Will this work?

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Will this work?
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tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Fri Nov 27, 15 2:53 pm Post subject: Will this work?

This is supposed to be a trellissy/pergola thing to support wisteria type climbers around the patio, the bases of the posts will be sliding over (and bolted through) RSJ's from the old house that have been concreted into place @ appx 3000mm centres, can take 100xwhatever thickness.

Lots of questions but mainly:

1. I'm assuming fresh sawn oak would be the best material for this, is that correct?

2. I've sized the sections of timber I've used just on gut feel on strength, with no idea of stock sizes or most economical way to do this. So, are the sections man enough, is there a cheaper way to do it?

3. The notches in the various bits of timber are again based on gut feel, do they look OK

4. I'm assuming that the timbers will need mechanical fixings to one another, what should they be?

All advice appreciated. It needs to be cheap but also durable, don't really want to be replacing it in 10 yrs time when there's 2 tonnes of wisteria on it.

Click to download file

dpack

Joined: 02 Jul 2005
Posts: 46207
Location: yes

Posted: Fri Nov 27, 15 3:26 pm Post subject:

the notches in the cross beam are too deep in the drawing ,less than half the depth of the beam would be better.

overkill of inforegarding green oak jointing but it covers any you might need. avoiding metal fixings is probably best for outside stuff but if needs must stainless steel is yer kit

i see no reason not to use oak but it will last a lot longer if it gets treated with boiled linseed oil between cutting and construction(the beat way to buy oil is in bulk from a decorators merchants the darker stuff is quite cheap ) dont use the stuff with dryers unless you dont mind the oak going a funny colour

chestnut lasts well outside but im not sure it is as easy to work or available in suitable sizes at a good price

oak is ace to work with so long as you have a decent saw,drill and chisel

with such a construction a good drawing will avoid most problems but getting the base accurate is vital to making the thing unless you want to make each stick to fit rather than start with a pile of pre cut bits that join up like mechano.

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Fri Nov 27, 15 3:32 pm Post subject:
Do you think the cross members are thick enough at 30mm?

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Fri Nov 27, 15 4:15 pm Post subject:
I've got loads of Danish oil, will that do the trick rather than linseed?

onemanband

Joined: 26 Dec 2010
Posts: 1473
Location: NCA90

Posted: Fri Nov 27, 15 5:56 pm Post subject:

1. IMO yes for durability and looks but not cost.
2. Sawmill I use, cut to order, so no stock sizes. They price by volume, so no price difference between sizes.
3. I would agree with dpack, tho I don't know a 'rule of thumb' for sizes.
4. Stainless steel ringshanks. Sawmill may sell them.

30x150 will be strong enough, but how far are they spanning ? If the span is too big they might bow/twist (horizontally as opposed to sagging) My guess would be max 1.2m span between supports or noggins to prevent bowing.

I take it the rsj's are to keep the post feet clear of the ground - and/or supporting the posts in such a manner that if the post bottom rots the structure is not compromised.

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Fri Nov 27, 15 7:25 pm Post subject:
Yep rsjs are to keep timber out of the ground. Need to decide on span

dpack

Joined: 02 Jul 2005
Posts: 46207
Location: yes

Posted: Fri Nov 27, 15 11:27 pm Post subject:

noggins is a good idea ,they do add considerable stability.

im not sure how much a mature wisteria weighs but if in full leaf it will provide quite a "sail" in wind but with 150 x 30 on maybe 400 centers(your drawing seems that with 100 centers it will be more wood than air on top) the top timber work will be strong , i might go for maybe 150x 150 for the uprights and have a pair of uprights each end

the issue that needs thought is attaching the top to the uprights and making sure the uprights are braced so as a wind cannot "fold" the structure to either side or end and that the sole plate/rsj is solidly attached to the floor to avoid any "tumbleweed " type excitement
a simple triangle brace from uprights to roof (along and across from each post should hold the top part rigid ,the joint to the sole plate/rsj can easily be braced in the along direction with a triangular brace,the side to side direction might need a pair of short 90 degree extension to the sole plate/rsj to hold the side to side braces on each side.

dpack

Joined: 02 Jul 2005
Posts: 46207
Location: yes

Posted: Fri Nov 27, 15 11:34 pm Post subject:
re dimensions for the overall structure the golden rules of rectangles and rectangular solids might help with proportions

Mistress Rose

Joined: 21 Jul 2011
Posts: 15966

Posted: Sat Nov 28, 15 7:30 am Post subject:

I think your beams are cut too deep too. You only really need a fairly shallow trough for the cross beams to sit in. Otherwise I wouldn't like to comment on the dimensions of the beams as I don't know to much about that. You should be able to get some idea by looking up dimensions for timber framing on the internet.

Oak is fine untreated for at least 20 years, but make sure you have all the sap wood cut off. Don't use concrete of mild steel on it. Traditionally it is fastened with oak pegs, and these are quite strong enough and of course can't be corroded by the tannins in the wood.

Chestnut is an alternative, and if you are willing to go for round wood, you could make the whole thing a lot cheaper. Durability outdoors is similar.

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Sat Nov 28, 15 10:44 pm Post subject:
I've looked at chestnut previously, certainly couldnt find anyone locally

Mistress Rose

Joined: 21 Jul 2011
Posts: 15966

Posted: Sun Nov 29, 15 8:39 am Post subject:

Sadly there doesn't seem to much chestnut in Essex. We are fortunate here that we are quite near the chestnut growing areas of Sussex/Surrey/Kent. If we want chestnut we just chat to a member of our coppice group, or another man we know, depending on what is needed. We get some oak from our own wood, but most of that is better for roofing shingles than beams. We did get one trunk that has been down a long time that we hope will mill well though.

Ty Gwyn

Joined: 22 Sep 2010
Posts: 4613
Location: Lampeter

Posted: Sun Nov 29, 15 10:53 am Post subject:
Your neighbours in Dorset give a good sizing and price list, https://r.search.yahoo.com/_ylt=A7x9UnH711pW1VsA.qV3Bwx.;_ylu=X3oDMTByam1ucWFtBHNlYwNzcgRwb3MDNwRjb2xvA2lyMgR2dGlkAw--/RV=2/RE=1448822907/RO=10/RU=http%3a%2f%2fwww.dorsetfencingsupplies.co.uk%2fchestnut_fencing.html/RK=0/RS=zqSkvkihAqLPk_SsQscRHipPndk-

mousjoos

Joined: 05 Jun 2006
Posts: 1986
Location: VERY Sunny SW France

Posted: Sun Nov 29, 15 11:08 am Post subject:

Have you tried Atkin & Cripps in Bishops Stortford ?

Also many years ago we bought timber from a firm near Maldon, whose name now escapes me

Other than that, I can only suggest folks like Blumsoms, Silvermans, or Goldbergs...haven't googled to see if these places still trade, but as they are (or were) importers you may have more luck...chestnut may not be "exotic" enough for them, but here it's a staple timber so may be viable for them to import

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Sun Nov 29, 15 1:07 pm Post subject:
I'll try the bishops stortfotd one, the othersdefinitely dont Thanks all

Pilsbury

Joined: 13 Dec 2004
Posts: 5645
Location: East london/Essex

Posted: Sun Nov 29, 15 11:24 pm Post subject:
There are also about 6 timber merchants just off the a13 towards thames view, turn right insted of left at the junction thstvyou use to head to me. I remember my dad saying there was one or 2 thst did some ofvthe more exotic hardwoods.

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