Best type of wood for external use (under the carport)

[GT]

Can anyone offer any advice on the best wood to buy for my carport top?

I know very little about wood, I just want to buy the correct stuff and not have to replace it after a couple of years.

The wood that's there now is probably over 20 years old, and it's looking a bit rotten now, due for replacement.

It needs to be 100mm x 75mm and about 15m total length (3 x 5m supports for the panels).

I take it I need some kind of treated stuff, but do I ask for any particular type at the timber yard? do I need to paint it with any special paint etc.? can I avoid having to paint it every year?

I'm not too worried about the cost, as I don't need a huge amount and I hope to get at least 10 years from it.

Also, can anyone offer their thouhgts on the type of panneling to use? The original stuff was corrugated plastic (that common stuff!), but i've been looking at that smooth flat pannelling (double or triple wall whatever it's called!)

As you can tell, i'm no expert on DIY; so I value the advice of others such as yourselves.

Thanks in advance to anyone who helps. Graham

[lofty]

if its wood to wood then weatherproof pva is the best ,normally in a blue rather than green plastic bottle. for wood to something else then ask about gripfill ,much better than no nails and other copies. hope this helps

[lofty]

sorry read your thing wrong thought it read glue , sounds like a rip it down and start again job

[Grunff]

Pressure treated softwood. While you can get this from the sheds, you'll get a better deal, and usually better timber if you find yourself a nice timber yard.

Most pressure treated wood has a greenish/brownish colour. It comes in both rough-sawn and planed - you choose, depending on the desired finish. You can finish it with an exterior wood stain if you want, but if left untreated it will last more than 20 years. Some of our gates are over 30 years old and still in good condition.

[Andy Dingley]

Larch, maybe douglas fir (depending a bit on what's cheapest locally)

Avoid pressure treated, if you can, because timber thaat simply doesn't need treatment outlasts timber that's treated.

That's roughly 4 cubic feet, which is about £64 best price I could get for larch today. You'll pay more because of machining etc.

Most timber merchants supplying the building trade are rubbish. Find somewhere decent like these people and you'll save a fortune and get better timber.

[Grunff]

Really? That's interesting. I've no experience of how untreated larch or douglas fir ages. How would you expect say a bench made of larch to look after 10 years sitting in the sun/rain?

[The Natural Philosopher]

He's talking bollocks. All wood that is treated lasts longer than almost any wood that is not, apart from a few exceptions like teak.

[Mark]

Hmm from the URL that he quoted

"We recommend that timber for outdoor use be pressure treated to give a long service life and thereby reduce the pressure to harvest more trees."

Im not saying that Larch would not be a better wood to use outside, but in the OPs situation treated crap pine would suffice.

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[Andy Dingley]

Larch is chock full of resins straight off the tree (makes great firewood!). In terms of "treatment" surroundling the cellulose and lignin there's just more impervious goop in a lump of larch than there ever is in something PT.

Larch is the standard timber these days for big timber frames

oak is too expensive to work with for most clients. If you're using it in an environment that's protected from the direct effects of weather (i.e. purlins, but not shingles), then you should see a century of good service from it.

I probably wouldn't use untreated larch as an outdoor tabletop, because that's a visually sensitive piece in a worst-case exposure. For furniture I just accept that it needs re-oiling every year or two. For a tabletop or a bench I can afford to use oak.

PT is also far from everything it's cracked up to be. The old stuff was incredibly toxic, the new stuff is still pretty toxic and is of uncertain reliability. It still has the problem that PT is only a thick surface treatment, so is of little use for framing - mortices fail after only a couple of years.

The main problem with PT though is the low-end quality of the timber used to make it. You're reliant entirely on the chemistry because the rubbish that goes to make up nearly all PT (unless you're very careful where you buy it and what you specify) has no inherent rot-resistance of its own.

Douglas fir is nowhere near as survivable outdoors as larch is, as it just doesn't have the resin content. It needs some surface treatment applied. However it's a nicer timber to work with than larch and is finer grained, straighter grained and doesn't have larch's tendency to twist. If it's under decent cover (I think we're talking carport rafters here) then it's entirely practical to use.

[Grunff]

Agreed as far as tabletops go, but what about fences, gates etc? Are you saying there's a realistic alternative to pressure treated?

I don't have a problem with the toxicity - lots of things are toxic, I just make sure I don't eat them :-)

Sure, it's no good or framing, but a gate made then pressure treated works pretty well.

Ok, that sounds like a fair comment.

[dom]

More important than exactly what type of wood is drainage and weather protection - if it is well painted, drains properly and isn't allowed to remain wet - reasonable quality pine shoud last longer than we do.

That said, sapele or meranti is very durable and very easy to work (I've made 17 gothic arched windows in the last few months).

I finished this with Sikkens Cetol 7 and Sikkens HLS - clear or coloured stain. This should only require recoating every 5 years or so.

If you can precut all your boards and fully treat them on all sides before installation, this should further improve durability.

(Remember if you buy pressure treated and then cut to length, you've just exposed an untreated area of the most vulnerable end-grain).

[Stuart Noble]

Check out recycled pitch pine. Not horrendously expensive IIRC and inherently water resistant.

[Andy Dingley]

Sweet chestnut. Excellent rot resistance untreated and it's more stable than larch.