Need to replace a 5m pergola beam

At the back of our garden is a patio with a pergola over it. The front of this faces the lawn and the two supporting posts are just under 5m apart.

The previous owners spanned this gap with a beam that was made up of

4 pieces of overlapping timber. Two main beams and two joining beams over lapping the join in the middle. The main beams are 6" by 2" which the overlapping ones are 6" by 1".

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This is rotting badly around the entire joint area and needs to be replaced. I'd like to replace it with a single beam if possible.

I assume that a single 6" by 2" beam (if available in the needed length) could replace the current beam.

Any suggestions or alternative materials?

Guy

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Reply to
Guy Dawson
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It would probably span 5m without noticeable sag, but you might have trouble getting one.

Reply to
The Medway Handyman

Does it depend perhaps on how much "just under" 5m is needed? Even after the b***** s****** Olympics have driven out most useful places there are still a few places around here which stock 4.8m lengths of rough sawn 150mm. Would something on the lines of

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be OK?

Reply to
Robin

In NZ I can buy 150x50 up to 6 metres long for NZ$4 per metre (2 GBP), treated to last in the ground indefinitely. I've bought lots of it lately for retaining walls and steps.

Reply to
Matty F

Or 75x225mm in 6m lengths ...

Reply to
Andy Burns

Well that's not that hard, how about the range from 2" below to 6" above ground level?

Reply to
Dave Liquorice

Indeed.

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be OK?

Thanks. Looks good. I'll be getting the tape measure out shortly...

Guy

-- --------------------------------------------------------------------- Guy Dawson@SMTP - snipped-for-privacy@cuillin.org.uk // ICBM - 6.15.16W 57.12.23N 986M

4.4>5.4 4.4>5.4 4.4>5.4 The Reality Check's in the Post! 4.4>5.4 4.4>5.4
Reply to
Guy Dawson

There's quite a selection at 4.8m so I hope that "just under" 5m is not "just over" 4.8m! Tape measure time...

Guy

-- --------------------------------------------------------------------- Guy Dawson@SMTP - snipped-for-privacy@cuillin.org.uk // ICBM - 6.15.16W 57.12.23N 986M

4.4>5.4 4.4>5.4 4.4>5.4 The Reality Check's in the Post! 4.4>5.4 4.4>5.4
Reply to
Guy Dawson

Many, many, years ago, my dad bought a secondhand telegraph pole, but I've no idea whether or where they still sell 'em.

Chris

Reply to
chrisj.doran%proemail.co.uk

If you have to join it, do it as close to the bearing end as possible not in the centre. Use a non-ferrous fixing and for such a join I suggest both phenol resorcinol type glue and a mechanical fixing such as multiple brass screws with the glue - look up the spacings and overlaps for a proper mechanical engineer connection. Use only one of the following: Copper oxide, monoethanolamine and quaternary ammonium compounds; Copper Dimethyldithiocarbamate; Ammoniacal Copper Citrate - the current ingredients replacing the old CCA as your pressure treatment supplied timber and do not cut it - get the merchant to treat it at the sizes you want with the water based pressure vessel (do not confuse with AQuaVAC which is a water based replacement of VACVAC and comparatively useless) which allows chemical combination with the hydroxyl groups in the timber. I would specifically go and find one that is bent (the bigger the better) and curved and use the curve as a precamber so when the duration of load effects affect the beam it will end up straight! chris

Reply to
chris

20 odd years back we installed fencing to keep rabbits out of the vegetable garden. We used pressure treated posts except at the very end when we ran short and a few un-treated posts were used.

As it turned out the 0.22 was better at keeping the bunnies at bay and also had side benefits so eventually they gave up and moved to easier pastures.

Couple of years back I had reason to remove the last few posts. The untreated ones snapped off at ground level with ease. The treated post were easily removed in one piece, still in excellent condition, and re- used else where.

The supplier of our treated posts also treats telephone poles.

Paul Mc Cann

Reply to
fred

For a pergola I'd probably make it from multiple pieces. Two lengths with a long scarf joint (18") in the middle, if that was long enough, otherwise a short scarf and thickeneres top & bottom. The scarf joint would be a complicated hooked one - search for medieval or traditional Japanese scarfs. For simplicity there would be vertical stainless hardware through it.

Personally I find plain beams a bit dull and I actually like this sort of carpentry adding detail to them. I'd even do things like chamfering the edges, to highlight the joinery.

5m beams are easy to get, but you're then dealing with the big guys who are fewer, further and have to use a bigger truck for delivery. It could turn costly, depending on where you are and how soon you want it. My place has cheap delivery for one-offs, if I can wait a week or two until they're already going past the door (and I live near a main road anyway).

I'd make this out of larch. Good garden wood. Ideally check for a good resinous bit, as it does vary (and thus in rot resistance) and there's also some that's very twisty. Larch is cheap(-ish) at present, as a lot of small larch stands (often in parks & arboreta) are being clear- cut to get rid of them, if they're near to hardwoods. There's a concern that they're a vector fot the sudden oak death fungus.

Reply to
Andy Dingley

I'm not sure what you mean by 2" below. For some odd reason the H4 timber (treated for in-ground) is cheaper than the H3 timber (outdoor above ground). So I use H4 for everything.

Reply to
Matty F

From a point 2" below the level of the ground.

The various fungi that cause rot have a prefered level of moisture in the timber. In most grounds it is too wet and/or lacks oxygen, in air it is too dry. There is a "Goldilocks" band starting just below ground level and extending a few inches above where conditions are "just right". This is why woodem posts fail at ground level.

Reply to
Dave Liquorice

I have never had an H4 treated post fail. In NZ we have huge forests of Pinus Radiata. That is ideal to absorb any nasty chemicals that one would need to stop rot or borer and even sea creatures from attacking the wood.

I have never understood why the UK does not have a similar system of timber treatment. I grant that paranoid people don't like some of the chemicals used. The UK should import NZ timber. It's real cheap and excellent quality.

Here are the treatment types available in NZ.

H1: Inside, Above ground, Dry

H2: treated against termites. NZ does not have termites.

H3: Outside, Above ground.

H4: Outside, In ground. High fungal decay and termite hazard

H5: Outside, In ground or fresh water.

H6: Marine water exposure.

Reply to
Matty F

I wouldn't expect a treated post to fail either. Looking at your list anything below H4 would fail near ground level.

I like that scale you have quoted. I'm not aware of anything similar over here. You get "treated" and that's about all you can find out.

Nothing about the method (brushed (how many coats at how many l/m^2), dipped (how long), vacuum impregnation, etc), or the chemicals used.

Reply to
Dave Liquorice

Seems NZ wood ends up marked with "XXX YY ZZ + logo", where XXX tells you who processed it, YY tells you what with, ZZ tells you what hazard level it will withstand.

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actual presure/vacuum/dipping/brushing treatment method doesn't seem be included in the numbering system, though it references standards the timber has to meet.

Reply to
Andy Burns

Wouldn't mind some Kauri Pine, but I bet that isn't cheap. My favourite timber of all time I think

Reply to
stuart noble

I believe it's mostly vacuum impregnation, and the chemicals used may be banned in the UK - copper chromium arsenate, although the H4 timber I am currently using seems to use something else. Pinus radiata absorbs treatment well.

Reply to
Matty F

I have a whole house built out of Kauri. I have lots of old 4x2 and even some 6x4 and 6x6 Kauri that I will make small things out of when I get old!

Reply to
Matty F

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