1. Home
  2. UK Do-It-Yourself Forum
  3. Custom sized decking joists...

Custom sized decking joists...

Hi All,

I have a question about pressure-treated decking joists:

Our house has a decked cantilever balcony around 2 sides on the 1st floor, where the balcony joists protrude about 1 metre from the outside wall, and go right through the cavity wall and bolt to the floor joists on the inside. (Hope you can understand this description!)

Anyway, it's all rotten and I have now removed most of the old joists, leaving just slots in the brickwork ready to accept some new joists. Obviously I want to replace with pressure treated decking joists, as I don't fancy doing this job again for a while! However, I'm having problems sourcing joists that will fit into my existing slots...

I've determined that the joist sizes I need are 2.4m long, 43mm thick, and 170mm tall, i.e. not a standard size. (This is about 1 or 2 mm undersized so I can be sure they'll fit - don't know whether I need to take shrinkage/expansion into account here?) However ringing round the local timber merchants, one has said that you can't plane pressure treated joists as you'll lose the weather resistance, and one has said they can saw it but not plane it (for the same reason)!!??

Now some things I've read tell me the pressure treatment penetrates right to the middle of the wood, but is this the case? Is it a waste of time to plane pressure treated joists? Surely sawing would give the same problem if it is an issue?

Thanks, Ben.

Reply to
Ben Willcox
Loading thread data ...

Pressure treatment goes in a few mm, but there is definitely more at the surface than in the middle. The only reason I can think of that the timber merchant thinks they can saw it, is that they plan to paint something on the sawn surface - and you can get more liquid to stick to a sawn surface than a planed one.

Why not make the holes a bit bigger? Lots of people here rave about SDS drills (I've never used one). It sounds like the sort of thing a chisel attachment ought to make short(ish) work of.

Reply to
martinfrompi

Go to Jewsons and get them to cut the timber to whatever size you want and treat it for you.

Reply to
Chris Bacon

Hi Martin, thanks for the reply.

You know, I'd never actually thought about enlarging the holes... I had totally discounted it as I figured enlarging 45 holes in 2 layers of brick wall would be out of the question. However now you suggested it, I've looked and 150mm x 47mm joists are a common size, so I'd only actually have to enlarge the width by 4mm (which is mortar anyway) so might not be too hard. I hope the reduction on the vertical by 20mm wouldn't matter much strength wise (I think the joist spacing is about 16 inches but thats guessing from memory...)?

Cheers, Ben.

Reply to
Ben Willcox

Don't use them - they're not weatherproof. If you want them to last, a timber that's inherently rot-resistant (larch or oak, depending on budget) will last far longer than crapwood doused in poisons.

Reply to
Andy Dingley

Hi,

Sounds like you need to speak to a good sawmill with pressure treating facilities, or a very good timber merchant who can order special sizes and arrange for pressure treating.

One way go would be to get strength/stress graded timber graded for wet conditions, sawn to spec, and pressure treated with a copper based preservative.

A structural engineer with the right experience would be able to calculate the safe loading on the balcony.

Normal decking joists aren't strength graded, may be made of poor timber that will warp/twist, and the preservative may only be a wax based water repellent.

See also:

Depending on the rest of the balcony and it's design, if you're lucky you may be able to get oak at a competitive price, though it's not normally strength graded.

cheers, Pete.

Reply to
Pete C

Clifford Jones timber in Ruthin will almost certanly be able to supply your need, however you may have a shock at the price, even though it will be the cheepest of 2 or 3 I could recommend.

Rick

Reply to
Rick

Hi guys, thanks for all the responses. As Chris suggested I called my local Jewsons, and they said they could cut to size and send it off to be pressure treated (none of the other local merchants I rang would do this).

They quoted me 325 quid inc VAT for 46 off 2.4m x 43mm x 170mm, with a taper cut at one end to match the originals. (works out around 2.50 per metre)

Dunno whether this is a good price or not...?! I'm guessing oak would cost me a little more than that!

Rick thanks for the recommendation however I think delivery costs would be prohibitive so would be better to try and get it as local as I can (I'm in Telford, Shropshire).

Cheers, Ben.

Reply to
Ben Willcox

Phone and find out

formatting link

Reply to
Andy Dingley

Find a decent timber merchant and ask them to cut standard untreated C16 wood to the correct size then have it tannelised. If they don't have the equipment then their supplier will.

Reply to
Mike

In message , Ben Willcox writes

I'd snap their hand off at that. I reckon that's only slightly above the going rate for 50x170, and given the amount of work its going to save you....no brainer as they say.

Reply to
Steven Briggs

Thats 12 quid a cubic foot, you would have to pay a couple of quid more for oak, but not much, and then you would have the good old transport problem back :-(

Rick

Reply to
Rick

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.