General advice / opinions sought... joists vs lamination

[blurk99]

maybe this ought to be in another section??

Which is stronger - a 6inch x 3inch 'joist' or a lamination made from three 6inch x 1inch planks???

my problem (1 of them...) is my garage roof is sagging - the internal measurements are 3.7mtr wide, 5.5mtr long, the roof is 'supported' by three 6mtr long, 38mm wide joists - one at the ridge and one each half way down the sides

my plan is to use 2 or 3 'joists' across the garage (resting on 'fenceposts' cut to length) with a central support that will push the ridge back up to it's correct height

i've also noticed that the sides are bowing out - the 3.7mtr width is at the end walls and in the middle of the wall they are 10cm further apart, so i'm planning on pulling them in with a ratchet strap before bolting through into the new supports for the roof frames, the new supports will be held the correct width apart by the frames

can anyone tell me whether what i'm planning is stupid / dangerous / easily achieved by a different method? would a steel support make more sense? any ideas about the weight of the roof itself? i'd reckon on 25sq mtr of 12mm T+G covered with pretty simple membrane then marley roofing felt 'tiles' - about 200kg all in???

cheers ladies and gents - all suggestions and ideas gratefully received (there's one caveat, can only get access to the edges - an old BMW that refuses to move is stuck in the garage, that's going to take about 2 years to get her up and running, i'd like to get this sorted this side of heavy snowfall if it arrives this year!)

cheers

jim

 

[Allylearm]

I built a recent tenement the floors were all made in BCi Truss rafter I have done others with metal web joists, both are very strudy and easy to manufacture and fit. They should be cheaper than laminate though you may be looking for visual where the lamanate/solid would look more pleasing.

Choices choices.

 

[slimshady]

I would presume that in order of strongest....
solid hardwood beam 6x3
solid softwood beam 6x3
joint 4'th = laminate DIY, on extra presumption that you'd be over cautious on glueing and or extra re-inforcement by way of some bolts.
joint 4'th = laminate beam by a professional
As an example my workshop (7.5 x 3.6 mtr) is using 2 lots of doubled 8"x2" at 2.5 mtr gaps, each holding an 8"x2" (king) post that in-tern holds the 8"x2" ridge.
I can look up the beam sizes of soft/hardwood if you wish.

Alex.

 

[OLD]

I think i would Acro prop the three timbers in the middle of the span to see if the roof will go back straight reversing there sagging action, then make up 'A' frames 3 as planned with posts to support. 'A' frames to fit what you have, look at old designs on the net for construction details a triangle is a strong structure.Shorter Acros will help when installing and fitting posts.

 

[blurk99]

cheers chaps - i was thinking about a-frames, but those engineered beams ^^ Boise Cascade things look pretty decent, then i found Eazi-Joist (or something very similar) and i'm having a chap get back to me about the price for 3 made to measure with a 6 inch depth instead of the usual 10 inch... i think i've got the wrong idea about 'laminating' - manufacturers lay the timber pieces 'flat' for my thinking and you end up with an enormous joist / beam that wasn't what i was thinking of - i'm thinking of three planks, on edge for 'beam strength', glued and bolted together with a single central post to post to lift the ridge...

anyhow, these eazi-joists should be capable of holding 2.5 ton over a 3.5 mtr span if it's an 250mm deep beam, so my thinking tells me a 180mm beam must be capable of holding 200kg or so, it's just a question of whether the pressed metal webbing can be made to fit between the top and bottom chords

jim

 

[Digit]

My answer would be a question Jim. Whch way are the grains running?
Withing certain dimensional limits, two beams, with space between on deep beams, with ply shear members glued and screwed to the sides are far the strongest for the amount of timber used.

Roy.

 

[blurk99]

didn't think of building my own 'box' section with ply sides - DOH!
i've got 2 8inch deep eazi-joists coming my way at the weekend - site surplus costing £20 each, i'll get them fitted up and get my ridge (relatively) straight at the weekend

cheers

jim