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Thread: ??f7, F8, Mpg?????
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9th May 2003, 11:33 AM #1
??f7, F8, Mpg?????
OK, what does this all mean when I look at the timber stock at bunnings, what do I buy?
Geoffrey
I love work, it fasinates me, I could sit around and watch it all day.
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9th May 2003 11:33 AM # ADSGoogle Adsense Advertisement
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9th May 2003, 12:07 PM #2DavidG Guest
Stress Grading
The building industry to which a large proportion of green scantling material goes, makes particular use of stress grading through the National Timber Framing Code. The Framing Code prescribes a strength for all timber used for structural purposes. This code uses the 'F Rating', a measure of the modulus of elasticity of timber. The F rating has a number of categories namely, F4, F5, F7, F8, F11,F14, F17, F22 and F27. The higher the grade the better the strength of the timber.
Much of Australia's softwood and hardwood timber is now mechanically stress-graded whereby a lateral force is applied to a piece of timber with the amount of timber deflection providing a strength rating (refer Australian Standards 1748 and 1749-1978). Australian hardwoods range in F rating from F4 to F27 while softwoods are commonly in the range of F5-F8 with some mills now cutting lengths to F11.
F4 Red
F5 Black
F7 Blue
F8 Green
F11 Purple
F14 Orange
F17 Yellow
F22 White
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11th May 2003, 11:10 PM #3
now how does f** relate to MPG**?
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11th May 2003, 11:20 PM #4Banned
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It's MGP and it is short for Machine Graded Pine.
Check this out
www.structuraldesigns.com.au/FAQs/Timber/MGP.htm
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13th August 2003, 01:37 PM #5Senior Member
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I have had some quotes from various reblockers, and I'm getting a little confused because of all the different timber standards they refer to.
With regards to replacing bearers and joists, they discuss F17, M8 (I think), one guy said he would use treated pine (but what grade?) etc. Hence my confusion.
Also confused as to whether the timber being used is green or dried. Using green bearers will just mean they need to be repacked in 3 months time.
So what grade should I be insisting they use for bearers and joists? The existing bearers just look like 100x70s, and the joists look like 90x45s.
Is it Ok to use treated pine joists, so long as they are Fxx minimum?
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13th August 2003, 11:31 PM #6
JohnG, the trouble here is that you are asking the contractor to write the specifications as well as quote on the job. What you need to do is get an engineer to look at your job and write the specs and then get all the contractors to quote on that. Now the engineer is going to cost some serious money so you will probably spend more on him than you might save on the quotes. The other alternative is to buy yourself a TRADAC manual and write the specs yourself out of the relevant tables. That way you will get the correct timber for the job and you will be able to compare apples to apples.
Mick
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14th August 2003, 02:52 PM #7Senior Member
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Sorry, I should have been clearer.
I'm not building a whole house. I'm just replacing the bearers and joists in a small area (bathroom). It is not a structural area (i.e. not near walls, no second storey etc).
In total we will use no more than maybe 20m of timber. Therefore cost is not a big factor. I just want it done properly without me having to repair it in 5 years time.
The reblocker I'm thinking of using said he would be using treated pine. I wanted to know if this would be OK, or if using treated pine is dodgy (since I always thought you used kiln dried hardwood for stability).
For example, the floor in the kitchen is now uneven, supposedly because the original joists used (4 years ago before we bought) were green F? timbers, that have since shrunk and warped. I wanted to make sure we didn't make the same mistake.
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14th August 2003, 09:27 PM #8Senior Member
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John,
Your contractor may have chosen treated pine because it is a bathroom and he want to avoid any future troubles with possible water leakage etc.
If you post the dimensions of the area (and any possible heavy loads loads such as spa...), bearer/ joist spacings and what type of floor covering you intent to use, then I can check the strength grading/sizes for you.
Regards,
Theva
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15th August 2003, 01:02 PM #9Senior Member
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It's approx 2m x 2m, joists at 450 centres.
No load (just open floor).
Floor covering will be tiles on timber/structafloor/concrete sheet.
I am asking about stability, rather than strength. Because of the tiles, I don't want any future floor movement. Therefore I want to make sure he doesn't use green timbers, because they will dry and shrink, and therefore the floor will move.
That's why I was worried about TP, since my understanding is that it is almost always green. Unless a particular grade means that it is dried timber?
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15th August 2003, 02:30 PM #10
span tables
According to my span tables (which are for W41C - cyclonic area with winds ti 41 M per second, a bit over the top but as the table I'm using is for not load bearing it should be pretty close)
Bearers not supporting roof loads - Single span
Span 2.1M
Spacing 3.6M (next down is 1.8M)
Seasoned timber:
F4 240x70 or
F5 240x70 or
F7 190x70 or
F8/F11/F17/F22 170x70 or
F27 140x70
Floor Joists @450 centres single span, not supporting roof loads.
Span 2.1M
Seasoned timber:
F4 140x35/140x45 or
F5/F7 140x35/120x45 or
F8/F11/F14/F17/F22 120x35/120x45 or
F27 120x35/90x45
Of course if your spans are greater than 2.1M you can throw those figures out the window. You should be able to get treated pine kiln dried, my timber yard has its own kiln as well as treatment facilities so surely someone in Melbourne must have the same.
Mick
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16th August 2003, 09:10 PM #11Senior Member
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John,
Floor frame stability:
Pine is more dimensionaly stable than hardwoods when they dry out (3-5% shrinkage compared to up to 12% depending on the species).
AS 1684 (timber framing standard tingy) recommends the use of low shrinkage species (if unseasoned) or “make allowance” for shrinkage if you are using unseasoned timber for bearers / joists.
CCA treated pine (to H4) goes through some drying process to eliminate the chemicals leaching out / drying the surface by air drying for 4 to 6 weeks or by accelerated steam drying processes.
In short it is semi seasoned when it comes out of the treatment process and in to the market.
Structural grade H4 CCA treated pine of F7/MGP12 grade should be fairly stable because it will have less imperfections than F5/MGP10 grade.
So your contractor is making sensible suggestions.
I will email you the relevant tables form AS 1684 (once I workout how the scaner thingy works) so you can work the spacing / span / sizes for yourself; don’t want to post it on BB for copyright reasons.
Structural flooring:
Structral flooring of 19mm thick timber flooring or something similar in strength is required under tiles. In my case, I will use 15mm thick compressed fibre cement sheets with 450mm joist spacing (pricey- app $75/sq m for sheets, but similar to timber flooring costs).
There is a lot of info at the following site; worth a look if required:
http://www.jameshardie.com.au/buildi..._sub.asp?id=10
Hope it is of some help.
Regards,
ThevaLast edited by Theva; 16th August 2003 at 09:28 PM.
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17th August 2003, 12:01 AM #12
I don't think one can use treated pine for frame or subfloor in dwellings, due to arsenic fumes. I know a guy who had a log cabin built and the builder used treated pine. The owner ended up in hospital after a year with arsenic poisoning and sued the builder.
Treated pine is kiln dry, hardwood is green, yet I would recommend you do not use treated pine but hardwood, and have a nice 19mm compressed fibro over the joists and no timber flooring of any sort.
Typically floors in a brick veneer home are: bearers at 1.8m span hardwood 100mm x 75mm and joists hardwood 100x50. You say your toilet is 2.1 but you don't say the span for bearers and joists you may well have a pier in the center of your toilet.
Unless you have a lot of room under the house, you would try to avoid knocking bricks out of your piers, and if you had hardwood and now want to use pine that is F4, you will need to go way way bigger and so way lower with your bearers and joists.
To avoid any movement in hardwood builders usually "kill" the bearers by cutting 2" into the bearer right over the pier so that there will be no movement once it dries. If you use good quality hardwood, and you won’t find good quality at Bunning’s, and if you use compressed fibro 19mm and no timber flooring you will have no problems whatsoever.
At risk of sounding pedantic I would suggest that someone proposing to use treated pine for joists is someone I wouldn't hire.
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17th August 2003, 12:23 AM #13Banned
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There is no way you could get arsenic poisoning from living in a treated pine structure, unless you set fire to it and breathed the fumes, or spent your evenings sucking on the walls. They use it in playgrounds for heaven's sake.
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17th August 2003, 12:28 AM #14
For outdoors it is ok.
The arsenic fumes escape whe the temperature increases like it is the case for frames in a cladded house, and accumulate indoors. I am pritty sure they are totaly banned from use in framing or subflooring for indoors but I would check with the council anyway.
The treated pine as we know it, trated with arsenic and copper sulfate will be a thing of the past anyway they will be soon totaly banned and replaced with a less dangerous treatment.
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17th August 2003, 05:02 AM #15Senior Member
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CCA treated timber is dried after treatement to stop any surface leaching. Arsanic doesn't evoporate; only way one can get affected (other than as Ken sugested) is by surface contact or by inhaling timber dust while construction - tradesmen should use approporiate safetygear as always - they know what to do.
There are no plans to ban CCA or creasote treated timber in Australia. Well, it is "green" hehehe.
If you have CCA trated timber outdoors then feed you dogs properly before they take on chewing on CCA trated timber; can be very bad for them.
As for cats, they are welcome to CCA treated timber; that will save few native birds.
Regards,
ThevaLast edited by Theva; 17th August 2003 at 05:21 AM.