Joists: to treat or not to treat that is the question

[ToughButterCup]

Just got some prices for POSIs: there are two prices; one for treated joists, and the other for -errrm- untreated joists.

 

First: why do you need to treat joists? They can't misbehave, or be rude, and so

Is it worth it? The price difference is £100+ for quite a few

 

The architects notes specify treatment for the wall plate for the joists, but doesn't mention treatment for the joists themselves.

[MikeSharp01]

Good to see you are back on the horse Ian. Not sure you should need treated Joists as it is good practice to have treated timber next to masonry IIRCC but no where else. PS but probably wait for an expert.

 

Edited September 20, 2017 by MikeSharp01
PS

[SteamyTea]

I would think it is all down to the air movement around them.

If there is virtually no movement, then even will a low condensation risk, there is still the possibility that rotting of some sort could take place.

Though it may just be a method to add value to a tried and tested product.

[Construction Channel]

1 hour ago, recoveringacademic said:

Just got some prices for POSIs: there are two prices; one for treated joists, and the other for -errrm- untreated joists.

 

First: why do you need to treat joists? They can't misbehave, or be rude, and so

Is it worth it? The price difference is £100+ for quite a few

 

The architects notes specify treatment for the wall plate for the joists, but doesn't mention treatment for the joists themselves.

 

is that £100 per joist or for the lot?

if its per joist i wouldnt bother as it hasnt been specified, If you wanted to be fancy you could buy a tub of treatment and coat the first 300mm ish of each joist before you install them.

 

Iv never worked with them so it might be best to find someone (on here) that has and see what they did, technically internal timber shouldnt need treatment........

[PeterW]

Buy them untreated. 

 

You can get Sika for £30 for 5 litres of the universal one and a sprayer is £9.... that's all of them done and it's quick and you can also use it to do other stuff too. 

[Gone West]

I have metal web joists in a timber frame and they are untreated. BCO wanted timber outside of the external racking treated but anything else could be untreated.

[Dudda]

I presume it’s 100 extra for them all as the difference between treated and untreated timber is about 2-4% extra I’ve found. Probably £2-5 a joist depending on how many you have? If they're looking for 100+ a joist he's having a laugh.

It’s not just wet rot you need to worry about which is why you treat the wall plate and end of joists and rafters. Treated timber also helps prevent dry rot. I’ve a 1970’s house I’m refurbishing and found a bit of beetle infestation around a first floor ensuite which is also above a utility. The heat and steam from showers and the dryer, washing machine, damp clothes and hot water cylinder all helped create the perfect environment. Its in the joists and studs in this area which wasn't visible when purchasing so all my new timber going in is treated and existing is getting treatment in situ where it's not getting replaced. While not that expensive the painting of the treatment is time consuming and dry timber soaks up a lot so you end up using far more than you think.  Additionally when you paint on the preservative it’s only penetrating circa 5mm which is fine but makes you worried when you drill a hole for a pipe or cable later. When you purchase treated timber it’s usually pressure treated so the preservative goes deep into the timber. You’ll notice this when you go cutting and drilling.

For only 100 extra and peace of mind I’d go for it.

[ToughButterCup]

Thanks folks: presumably the same @PeterW treatment (above) can be given to the wall plate(s). But then again @Dudda says it's probably a bit of a 'shortcut'

Hmmm. Must look at the spreadsheet again.

 

Thanks, interesting

[PeterW]

You can use Sika on any timber. The benefit is you decide where to treat. And you are treating for everything not just damp or rot as this treats for boring insects etc. 

 

As posijoists can't be drilled or notched then as long as you treat all surfaces then it's done for the life of the timber. 

 

All depends on cost vs time. If your time is "free" then it isn't a big job - took me about 20 mins to do about 70m of 6x2 all four sides and in situ. 

[Ferdinand]

If you do it by dunking them in a bath for a few they can suck up a LOT of treatment.

[Simplysimon]

@recoveringacademic the joists don't need it but as stated buy the wallplate treated it's vacuum/pressure treated and far better than using brush/spray