too... Wait - let me go check...
I saw a program on the Formosa termites. They were imported by our military when they closed down a base in the Philippines. They built the boxes for the equipment out of wood they harvested locally and when they unpacked them they took the wood boxes to a landfill. Perfect conditions for termites. Buried wood.
Waters got here before me. Complete agreement here. In our area some communities are requiring a sill seal and the PT lumber and a certificate of method of treatment! Down in Charlotte, NC the requirement is a double bottom plate of PT, sill seal and termite protection(chemical and flashing).
ciao, ted
Make sure the plates that aren't green aren't borate treated. The borate treated 2X4s have a slight blue tint to them. Borate treated is fine on inside walls. I'm not sure if borate treated wood was around when your house was built.
What happens on a slab is that if it carcks and the crack is wide enough the termites come up through the crack and get into an interior wall. I had a wall like in the middle of one house that was on a slab.
Edited 2/1/2008 12:48 am ET by popawheelie
I wonder where this leaves me with the untreated plates that are original to the house (and a couple the previous owner installed).
Is this one of those situations where sills that weren't pressure treated on concrete slabs were the standard at one time, but now pressure treated is required as an improvement? In other words, pressure treated is highly advisable, so it is now required, but regular wood is still functional in this application?
And maybe this is another situation where I have less to worry about because I live in San Diego (little rain). My home is built in decomposed granite and has excellent drainage (for the few times it does rain). Also, I've taped heavy plastic squares over a few areas of my slab, and moisture does not build up.
Make sure the plates that aren't green aren't borate treated. The borate treated 2X4s have a slight blue tint to them. Borate treated is fine on inside walls.
Are you sure about that?
Borates are fine for exterior wall plates and blocking as they perform the functions needed in that use...resist decay, resist pest infestation, resist fungal/mildew growth.
Borates are not corrosive like the ACQ treated lumber and do not require special fasteners or hardware.
Borates cannot be used if exposed to rain water because the rain will eventually leach away the borates. No decks are done in Borates. In good building practices the bottm plates will be dry and not exposed to rain water.
I see architectural specifications and installations of borate treated lumber for exterior and interior bottom plates, window & door framing and roof blocking on most of the buildings I inspect for the owners or architects.
...........Iron Helix
Here I'd say we have mild to average problems with termites. When building slab houses, we can either 1) do an under slab termite treatment (before the concrete is poured) or 2) after the house is framed (but before the house wrap goes on), we can treat the bottom two feet of the entire house with a borate chemical - we use Boracare (sp?). One advantage to Boracare is that then the bottom 2' of the sheathing gets sprayed too, which wouldn't happen with the more conventional under slab treatment. Either insecticide treatment is fully acceptable to local building inspectors. As an aside, I always make sure my carps don't have any sheathing in contact with the concrete. See attached pic (sorry about the size dialup users).
So, as you say, borates can be used effectively on interior or exterior walls.
BTW - Boracare is a clear chemical, but when they dilute it with water, they add a blue-green dye. The dye just helps them see what has and hasn't been treated, but it is really not essential.
To the OP: Here, in new construction, all framing lumber that is in contact with the slab is treated, although I don't know exactly what they did 25 years ago. I like using sill seal too - even on the interior walls. OTOH, if some of the interior wall plate material isn't treated on your current house I wouldn't worry about it too much, but if you are worried, at least about the termite aspect, you could probably have someone come in and spray Boracare or similar. It's fairly inert to humans and pets - except probably in California where a scientific study found that if rats eat 10 times their body weight of the pure chemical per day they get sick. :-) Regarding the possibility of rot - after 25 years or whatever of no rot (assuming here), and especially in your climate, I wouldn't worry about it in the least bit.
You are right. I wasn't sure if borate treated wood was ok on outside walls or not. So I worded it as inside walls. I try not to be to alarmist with stuff like this. Does he need to change them all out. It's a toss up I think.